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MASSIRE Aurélien

PhD, Post-doctoral Fellow

aurelien.massire@univ-amu.fr
Tel : +33 4 91 38 62 61
Key Words
- Parallel transmission
- Spinal cord
- Multiparametric quantitative MRI
- RF pulse design

Current Research Interest and projects


My research project is centred on the development of innovative MR methods for human spinal cord (SC) proton imaging at 7 Tesla, using a cervical 8TX/8RX RF coil-array prototype. High-resolution multiparametric MRI data are acquired to improve the non-invasive characterization of the healthy and pathological SC.

As 7T SC imaging is challenged by RF field inhomogeneity, high specific absorption rate (SAR), magnetic susceptibility and physiological motion artifacts, the project requires RF pulse and MRI sequence design, and also enabling the parallel transmission (pTx) capabilities of the coil in order to use its full potential. The expected benefits of pTx are: signal and contrast artifact mitigation, acquisition time and SAR decrease, and image resolution enhancement.

I am working under the supervision of Virginie Callot (CNRS DR2).

My current activities at CRMBM (Massire et al. January 2017)

Awards



- ISMRM Summa Cum Laude merit award. 24th ISMRM, Singapore, 2016. Massire et al., #1130.
- 2014 Best PhD Thesis award. French Society of Magnetic Resonance in Biology and Medicine.
- ISMRM Magna Cum Laude merit award. 22nd ISMRM, Milan, 2014. Massire et al., #0945.

Patents


Use of an optimal control algorithm for the design of MRI refocusing pulses with phase-free rotation axis. Patent WO2015158814.

Publications

2016

Journal Article

  • MASSIRE A., TASO M., BESSON P., GUYE M., RANJEVA J. - P., CALLOT V. “High-resolution multi-parametric quantitative magnetic resonance imaging of the human cervical spinal cord at 7T.”. NeuroImage [En ligne]. 2016. Vol. 143, p. 58-69. Disponible sur : < http://dx.doi.org/10.1016/j.neuroimage.2016.08.055 > (consulté le no date)
    Résumé : Quantitative MRI techniques have the potential to characterize spinal cord tissue impairments occurring in various pathologies, from both microstructural and functional perspectives. By enabling very high image resolution and enhanced tissue contrast, ultra-high field imaging may offer further opportunities for such characterization. In this study, a multi-parametric high-resolution quantitative MRI protocol is proposed to characterize in vivo the human cervical spinal cord at 7T. Multi-parametric quantitative MRI acquizitions including T1, T2(*) relaxometry mapping and axial diffusion MRI were performed on ten healthy volunteers with a whole-body 7T system using a commercial prototype coil-array dedicated to cervical spinal cord imaging. Automatic cord segmentation and multi-parametric data registration to spinal cord templates enabled robust regional studies within atlas-based WM tracts and GM horns at the C3 cervical level. T1 value, cross-sectional area and GM/WM ratio evolutions along the cervical cord were also reported. An original correction method for B1(+)-biased T1 mapping sequence was additionally proposed and validated on phantom. As a result, relaxometry and diffusion parameters derived from high-resolution quantitative MRI acquizitions were reported at 7T for the first time. Obtained images, with unmatched resolutions compared to lower field investigations, provided exquisite anatomical details and clear delineation of the spinal cord substructures within an acquisition time of 30min, compatible with clinical investigations. Regional statistically significant differences were highlighted between WM and GM based on T1 and T2* maps (p<10(-3)), as well as between sensory and motor tracts based on diffusion tensor imaging maps (p<0.05). The proposed protocol demonstrates that ultra-high field spinal cord high-resolution quantitative MRI is feasible and lays the groundwork for future clinical investigations of degenerative spinal cord pathologies.
    Mots-clés : crmbm, diffusion tensor imaging, Quantitative MRI, Relaxometry mapping, spinal cord, Template-based segmentation, Ultra-high field.

2015

Journal Article

2014

Journal Article
  • BOULANT N., BOTTLAENDER M., UHRIG L., GIACOMINI E., LUONG M., AMADON A., MASSIRE A., LARRAT B., VIGNAUD A. “FID navigator-based MR-Thermometry method to monitor small temperature changes in the brain of ventilated animals.”. 01 November 2014.


