Proton MR spectroscopic imaging (MRSI) at higher magnetic fields (B 0) suffers metabolite localization errors from different chemical-shift displacements (CSDs) if spatially-selective excitation is used. This phenomenon is exacerbated by the decreasing radiofrequency (RF) field strength, B1, at higher B0s, precluding its suppression with stronger gradients. To address this, two new methods are proposed: 1) segmenting the volume-of-interest (VOI) into several slabs, allowing proportionally stronger slice-select gradients; and 2) sequentially cascading rather than superposing the components of the Hadamard selective pulses used for reasons of better point-spread function (PSF) to localize the few slices within each slab. This can reduce the peak B1 to that of a single slice. Combining these approaches permits us to increase the selective gradient four- to eightfold per given B1, to 12 or 18mT/m for 4- or 2-cm VOIs. This "brute force" approach reduces the CSD to under 0.05 cm/ppm at 7T, or less than half that at 3T.
- Chemical shift displacement
- Hadamard encoding
- High field
- Magnetic resonance spectroscopic imaging (MRSI)
- Selective pulses
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging