Partenaires

CRMBM



Search

On this website

On the whole CNRS Web

CNRS

AMU
AMU

Home page > Directory

DUHAMEL Guillaume

CNRS Research Associate (CR1)
PhD in Physics, HDR

Myelin Imaging research group leader

guillaume.duhamel@univ-amu.fr
Phone : +33 491 386 260 / 324 813
Key Words
- Inhomogenous Magnetization Transfer (ihMT)
- MR Physics / MR Method developments
- Perfusion Imaging (Arterial Spin Labeling)
- Quantitative Brain Multimodal imaging

ihMT (inhomogenous Magnetization Transfer imaging) Project


The objective of this project is the development of a new quantitative technique to assess in vivo myelin content with MRI. Despite its high clinical relevance such a tool does not exist yet. The proposed method, completely original, is based on magnetization transfer and relies on the capacity to isolate the contribution of inhomogeneously broadened components of the NMR spectrum that are usually ignored in traditionnal MT models. This technique is referred to as inhomogeneous Magnetization Transfer (ihMT).
  • ihMT project team

    - Guillaume Duhamel, PhD (CNRS Research Associate)
    - Olivier Girard, PhD (AMU Research Engineer)
    - Arnaud Le Troter, PhD (CNRS Research Engineer)
    - Valentin Prevost, PhD student, Neurosciences
    - Samira Mchinda, PhD student, Neurosciences
    - Victor Carvalho, PhD student, Neurosciences
BIDMC, Harvard Medical School
- David C. Alsop, PhD, Pr. of Radiology
- Gopal Varma, PhD
    • Past Trainees
    • 2017
      - Maeva Cotinat, M2 trainee / Neurology fellow- Master of Neurosciences, Aix-Marseille University
      - Robin Draveny, M2 trainee/4th year of INP, Phelma Engineer School, Grenoble University
    • 2016
      - Elise Van Obberghen, M2 trainee / Neurologist fellow- Master of Neurosciences, Aix-Marseille University
    • 2015
      - Yunfei Yang, M2 trainee/4th year of UTC Compiègne Engineer School (Compiègne)
      -  Charles-Henri Andrieu, M1 trainee, International Master of photonics (POESII-Europhotonics), Aix-Marseille University
    • 2014
      - Guilherme Ribeiro, M2 trainee/4th year of Polytech Engineer School (Marseille)
  • ihMT project Grant Supports
    • ANR - Agence Nationale pour la Recherche- AAPG 2017
      verISMO: Validation of inhomogeneous Magnetization Transfer (ihMT) as a specific and sensitive in vivo myelin biomarker
    • ARSEP - Fondation pour l’aide à la recherche sur la sclérose en Plaques- 2017
      Apport clinique du transfert d’aimantation inhomogène (ihMT) pour l’imagerie spécifique de la myéline dans la sclérose en plaques
    • SATT Sud Est - Sociéte Accélération Transfert de Technologies - 2017
      Application of inhomogeneous Magnetization Transfer (ihMT) MRI, a new myelin specific MRI contrast, to Multiple Sclerosis
      Maturation brevet PCT/EP2017/0156978 Method for enhancing the ihMT sensitivity of steady-state gradient echo acquisitions in an MRI system et brevet PCT/IB2017/000177 Method for improving spinal cord contrast in magnetic resonance imaging
    • European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No713750, COFUND 2016
      Investigation of magnetization transfer in myelin using magnetic resonance imaging and spectroscopy
    • IRME -Institut pour la Recherche sur la Moelle Epinière- 2016
      Specific Spinal Cord Myelin imaging by inhomogeneous Magnetization Transfer (ihMT) MRI
    • Réseau PACASEP, 2015
      Optimisation théorique et expérimentale de l’imagerie du transfert d’aimantation inhomogène par IRM en vue d’applications cliniques
    • ARSEP - Fondation pour l’aide à la recherche sur la sclérose en Plaques- 2015
      Development of a 3D inhomogeneous Magnetization Transfer (ihMT) technique, a new myelin specific MRI contrast, and first application to MS patients
    • Fondation A*MIDEX - (Investissements d’avenir), AAP « Excellence Academy – PhD Collegium » 2014, ANR-11-IDEX-0001-02
      Inhomogeneous Magnetization Transfer Imaging at high magnetic field (11.75T) for specific myelin imaging
    • IRME - Institut pour la Recherche sur la Moelle Epinière, 2012
      Mesure de la perfusion Médullaire par IRM pour la caractérisation des patients atteints de Traumatismes
  • ihMT project - Main Results

The ihMT project involves studies of underlying mechanisms and Physical characterization of this new contrast, validation of the technique as a myelin specific biomarker and Clinical applications.
The project mainly relies on MR Physics (modeling, numerical simulations), methodological developments (MR techniques, post-processing tools) transversally performed on specific phantoms/small animal using preclinical 7T&11.75T MR scanners, and on humans using clinical research 1.5T&3T MR scanners. This part of the project is developed in close collaboration with the division of MR research (Dir. D Alsop) of Beth Israel Deaconess Medical Center (Harvard Medical School, Boston, USA).
Clinical application of ihMT on MS patients is under investigation within protocols developed in collaboration with the department of Neurology (Dir. Jean Pelletier) of La Timone Hospital (Marseille).

    • Princeps Experiment: MT effects arise from exchange with one or more pools of magnetization with a wide, dipolar broadened line shape. A broad line is actually the instantaneous summation of many individual lines with different offset frequencies. Typically, spin components of these lines move rapidly from one frequency to another such that the different lines cannot be separated by RF excitation or saturation with RF powers available in vivo. Such rapidly exchanging lines are known as homogeneously broadened lines. The absence of the usual mechanisms, by which homogeneous broadening is achieved, suggest that inhomogeneous broadening may be present in large membranes, the main constituent of the myelin sheath.
      The ihMT technique is a method to detect the transfer of inhomogeneously broadened magnetization in the presence of a larger background of homogeneous MT. The resulting signal appears highly specific for myelinated structures (Fig. 1).


Fig. 1 Illustration of ihMT (d, e) specificity for myelinated structures. (a) anatomic and (b, c) regular MT. (From Varma et al, Magn Reson Med. 2015 Feb;73(2):614-22)

    • Experimental optimization at 1.5T: Optimization of the pulsed saturation scheme parameters, including the pulse width, the interpulse repetition time, the total saturation duration and the RF saturation power to increase the ihMT sensitivity and the contrast specificity allowed optimizing the ihMT contrast for practical clinical imaging experiments, and measuring the underlying contrast mechanisms and parameter dependencies that will contribute to a broader understanding of a quantitative ihMT model. (Fig. 2).

Fig. 2: (left) Typical optimized inhomogeneous ihMT images of CNS tissues and corresponding T2-weighted TSE acquisitions at 1.5T. (right) Pulse width and interpulse repetition time optimization. IhMT ratios in IC and cGM are shown as a function of the energy deposition ETR for different pulse widths and interpulse repetition times. (From Girard et al, Magn Reson Med. 2015 Jun;73(6):2111-21)
    • Physical Characterization: ihMT contrast can be explained physically as a dipolar order effect within bound molecules. In vivo data was qualitatively and quantitatively consistent with this physical theory. The inclusion of a dipolar reservoir in the existing two pool model for MT provided the means to model ihMT. By comparing the more effective saturation of dual frequency irradiation with the weaker saturation of single frequency irradiation, ihMT highlighted dipolar order effects in longer T1D tissues. Under this interpretation, contrast between myelinated tissues and other tissue types resulted from combined differences in T1D, the dipolar order relaxation time and f, the fraction of the bound pool with non-trivial T1Ds. This approach provided access to a new form of MRI contrast based on T1D differences between tissues.(Fig. 3).

Fig. 3: (left) Illustration of the model considered for bound pool magnetization and its internal dipolar interactions. Zeeman and dipolar reservoirs are derived from the same motion-restricted bound pool spins, but they change independently (a), and only interact in the presence of RF irradiation (b) according to Provotorov theory. (right) Plots of average data across IC ROI from single subject with dashed lines from fits to: (b) two bound pools Morrison model; and, (d) two bound pools CAA model. (From Varma et al, J Magn Reson. 2015 Nov;260:67-76)
    • ihMT vs MT-Asymmetry: The use of the double subtraction MT(+) + MT(-) - (MT(+/-) + MT(-/+)) to generate ihMT signal showed efficient correction for MT-asymmetry at 11.75T as long as⎪MTRasym⎪<4%. In this restricted range, MT-asymmetry signal did not contaminate ihMT quantification significantly. At 11.75T, it is suggested that the use of a center frequency in the range of -200 Hz<fc<-100 Hz (i.e. -0.4ppm< fc <-0.2ppm), that is the range of values that null MTRasym in Mu, would ensure close to optimal conditions are fulfilled over the whole brain. Beyond strong theoretical arguments, the distinct nature of MT-asymmetry and ihMT contrasts was further evidenced experimentally by measurement of non-zero ihMTR values for zero MT-asymmetry signal and subsequently emphasized by independent behaviors when varying the saturation parameters. IhMT varied non-linearly with saturation power, as opposed to the linear decrease of MTRasym over the explored range. Also the dependency of MTRasym and ihMTR on the interpulse delay (Δt) showed different behaviors, which highlighted fundamental differences in the rates of magnetization saturation transfer mechanism involved in each contrast. (Fig. 4).

Fig. 4: (left) Representative sets of single shot ihMT-RARE images (MT+, MT-, MTR, ihMTR, MTRasym) obtained on mouse at 11.75T, qualitatively illustrating the different nature of MT, ihMT and MT asymmetry contrasts. (right) MTR (a, d), MTRasym (b, e) and ihMTR (c, f) variations with fc values measured in IC. Saturation parameters were: PW/∆t=1/1.3ms, ETR=30 μT2.s and 60 μT2.s (a-c). PW/∆t=1/1.3ms, 3/3.3ms and 5/5.3ms, ETR=30 μT2.s (d-f). (From Prevost et al, MAGMA. 2016 Aug;29(4):699-709
    • Spinal Cord ihMT: Challenges for SC ihMT studies include a relatively coarse resolution compared to the small size of the cord, the presence of susceptibility effects from surrounding tissues, and most importantly sensitivity to the pulsatility of the cerebrospinal fluid (CSF), which induces motion in and around the cord. Indeed, in comparison with conventional MT, such motion may have more dramatic impact on ihMT because it has lower sensitivity (ihMT signal on the order of 10% of the unsaturated signal) and requires data subtraction from multiple images potentially acquired at different phases of motion. We presented a complete strategy for cervical SC ihMT imaging free of CSF pulsatility artifacts. The proposed method combines electro-cardiogram (ECG) synchronization and retrospective data pairing. This strategy aims at correcting for signal variations of long T1-components, such as CSF, that occur when a variable recovery delay is introduced in the sequence as a consequence of variable cardiac cycle. In comparison with other strategies correcting for such T1-recovery effects, the proposed method is model-free as it simply matches images acquired with a similar recovery period. A semi-automatic algorithm for data correction is presented along with accurate ihMT ratio quantification of the cord. Exquisite resulting image quality of the SC opens great possibility for further in vivo characterization of SC physiopathology using MRI. (Fig. 5).

Fig. 5: Effect of ECG synchronization on SC data. (a) Reference ECG triggered anatomical scan (T2w FSE) and corresponding MTR (b) and ihMTR (c) map obtained using optimized protocol (ECG synchronization and retrospective data pairing for ihMT). Examples of non-triggered acquisitions acquired on two different volunteers are displayed in (d) - (g). Whereas MTR data do not evidence strong signs of motion artifacts in the cord area (b) vs (d) and (e), the ihMTR data reconstructed from the same datasets show particularly strong CSF pulsatile artifacts ((f) and (g), green arrows), consistent with increased motion sensitivity of an image-subtraction based technique. ECG synchronization combined with the retrospective bias correction algorithm recovers exquisite SC image quality (c). (From Girard et al, Magn Reson Med. 2017 Feb;77(2):581-591)
    • Measurement of T1D using ihMT: This paper describes a technique that can be used in vivo to measure the dipolar relaxation time, T1D, of macromolecular protons contributing to magnetization transfer (MT) in tissues and to produce quantitative T1D maps. The technique builds upon the inhomogeneous MT (ihMT) technique that is particularly sensitive to tissue components with long T1D. A standard ihMT experiment was altered to introduce a variable time for switching between positive and negative offset frequencies for RF saturation. A model for the dependence of ihMT was developed and used to fit data acquired in vivo. Application of the method to images from brains of healthy volunteers produced values of T1D=(5.9 +/- 1.2) ms in gray matter and T1D=(6.2 +/- 0.4) ms in white matter regions and provided maps of the T1D parameter. The model and experiments described provide access to a new relaxation characteristic of tissue with potentially unique diagnostic information. (Fig. 6).

