Short-echo-time magnetic resonance spectroscopy of single voxel with arbitrary shape in the living human brain using segmented two-dimensional selective radiofrequency excitations based on a blipped-planar trajectory

The target regions of single-voxel MR spectroscopy often deviate from the cuboidal volume acquired with localization methods based on cross-sectional RF excitations. To diminish partial volume effects spatially 2D-selective RF excitations (2DRF) have been used to excite anatomically defined regions of interest (ROIs). Thereby, segmentation of the 2DRF has been applied to avoid excessive pulse durations yielding “virtual” excitation profiles that are defined upon averaging multiple acquisitions obtained with the different segments. In this work, the feasibility of segmented 2DRF for single-voxel 1H-MR spectroscopy of arbitrarily shaped voxel in the living human brain is demonstrated. The 2DRF segments were chosen to cover a single line of a blipped-planar trajectory in order to minimize chemical shift displacement artifacts and achieve standard echo times of 30 ms. To eliminate unwanted side excitations, a refocusing RF excitation in the blip direction was used. Phantom experiments demonstrate the high spatial selectivity achieved, i.e., the absence of significant signal contaminations from regions outside of the target volume. Although the signal obtained per volume is reduced compared to cross-sectional localization, the better volume coverage of anatomically defined ROIs can deliver an improved signal-to-noise ratio for irregularly shaped ROIs.