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Journal Article

  • Chen, Z, Zhang, X, Yuan, C, Zhao, X & van Osch, MJP 2016, “Measuring the labeling efficiency of pseudocontinuous arterial spin labeling”, Magnetic Resonance in Medicine.
    Résumé : PURPOSE: Optimization and validation of a sequence for measuring the labeling efficiency of pseudocontinuous arterial spin labeling (pCASL) perfusion MRI. METHODS: The proposed sequence consists of a labeling module and a single slice Look-Locker echo planar imaging readout. A model-based algorithm was used to calculate labeling efficiency from the signal acquired from the main brain-feeding arteries. Stability of the labeling efficiency measurement was evaluated with regard to the use of cardiac triggering, flow compensation and vein signal suppression. Accuracy of the measurement was assessed by comparing the measured labeling efficiency to mean brain pCASL signal intensity over a wide range of flip angles as applied in the pCASL labeling. RESULTS: Simulations show that the proposed algorithm can effectively calculate labeling efficiency when correcting for T1 relaxation of the blood spins. Use of cardiac triggering and vein signal suppression improved stability of the labeling efficiency measurement, while flow compensation resulted in little improvement. The measured labeling efficiency was found to be linearly (R = 0.973; P < 0.001) related to brain pCASL signal intensity over a wide range of pCASL flip angles. CONCLUSION: The optimized labeling efficiency sequence provides robust artery-specific labeling efficiency measurement within a short acquisition time (∼30 s), thereby enabling improved accuracy of pCASL CBF quantification. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
    Mots-clés : Arterial spin labeling (ASL), labeling efficiency, MRI, perfusion imaging, pseudocontinuous.

  • Zhang, X, Ghariq, E, Hartkamp, NS, Webb, AG & van Osch, MJP 2016, “Fast cerebral flow territory mapping using vessel encoded dynamic arterial spin labeling (VE-DASL)”, Magnetic Resonance in Medicine, vol. 75, no. 5, p. 2041-2049.
    Résumé : PURPOSE: Whole-brain territory mapping using planning-free vessel-encoded pseudocontinuous arterial-spin-labeling (VE-pCASL) takes approximately 5 min, which is frequently considered too long for standard clinical protocols. In this study, vessel-encoded dynamic-ASL (VE-DASL) is optimized to achieve fast (< 30 s) cerebral flow territory mapping, especially aimed for the acute setting. METHODS: VE-DASL is based on the creation of a continuous stream of magnetically labeled or unlabeled blood with different encoding patterns for each feeding artery, whose inflow into the brain tissue is monitored continuously. This approach leads to unique signal fluctuation within each flow territory, enabling reconstruction of individual flow territories by means of clustering techniques followed by linear regression. RESULTS: VE-DASL was implemented and validated both as single slice and whole-brain method. In vivo results showed reasonable agreement with the "gold-standard" reference maps obtained from VE-pCASL. The Dice similarity coefficient which represents the fractional overlap between VE-DASL and "gold-standard" VE-pCASL territories ranged from 83.4% to 87.7% for the right internal cerebral artery (RICA), 81.7% to 83.1% for the left internal cerebral artery (LICA) and 64.3% to 71.8% for the vertebral arteries. CONCLUSION: VE-DASL has the potential to map the main flow territories with whole-brain coverage in a short scan duration (∼30 s).
    Mots-clés : acute stroke, arterial spin labeling, cerebral flow territory mapping, vessel encoded pCASL, vessel-encoded dynamic arterial spin labeling.


Journal Article

  • Zhang, X, Petersen, ET, Ghariq, E, De Vis, JB, Webb, AG, Teeuwisse, WM, Hendrikse, J & van Osch, MJP 2013, “In vivo blood T(1) measurements at 1.5 T, 3 T, and 7 T”, Magnetic Resonance in Medicine, vol. 70, no. 4, p. 1082-1086.
    Résumé : The longitudinal relaxation time of blood is a crucial parameter for quantification of cerebral blood flow by arterial spin labeling and is one of the main determinants of the signal-to-noise ratio of the resulting perfusion maps. Whereas at low and medium magnetic field strengths (B0), its in vivo value is well established; at ultra-high field, this is still uncertain. In this study, longitudinal relaxation time of blood in the sagittal sinus was measured at 1.5 T, 3 T, and 7 T. A nonselective inversion pulse preceding a Look-Locker echo planar imaging sequence was performed to obtain the inversion recovery curve of venous blood. The results showed that longitudinal relaxation time of blood at 7 T was ∼ 2.1 s which translates to an anticipated 33% gain in the signal-to-noise ratio in arterial spin labeling experiments due to T1 relaxation alone compared with 3 T. In addition, the linear relationship between longitudinal relaxation time of blood and B0 was confirmed.
    Mots-clés : 7 T, Adult, arterial spin labeling, Blood Flow Velocity, Blood Volume, Blood Volume Determination, Brain, Cerebrovascular Circulation, Female, Humans, Image Interpretation, Computer-Assisted, longitudinal relaxation time, magnetic field, Magnetic Resonance Angiography, Male, Reproducibility of Results, Sensitivity and Specificity, T1, Young Adult.
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