Short echo time 1H-MRSI of the human brain at 3T with minimal chemical shift displacement errors using adiabatic refocusing pulses

Abstract

The chemical shift displacement error (CSDE) is an often-underestimated problem in slice selection for localized proton spectroscopy at higher fields. With the proposed semi-localized by adiabatic selective refocusing (LASER) pulse sequence, this problem is dealt with by using RF pulses with bandwidths in the order of 5 kHz. A combination of conventional nonadiabatic slice-selective excitation of proton spins, together with double slice-selective refocusing of the spins by two pairs of adiabatic full-passage (APF) pulses, produces a spin echo in a volume of interest (VOI) at an echo time down to 30 ms. An illustration of the CSDE of conventional point-resolved spectroscopy (PRESS) and the semi-LASER sequence is shown with a measurement of the brain of a volunteer at 3T. With one application of the technique to a patient with a glioblastoma multiforme (GBM), its clinical functionality is demonstrated. With sharp selection profiles and a small CSDE, voxels close to the edge of the VOI can also be used for evaluation. With the additional advantage of being relatively insensitive for B(1) inhomogeneities, the semi-LASER technique can be viewed as a superior substitute for conventional PRESS MR spectroscopic imaging (MRSI) at 3T and beyond.