Multislice perfusion imaging in human brain using the
C-FOCI inversion pulse: comparison with hyperbolic secant.
Yongbi MN, Yang Y, Frank JA, Duyn JH.
Laboratory of Diagnostic Radiology Research, National Institutes of Health,
Bethesda, MD 20892, USA.
Perfusion studies based on pulsed arterial spin labeling have primarily applied
hyperbolic secant (HS) pulses for spin inversion. To optimize perfusion
sensitivity, it is highly desirable to implement the HS pulse with the same
slice width as the width of the imaging pulse. Unfortunately, this approach
causes interactions between the slice profiles and manifests as residual 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 labeled blood to reach
the imaging slice (transit time), causing loss of perfusion sensitivity as a
result of T(1) relaxation effects. In this study, we demonstrate 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 multislice perfusion imaging
on the cerebrum is presented, showing substantial improvement in slice
definition in vivo compared with the HS pulse. The sharper FOCI profile is shown
to reduce the physical gap (or "safety margin") between the inversion
and imaging slabs, resulting in a significant increase in perfusion signal
without residual contamination from static tissue. The mean +/- SE (n = 6) gray
matter perfusion-weighted signal (DeltaM/M(o)) without 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- and FOCI-FAIR sequences,
respectively. Compared with the HS-based data, the FOCI-FAIR results correspond
to an average increase in perfusion signal of up to between 26%-30%. Magn Reson
Med 42:1098-1105, 1999. Copyright 1999 Wiley-Liss, Inc.