Fig. 6:Representative images and maps from a single volunteer show dependence of ihMT on frequency switching time, tswitch, and ability for ihMTR(tswitch) data to produce maps of dipolar relaxation time T1D. (a) ihMTR images acquired for different switching times show decrease in ihMTR with tswitch. (b) Map of T1D from pixel-by-pixel fits, along with (c) measure of fit quality, and (d) output parameter ihMTR(tswitch = 0). (From Varma et al, Magn Reson Med. 2016 Nov 17. doi: 10.1002/mrm.26523
    • Preclinical implementation of ihMT: A pulsed inhomogeneous magnetization transfer (ihMT)‐prepared fast imaging sequence was implemented at 11.75 T for preclinical studies on mouse central nervous system. A strategy based on filtering the ihMT signal originating from short dipolar relaxation time (T1D) components is proposed. It involves increasing the repetition time of consecutive radiofrequency (RF) pulses of the dual saturation and allows improved signal specificity for long T1D myelinated structures. Furthermore, frequency offset, power and timing saturation parameters were adjusted to optimize the ihMT sensitivity. The optimization of the ihMT sensitivity, whilst preserving the strong specificity for the long T1D component of myelinated tissues, allowed measurements of ihMT ratios on the order of 4–5% in white matter (WM), 2.5% in gray matter (GM) and 1–1.3% in muscle. This led to high relative ihMT contrasts between myelinated tissues and others ( 3–4 between WM and muscle, and ≥2 between GM and muscle). Conversely, higher ihMT ratios ( 6–7% in WM) could be obtained using minimal T1D filtering achieved with short saturation pulse repetition time or cosine‐modulated pulses for the dual‐frequency saturation. This study represents a first stage in the process of validating ihMT as a myelin biomarker by providing optimized ihMT preclinical sequences, directly transposable and applicable to other preclinical magnetic fields and scanners. Finally, ihMT ratios measured in various central nervous system areas are provided for future reference.(Fig. 7).

Fig. 7:In vivo T1D‐filtered inhomogeneous magnetization transfer (ihMT) imaging. (A) M0 image including location of internal capsule (IC), cortical gray matter (cGM) and muscle (Mu) structures (top left). Typical mouse brain T1D map (bottom left) showing long T1D values in white matter (WM) and gray matter (GM) structures and short T1D values in muscle. Right: ihMT ratio (ihMTR) images (%) obtained for dual‐frequency‐offset saturation achieved with cosine‐modulated (CM) pulses and frequency‐alternating pulses with increasing values of Δt. (B) Quantitative ihMTR values measured in IC (red curve), cGM (orange curve) and Mu (green curve) and (C, D) corresponding ihMTR contrasts and contrast‐to‐noise ratios (CNRs) (between IC and Mu, blue curve; between cGM and Mu, black curve; between IC and cGM, red curve). (From Prevost et al, NMR in Biomedicine. 2017;30:e3706.
    • 3D Boosted ihMT: Purpose: To implement, characterize, and optimize an interleaved inhomogeneous magnetization transfer (ihMT) gradient echo sequence allowing for whole-brain imaging within a clinically compatible scan time. Theory and Methods: A general framework for ihMT modelling was developed based on the Provotorov theory of radiofrequency saturation, which accounts for the dipolar order underpinning the ihMT effect. Experimental studies and numerical simulations were performed to characterize and optimize the ihMT-gradient echo dependency with sequence timings, saturation power, and offset frequency. The protocol was optimized in terms of maximum signal intensity and the reproducibility assessed for a nominal resolution of 1.5mm isotropic. All experiments were performed on healthy volunteers at 1.5T. Results: An important mechanism driving signal optimization and leading to strong ihMT signal enhancement that relies on the dynamics of radiofrequency energy deposition has been identified. By taking advantage of the delay allowed for readout between ihMT pulse bursts, it was possible to boost the ihMT signal by almost 2-fold compared to previous implementation. Reproducibility of the optimal protocol was very good, with an intra-individual error < 2%. Conclusion: The proposed sensitivity-boosted and time-efficient steady-state ihMT-gradient echo sequence, implemented and optimized at 1.5T, allowed robust high-resolution 3D ihMT imaging of the whole brain within a clinically compatible scan time..(Fig. 8).

Fig. 8: 3D whole-Brain sensitivity-enhanced ihMT images. (From Mchinda et al, Magn Reson Med. 2017 doi: DOI 10.1002/mrm.26907)

  • ihMT project scientific publications


  • GIRARD O. M., CALLOT V., PREVOST V. H., ROBERT B., TASO M., RIBEIRO G., VARMA G., RANGWALA N., ALSOP D. C., DUHAMEL G. “Magnetization transfer from inhomogeneously broadened lines (ihMT): Improved imaging strategy for spinal cord applications.”. Magnetic Resonance in Medicine [En ligne]. January 2017. Vol. 77, p. 581-591. Disponible sur : < http://dx.doi.org/10.1002/mrm.26134 > (consulté le 10 March 2016)
    Résumé : Purpose Inhomogeneous magnetization transfer (ihMT) shows great promise for specific imaging of myelinated tissues. Whereas the ihMT technique has been previously applied in brain applications, the current report presents a strategy for cervical spinal cord (SC) imaging free of cerebrospinal fluid (CSF) pulsatility artifacts. Methods A pulsed ihMT preparation was combined with a single-shot HASTE readout. Electrocardiogram (ECG) synchronization was used to acquire all images during the quiescent phase of SC motion. However ihMT signal quantification errors may occur when a variable recovery delay is introduced in the sequence as a consequence of variable cardiac cycle. A semiautomatic retrospective correction algorithm, based on repetition time (TR) -matching, is proposed to correct for signal variations of long T1-components (e.g., CSF). Results The proposed strategy combining ECG synchronization and retrospective data pairing led to clean SC images free of CSF artifacts. Lower variability of the ihMT metrics were obtained with the correction algorithm, and allowed for shorter TR to be used, hence improving signal-to-noise ratio efficiency. Conclusion The proposed methodology enabled faster acquisitions, while offering robust ihMT quantification and exquisite SC image quality. This opens great perspectives for widening the in vivo characterization of SC physiopathology using MRI, such as studying white matter tracts microstructure or impairment in degenerative pathologies. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
    Mots-clés : crmbm, CSF pulsatility, ECG synchronization, ihMT, Inhomogeneous magnetization transfer, motion correction, myelin, snc, Spinal Cord, white matter.

  • GIRARD O. M., PREVOST V. H., VARMA G., COZZONE P. J., ALSOP D. C., DUHAMEL G. “Magnetization transfer from inhomogeneously broadened lines (ihMT): Experimental optimization of saturation parameters for human brain imaging at 1.5 Tesla.”. Magnetic Resonance in Medicine [En ligne]. June 2015. Vol. 73, n°6, p. 2111-2121. Disponible sur : < http://dx.doi.org/10.1002/mrm.25330 > (consulté le no date)
    Résumé : PURPOSE: Recently a new MR endogenous contrast mechanism was reported. It allows specifically imaging the magnetization transfer (MT) effect arising from inhomogeneously broadened components of the NMR spectrum, and was hence dubbed ihMT. Such unique NMR lineshape properties are presumably occurring in myelin because of its specifically ordered, multilayered sheath structure. Here, optimization of a pulsed ihMT preparation module is presented to provide guidance for future studies and improve the understanding of underlying contrast mechanisms. METHODS: This study was performed at 1.5 Tesla on healthy volunteers. A pulsed ihMT preparation was implemented in combination with a HASTE readout module. The pulse width, interpulse repetition time, total saturation duration and RF saturation power were considered for optimization of the ihMT sensitivity and contrast. RESULTS: An optimal configuration of the preparation module was derived, leading to 10% ihMT signal in internal capsule (relative to unsaturated data) and around 200% signal increase relative to gray matter, i.e., approximately 10-fold superior contrast compared with conventional MT ratios, measured under similar experimental conditions. CONCLUSION: Overall the ihMT sequence was robust, sensitive and very specific for white matter. These findings suggest great potential for assessing brain myelination and for better characterization of myelin related disorders. Magn Reson Med 73:2111-2121, 2015. © 2014 Wiley Periodicals, Inc.
    Mots-clés : crmbm, ihMT, inhomogeneously broadened lines, Magnetization transfer, myelin, snc, specificity, white matter.


  • PREVOST V. H., GIRARD O. M., MCHINDA S., VARMA G., ALSOP D. C., DUHAMEL G. “Optimization of inhomogeneous magnetization transfer (ihMT) MRI contrast for preclinical studies using dipolar relaxation time (T1D) filtering.”. NMR in Biomedicine [En ligne]. 1 June 2017. Vol. 30, n°6,. Disponible sur : < http://dx.doi.org/10.1002/nbm.3706 > (consulté le 18 August 2017)

  • PREVOST V. H., GIRARD O. M., VARMA G., ALSOP D. C., DUHAMEL G. “Minimizing the effects of magnetization transfer asymmetry on inhomogeneous magnetization transfer (ihMT) at ultra-high magnetic field (11.75 T).”. Magma (New York, N.Y.) [En ligne]. August 2016. Vol. 29, n°4, p. 699-709. Disponible sur : < http://dx.doi.org/10.1007/s10334-015-0523-2 > (consulté le no date)
    Résumé : OBJECTIVES: The recently reported inhomogeneous magnetization transfer technique (ihMT) has been proposed for specific imaging of inhomogeneously broadened lines, and has shown great promise for characterizing myelinated tissues. The ihMT contrast is obtained by subtracting magnetization transfer images obtained with simultaneous saturation at positive and negative frequency offsets (dual frequency saturation experiment, MT (+/-)) from those obtained with single frequency saturation (MT (+)) at the same total power. Hence, ihMT may be biased by MT-asymmetry, especially at ultra-high magnetic field. Use of the average of single positive and negative frequency offset saturation MT images, i.e., (MT (+)+MT (-)) has been proposed to correct the ihMT signal from MT-asymmetry signal. MATERIALS AND METHODS: The efficiency of this correction method was experimentally assessed in this study, performed at 11.75 T on mice. Quantitative corrected ihMT and MT-asymmetry ratios (ihMTR and MTRasym) were measured in mouse brain structures for several MT-asymmetry magnitudes and different saturation parameter sets. RESULTS: Our results indicated a "safe" range of magnitudes (/MTRasym/<4 %) for which MT-asymmetry signal did not bias the corrected ihMT signal. Moreover, experimental evidence of the different natures of both MT-asymmetry and inhomogeneous MT contrasts were provided. In particular, non-zero ihMT ratios were obtained at zero MTRasym values. CONCLUSION: MTRasym is not a confounding factor for ihMT quantification, even at ultra-high field, as long as MTRasym is restricted to ±4 %.
    Mots-clés : Biomedical Engineering, Computer Appl. in Life Sciences, crmbm, dipolar order, Dipolar relaxation time, Health Informatics, ihMT, Imaging / Radiology, Inhomogeneous magnetization transfer, MT-asymmetry, myelin, snc, Solid State Physics.

  • TASO M., GIRARD O. M., DUHAMEL G., LE TROTER A., FEIWEIER T., GUYE M., RANJEVA J. - P., CALLOT V. “Tract-specific and age-related variations of the spinal cord microstructure: a multi-parametric MRI study using diffusion tensor imaging (DTI) and inhomogeneous magnetization transfer (ihMT).”. NMR in biomedicine [En ligne]. June 2016. Vol. 29, n°6, p. 817-832. Disponible sur : < http://dx.doi.org/10.1002/nbm.3530 > (consulté le no date)
    Résumé : Being able to finely characterize the spinal cord (SC) microstructure and its alterations is a key point when investigating neural damage mechanisms encountered in different central nervous system (CNS) pathologies, such as multiple sclerosis, amyotrophic lateral sclerosis or myelopathy. Based on novel methods, including inhomogeneous magnetization transfer (ihMT) and dedicated SC probabilistic atlas post-processing, the present study focuses on the in vivo characterization of the healthy SC tissue in terms of regional microstructure differences between (i) upper and lower cervical vertebral levels and (ii) sensory and motor tracts, as well as differences attributed to normal aging. Forty-eight healthy volunteers aged from 20 to 70 years old were included in the study and scanned at 3 T using axial high-resolution T2 *-w imaging, diffusion tensor imaging (DTI) and ihMT, at two vertebral levels (C2 and C5). A processing pipeline with minimal user intervention, SC segmentation and spatial normalization into a reference space was implemented in order to assess quantitative morphological and structural parameters (cross-sectional areas, scalar DTI and MT/ihMT metrics) in specific white and gray matter regions of interest. The multi-parametric MRI metrics collected allowed upper and lower cervical levels to be distinguished, with higher ihMT ratio (ihMTR), higher axial diffusivity (λ∥ ) and lower radial diffusivity (λ⊥ ) at C2 compared with C5. Significant differences were also observed between white matter fascicles, with higher ihMTR and lower λ∥ in motor tracts compared with posterior sensory tracts. Finally, aging was found to be associated with significant metric alterations (decreased ihMTR and λ∥ ). The methodology proposed here, which can be easily transferred to the clinic, provides new insights for SC characterization. It bears great potential to study focal and diffuse SC damage in neurodegenerative and demyelinating diseases. Copyright © 2016 John Wiley & Sons, Ltd.
    Mots-clés : Aging, crmbm, diffusion tensor imaging (DTI), ihMT, inhomogeneous magnetization transfer (ihMT), microstructure, multi-parametric MRI, snc, Spinal Cord.

