Multislice perfusion imaging in human brain using the C-FOCI inversion pulse: Comparison with hyperbolic secant

Perfusion studies based on pulsed arterial spin labeling have primarily app lied hyperbolic secant (HS) pulses for spin inversion. To optimize perfusio n sensitivity, it is highly desirable to implement the HS pulse with the sa me slice width as the width of the imaging purse. Unfortunately, this appro ach causes interactions between the slice profiles and manifests as residua l signal from static tissue in the resultant perfusion image. This problem is currently overcome by increasing the selective HS width relative to the imaging slice width. However, this solution increases the time for the labe led blood to reach the imaging slice (transit time), causing loss of perfus ion sensitivity as a result of T-1 relaxation effects. in this study, we de monstrate that the preceding problems can be largely overcome by use of the C-shaped frequency offset corrected inversion (FOCI) pulse [Ordidge et al. , Magn Reson Med 1996;36:562]. The implementation of this pulse for multisl ice perfusion imaging on the cerebrum is presented, showing substantial imp rovement in slice definition in vivo compared with the HS pulse. The sharpe r FOCI profile is shown to reduce the physical gap (or "safety margin") bet ween the inversion and imaging slabs, resulting in a significant increase i n perfusion signal without residual contamination from static tissue. The m ean +/- SE (n = 6) gray matter perfusion-weighted signal (Delta M/M-o) with out the application of vascular signal suppression gradients were 1.19 +/- 0.10% (HS-flow-sensitive alternating inversion recovery [FAIR]), and 1.51 /- 0.11% for the FOCI-FAIR sequence. The corresponding values with Vascular signal suppression were 0.64 +/- 0.14%, and 0.91 +/- 0.08% using the HS- a nd FOCI-FAIR sequences, respectively. Compared with the MS-based data, the FOCI-FAIR results correspond to an average increase in perfusion signal of up to between 26%-30%. (C) 1999 Wiley-Liss, Inc.