Spatial Localization in NMR Spectroscopy in Vivo

Abstract

Spatial localization techniques are necessary for in vivo NMR spectroscopy involving heterogeneous organisms. Localization by surface coil NMR detection alone is generally inadequate for deep-lying organs due to contaminating signals from intervening surface tissues. However, localization to preselected planar volumes can be accomplished using a single selective excitation pulse in the presence of a pulsed magnetic field gradient, yielding depth-resolved surface coil spectra (DRESS). Within selected planes, DRESS are spatially restricted by the surface coil sensitivity profiles to disk-shaped volumes whose radii increase with depth, notwithstanding variations in the NMR signal density distribution. Nevertheless, DRESS is a simple and versatile localization procedure that is readily adaptable to spectral relaxation time measurements by adding inversion or spin-echo refocusing pulses or to in vivo solvent-suppressed spectroscopy of proton (1H) metabolites using a combination of chemical-selective RF pulses. Also, the spatial information gathering efficiency of the technique can be improved to provide simultaneous acquisition of spectra from multiple volumes by interleaving excitation of adjacent planes within the normal relaxation recovery period. The spatial selectivity can be improved by adding additional selective excitation spin-echo refocusing pulses to achieve full, three-dimensional point resolved spectroscopy (PRESS) in a single excitation sequence. Alternatively, for samples with short spin-spin relaxation times, DRESS can be combined with other localization schemes, such as image-selected in vivo spectroscopy (ISIS), to provide complete gradient controlled three-dimensional localization with a reduced number of sequence cycles.

Acute changes in extracellular volume fraction in skeletal muscle monitored by23Na NMR spectroscopy

“…One possible solution would be to use localized spectroscopy methods. Nevertheless, classical schemes such as point resolved spatially localized spectroscopy (PRESS) (Bottomley 1987) or stimulated echo acquisition mode (STEAM) (Frahm et al. 1989) would lead to too long echo times by preventing the acquisition of fast decaying 23 Na signals.…”

Increased Anterior Cingulate/Medial Prefrontal Cortical Glutamate and Creatine in Bipolar Depression

“…The scans were acquired in the following order: (1) Sagittal whole-brain scout for general orientation and positioning of subsequent scans, (2) T1-weighted and inversion-recovery (IR) weighted axial images (TR/TE ¼ 800/ 8 ms, 35 slices, 4 mm thickness with no gap for MRS voxel placement, (3) Single-voxel water-suppressed (Haase et al, 1985) PRESS (Bottomley, 1987) 1 HMRS (TR/TE ¼ 3s/30 ms, number of averages ¼ 256, voxel size 3 Â 3 Â 3 cm 3 ) of anterior cingulated/medial prefrontal cortex. PRESS was acquired with the GE proton brain examination (PROBE) technique, whereby four unsuppressed water free-induction decays were co-acquired for eddy current compensation, phase-correction, and normalization of local absolute metabolite levels.…”

Receive array magnetic resonance spectroscopy: Whitened singular value decomposition (WSVD) gives optimal Bayesian solution

“…Pointresolved spectroscopy (22,23), stimulated echo acquisition mode (STEAM) (22,24), and ultrashort echo time CSI (25) were used for localization. The WSVD algorithm was implemented in Cþþ, using the LAPACK (26) and Boost (http://www.boost.org/) libraries in the Siemens Image Calculation Environment, and run on the scanner.…”