  • VARMA G., GIRARD O. M., PREVOST V. H., GRANT A. K., DUHAMEL G., ALSOP D. C. “Interpretation of magnetization transfer from inhomogeneously broadened lines (ihMT) in tissues as a dipolar order effect within motion restricted molecules.”. Journal of Magnetic Resonance (San Diego, Calif.: 1997) [En ligne]. 7 September 2015. Vol. 260, p. 67-76. Disponible sur : < http://dx.doi.org/10.1016/j.jmr.2015.08.024 > (consulté le no date)
    Résumé : Comparison of off-resonance saturation with single and dual frequency irradiation indicates a contribution of inhomogeneously broadened lines to magnetization transfer in tissues. This inhomogeneous magnetization transfer (ihMT) phenomenon can be exploited to produce images that highlight tissues containing myelin, in vivo. Here, a model for ihMT is described that includes dipolar order effects from magnetization associated with motion-restricted macromolecules. In this model, equal irradiation at positive and negative frequency offsets eliminates dipolar order and achieves greater saturation than irradiation at a single offset frequency using the same power. Fitting of mouse and human volunteer brain data at different irradiation powers and offset frequencies was performed to assess the relevance of the model and approximate tissue parameters. A key parameter in determining ihMT signal was found to be the relaxation time T1D associated with the dipolar order reservoir and the fraction f of the semi-solid, bound magnetization that possessed a nonzero T1D. Indeed, better fits of myelinated tissue were achieved when assuming f≠1. From such fits, estimated T1Ds of mice in the white matter, (34±14)ms, were much longer than in muscle, T1D=(1±1)ms and the average f from white matter volunteer data was 2.2 times greater than that in grey matter. The combination of f and longer T1Ds was primarily responsible for the much higher ihMT in myelinated tissues, and provided explanation for the species variation. This dipolar order ihMT model should help guide future research, pulse sequence optimization, and clinical applications.
    Mots-clés : crmbm, Dipolar relaxation, ihMT, Inhomogeneous magnetization transfer, MT, myelin, Provotorov theory, Quantitative magnetization transfer, Saturation, snc, Spin temperature, SuperLorentzian lineshape.

  • VARMA G., DUHAMEL G., DE BAZELAIRE C., ALSOP D. C. “Magnetization transfer from inhomogeneously broadened lines: A potential marker for myelin.”. Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine [En ligne]. February 2015. Vol. 73, n°2, p. 614-622. Disponible sur : < http://dx.doi.org/10.1002/mrm.25174 > (consulté le no date)
    Résumé : PURPOSE: To characterize a new approach to magnetization transfer (MT) imaging with improved specificity for myelinated tissues relative to conventional MT. METHODS: Magnetization transfer preparation sequences were implemented with all radiofrequency power centered on a single frequency and also with power evenly divided between positive and negative frequencies. Dual frequency saturation was achieved both with short, alternating frequency pulses and with sinusoidal modulation of continuous irradiation. Images following preparation were acquired with a single shot fast spin echo sequence. Single and dual frequency preparation should achieve similar saturation of molecules except for those with inhomogenously broadened lines. Inhomogenous MT (IHMT) images were generated by subtraction of dual from single frequency prepared images. IHMT imaging was performed with different power and frequency in the brains of normal volunteers. RESULTS: The IHMT method demonstrated a greater white/gray matter ratio than conventional MT and virtual elimination of signal in scalp and other unmyelinated tissues. IHMT exceeded 5% of the fully relaxed magnetization in white matter. A broad frequency spectrum and signs of axonal angular dependence at high frequency were observed that are consistent with dipolar broadening. CONCLUSION: IHMT shows promise for myelin-specific imaging. Further study of physical mechanisms and diagnostic sensitivity are merited. Magn Reson Med 73:614-622, 2015. © 2014 Wiley Periodicals, Inc.
    Mots-clés : crmbm, ihMT, snc.
--- Exporter la sélection au format

Guillaume Duhamel’s Publications

2017

Journal Article

  • FOURÉ A., DUHAMEL G., VILMEN C., BENDAHAN D., JUBEAU M., GONDIN J. “Fast measurement of the quadriceps femoris muscle transverse relaxation time at high magnetic field using segmented echo-planar imaging.”. Journal of magnetic resonance imaging: JMRI [En ligne]. February 2017. Vol. 45, n°2, p. 356-368. Disponible sur : < http://dx.doi.org/10.1002/jmri.25355 > (consulté le no date)
    Résumé : PURPOSE: To assess and validate a technique for transverse relaxation time (T2 ) measurements of resting and recovering skeletal muscle following exercise with a high temporal resolution and large volume coverage using segmented spin-echo echo-planar imaging (sSE-EPI). MATERIALS AND METHODS: Experiments were performed on a 3T magnetic resonance imaging (MRI) scanner using a multislice sSE-EPI technique applied at different echo times (TEs). T2 measurements were first validated in vitro in calibrated T2 phantoms (range: 25-152 ms) by comparing sSE-EPI, standard spin-echo (SE), and multislice multiecho (MSME) techniques (using a fitting procedure or a 2-TEs calculation). In vivo measurements of resting T2 quadriceps femoris (QF) muscle were performed with both sSE-EPI and MSME sequences. Finally, sSE-EPI was used to quantify T2 changes in recovering muscle after an exercise. RESULTS: T2 values measured in vitro with sSE-EPI were similar to those assessed with SE (P > 0.05). In vitro and in vivo T2 measurements obtained with sSE-EPI were independent of the T2 determination procedure (P > 0.05). In contrast, both in vitro and in vivo T2 values derived from MSME were significantly different when using 2-TEs calculation as compared to the fitting procedure (P < 0.05). sSE-EPI allowed the detection of increased T2 values in the QF muscle immediately after exercise (+14 ± 9%), while lower T2 values were recorded less than 2 min afterwards (P < 0.05). CONCLUSION: sSE-EPI sequence is a relevant method to monitor exercise-induced T2 changes of skeletal muscles over large volume coverage and to detect abnormal patterns of muscle activation. LEVEL OF EVIDENCE: 1 J. Magn. Reson. Imaging 2017;45:356-368.
    Mots-clés : crmbm, Exercise, MRI, msk, skeletal muscle, spin-echo sequence, T2.


  • GIRARD O. M., CALLOT V., PREVOST V. H., ROBERT B., TASO M., RIBEIRO G., VARMA G., RANGWALA N., ALSOP D. C., DUHAMEL G. “Magnetization transfer from inhomogeneously broadened lines (ihMT): Improved imaging strategy for spinal cord applications.”. Magnetic Resonance in Medicine [En ligne]. January 2017. Vol. 77, p. 581-591. Disponible sur : < http://dx.doi.org/10.1002/mrm.26134 > (consulté le 10 March 2016)
    Résumé : Purpose Inhomogeneous magnetization transfer (ihMT) shows great promise for specific imaging of myelinated tissues. Whereas the ihMT technique has been previously applied in brain applications, the current report presents a strategy for cervical spinal cord (SC) imaging free of cerebrospinal fluid (CSF) pulsatility artifacts. Methods A pulsed ihMT preparation was combined with a single-shot HASTE readout. Electrocardiogram (ECG) synchronization was used to acquire all images during the quiescent phase of SC motion. However ihMT signal quantification errors may occur when a variable recovery delay is introduced in the sequence as a consequence of variable cardiac cycle. A semiautomatic retrospective correction algorithm, based on repetition time (TR) -matching, is proposed to correct for signal variations of long T1-components (e.g., CSF). Results The proposed strategy combining ECG synchronization and retrospective data pairing led to clean SC images free of CSF artifacts. Lower variability of the ihMT metrics were obtained with the correction algorithm, and allowed for shorter TR to be used, hence improving signal-to-noise ratio efficiency. Conclusion The proposed methodology enabled faster acquisitions, while offering robust ihMT quantification and exquisite SC image quality. This opens great perspectives for widening the in vivo characterization of SC physiopathology using MRI, such as studying white matter tracts microstructure or impairment in degenerative pathologies. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
    Mots-clés : crmbm, CSF pulsatility, ECG synchronization, ihMT, Inhomogeneous magnetization transfer, motion correction, myelin, snc, Spinal Cord, white matter.


  • PREVOST V. H., GIRARD O. M., MCHINDA S., VARMA G., ALSOP D. C., DUHAMEL G. “Optimization of inhomogeneous magnetization transfer (ihMT) MRI contrast for preclinical studies using dipolar relaxation time (T1D) filtering.”. NMR in Biomedicine [En ligne]. 1 June 2017. Vol. 30, n°6,. Disponible sur : < http://dx.doi.org/10.1002/nbm.3706 > (consulté le 18 August 2017)

2016

Journal Article

  • DOCHE E., LECOCQ A., MAAROUF A., DUHAMEL G., SOULIER E., CONFORT-GOUNY S., RICO A., GUYE M., AUDOIN B., PELLETIER J., RANJEVA J. - P., ZAARAOUI W. “Hypoperfusion of the thalamus is associated with disability in relapsing remitting multiple sclerosis.”. Journal of Neuroradiology. Journal De Neuroradiologie [En ligne]. 16 November 2016. Disponible sur : < http://dx.doi.org/10.1016/j.neurad.2016.10.001 > (consulté le no date)
    Résumé : BACKGROUND: While gray matter (GM) perfusion abnormalities have been evidenced in multiple sclerosis (MS) patients, the relationships with disability still remain unclear. Considering that atrophy is known to impact on perfusion, we aimed to assess perfusion abnormalities in GM of MS patients, outside atrophic regions and investigate relationships with disability. METHODS: Brain perfusion of 23 relapsing remitting MS patients and 16 matched healthy subjects were assessed at 3T using the pseudo-continuous arterial spin labeling magnetic resonance imaging technique. In order to locate potential GM perfusion abnormalities in regions spared by atrophy, we combined voxelwise comparisons of GM cerebral blood flow (CBF) maps (cortex and deep GM) (P<0.005, FWE-corrected) and voxel-based-morphometry analysis (P<0.005, FDR-corrected) to exclude atrophic regions. Disability was assessed using the Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Functional Composite score (MSFC). RESULTS: In patients, significant GM hypoperfusion outside atrophic regions was depicted only in bilateral thalami. No other cluster was found to be hypoperfused compared to controls. Perfusion of thalami was correlated to MSFC (P=0.011, rho=0.523). A trend of correlation was found between perfusion of thalami and EDSS (P=0.061, rho=-0.396). CONCLUSION: In relapsing remitting MS, perfusion abnormalities in thalamic regions contribute to disability. These findings suggest that functional impairments of thalami, representing a major brain hub, may disturb various cerebral functions even before structural damage.
    Mots-clés : Atrophy, crmbm, Disability, Multiple Sclerosis, perfusion, Pseudo-continuous arterial spin labeling, snc, Thalamus.

  • PREVOST V. H., GIRARD O. M., VARMA G., ALSOP D. C., DUHAMEL G. “Minimizing the effects of magnetization transfer asymmetry on inhomogeneous magnetization transfer (ihMT) at ultra-high magnetic field (11.75 T).”. Magma (New York, N.Y.) [En ligne]. August 2016. Vol. 29, n°4, p. 699-709. Disponible sur : < http://dx.doi.org/10.1007/s10334-015-0523-2 > (consulté le no date)
    Résumé : OBJECTIVES: The recently reported inhomogeneous magnetization transfer technique (ihMT) has been proposed for specific imaging of inhomogeneously broadened lines, and has shown great promise for characterizing myelinated tissues. The ihMT contrast is obtained by subtracting magnetization transfer images obtained with simultaneous saturation at positive and negative frequency offsets (dual frequency saturation experiment, MT (+/-)) from those obtained with single frequency saturation (MT (+)) at the same total power. Hence, ihMT may be biased by MT-asymmetry, especially at ultra-high magnetic field. Use of the average of single positive and negative frequency offset saturation MT images, i.e., (MT (+)+MT (-)) has been proposed to correct the ihMT signal from MT-asymmetry signal. MATERIALS AND METHODS: The efficiency of this correction method was experimentally assessed in this study, performed at 11.75 T on mice. Quantitative corrected ihMT and MT-asymmetry ratios (ihMTR and MTRasym) were measured in mouse brain structures for several MT-asymmetry magnitudes and different saturation parameter sets. RESULTS: Our results indicated a "safe" range of magnitudes (/MTRasym/<4 %) for which MT-asymmetry signal did not bias the corrected ihMT signal. Moreover, experimental evidence of the different natures of both MT-asymmetry and inhomogeneous MT contrasts were provided. In particular, non-zero ihMT ratios were obtained at zero MTRasym values. CONCLUSION: MTRasym is not a confounding factor for ihMT quantification, even at ultra-high field, as long as MTRasym is restricted to ±4 %.
    Mots-clés : Biomedical Engineering, Computer Appl. in Life Sciences, crmbm, dipolar order, Dipolar relaxation time, Health Informatics, ihMT, Imaging / Radiology, Inhomogeneous magnetization transfer, MT-asymmetry, myelin, snc, Solid State Physics.

