Feasibility of pseudocontinuous arterial spin labeling at 7 T with whole-brain coverage.
OBJECTIVE
We studied the feasibility of pseudocontinuous arterial spin labeling (pCASL) at 7 T.


METHODS
Simulations were performed to find the optimal labeling parameters for pCASL, with particular attention to the maximum-allowed specific absorption rate (SAR). Subsequently, pCASL experiments (four volunteers) were performed to find the B1 efficiency at the labeling position with and without high-permittivity pads placed around the head, and to study the optimal labeling duration (four separate volunteers). Finally, feasibility of whole-brain pCASL imaging was tested.


RESULTS
Simulations showed that a lower B1 efficiency should be compensated by a lower effective flip angle of the labeling, a moderately shorter labeling duration, and a longer repetition time. B1 efficiency in the internal carotid arteries just below the carotid siphon was approximately 55% and 35% with and without high-permittivity pads, respectively. In vivo experiments showed an optimal labeling duration of 1,500 ms, although longer labeling durations up to 2,500 ms resulted in similar signal-to-noise efficiency. Whole-brain pCASL imaging was demonstrated in a single volunteer.


CONCLUSIONS
Despite decreased B1 efficiency, sufficient labeling efficiency can be achieved for whole-brain pCASL at 7 T with high-permittivity pads. However, image quality is still limited compared with 3 T, probably due to imaging instabilities, and further research is needed to elucidate this.
Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center (LUMC), C3-Q, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. ghariq@lumc.nl
Eidrees
E
Ghariq
Wouter M
WM
Teeuwisse
Andrew G
AG
Webb
Matthias J P
MJ
van Osch
D000328:Adult; D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D002343:Carotid Artery, Internal / Q000502:physiology; D002536:Cerebral Arteries / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012039:Regional Blood Flow; D059629:Signal-To-Noise Ratio; D013113:Spin Labels
D013113:Spin Labels