  • MASSIRE A., VIGNAUD A., ROBERT B., LE BIHAN D., BOULANT N., AMADON A. “Parallel-transmission-enabled three-dimensional T2-weighted imaging of the human brain at 7 Tesla.”. Magnetic Resonance in Medicine [En ligne]. 2014. Disponible sur : < http://dx.doi.org/10.1002/mrm.25353 >
    Résumé : Purpose: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel-transmission to obtain high-quality T2-weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. Methods: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit-SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a kT-point trajectory to simultaneously mitigate B1+ and ΔB0 nonuniformities. Results: In vivo experiments showed that exploiting parallel-transmission at 7T with the proposed methodology produces high quality T2-weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. Conclusion: This work demonstrates that the adopted formalism based on optimal control, combined with the kT-point method, successfully enables three-dimensional T2-weighted brain imaging at 7T devoid of artifacts resulting from B1+ inhomogeneity. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Mots-clés : B1+ inhomogeneity mitigation, Optimal control theory, parallel transmission, Refocusing, T2-weighted imaging.

2013

Journal Article


  • BOULANT N., MASSIRE A., AMADON A., VIGNAUD A. “Radiofrequency pulse design in parallel transmission under strict temperature constraints.”. Magnetic Resonance in Medicine [En ligne]. 01 October 2013. p. n/a–n/a. Disponible sur : < http://dx.doi.org/10.1002/mrm.24974 >
    Résumé : Purpose To gain radiofrequency (RF) pulse performance by directly addressing the temperature constraints, as opposed to the specific absorption rate (SAR) constraints, in parallel transmission at ultra-high field. Methods The magnitude least-squares RF pulse design problem under hard SAR constraints was solved repeatedly by using the virtual observation points and an active-set algorithm. The SAR constraints were updated at each iteration based on the result of a thermal simulation. The numerical study was performed for an SAR-demanding and simplified time of flight sequence using B1 and ΔB0 maps obtained in vivo on a human brain at 7T. Results The proposed adjustment of the SAR constraints combined with an active-set algorithm provided higher flexibility in RF pulse design within a reasonable time. The modifications of those constraints acted directly upon the thermal response as desired. Conclusion Although further confidence in the thermal models is needed, this study shows that RF pulse design under strict temperature constraints is within reach, allowing better RF pulse performance and faster acquisitions at ultra-high fields at the cost of higher sequence complexity. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Mots-clés : high field, parallel transmission, RF pulse design, SAR, Temperature.

  • HOYOS-IDROBO A., WEISS P., MASSIRE A., AMADON A., BOULANT N. “On Variant Strategies To Solve The Magnitude Least Squares Optimization Problem In Parallel Transmission Pulse Design And Under Strict SAR And Power Constraints.”. IEEE Transactions on Medical Imaging [En ligne]. 01 December 2013. Vol. Early Access Online,. Disponible sur : < http://dx.doi.org/10.1109/TMI.2013.2295465 > (consulté le no date)
    Résumé : Parallel transmission is a very promising candidate technology to mitigate the inevitable radiofrequency (RF) field inhomogeneity in magnetic resonance imaging (MRI) at ultra-high field (UHF). For the first few years, pulse design utilizing this technique was expressed as a least squares problem with crude power regularizations aimed at controlling the specific absorption rate (SAR), hence the patient safety. This approach being suboptimal for many applications sensitive mostly to the magnitude of the spin excitation, and not its phase, the magnitude least squares (MLS) problem then was first formulated in 2007. Despite its importance and the availability of other powerful numerical optimization methods, the MLS problem yet has been faced almost exclusively by the pulse designer with the so-called variable exchange method. In this paper, we investigate various two-stage strategies consisting of different initializations and nonlinear programming approaches, and incorporate directly the strict SAR and hardware constraints. Several schemes such as sequential quadratic programming (SQP), interior point (I-P) methods, semidefinite programming (SDP) and magnitude squared least squares (MSLS) relaxations are studied both in the small and large tip angle regimes with RF and static field maps obtained in-vivo on a human brain at 7 Tesla. Convergence and robustness of the different approaches are analyzed, and recommendations to tackle this specific problem are finally given. Small tip angle and inversion pulses are returned in a few seconds and in under a minute respectively while respecting the constraints, allowing the use of the proposed approach in routine.
    Mots-clés : Magnetic Resonance Imaging, Mathematical programming, optimization, RF parallel transmission.