  • TASO M., GIRARD O. M., DUHAMEL G., LE TROTER A., FEIWEIER T., GUYE M., RANJEVA J. - P., CALLOT V. “Tract-specific and age-related variations of the spinal cord microstructure: a multi-parametric MRI study using diffusion tensor imaging (DTI) and inhomogeneous magnetization transfer (ihMT).”. NMR in biomedicine [En ligne]. June 2016. Vol. 29, n°6, p. 817-832. Disponible sur : < http://dx.doi.org/10.1002/nbm.3530 > (consulté le no date)
    Résumé : Being able to finely characterize the spinal cord (SC) microstructure and its alterations is a key point when investigating neural damage mechanisms encountered in different central nervous system (CNS) pathologies, such as multiple sclerosis, amyotrophic lateral sclerosis or myelopathy. Based on novel methods, including inhomogeneous magnetization transfer (ihMT) and dedicated SC probabilistic atlas post-processing, the present study focuses on the in vivo characterization of the healthy SC tissue in terms of regional microstructure differences between (i) upper and lower cervical vertebral levels and (ii) sensory and motor tracts, as well as differences attributed to normal aging. Forty-eight healthy volunteers aged from 20 to 70 years old were included in the study and scanned at 3 T using axial high-resolution T2 *-w imaging, diffusion tensor imaging (DTI) and ihMT, at two vertebral levels (C2 and C5). A processing pipeline with minimal user intervention, SC segmentation and spatial normalization into a reference space was implemented in order to assess quantitative morphological and structural parameters (cross-sectional areas, scalar DTI and MT/ihMT metrics) in specific white and gray matter regions of interest. The multi-parametric MRI metrics collected allowed upper and lower cervical levels to be distinguished, with higher ihMT ratio (ihMTR), higher axial diffusivity (λ∥ ) and lower radial diffusivity (λ⊥ ) at C2 compared with C5. Significant differences were also observed between white matter fascicles, with higher ihMTR and lower λ∥ in motor tracts compared with posterior sensory tracts. Finally, aging was found to be associated with significant metric alterations (decreased ihMTR and λ∥ ). The methodology proposed here, which can be easily transferred to the clinic, provides new insights for SC characterization. It bears great potential to study focal and diffuse SC damage in neurodegenerative and demyelinating diseases. Copyright © 2016 John Wiley & Sons, Ltd.
    Mots-clés : Aging, crmbm, diffusion tensor imaging (DTI), ihMT, inhomogeneous magnetization transfer (ihMT), microstructure, multi-parametric MRI, snc, Spinal Cord.

  • VARMA G., GIRARD O. M., PREVOST V. H., GRANT A. K., DUHAMEL G., ALSOP D. C. “In vivo measurement of a new source of contrast, the dipolar relaxation time, T1D , using a modified inhomogeneous magnetization transfer (ihMT) sequence.”. Magnetic Resonance in Medicine [En ligne]. 17 November 2016. Disponible sur : < http://dx.doi.org/10.1002/mrm.26523 > (consulté le no date)
    Résumé : PURPOSE: This paper describes a technique that can be used in vivo to measure the dipolar relaxation time, T1D , of macromolecular protons contributing to magnetization transfer (MT) in tissues and to produce quantitative T1D maps. THEORY AND METHODS: The technique builds upon the inhomogeneous MT (ihMT) technique that is particularly sensitive to tissue components with long T1D . A standard ihMT experiment was altered to introduce a variable time for switching between positive and negative offset frequencies for RF saturation. A model for the dependence of ihMT was developed and used to fit data acquired in vivo. RESULTS: Application of the method to images from brains of healthy volunteers produced values of T1D  = (5.9 ± 1.2) ms in gray matter and T1D  = (6.2 ± 0.4) ms in white matter regions and provided maps of the T1D parameter. CONCLUSION: The model and experiments described provide access to a new relaxation characteristic of tissue with potentially unique diagnostic information. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

2015

Journal Article

  • GIRARD O. M., PREVOST V. H., VARMA G., COZZONE P. J., ALSOP D. C., DUHAMEL G. “Magnetization transfer from inhomogeneously broadened lines (ihMT): Experimental optimization of saturation parameters for human brain imaging at 1.5 Tesla.”. Magnetic Resonance in Medicine [En ligne]. June 2015. Vol. 73, n°6, p. 2111-2121. Disponible sur : < http://dx.doi.org/10.1002/mrm.25330 > (consulté le no date)
    Résumé : PURPOSE: Recently a new MR endogenous contrast mechanism was reported. It allows specifically imaging the magnetization transfer (MT) effect arising from inhomogeneously broadened components of the NMR spectrum, and was hence dubbed ihMT. Such unique NMR lineshape properties are presumably occurring in myelin because of its specifically ordered, multilayered sheath structure. Here, optimization of a pulsed ihMT preparation module is presented to provide guidance for future studies and improve the understanding of underlying contrast mechanisms. METHODS: This study was performed at 1.5 Tesla on healthy volunteers. A pulsed ihMT preparation was implemented in combination with a HASTE readout module. The pulse width, interpulse repetition time, total saturation duration and RF saturation power were considered for optimization of the ihMT sensitivity and contrast. RESULTS: An optimal configuration of the preparation module was derived, leading to 10% ihMT signal in internal capsule (relative to unsaturated data) and around 200% signal increase relative to gray matter, i.e., approximately 10-fold superior contrast compared with conventional MT ratios, measured under similar experimental conditions. CONCLUSION: Overall the ihMT sequence was robust, sensitive and very specific for white matter. These findings suggest great potential for assessing brain myelination and for better characterization of myelin related disorders. Magn Reson Med 73:2111-2121, 2015. © 2014 Wiley Periodicals, Inc.
    Mots-clés : crmbm, ihMT, inhomogeneously broadened lines, Magnetization transfer, myelin, snc, specificity, white matter.


  • GONDIN J., THÉRET M., DUHAMEL G., PEGAN K., MATHIEU J. R. R., PEYSSONNAUX C., CUVELLIER S., LATROCHE C., CHAZAUD B., BENDAHAN D., MOUNIER R. “Myeloid HIFs Are Dispensable for Resolution of Inflammation during Skeletal Muscle Regeneration.”. The Journal of Immunology [En ligne]. 1 April 2015. Vol. 194, n°7, p. 3389-3399. Disponible sur : < http://dx.doi.org/10.4049/jimmunol.1401420 > (consulté le 5 October 2015)
    Résumé : Besides their role in cellular responses to hypoxia, hypoxia-inducible factors (HIFs) are involved in innate immunity and also have anti-inflammatory (M2) functions, such as resolution of inflammation preceding healing. Whereas the first steps of the inflammatory response are associated with proinflammatory (M1) macrophages (MPs), resolution of inflammation is associated with anti-inflammatory MPs exhibiting an M2 phenotype. This M1 to M2 sequence is observed during postinjury muscle regeneration, which provides an excellent paradigm to study the resolution of sterile inflammation. In this study, using in vitro and in vivo approaches in murine models, we demonstrated that deletion of hif1a or hif2a in MPs has no impact on the acquisition of an M2 phenotype. Furthermore, using a multiscale methodological approach, we showed that muscles did not require macrophagic hif1a or hif2a to regenerate. These results indicate that macrophagic HIFs do not play a crucial role during skeletal muscle regeneration induced by sterile tissue damage.
    Mots-clés : crmbm, msk.

  • JUBEAU M., LE FUR Y., DUHAMEL G., WEGRZYK J., CONFORT-GOUNY S., VILMEN C., COZZONE P. J., MATTEI J. P., BENDAHAN D., GONDIN J. “Localized metabolic and t2 changes induced by voluntary and evoked contractions.”. Medicine and Science in Sports and Exercise [En ligne]. May 2015. Vol. 47, n°5, p. 921-930. Disponible sur : < http://dx.doi.org/10.1249/MSS.0000000000000491 > (consulté le no date)
    Résumé : PURPOSE: This study compared the metabolic and activation changes induced by electrically evoked (neuromuscular electrical stimulation (NMES)) and voluntary (VOL) contractions performed at the same submaximal intensity using P chemical shift imaging (CSI) and T2 mapping investigations. METHODS: Fifteen healthy subjects were asked to perform both NMES and VOL protocols with the knee extensors (i.e., 232 isometric contractions at 30% of maximal force) inside a 3-T scanner for two experimental sessions. During the first session, metabolic variations, i.e., phosphocreatine (PCr), inorganic phosphate (Pi), and pH, were recorded using localized P CSI. During a second session, T2 maps of the knee extensors were obtained at rest and immediately after each exercise. Voxels of interest were selected from the directly stimulated vastus lateralis and from the nondirectly stimulated rectus femoris/vastus intermedius muscles. RESULTS: PCr depletion recorded throughout the NMES session was significantly larger in the vastus lateralis as compared with the rectus femoris/vastus intermedius muscles for both conditions (VOL and NMES). A higher occurrence of Pi splitting and a greater acidosis was found during NMES as compared with VOL exercise, illustrating the heterogeneous activation of both slow and fast muscle fibers. T2 changes were greater after NMES as compared with VOL for both muscles but were not necessarily related to the localized metabolic demand. CONCLUSION: We provided direct evidence that the metabolic demand was strongly related to both the exercise modality and the site of stimulation. On the basis of the occurrence of Pi splitting, we suggested that NMES can activate fast muscle fibers even at low force levels.
    Mots-clés : crmbm, msk.


  • PREVOST V. H., GIRARD O. M., CALLOT V., COZZONE P. J., DUHAMEL G. “Fast imaging strategies for mouse kidney perfusion measurement with pseudocontinuous arterial spin labeling (pCASL) at ultra high magnetic field (11.75 tesla).”. Journal of Magnetic Resonance Imaging [En ligne]. 1 October 2015. Vol. 42, n°4, p. 999-1008. Disponible sur : < http://dx.doi.org/10.1002/jmri.24874 > (consulté le 5 October 2015)
    Résumé : Background To derive an adapted protocol at ultra high magnetic field for mouse kidney perfusion measurements using pCASL in combination with three widely available fast imaging readouts: segmented SE EPI (sSE EPI), RARE, and TrueFISP. Methods pCASL sSE EPI, pCASL RARE, and pCASL TrueFISP were used for the acquisition of mouse kidney perfusion images in the axial and coronal planes at 11.75T. Results were compared in terms of perfusion sensitivity, signal-to-noise ratio (SNR), blood flow values, intrasession and intersession repeatability, and image quality (subjectively classified into three grades: good, satisfactory, and unacceptable). Results Renal cortex perfusion measurements were performed within 2 min with pCASL RARE/pCASL TrueFISP and 4 min with pCASL sSE EPI. In an axial direction, SNR values of 6.6/5.6/2.8, perfusion sensitivity values of 16.1 ± 3.7/13.6 ± 2.4/13.4 ± 1.0 %, blood flow values of 679 ± 149/466 ± 111/572 ± 46 mL/100 g/min and in-ROI variations values of 192/161/181 mL/100 g/min were obtained with pCASL sSE EPI/pCASL RARE/pCASL TrueFISP. Highest SNR per unit of time (1.8) and highest intra/intersession reliability (92.9% and 95.1%) were obtained with pCASL RARE, which additionally presented highly reproducible satisfactory image quality. In coronal plane, significantly lower SNR, perfusion sensitivity and perfusion values were obtained for all techniques compared with that in the axial plane (P < 0.05) due to magnetization saturation effects. Conclusion pCASL RARE demonstrated more advantages for longitudinal preclinical kidney perfusion studies at ultra high magnetic field. J. Magn. Reson. Imaging 2015;42:999–1008.
    Mots-clés : crmbm, high magnetic field, mouse kidney, perfusion, pseudocontinuous ASL, RBF, snc.

