T1rho contrast in functional magnetic resonance imaging.

The application of T1 in the rotating frame (T1rho) to functional MRI in humans was studied at 3 T. Increases in neural activity increased parenchymal T1rho. Modeling suggested that cerebral blood volume mediated this increase. A pulse sequence named spin-locked echo planar imaging (SLEPI) that produces both T1rho and T2* contrast was developed and used in a visual functional MRI (fMRI)experiment. Spin-locked contrast significantly augments the T2* blood oxygen level-dependent (BOLD) contrast in this sequence. The total functional contrast generated by the SLEPI sequence (1.31%) was 54% larger than the contrast (0.85%) obtained from a conventional gradient-echo EPI sequence using echo times of 30 ms. Analysis of image SNR revealed that the spin-locked preparation period of the sequence produced negligible signal loss from static dephasing effects. The SLEPI sequence appears to be an attractive alternative to conventional BOLD fMRI, particularly when long echo times are undesirable, such as when studying prefrontal cortex or ventral regions, where static susceptibility gradients often degrade T2*-weighted images.