  • MASSIRE A., CLOOS M. A., VIGNAUD A., LE BIHAN D., AMADON A., BOULANT N. “Design of non-selective refocusing pulses with phase-free rotation axis by gradient ascent pulse engineering algorithm in parallel transmission at 7T.”. Journal of Magnetic Resonance [En ligne]. 2013. Vol. 230, p. 76-83. Disponible sur : < http://dx.doi.org/10.1016/j.jmr.2013.01.005 >
    Résumé : At ultra-high magnetic field (≥ 7T), B1 and ΔB0 non-uniformities cause undesired inhomogeneities in image signal and contrast. Tailored radiofrequency pulses exploiting parallel transmission have been shown to mitigate these phenomena. However, the design of large flip angle excitations, a prerequisite for many clinical applications, remains challenging due the non-linearity of the Bloch equation. In this work, we explore the potential of gradient ascent pulse engineering to design non-selective spin-echo refocusing pulses that simultaneously mitigate severe B1 and ΔB0 non-uniformities. The originality of the method lays in the optimization of the rotation matrices themselves as opposed to magnetization states. Consequently, the commonly used linear class of large tip angle approximation can be eliminated from the optimization procedure. This approach, combined with optimal control, provides additional degrees of freedom by relaxing the phase constraint on the rotation axis, and allows the derivative of the performance criterion to be found analytically. The method was experimentally validated on an 8-channel transmit array at 7T, using a water phantom with B1 and ΔB0 inhomogeneities similar to those encountered in the human brain. For the first time in MRI, the rotation matrix itself on every voxel was measured by using Quantum Process Tomography. The results are complemented with a series of spin-echo measurements comparing the proposed method against commonly used alternatives. Both experiments confirm very good performance, while simultaneously maintaining a low energy deposition and pulse duration compared to well-known adiabatic solutions.

2012

Journal Article

  • MASSIRE A., CLOOS M. A., LUONG M., AMADON A., VIGNAUD A., WIGGINS C. J., BOULANT N. “Thermal simulations in the human head for high field MRI using parallel transmission.”. Journal of Magnetic Resonance Imaging [En ligne]. 2012. Vol. 35, n°6, p. 1312-1321. Disponible sur : < http://dx.doi.org/10.1002/jmri.23542 >
    Résumé : PURPOSE: To investigate, via numerical simulations, the compliance of the specific absorption rate (SAR) versus temperature guidelines for the human head in magnetic resonance imaging procedures utilizing parallel transmission at high field. MATERIALS AND METHODS: A combination of finite element and finite-difference time-domain methods was used to calculate the evolution of the temperature distribution in the human head for a large number of parallel transmission scenarios. The computations were performed on a new model containing 20 anatomical structures. RESULTS: Among all the radiofrequency field exposure schemes simulated, the recommended 39°C maximum local temperature was never exceeded when the local 10-g average SAR threshold was reached. On the other hand, the maximum temperature barely complied with its guideline when the global SAR reached 3.2 W/kg. The maximal temperature in the eye could very well rise by more than 1°C in both cases. CONCLUSION: Considering parallel transmission, the recommended values of local 10-g SAR may remain a relevant metric to ensure that the local temperature inside the human head never exceeds 39°C, although it can lead to rises larger than 1°C in the eye. Monitoring temperature instead of SAR can provide increased flexibility in pulse design for parallel transmission.
    Mots-clés : Body Temperature, Computer Simulation, Dose-Response Relationship, Radiation, Head, Humans, Magnetic Fields, Magnetic Resonance Imaging, Models, Biological, Radiation Dosage.
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