Transfer insensitive labeling technique (TILT): Application to multislice functional perfusion imaging

Cerebral blood flow can be studied in a multislice mode with a recently proposed perfusion sequence using inversion of water spins as an endogenous tracer without magnetization transfer artifacts. The magnetization transfer insensitive labeling technique (TILT) has been used for mapping blood flow changes at a microvascular level under motor activation in a multislice mode. In TILT, perfusion mapping is achieved by subtraction of a perfusion- sensitized image from a control image. Perfusion weighting is accomplished by proximal blood labeling using two 90°radiofrequency excitation pulses. For control preparation the labeling pulses are modified such that they have no net effect on blood water magnetization. The percentage of blood flow change, as well as its spatial extent, has been studied in single and multislice modes with varying delays between labeling and imaging. The average perfusion signal change due to activation was 36.9 ± 9.1% in the single-slice experiments and 38.1 ± 7.9% in the multislice experiments. The volume of activated brain areas amounted to 1.51 ± 0.95 cm³ in the contralateral primary motor (M1) area, 0.90 ± 0.72 cc in the ipsilateral M1 area, 1.27 ± 0.39 cm³ in the contralateral and 1.42 ± 0.75 cm³ in the ipsilateral premotor areas, and 0.71 ± 0.19 cm³ in the supplementary motor area.