Simultaneous multi-slice (SMS) or multiband (MB) imaging has recently been attempted for arterial spin labeled (ASL) perfusion MRI in conjunction with echo-planar imaging (EPI) readout. It was found that SMS-EPI can reduce the T1 relaxation effect of the label and improve image coverage and resolution with little penalty in signal-to-noise ratio (SNR). However, EPI still suffers from geometric distortion and signal dropout from field inhomogeneity effects especially at high and ultrahigh magnetic fields. Here we present a novel scheme for achieving high fidelity distortion-free quantitative perfusion imaging by combining pseudo-continuous ASL (pCASL) with SMS Turbo-FLASH (TFL) readout at both 3 and 7T. Bloch equation simulation was performed to characterize and optimize the TFL-based pCASL perfusion signal. Two MB factors (3 and 5) were implemented in SMS-TFL pCASL and compared with standard 2D TFL and EPI pCASL sequences. The temporal SNR of SMS-TFL pCASL relative to that of standard TFL pCASL was 0.76±0.10 and 0.74±0.11 at 7T and 0.70±0.05 and 0.65±0.05 at 3T for MB factor of 3 and 5, respectively. By implementing background suppression in conjunction with SMS-TFL at 3T, the relative temporal SNR improved to 0.84±0.09 and 0.79±0.10 for MB factor of 3 and 5, respectively. Compared to EPI pCASL, significantly increased temporal SNR (p<0.001) and improved visualization of orbitofrontal cortex were achieved using SMS-TFL pCASL. By combining SMS acceleration with TFL pCASL, we demonstrated the feasibility for whole brain distortion-free quantitative mapping of cerebral blood flow at high and ultrahigh magnetic fields.
Bibliographical noteFunding Information:
This research was supported by the National Institute of Health (NIH) Grants R01-MH080892 , R01-NS081077 , and R01-EB014922 , the NIH Human Connectome Project ( NIH U54MH091657 ), the Biomedical Technology Resource Centers (BTRC) National Center for Research Resources (NCRR; P41 RR08079 ), the National Institute of Biomedical Imaging and Bioengineering (NIBIB; P41 EB015894 ) and the Siemens Healthcare USA, Inc. In addition, the authors would like to acknowledge Robert Smith for the helpful discussion on the manuscript and Kay Jann for the statistical analysis.
- Arterial spin labeling (ASL)
- Cerebral blood flow (CBF)
- Multiband (MB)
- Simultaneous multi-slice (SMS)
- Turbo-FLASH (TFL)