Fast and high resolution MRSI without aliasing using online SFAS and multiple regions of support

Introduction When localized magnetic resonance spectroscopic imaging (MRSI) is performed, unperfected signal saturation outside the region of interest (ROI) is typically encountered. This undesired signal can cause aliasing and signal contamination if fast high resolution MRSI is conducted by simply reducing FOV (i.e. Zoom MRSI). Alternatively, one can use the sequential forward array selection (SFAS) method to obtain the same resolution MRSI with the same or less data acquisition time required by the Zoom MRSI method [1]. In this work, we demonstrate that online SFAS can not only provide high resolution MRSI with less data acquisition time but also eliminate the aliasing unsaturated signal. Methods The ROI of the spectroscopic imaging slice was planned on a T1 weighted scout image (data matrix = 256x256, FOV 256cm). The MRSI was conducted by using a 3D localized adiabatic spin echo refocusing (LASER) sequence with two dimensions of phase encoding [2]. Water suppression was provided by an initial broadband semi-selective excitation pulse and frequency selective DANTE pulse applied to the water resonance. The data were acquired with a reduced number of nonuniform phase encodes using the online SFAS over an FOV of 256x256mm resulting in an acquisition time of 8 minutes (TR/TE of 2000/75 ms) and a nominal voxel size of 0.64cc (thk=1 cm). Free induction decay data were processed with 6 Hz line broadening, 50Hz convolution difference, and 1D FFT. The resulting spectra were processed by using projections onto convex sets reconstruction to generate MRSI [1]. Results