Faculty Bibliography

Multivoxel 3D localized proton spectroscopy using a hybrid of 1D 8th-order transverse Hadamard spectroscopic imaging (HSI) with 2D chemical shift imaging (CSI) is demonstrated in human brain. The spatially selective HSI pulse incorporates naturally into the PRESS sequence (TE = 135 ms), which then both excites an 8 x 8 x 6 cm parallelepiped volume of interest (VOI) and subdivides it into eight slices. The planes of these slices are further partitioned into 16 x 16 voxel arrays using 2D CSI to yield 8 x 8 x 8 voxels within the VOI. Simultaneous 3D coverage yields good voxel signal-to-noise (8, 12, and 22 for choline, creatine, and N-acetylaspartate, respectively) from these 0.75-ml voxels, in approximately 45 min. The high spatial isolation allows localization to within less than 1 cm from the skull without fat contamination

We report acquisition of 3D image-guided localized proton spectroscopy (1H-MRS) in the human brain on a standard clinical imager. 3D coverage is achieved with a hybrid of chemical shift imaging (CSI) and transverse Hadamard spectroscopic imaging (HSI). 16 x 16 x 4 arrays of 3.5 and 1 ml voxels were obtained in 27 min. The spatially selective HSI 90 degrees pulses incorporate naturally into a PRESS double spin-echo sequence to subdivide the VOI into four partitions along its short axis. 2D CSI (16 x 16) is performed along the other long axes. Because the hybrid excites the spins in the entire VOI, a square-root-N signal-to-noise-ratio (SNR) gain per given examination time is realized compared with sequentially interleaving N 2D slices. A two-fold gain in sensitivity is demonstrated in the brain for N = 4

A hybrid of two localized spectroscopy techniques, chemical shift imaging (CSI) and Hadamard spectroscopic imaging (HSI), is used to obtain an array of 16 x 16 x 4 (3 x 3 x 3 cm3 voxels) proton-decoupled phosphorus (31P) spectra of human brain. For equal spatial resolution, this organ's oblate shape requires fewer axial than coronal or sagittal slices. These different spatial requirements are well suited to 1D, 4th order, transverse HSI in the axial direction, combined with 2D 16 x 16 CSI in the other two orientations. The reduced localization matrix (16 x 16 x 4 over just the brain versus a cubic-16 x 16 x 16 matrix of equal resolution, over the entire head) may proportionally shorten data acquisition if the voxel size is not signal-to-noise limited. In addition, the use of Hadamard encoding can improve the intervoxel spectral isolation