  • VARMA G., GIRARD O. M., PREVOST V. H., GRANT A. K., DUHAMEL G., ALSOP D. C. “Interpretation of magnetization transfer from inhomogeneously broadened lines (ihMT) in tissues as a dipolar order effect within motion restricted molecules.”. Journal of Magnetic Resonance (San Diego, Calif.: 1997) [En ligne]. 7 September 2015. Vol. 260, p. 67-76. Disponible sur : < http://dx.doi.org/10.1016/j.jmr.2015.08.024 > (consulté le no date)
    Résumé : Comparison of off-resonance saturation with single and dual frequency irradiation indicates a contribution of inhomogeneously broadened lines to magnetization transfer in tissues. This inhomogeneous magnetization transfer (ihMT) phenomenon can be exploited to produce images that highlight tissues containing myelin, in vivo. Here, a model for ihMT is described that includes dipolar order effects from magnetization associated with motion-restricted macromolecules. In this model, equal irradiation at positive and negative frequency offsets eliminates dipolar order and achieves greater saturation than irradiation at a single offset frequency using the same power. Fitting of mouse and human volunteer brain data at different irradiation powers and offset frequencies was performed to assess the relevance of the model and approximate tissue parameters. A key parameter in determining ihMT signal was found to be the relaxation time T1D associated with the dipolar order reservoir and the fraction f of the semi-solid, bound magnetization that possessed a nonzero T1D. Indeed, better fits of myelinated tissue were achieved when assuming f≠1. From such fits, estimated T1Ds of mice in the white matter, (34±14)ms, were much longer than in muscle, T1D=(1±1)ms and the average f from white matter volunteer data was 2.2 times greater than that in grey matter. The combination of f and longer T1Ds was primarily responsible for the much higher ihMT in myelinated tissues, and provided explanation for the species variation. This dipolar order ihMT model should help guide future research, pulse sequence optimization, and clinical applications.
    Mots-clés : crmbm, Dipolar relaxation, ihMT, Inhomogeneous magnetization transfer, MT, myelin, Provotorov theory, Quantitative magnetization transfer, Saturation, snc, Spin temperature, SuperLorentzian lineshape.

  • VARMA G., DUHAMEL G., DE BAZELAIRE C., ALSOP D. C. “Magnetization transfer from inhomogeneously broadened lines: A potential marker for myelin.”. Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine [En ligne]. February 2015. Vol. 73, n°2, p. 614-622. Disponible sur : < http://dx.doi.org/10.1002/mrm.25174 > (consulté le no date)
    Résumé : PURPOSE: To characterize a new approach to magnetization transfer (MT) imaging with improved specificity for myelinated tissues relative to conventional MT. METHODS: Magnetization transfer preparation sequences were implemented with all radiofrequency power centered on a single frequency and also with power evenly divided between positive and negative frequencies. Dual frequency saturation was achieved both with short, alternating frequency pulses and with sinusoidal modulation of continuous irradiation. Images following preparation were acquired with a single shot fast spin echo sequence. Single and dual frequency preparation should achieve similar saturation of molecules except for those with inhomogenously broadened lines. Inhomogenous MT (IHMT) images were generated by subtraction of dual from single frequency prepared images. IHMT imaging was performed with different power and frequency in the brains of normal volunteers. RESULTS: The IHMT method demonstrated a greater white/gray matter ratio than conventional MT and virtual elimination of signal in scalp and other unmyelinated tissues. IHMT exceeded 5% of the fully relaxed magnetization in white matter. A broad frequency spectrum and signs of axonal angular dependence at high frequency were observed that are consistent with dipolar broadening. CONCLUSION: IHMT shows promise for myelin-specific imaging. Further study of physical mechanisms and diagnostic sensitivity are merited. Magn Reson Med 73:614-622, 2015. © 2014 Wiley Periodicals, Inc.
    Mots-clés : crmbm, ihMT, snc.

2014

Journal Article


  • DUHAMEL G., PREVOST V., GIRARD O. M., CALLOT V., COZZONE P. J. “High-resolution mouse kidney perfusion imaging by pseudo-continuous arterial spin labeling at 11.75T.”. Magnetic Resonance in Medicine [En ligne]. 1 March 2014. Vol. 71, n°3, p. 1186-1196. Disponible sur : < http://dx.doi.org/10.1002/mrm.24740 > (consulté le 29 October 2014)
    Résumé : Purpose Quantitative measure of blood flow provides important information regarding renal function, nephropathies and viability of kidney transplantation. Therefore, a method that would allow quantitative and reliable assessment of the renal microvascular perfusion would be very valuable. Arterial spin labeling Magnetic Resonance Imaging has started to be widely used for human studies. For rodents though, despite the increasing number of transgenic mouse models, renal perfusion Magnetic Resonance Imaging has been only sparsely reported. This study investigated the use of FAIR (flow-sensitive alternating inversion recovery) and pseudo-continuous arterial spin labeling (pCASL) for mouse renal blood flow measurements. Methods FAIR and pCASL were compared in terms of sensitivity, absolute quantification, reproducibility and flexibility of implementation. Multislice and coronal imaging were also investigated. Studies were performed at 11.75 T with volumic transmitter/receiver radiofrequency coils and fast imaging. Results pCASL demonstrated better experimental flexibility and higher sensitivity compared to FAIR (> +20%). Renal blood flow values in the range of 550–750 mL/100 g/min for the cortex and of 140–230 mL/100 g/min for the medulla, consistent with literature data, were measured. Conclusion pCASL was successfully applied at very high field for mouse renal blood flow measurements, demonstrating high sensitivity, flexibility and multislice imaging capability. pCASL may be considered as a method of choice for mouse kidney perfusion studies. Magn Reson Med 71:1186–1196, 2014. © 2013 Wiley Periodicals, Inc.
    Mots-clés : crmbm, high magnetic field, mouse kidney, perfusion, pseudo-continuous ASL, RBF.

  • FOURÉ A., NOSAKA K., WEGRZYK J., DUHAMEL G., LE TROTER A., BOUDINET H., MATTEI J. - P., VILMEN C., JUBEAU M., BENDAHAN D., GONDIN J. “Time course of central and peripheral alterations after isometric neuromuscular electrical stimulation-induced muscle damage.”. PloS One [En ligne]. 2014. Vol. 9, n°9, p. e107298. Disponible sur : < http://dx.doi.org/10.1371/journal.pone.0107298 > (consulté le no date)
    Résumé : Isometric contractions induced by neuromuscular electrostimulation (NMES) have been shown to result in a prolonged force decrease but the time course of the potential central and peripheral factors have never been investigated. This study examined the specific time course of central and peripheral factors after isometric NMES-induced muscle damage. Twenty-five young healthy men were subjected to an NMES exercise consisting of 40 contractions for both legs. Changes in maximal voluntary contraction force of the knee extensors (MVC), peak evoked force during double stimulations at 10 Hz (Db10) and 100 Hz (Db100), its ratio (10∶100), voluntary activation, muscle soreness and plasma creatine kinase activity were assessed before, immediately after and throughout four days after NMES session. Changes in knee extensors volume and T2 relaxation time were also assessed at two (D2) and four (D4) days post-exercise. MVC decreased by 29% immediately after NMES session and was still 19% lower than the baseline value at D4. The decrease in Db10 was higher than in Db100 immediately and one day post-exercise resulting in a decrease (-12%) in the 10∶100 ratio. On the contrary, voluntary activation significantly decreased at D2 (-5%) and was still depressed at D4 (-5%). Muscle soreness and plasma creatine kinase activity increased after NMES and peaked at D2 and D4, respectively. T2 was also increased at D2 (6%) and D4 (9%). Additionally, changes in MVC and peripheral factors (e.g., Db100) were correlated on the full recovery period, while a significant correlation was found between changes in MVC and VA only from D2 to D4. The decrease in MVC recorded immediately after the NMES session was mainly due to peripheral changes while both central and peripheral contributions were involved in the prolonged force reduction. Interestingly, the chronological events differ from what has been reported so far for voluntary exercise-induced muscle damage.
    Mots-clés : Adult, crmbm, Electric Stimulation, Electromyography, Exercise, Humans, Isometric Contraction, Knee, Male, Muscle Contraction, Muscle Fatigue, Neuromuscular Diseases.

  • GONDIN J., VILMEN C., COZZONE P. J., BENDAHAN D., DUHAMEL G. “High-field (11.75T) multimodal MR imaging of exercising hindlimb mouse muscles using a non-invasive combined stimulation and force measurement device.”. NMR in biomedicine [En ligne]. August 2014. Vol. 27, n°8, p. 870-879. Disponible sur : < http://dx.doi.org/10.1002/nbm.3122 > (consulté le no date)
    Résumé : We have designed and constructed an experimental set-up allowing electrical stimulation of hindlimb mouse muscles and the corresponding force measurements at high-field (11.75T). We performed high-resolution multimodal MRI (including T2 -weighted imaging, angiography and diffusion) and analysed the corresponding MRI changes in response to a stimulation protocol. Mice were tested twice over a 1-week period to investigate the reliability of mechanical measurements and T2 changes associated with the stimulation protocol. Additionally, angiographic images were obtained before and immediately after the stimulation protocol. Finally, multislice diffusion imaging was performed before, during and immediately after the stimulation session. Apparent diffusion coefficient (ADC) maps were calculated on the basis of diffusion weighted images (DWI). Both force production and T2 values were highly reproducible as illustrated by the low coefficient of variation (<8%) and high intraclass correlation coefficient (≥0.75) values. Maximum intensity projection angiographic images clearly showed a strong vascular effect resulting from the stimulation protocol. Although a motion sensitive imaging sequence was used (echo planar imaging) and in spite of the strong muscle contractions, motion artifacts were minimal for DWI recorded under exercising conditions, thereby underlining the robustness of the measurements. Mean ADC values increased under exercising conditions and were higher during the recovery period as compared with the corresponding control values. The proposed experimental approach demonstrates accurate high-field multimodal MRI muscle investigations at a preclinical level which is of interest for monitoring the severity and/or the progression of neuromuscular diseases but also for assessing the efficacy of potential therapeutic interventions.
    Mots-clés : crmbm.

2013

Journal Article

  • GINESTE C., DUHAMEL G., LE FUR Y., VILMEN C., COZZONE P. J., NOWAK K. J., BENDAHAN D., GONDIN J. “Multimodal MRI and (31)P-MRS Investigations of the ACTA1(Asp286Gly) Mouse Model of Nemaline Myopathy Provide Evidence of Impaired In Vivo Muscle Function, Altered Muscle Structure and Disturbed Energy Metabolism.”. PloS one [En ligne]. 2013. Vol. 8, n°8, p. e72294. Disponible sur : < http://dx.doi.org/10.1371/journal.pone.0072294 > (consulté le no date)
    Résumé : Nemaline myopathy (NM), the most common non-dystrophic congenital disease of skeletal muscle, can be caused by mutations in the skeletal muscle α-actin gene (ACTA1) (~25% of all NM cases and up to 50% of severe forms of NM). Muscle function of the recently generated transgenic mouse model carrying the human Asp286Gly mutation in the ACTA1 gene (Tg(ACTA1)(Asp286Gly)) has been mainly investigated in vitro. Therefore, we aimed at providing a comprehensive picture of the in vivo hindlimb muscle function of Tg(ACTA1)(Asp286Gly) mice by combining strictly noninvasive investigations. Skeletal muscle anatomy (hindlimb muscles, intramuscular fat volumes) and microstructure were studied using multimodal magnetic resonance imaging (Dixon, T2, Diffusion Tensor Imaging [DTI]). Energy metabolism was studied using 31-phosphorus Magnetic Resonance Spectroscopy ((31)P-MRS). Skeletal muscle contractile performance was investigated while applying a force-frequency protocol (1-150 Hz) and a fatigue protocol (6 min-1.7 Hz). Tg(ACTA1)(Asp286Gly) mice showed a mild muscle weakness as illustrated by the reduction of both absolute (30%) and specific (15%) maximal force production. Dixon MRI did not show discernable fatty infiltration in Tg(ACTA1)(Asp286Gly) mice indicating that this mouse model does not reproduce human MRI findings. Increased T2 values were observed in Tg(ACTA1)(Asp286Gly) mice and might reflect the occurrence of muscle degeneration/regeneration process. Interestingly, T2 values were linearly related to muscle weakness. DTI experiments indicated lower λ2 and λ3 values in Tg(ACTA1)(Asp286Gly) mice, which might be associated to muscle atrophy and/or the presence of histological anomalies. Finally (31)P-MRS investigations illustrated an increased anaerobic energy cost of contraction in Tg(ACTA1)(Asp286Gly) mice, which might be ascribed to contractile and non-contractile processes. Overall, we provide a unique set of information about the anatomic, metabolic and functional consequences of the Asp286Gly mutation that might be considered as relevant biomarkers for monitoring the severity and/or the progression of NM and for assessing the efficacy of potential therapeutic interventions.
    Mots-clés : crmbm.

