Multi-slice perfusion-based functional MRI using the FAIR technique: comparison of CBF and BOLD effects

Perfusion-weighted imaging techniques employing blood water protons as an endogenous tracer have poor temporal resolution because each image should be acquired with an adequate spin 'tagging' time. Thus, perfusion-based functional magnetic resonance imaging studies are typically performed on a single slice. To alleviate this problem, a multi-slice flow-sensitive alternating inversion recovery technique has been developed. Following a single inversion pulse and a delay time, multi-slice echo-planar images are acquired sequentially without any additional inter-image delay. Thus, the temporal resolution of multi-slice FAIR is almost identical to that of single slice techniques. The theoretical background for multi-slice FAIR is described in detail. The multi-slice FAIR technique has been successfully applied to obtain three-slice cerebral blood flow based functional images during motor tasks. The relative CBF change in the contralateral motor/sensory area during unilateral thumb-digit opposition is 45.0+/-12.2% (n=9), while the blood oxygenation level dependent signal change is 1.5+/-0.4 SD%. Relative changes of the oxygen consumption rate can be estimated from CBF and BOLD changes using FAIR. The BOLD signal change is not correlated with the relative CBF increase, and thus caution should be exercised when interpreting the BOLD change as a quantitative index of the CBF change, especially in inter-subject comparisons.