On the application of susceptibility-weighted ultra-fast low-angle RARE experiments in functional MR imaging

The applicability of displaced, split-echo, and phase-cycled variants of the blood oxygenation level-dependent (BOLD) sensitized ultra-fast low-angle rapid acquisition and relaxation enhancement (UFLARE) technique for the mapping of brain function are examined in functional magnetic resonance imaging (fMRI) experiments at high magnetic field strength (3 T). Activation maps are presented for visual and motor-sensory activation. For the visual studies the range of the stimulation-associated signal intensity changes is 5-7% in voxels containing mainly gray matter and 10-15% in voxels dominated by larger vessels. The motor studies reveal signal changes of 5-10% in the primary motor cortex and in the supplementary motor area. For gray matter, T2* increases from 31.2 +/- 1.5 msec under baseline conditions to 33.0 +/- 1.5 msec during periods of visual stimulation. The results clearly demonstrate that T2*-weighted UFLARE is a robust and reliable method for detection of brain activation. The relative pros and cons of displaced, split-echo, and phase-cycled T2*-sensitized UFLARE versions are discussed for fMRI applications. Since the susceptibility weighting can be freely adjusted from zero upward, the UFLARE variants used are particularly suitable for functional examinations in regions with poor magnetic field homogeneity and at high magnetic field strengths.