  • TACHROUNT M., DUHAMEL G., LAURIN J., MARQUESTE T., DE PAULA A. M., DECHERCHI P., COZZONE P. J., CALLOT V. “In vivo short TE localized (1) H MR spectroscopy of mouse cervical spinal cord at very high magnetic field (11.75 T).”. Magnetic resonance in medicine [En ligne]. May 2013. Vol. 69, n°5, p. 1226-1232. Disponible sur : < http://dx.doi.org/10.1002/mrm.24360 > (consulté le no date)
    Résumé : MR spectroscopy allows a noninvasive assessment of metabolic information in healthy and pathological central nervous system. Whereas MR spectroscopy has been extensively applied in the brain, only few spectroscopic studies of the spinal cord (SC) have been performed so far. For mice, due to additional technical challenges, in vivo (1) H SC MRS has not yet been reported. In this work, the feasibility of short echo time localized proton magnetic resonance spectroscopy using Point RESolved Spectroscopy sequence for the examination of mouse cervical SC at 11.75 T is presented. Several optimizations were performed to improve the static field homogeneity, to reduce physiological motion effects and lipid contaminations arising from SC surrounding tissues, and to provide a careful metabolic quantification. Satisfactory spectrum quality was obtained. The described protocol allowed reliable quantification of five metabolites in the cervical SC. The mean reproducibility regarding the quantification of tNAA, tCr and tCho was ≥ 80%, > 70% for mI and > 55% for Glu, whereas the intersubject variabilities were ≤ 21%. The application of this protocol to transgenic mouse models in pathological conditions such as SC injury or neurodegenerative diseases may thus provide complementary information to MRI and increase our understanding of such pathologies. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.
    Mots-clés : Algorithms, Animals, Cervical Vertebrae, crmbm, Magnetic Resonance Spectroscopy, Male, Mice, Mice, Inbred C57BL, Protons, Reproducibility of Results, Sensitivity and Specificity, Spinal Cord, Tissue Distribution.

2012

Journal Article

  • DUHAMEL G., CALLOT V., TACHROUNT M., ALSOP D. C., COZZONE P. J. “Pseudo-continuous arterial spin labeling at very high magnetic field (11.75 T) for high-resolution mouse brain perfusion imaging.”. Magnetic resonance in medicine [En ligne]. May 2012. Vol. 67, n°5, p. 1225-1236. Disponible sur : < http://dx.doi.org/10.1002/mrm.23096 > (consulté le no date)
    Résumé : With the increasing number of transgenic mouse models of human brain diseases, there is a need for a sensitive method that allows assessing quantitative whole brain perfusion within a reasonable scan time. Arterial spin labeling (ASL), an MRI technique that permits the noninvasive quantification of cerebral blood flow, has been used to assess rodents brain perfusion. For mice, the reported experiments performed with continuous or pulsed ASL were challenged by poor multislice capability, limited sensitivity, or quantification issues. Here, the recently proposed pseudo-continuous ASL strategy, which has shown great promise for human studies, was investigated for mouse brain perfusion imaging at 11.75 T. Pseudo-continuous ASL was experimentally optimized and compared with a standard flow-sensitive alternating inversion recovery sequence for sensitivity, robustness, absolute quantification, and multislice imaging capability. A sensitivity gain up to 40% and clear advantages for multislice imaging are obtained with pseudo-continuous ASL.
    Mots-clés : Algorithms, Animals, Blood Flow Velocity, Brain, Cerebrovascular Circulation, crmbm, Image Enhancement, Image Interpretation, Computer-Assisted, Magnetic Resonance Angiography, Male, Mice, Mice, Inbred C57BL, Models, Animal, Reproducibility of Results, Sensitivity and Specificity, Spin Labels.

2011

Book Section
  • CALLOT V., DUHAMEL G., KOBER F. “Spinal cord - MR of rodent models.”. In : Methods in molecular biology (Clifton, N.J.). [s.l.] : [s.n.], 2011. p. 355-383.
    Résumé : Different MR techniques, such as relaxation times, diffusion, perfusion, and spectroscopy have been employed to study rodent spinal cord. In this chapter, a description of these methods is given, along with examples of normal metrics that can be derived from the MR acquisitions, as well as examples of applications to pathology.
    Mots-clés : Animals, crmbm, Diffusion Magnetic Resonance Imaging, Mice, Rats, Rodentia, Spinal Cord.
  • KOBER F., DUHAMEL G., CALLOT V. “Cerebral perfusion MRI in mice.”. In : Methods in molecular biology (Clifton, N.J.). [s.l.] : [s.n.], 2011. p. 117-138.
    Résumé : Perfusion MRI is a tool to assess the spatial distribution of microvascular blood flow. Arterial spin labeling (ASL) is shown here to be advantageous for quantification of cerebral microvascular blood flow (CBF) in rodents. This technique is today ready for assessment of a variety of murine models of human pathology including those associated with diffuse microvascular dysfunction. This chapter provides an introduction to the principles of CBF measurements by MRI along with a short overview over applications in which these measurements were found useful. The basics of commonly employed specific arterial spin-labeling techniques are described and theory is outlined in order to give the reader the ability to set up adequate post-processing tools. Three typical MR protocols for pulsed ASL on two different MRI systems are described in detail along with all necessary sequence parameters and technical requirements. The importance of the different parameters entering theory is discussed. Particular steps for animal preparation and maintenance during the experiment are given, since CBF regulation is sensitive to a number of experimental physiological parameters and influenced mainly by anesthesia and body temperature.
    Mots-clés : Anesthesia, Animals, Cerebrovascular Circulation, crmbm, Magnetic Resonance Imaging, Mice.

2010

Journal Article

  • CALLOT V., DUHAMEL G., LE FUR Y., DECHERCHI P., MARQUESTE T., KOBER F., COZZONE P. J. “Echo planar diffusion tensor imaging of the mouse spinal cord at thoracic and lumbar levels: A feasibility study.”. Magnetic resonance in medicine [En ligne]. April 2010. Vol. 63, n°4, p. 1125-1134. Disponible sur : < http://dx.doi.org/10.1002/mrm.22301 > (consulté le no date)
    Résumé : Diffusion tensor imaging is increasingly used for probing spinal cord (SC) pathologies, especially in mouse models of human diseases. However, diffusion tensor imaging series requires a long acquisition time and mouse experiments rarely use rapid imaging techniques such as echo planar imaging. A recent preliminary study demonstrated the feasibility and robustness of the echo planar imaging sequence for mouse cervical SC diffusion tensor imaging investigations. The feasibility of echo planar imaging at thoracic and lumbar levels, however, remained unknown due to bulk motion, field inhomogeneities, and off-centering of the SC in the axial plane. In the present study, the feasibility and the robustness of an echo planar imaging-based diffusion tensor imaging sequence for mouse thoracic and lumbar SC investigations is demonstrated. Quantitative and accurate diffusion tensor imaging metrics, as well as high spatially resolved images, have been obtained. This successful demonstration may open new perspectives in the field of mouse SC imaging. Echo planar imaging is used in several imaging modalities, such as relaxometry or perfusion, and may prove to be very attractive for multimodal MR investigations to acquire a more detailed characterization of the SC tissue.
    Mots-clés : Analysis of Variance, Animals, crmbm, Diffusion Magnetic Resonance Imaging, Echo-Planar Imaging, Feasibility Studies, Image Processing, Computer-Assisted, Lumbar Vertebrae, Male, Mice, Sensitivity and Specificity, Spinal Cord, Thoracic Vertebrae.

2009

Journal Article

  • DUHAMEL G., CALLOT V., DECHERCHI P., LE FUR Y., MARQUESTE T., COZZONE P. J., KOBER F. “Mouse lumbar and cervical spinal cord blood flow measurements by arterial spin labeling: sensitivity optimization and first application.”. Magnetic Resonance in Medicine [En ligne]. August 2009. Vol. 62, n°2, p. 430-439. Disponible sur : < http://dx.doi.org/10.1002/mrm.22015 > (consulté le no date)
    Résumé : In spinal cord injuries (SCI), tissue edema and consequent ischemia play an important role in neuronal damage. The assessment of quantitative spinal cord blood flow (SCBF) would be very valuable to help in understanding SCI pathophysiology. SCBF has previously been measured in animals with invasive techniques such as hydrogen clearance or labeled microspheres. A recent preliminary study also demonstrated the feasibility of assessing cervical SCBF by MRI with arterial spin labeling (ASL). However, due to bulk motion and field inhomogeneities, the feasibility of perfusion MRI at lower levels of the SC (thoracic, lumbar) remained an open question. In the present study, absolute SCBF measurements were carried out at both the cervical C3 and lumbar L1 levels of mouse SC using an adapted presaturated flow-sensitive alternating inversion recovery (presat-FAIR) ASL technique at 11.75T. Quantitative SCBF maps (resolution of 133 x 133 microm(2)) showed significantly lower gray matter (GM) perfusion values at the L1 level as compared to the C3 level (6% and 11% for the ventral and dorsal horns and 8% for total GM). The presat-FAIR technique was then successfully applied to a mouse model of hemisection performed at the L1 level, illustrating the potential of ASL to help in SC pathology characterization.
    Mots-clés : Animals, Arteries, Blood Flow Velocity, Cervical Vertebrae, crmbm, Image Enhancement, Information Storage and Retrieval, Lumbar Vertebrae, Magnetic Resonance Angiography, Male, Mice, Mice, Inbred C57BL, Reproducibility of Results, Rheology, Sensitivity and Specificity, Spin Labels, Spinal Cord.

2008

Journal Article

  • CALLOT V., DUHAMEL G., COZZONE P. J., KOBER F. “Short-scan-time multi-slice diffusion MRI of the mouse cervical spinal cord using echo planar imaging.”. NMR in biomedicine [En ligne]. October 2008. Vol. 21, n°8, p. 868-877. Disponible sur : < http://dx.doi.org/10.1002/nbm.1274 > (consulté le no date)
    Résumé : Mouse spinal cord (SC) diffusion-weighted imaging (DWI) provides important information on tissue morphology and structural changes that may occur during pathologies such as multiple sclerosis or SC injury. The acquisition scheme of the commonly used DWI techniques is based on conventional spin-echo encoding, which is time-consuming. The purpose of this work was to investigate whether the use of echo planar imaging (EPI) would provide good-quality diffusion MR images of mouse SC, as well as accurate measurements of diffusion-derived metrics, and thus enable diffusion tensor imaging (DTI) and highly resolved DWI within reasonable scan times. A four-shot diffusion-weighted spin-echo EPI (SE-EPI) sequence was evaluated at 11.75 T on a group of healthy mice (n = 10). SE-EPI-derived apparent diffusion coefficients of gray and white matter were compared with those obtained using a conventional spin-echo sequence (c-SE) to validate the accuracy of the method. To take advantage of the reduction in acquisition time offered by the EPI sequence, multi-slice DTI acquisitions were performed covering the cervical segments (six slices, six diffusion-encoding directions, three b values) within 30 min (vs 2 h for c-SE). From these measurements, fractional anisotropy and mean diffusivities were calculated, and fiber tracking along the C1 to C6 cervical segments was performed. In addition, high-resolution images (74 x 94 microm(2)) were acquired within 5 min per direction. Clear delineation of gray and white matter and identical apparent diffusion coefficient values were obtained, with a threefold reduction in acquisition time compared with c-SE. While overcoming the difficulties associated with high spatially and temporally resolved DTI measurements, the present SE-EPI approach permitted identification of reliable quantitative parameters with a reproducibility compatible with the detection of pathologies. The SE-EPI method may be particularly valuable when multiple sets of images from the SC are needed, in cases of rapidly evolving conditions, to decrease the duration of anesthesia or to improve MR exploration by including additional MR measurements.
    Mots-clés : Anatomy, Cross-Sectional, Animals, Cervical Vertebrae, crmbm, Diffusion Magnetic Resonance Imaging, Echo-Planar Imaging, Image Enhancement, Image Interpretation, Computer-Assisted, Male, Mice, Mice, Inbred C57BL, Spinal Cord.

  • DUHAMEL G., CALLOT V., COZZONE P. J., KOBER F. “Spinal cord blood flow measurement by arterial spin labeling.”. Magnetic Resonance in Medicine [En ligne]. April 2008. Vol. 59, n°4, p. 846-854. Disponible sur : < http://dx.doi.org/10.1002/mrm.21567 > (consulté le no date)
    Résumé : The assessment of spinal cord (SC) hemodynamics, and especially SC blood flow (SCBF), plays a key role in the pathophysiological description and understanding of many SC diseases such as ischemia, or spinal cord injury. SCBF has been previously measured in animals with invasive techniques such as autoradiography or labeled microspheres; no MR technique, however, has been proposed so far. The possibility of quantitatively measuring SCBF in mice using MRI was investigated using a presaturated FAIR (flow-sensitive alternating inversion recovery) arterial spin labeling (ASL) technique. SCBF measurements were performed at the cervical level of the mouse as well as on the brain so as to use cerebral blood flow (CBF) values as internal references. With a spatial resolution of 133 x 133 microm(2) for the SCBF maps, absolute regional perfusion values could be measured within the different structures of the SC (gray matter, white matter, and cerebrospinal fluid area). Similar perfusion values were found in SC gray matter (330+/-90 mL/100g/min) and in brain (295+/-22 mL/100g/min for thalamus). This result, in agreement with SCBF/CBF measurements performed with non-MR techniques, opens new perspectives for noninvasive longitudinal and in vivo animal studies. Application to human experiments may also be possible.
    Mots-clés : Animals, Blood Flow Velocity, crmbm, Image Interpretation, Computer-Assisted, Magnetic Resonance Imaging, Male, Mice, Mice, Inbred C57BL, Microcirculation, Spin Labels, Spinal Cord.

