REDUCTION OF SUSCEPTIBILITY EFFECTS IN BOLD FMRI USING TAILORED RF PULSES: BRAIN

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Introduction: High speed fMRI is desirable since it allows (1) dynamically imaging functional events; (2) reducing motion artifacts. Partial k-space (PK) imaging increases speed by collecting fewer phase encodes while preserving spatial resolution. PK can also be used in the readout direction to reduce echo time, leading to reduced flow and/or susceptibility dephasing. This study examines the feasibility of PK fMRI technique. Method: MR data were acquired on a GE 1.5 T scanner. Motor cortex activation images were obtained by running a GRE-EPI (single 4mm slice, TR/TE/FOV = 375ms/40ms/240mm, 4 shots, 160 frames in 240s, 128x128 matrix, finger apposition alternated between the left and right hands every 20s) and a 2D spiral sequence (8 slices of 3mm thickness, TR/TE/FA/FOV = 640ms/40ms/ 63o/240mm, 4 interleaves, 100 frames in 256s, resting state alternated with right hand finger tapping every 20s). The spiral data were regridded onto a 128x128 Fourier grid so that PK simulation could be carried out. PK reconstruction was performed using the homodyne approach. Results: The PK activation patterns are highly similar to that of FK. Although PK images have reduced SNR than the FK images, they don't have reduced spatial resolution nor significant ringing or blurring. Discussion and Conclusions: Our results demonstrate the feasibility of PK fMRI technique. A 2D PK technique can save nearly 1/2 scan time, while a 3D PK scan can obtain close to 4 times higher temporal resolution. The time savings can be used to collect more frames to increase statistical power or to cover more slices. The reduced time for each time frame allows using longer TR, leading to improved CNR and/or inflow charateristics. The same time per frame can be used to increase spatial resolution if so desired. Considering that PK imaging techniques are widely available, it represents a promising approach for brain functional mapping.