SNR-efficient whole-brain pseudo-continuous arterial spin labeling perfusion imaging at 7 T.

PURPOSE: To optimize pseudo-continuous arterial spin labeling (PCASL) parameters to maximize SNR efficiency for RF power constrained whole brain perfusion imaging at 7 T.

METHODS

We used Bloch simulations of pulsatile laminar flow to optimize the PCASL parameters for maximum SNR efficiency, balancing labeling efficiency and total RF power. The optimization included adjusting the inter-RF pulse spacing (TRPCASL), mean B1 + (B1 + ave), slice-selective gradient amplitude (Gmax), and mean gradient amplitude (Gave). In vivo data were acquired from six volunteers at 7 T to validate the optimized parameters. Dynamic B0-shimming and flip angle adjustments were used to avoid needing to make the PCASL parameters robust to B0/B1 + variations.

RESULTS

The optimized PCASL parameters achieved a significant (3.3×) reduction in RF power while maintaining high labeling efficiency. This allowed for longer label durations and minimized deadtime, resulting in a 118% improvement in SNR efficiency in vivo compared to a previously proposed protocol. Additionally, the static tissue response was improved, reducing the required distance between labeling plane and imaging volume.

CONCLUSION

These optimized PCASL parameters provide a robust and efficient approach for whole brain perfusion imaging at 7 T, with significant improvements in SNR efficiency and reduced specific absorption rate burden.