  • KOBER F., DUHAMEL G., COZZONE P. J. “Experimental comparison of four FAIR arterial spin labeling techniques for quantification of mouse cerebral blood flow at 4.7 T.”. NMR in biomedicine [En ligne]. October 2008. Vol. 21, n°8, p. 781-792. Disponible sur : < http://dx.doi.org/10.1002/nbm.1253 > (consulté le no date)
    Résumé : Pulsed arterial spin labeling (ASL) is an attractive and robust method for quantification of rodent cerebral blood flow (CBF) in particular, although there is a need for sensitivity optimization. Look-Locker flow-sensitive alternating inversion recovery (FAIR) echo planar imaging (EPI) (LLFAIREPI) was expected to be a likely candidate for assessing sensitivity, although it has not yet been applied to rodents. In this study, the performance of two FAIR techniques and two Look-Locker FAIR techniques were compared in mouse brain at 4.7 T. FAIR-EPI (single inversion time, FAIREPI-1TI), FAIR-EPI (eight inversion times, FAIREPI-8TI), LLFAIREPI and Look-Locker FAIR gradient echo (LLFAIRGE) sequences were implemented with equal spatial resolution and equal FAIR preparation modules. Measurements were carried out sequentially on the brain in 10 healthy mice, and quantitative CBF maps were obtained after different acquisition times up to 23 min. All methods gave similar group variability in CBF. Especially at shorter acquisition times, LLFAIREPI gave lower relative variations in CBF within selected brain regions than the other techniques at the same acquisition time. The Look-Locker techniques, however, overestimated CBF compared with classical FAIR-EPI, which was attributed to bulk flow in arterioles and T(2) effects. The image quality with LLFAIREPI was less reproducible within the group. Both FAIREPI-1TI and LLFAIREPI appear to be good candidates for serial rapid measurement of CBF, but LLFAIREPI has the additional advantage that apparent T(1) can be measured simultaneously with CBF.
    Mots-clés : Animals, Cerebral Arteries, Cerebrovascular Circulation, crmbm, Image Interpretation, Computer-Assisted, Magnetic Resonance Angiography, Male, Mice, Mice, Inbred C57BL, Reproducibility of Results, Rheology, Sensitivity and Specificity, Spin Labels.

2007

Journal Article

  • CALLOT V., DUHAMEL G., COZZONE P. J. “In vivo mouse spinal cord imaging using echo-planar imaging at 11.75 T.”. Magma (New York, N.Y.) [En ligne]. October 2007. Vol. 20, n°4, p. 169-173. Disponible sur : < http://dx.doi.org/10.1007/s10334-007-0079-x > (consulté le no date)
    Résumé : OBJECT: To evaluate the feasibility of mouse spinal cord MR imaging using echo-planar imaging (EPI). MATERIALS AND METHODS: Optimized multi-shot spin-echo-EPI sequences were compared to conventional spin-echo (c-SE) at 11.75 T and used for high-spatially resolved acquisitions and relaxation-time measurements. RESULTS: Good quality images were obtained, with clear delineation of gray and white matter. Acquisition-time gain factor was up to 6 (vs. c-SE) and resolution up to 74 x 94 microm2 was achieved. T1 and T2 relaxation times were reliably measured. CONCLUSION: High-temporally and spatially resolved mouse spinal cord EPI imaging is feasible. This technique should greatly benefit to long acquisition-time experiments (diffusion imaging) and imaging of rapidly-evolving pathologies.
    Mots-clés : Animals, crmbm, Echo-Planar Imaging, Mice, Reproducibility of Results, Sensitivity and Specificity, Spinal Cord.

2006

Journal Article

  • DE BAZELAIRE C., ROFSKY N. M., DUHAMEL G., ZHANG J., MICHAELSON M. D., GEORGE D., ALSOP D. C. “Combined T2* and T1 measurements for improved perfusion and permeability studies in high field using dynamic contrast enhancement.”. European radiology [En ligne]. September 2006. Vol. 16, n°9, p. 2083-2091. Disponible sur : < http://dx.doi.org/10.1007/s00330-006-0198-1 > (consulté le no date)
    Résumé : This study analyzed the T2* effect of extracellularly distributed gadolinium contrast agents in arterial blood during tumor studies using T1-weighted sequences at high field strength. A saturation-prepared dual echo sequence with echo times of 1.5 and 3.5 ms was employed at 3 T to simultaneously characterize T1 and T2* of arterial blood during bolus administration of Gd-DTPA in 28 patients with body tumors. T2* effect and T1 effect of Gd-DTPA on image intensity of whole blood were calibrated in human blood samples with different concentrations of contrast agent. T2* was used to estimate concentration near the peak of the bolus. T1 was used to measure lower concentrations when T2* was not significant. T2* was measurable on calibration curves for Gd-DTPA concentrations higher than 4 mM. This concentration was exceeded in 18 patients. The mean signal intensity reduction because of T2* effect was estimated at 22+/-14% of the T2* compensated signal. Using T2* measurements reduced underestimations of peak arterial Gd-DTPA concentration (59 +/- 38%) and overestimation of permeability Ktrans (58%). The T2* effect of gadolinium contrast agents should therefore be accounted for when performing tumors study with T1-weighted sequences at high field strength.
    Mots-clés : Aorta, Calibration, Carcinoma, Renal Cell, Contrast Media, Gadolinium DTPA, Humans, Image Enhancement, Lung Neoplasms, Magnetic Resonance Angiography, Permeability, Phantoms, Imaging.

  • DUHAMEL G., SCHLAUG G., ALSOP D. C. “Measurement of arterial input functions for dynamic susceptibility contrast magnetic resonance imaging using echoplanar images: comparison of physical simulations with in vivo results.”. Magnetic resonance in medicine [En ligne]. March 2006. Vol. 55, n°3, p. 514-523. Disponible sur : < http://dx.doi.org/10.1002/mrm.20802 > (consulté le no date)
    Résumé : Measurement of the arterial input bolus shape is essential to the quantification of mean transit time and blood flow with dynamic susceptibility contrast (DSC) MRI. Input functions derived from the echoplanar signal intensity within or near arteries are highly nonlinear, yet such input functions are widely used. We employed a physical model for the echoplanar signal intensity from an artery as a function of contrast agent concentration, artery size, and angle to the magnetic field to test approaches for the measurement of the arterial input function. The simulated results confirmed the strong nonlinearity of signal in the neighborhood of vessels. Of the input function measurement methods considered, the simulations suggested that measurement of signal near but not within a large vessel is most accurate, but mean transit times (MTT) calculated with these input functions are highly sensitive to peak bolus concentration. Input functions determined from voxels demonstrating the shortest first moment overestimated the MTT but the measured MTTs were more robust to changes in peak concentration. Characteristics of the measured in vivo input functions were consistent with the simulations. Our results emphasize the important contribution of input function errors to the uncertainty in MTT and blood flow imaging with DSC MRI.
    Mots-clés : Adult, Arteries, Blood Circulation, Echo-Planar Imaging, Humans, Male, Models, Theoretical, Physical Stimulation.

2005

Journal Article

  • DE BAZELAIRE C., ROFSKY N. M., DUHAMEL G., MICHAELSON M. D., GEORGE D., ALSOP D. C. “Arterial spin labeling blood flow magnetic resonance imaging for the characterization of metastatic renal cell carcinoma(1).”. Academic radiology [En ligne]. March 2005. Vol. 12, n°3, p. 347-357. Disponible sur : < http://dx.doi.org/10.1016/j.acra.2004.12.012 > (consulté le no date)
    Résumé : RATIONALE AND OBJECTIVE: This study sought to assess the feasibility of arterial spin labeling (ASL) blood flow (BF) magnetic resonance imaging (MRI) for the study of metastatic renal cell carcinoma (RCC) in the body, where the respiratory, cardiac, and peristaltic motions present challenges when applying ASL. MATERIALS AND METHODS: ASL was performed using a background-suppressed single-section flow-alternating inversion recovery (FAIR) preparation and a single-shot fast spin-echo imaging sequence on a 3.0-T whole body imager. Tumor BF was evaluated for 26 patients with RCC metastatic to the liver, bone, lung, or lymph nodes before VEGF receptor inhibitor therapy. Two cases with tumor size change after treatment were also scanned 1 month after therapy. For validation, kidney cortex BF in five normal volunteers was measured with the same technique and compared with literature values. RESULTS: ASL was successfully performed in all normal volunteers and in 20 of 26 patients. The six failures resulted from a systematic error, which can be avoided in future studies. For normal volunteers, measured kidney cortex BF was 275 +/- 14 mL/min/100 g, a value consistent with the literature. ASL determined tumor BF averaged across tumor volume and subjects was 194 mL/min/100 g (intersubject SD = 100), resulting in high perfusion signal and conspicuity of lesions. Bright signal was also seen in large vessels and occasionally in bowel. In the two cases studied 1 month after therapy, ASL perfusion changes were consistent with tumor size changes. CONCLUSION: With background suppression, ASL MRI is a feasible method for quantifying BF in patients with renal cell carcinoma. This technique may be useful for evaluating tumor response to antiangiogenic agents.
    Mots-clés : Antineoplastic Agents, Bone Neoplasms, Carcinoma, Renal Cell, Cohort Studies, Contrast Media, Feasibility Studies, Female, Follow-Up Studies, Humans, Image Processing, Computer-Assisted, Kidney Neoplasms, Liver Neoplasms, Lung Neoplasms, Lymphatic Metastasis, Magnetic Resonance Imaging, Male, Phthalazines, Protein Kinase Inhibitors, Pyridines, Receptors, Vascular Endothelial Growth Factor, Regional Blood Flow, Spin Labels.

  • GARCIA D. M., DUHAMEL G., ALSOP D. C. “Efficiency of inversion pulses for background suppressed arterial spin labeling.”. Magnetic resonance in medicine [En ligne]. August 2005. Vol. 54, n°2, p. 366-372. Disponible sur : < http://dx.doi.org/10.1002/mrm.20556 > (consulté le no date)
    Résumé : Background suppression strategies for arterial spin labeling (ASL) MRI offer reduced noise from motion and other system instabilities. However, the inversion pulses used for suppression can also attenuate the ASL signal, which may offset the advantages of background suppression. Numerical simulations were used to optimize the inversion efficiency of four candidate pulses over a range of radiofrequency (RF) and static magnetic field variations typical of in vivo imaging. Optimized pulses were then used within a pulsed ASL sequence to assess the pulses' in vivo inversion efficiencies for ASL. The measured in vivo inversion efficiency was significantly lower than theoretical predictions (e.g., 93% experimental compared to 99% theoretical) for the tangent hyperbolic pulse applied in a background suppression scheme. This inefficiency was supported by an in vitro study of human blood. These results suggest that slow magnetization transfer (MT) in blood, either with bound water or macromolecular protons, dominates the inversion inefficiency in blood. Despite the attenuated signal relative to unsuppressed ASL, the signal-to-noise ratio (SNR) with suppression was improved by 23-110% depending on the size of the region measured. Knowledge of efficiency will aid optimization of the number of suppression pulses and provide more accurate quantification of blood flow.
    Mots-clés : Adult, Algorithms, Arteries, Blood Flow Velocity, Brain, Female, Hemorheology, Humans, Image Processing, Computer-Assisted, Magnetic Resonance Imaging, Male, Models, Theoretical, Phantoms, Imaging, Spin Labels, Subtraction Technique.

  • PENET M. - F., VIOLA A., CONFORT-GOUNY S., LE FUR Y., DUHAMEL G., KOBER F., IBARROLA D., IZQUIERDO M., COLTEL N., GHARIB B., GRAU G. E., COZZONE P. J. “Imaging experimental cerebral malaria in vivo: significant role of ischemic brain edema.”. The Journal of Neuroscience: The Official Journal of the Society for Neuroscience [En ligne]. 10 August 2005. Vol. 25, n°32, p. 7352-7358. Disponible sur : < http://dx.doi.org/10.1523/JNEUROSCI.1002-05.2005 > (consulté le no date)
    Résumé : The first in vivo magnetic resonance study of experimental cerebral malaria is presented. Cerebral involvement is a lethal complication of malaria. To explore the brain of susceptible mice infected with Plasmodium berghei ANKA, multimodal magnetic resonance techniques were applied (imaging, diffusion, perfusion, angiography, spectroscopy). They reveal vascular damage including blood-brain barrier disruption and hemorrhages attributable to inflammatory processes. We provide the first in vivo demonstration for blood-brain barrier breakdown in cerebral malaria. Major edema formation as well as reduced brain perfusion was detected and is accompanied by an ischemic metabolic profile with reduction of high-energy phosphates and elevated brain lactate. In addition, angiography supplies compelling evidence for major hemodynamics dysfunction. Actually, edema further worsens ischemia by compressing cerebral arteries, which subsequently leads to a collapse of the blood flow that ultimately represents the cause of death. These findings demonstrate the coexistence of inflammatory and ischemic lesions and prove the preponderant role of edema in the fatal outcome of experimental cerebral malaria. They improve our understanding of the pathogenesis of cerebral malaria and may provide the necessary noninvasive surrogate markers for quantitative monitoring of treatment.
    Mots-clés : Animals, Blood-Brain Barrier, Brain, Brain Edema, Brain Ischemia, Cerebral Hemorrhage, Cerebrovascular Circulation, crmbm, Female, Magnetic Resonance Angiography, Magnetic Resonance Imaging, Malaria, Cerebral, Mice, Mice, Inbred CBA, Neurons.

2004

Book Section
Journal Article

  • DE BAZELAIRE C. M. J., DUHAMEL G. D., ROFSKY N. M., ALSOP D. C. “MR imaging relaxation times of abdominal and pelvic tissues measured in vivo at 3.0 T: preliminary results.”. Radiology [En ligne]. March 2004. Vol. 230, n°3, p. 652-659. Disponible sur : < http://dx.doi.org/10.1148/radiol.2303021331 > (consulté le no date)
    Résumé : PURPOSE: To measure T1 and T2 relaxation times of normal human abdominal and pelvic tissues and lumbar vertebral bone marrow at 3.0 T. MATERIALS AND METHODS: Relaxation time was measured in six healthy volunteers with an inversion-recovery method and different inversion times and a multiple spin-echo (SE) technique with different echo times to measure T1 and T2, respectively. Six images were acquired during one breath hold with a half-Fourier acquisition single-shot fast SE sequence. Signal intensities in regions of interest were fit to theoretical curves. Measurements were performed at 1.5 and 3.0 T. Relaxation times at 1.5 T were compared with those reported in the literature by using a one-sample t test. Differences in mean relaxation time between 1.5 and 3.0 T were analyzed with a two-sample paired t test. RESULTS: Relaxation times (mean +/- SD) at 3.0 T are reported for kidney cortex (T1, 1,142 msec +/- 154; T2, 76 msec +/- 7), kidney medulla (T1, 1,545 msec +/- 142; T2, 81 msec +/- 8), liver (T1, 809 msec +/- 71; T2, 34 msec +/- 4), spleen (T1, 1,328 msec +/- 31; T2, 61 msec +/- 9), pancreas (T1, 725 msec +/- 71; T2, 43 msec +/- 7), paravertebral muscle (T1, 898 msec +/- 33; T2, 29 msec +/- 4), bone marrow in L4 vertebra (T1, 586 msec +/- 73; T2, 49 msec +/- 4), subcutaneous fat (T1, 382 msec +/- 13; T2, 68 msec +/- 4), prostate (T1, 1,597 msec +/- 42; T2, 74 msec +/- 9), myometrium (T1, 1,514 msec +/- 156; T2, 79 msec +/- 10), endometrium (T1, 1,453 msec +/- 123; T2, 59 msec +/- 1), and cervix (T1, 1,616 msec +/- 61; T2, 83 msec +/- 7). On average, T1 relaxation times were 21% longer (P <.05) for kidney cortex, liver, and spleen and T2 relaxation times were 8% shorter (P <.05) for liver, spleen, and fat at 3.0 T; however, the fractional change in T1 and T2 relaxation times varied greatly with the organ. At 1.5 T, no significant differences (P >.05) in T1 relaxation time between the results of this study and the results of other studies for liver, kidney, spleen, and muscle tissue were found. CONCLUSION: T1 relaxation times are generally higher and T2 relaxation times are generally lower at 3.0 T than at 1.5 T, but the magnitude of change varies greatly in different tissues.
    Mots-clés : Abdomen, Adult, Artifacts, Bone Marrow, Female, Humans, Image Enhancement, Image Processing, Computer-Assisted, Lumbar Vertebrae, Magnetic Resonance Imaging, Male, Pelvis, Reference Values.

2003

Journal Article

  • CHOQUET P., HYACINTHE J. - N., DUHAMEL G., GRILLON E., LEVIEL J. - L., CONSTANTINESCO A., ZIEGLER A. “Method to determine in vivo the relaxation time T1 of hyperpolarized xenon in rat brain.”. Magnetic resonance in medicine [En ligne]. June 2003. Vol. 49, n°6, p. 1014-1018. Disponible sur : < http://dx.doi.org/10.1002/mrm.10471 > (consulté le no date)
    Résumé : The magnetic polarization of the stable (129)Xe isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized (129)Xe MRI should allow quantitative mapping of cerebral blood flow with better spatial resolution than scintigraphic techniques. A parameter necessary for this quantitation, and not previously known, is the longitudinal relaxation time (T(1) (tissue)) of (129)Xe in brain tissue in vivo: a method for determining this is reported. The time course of the MR signal in the brain during arterial injection of hyperpolarized (129)Xe in a lipid emulsion was analyzed using an extended two-compartment model. The model uses experimentally determined values of the RF flip angle and the T(1) of (129)Xe in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T(1) (tissue) = 3.6 +/- 2.1 sec (+/-SD, n = 6). This method enables quantitative mapping of cerebral blood flow.
    Mots-clés : Animals, Brain, Cerebrovascular Circulation, Magnetic Resonance Spectroscopy, Male, Models, Neurological, Rats, Rats, Sprague-Dawley, Xenon Isotopes.

  • DUHAMEL G., DE BAZELAIRE C., ALSOP D. C. “Evaluation of systematic quantification errors in velocity-selective arterial spin labeling of the brain.”. Magnetic resonance in medicine [En ligne]. July 2003. Vol. 50, n°1, p. 145-153. Disponible sur : < http://dx.doi.org/10.1002/mrm.10510 > (consulté le no date)
    Résumé : Velocity-selective (VS) sequences potentially permit arterial spin labeling (ASL) perfusion imaging with labeling applied very close to the tissue. In this study the effects of cerebrospinal fluid (CSF) motion, radiofrequency (RF) field imperfections, and sequence timing parameters on the appearance and quantitative perfusion values obtained with VS-ASL were evaluated. Large artifacts related to CSF motion were observed with moderate velocity weighting, which were removed by inversion recovery preparation at the cost of increased imaging time. Imperfect refocusing and excitation pulses resulting from nonuniform RF fields produced systematic errors in the ASL subtraction images. A phase cycling scheme was introduced to eliminate these errors. Quantitative perfusion images were obtained with CSF suppression and phase cycling. Gray matter blood flow of 27.7 ml 100 g(-1) min(-1), approximately half the value reported in studies using spatially-selective ASL, was measured. Potential sources for this underestimation are discussed.
    Mots-clés : Adult, Artifacts, Blood Flow Velocity, Brain, Cerebral Arteries, Cerebrospinal Fluid, Cerebrovascular Circulation, Female, Humans, Image Enhancement, Magnetic Resonance Imaging, Male, Reproducibility of Results, Sensitivity and Specificity, Spin Labels.

2002

Journal Article

2001

Journal Article
  • DUHAMEL G., CHOQUET P., GRILLON E., LAMALLE L., LEVIEL J. L., ZIEGLER A., CONSTANTINESCO A. “Xenon-129 MR imaging and spectroscopy of rat brain using arterial delivery of hyperpolarized xenon in a lipid emulsion.”. Magnetic resonance in medicine. August 2001. Vol. 46, n°2, p. 208-212.
    Résumé : Hyperpolarized (129)Xe dissolved in a lipid emulsion constitutes an NMR tracer that can be injected into the blood stream, enabling blood-flow measurement and perfusion imaging. A small volume (0.15 ml) of this tracer was injected in 1.5 s in rat carotid and (129)Xe MR spectra and images were acquired at 2.35 T to evaluate the potential of this approach for cerebral studies. Xenon spectra consistently showed two resonances, at 194.5 ppm and 199.0 ppm relative to the gas peak. The signal-to-noise ratio (SNR) obtained for the two peaks was sufficient (ranging from 12 to 90) to follow their time courses. 2D transverse-projection xenon images were obtained with an in-plane resolution of 900 microm per pixel (SNR range 8-15). Histological analysis revealed no brain damage except in two rats that had received three injections.
    Mots-clés : Animals, Brain, Emulsions, Injections, Intravenous, Lipids, Magnetic Resonance Spectroscopy, Rats, Signal Processing, Computer-Assisted, Xenon Isotopes.
  • KOBER F., WOLF P. E., VERMEULEN G., DUHAMEL G., LAMALLE L., LEVIEL J. L., DÉCORPS M., ZIEGLER A. “Rat lung MRI using low-temperature prepolarized helium-3.”. Magnetic Resonance in Medicine. June 2001. Vol. 45, n°6, p. 1130-1133.
    Résumé : The purpose of this study was to evaluate the recently proposed technique of 3He prepolarization at low temperature and high field (Kober et al. Magn Reson Med 1999; 41:1084-1087) for fast imaging of the lung. Helium-3 was cooled to 2.4 K in a magnetic field of 8 Tesla to obtain a polarization of 0.26%. The polarized 3He was warmed up to room temperature and transferred to a rat, with a final polarization of about 0.1%, large enough for acquiring a 3D image of the rat lung in 30 s.
    Mots-clés : Animals, Cold Temperature, Helium, Image Enhancement, Image Processing, Computer-Assisted, Imaging, Three-Dimensional, Isotopes, Lung, Magnetic Resonance Imaging, Rats.

2000

Journal Article
  • DUHAMEL G., CHOQUET P., LEVIEL J. L., STEIBEL J., LAMALLE L., JULIEN C., KOBER F., GRILLON E., DEROUARD J., DÉCORPS M., ZIEGLER A., CONSTANTINESCO A. “In vivo 129Xe NMR in rat brain during intra-arterial injection of hyperpolarized 129Xe dissolved in a lipid emulsion.”. Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie. June 2000. Vol. 323, n°6, p. 529-536.
    Résumé : Hyperpolarized 129Xe was dissolved in a lipid emulsion and administered to anaesthetized rats by manual injections into the carotid (approximately 1-1.5 mL in a maximum time of 30 s). During injection, 129Xe NMR brain spectra at 2.35 T were recorded over 51 s, with a repetition time of 253 ms. Two peaks assigned to dissolved 129Xe were observed (the larger at 194 +/- 1 ppm assigned to intravascular xenon and the smaller at 199 +/- 1 ppm to xenon dissolved in the brain tissue). Their kinetics revealed a rapid intensity increase, followed by a plateau (approximately 15 s duration) and then a decrease over 5 s. This behaviour was attributed to combined influences of the T1 relaxation of the tracer, of radiofrequency sampling, and of the tracer perfusion rate in rat brain. Similar kinetics were observed in experiments carried out on a simple micro-vessel phantom. An identical experimental set-up was used to acquire a series of 2D projection 129Xe images on the phantom and the rat brain.
    Mots-clés : Animals, Brain, Emulsions, Fat Emulsions, Intravenous, Injections, Intra-Arterial, Magnetic Resonance Spectroscopy, Male, Rats, Rats, Sprague-Dawley, Xenon Isotopes.

1999

Journal Article
  • KOBER F., WOLF P. E., LEVIEL J. L., VERMEULEN G., DUHAMEL G., DELON A., DEROUARD J., DÉCORPS M., ZIEGLER A. “Low-temperature polarized helium-3 for MRI applications.”. Magnetic Resonance in Medicine. June 1999. Vol. 41, n°6, p. 1084-1087.
    Résumé : The first 3He nuclear magnetic resonance (NMR) experiments using low-temperature prepolarization are presented. 3He cells were polarized at 4.2 K and 4.7 T, transported to another magnet, heated to room temperature, and used for NMR experiments at 2.35 T. Cells with and without a rubidium coating were tested. In both cases, the NMR signal was greater than 100 times the thermal equilibrium signal. No evidence of a rubidium coating effect on the longitudinal relaxation time T1 of 3He (500 mbar) at 4.2 K could be demonstrated. NMR gradient-echo images of the cells were acquired.
    Mots-clés : Helium, Humans, Isotopes, Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, Rubidium.
--- Exporter la sélection au format