[PDF][PDF] Spatial localization in NMR spectroscopy in vivo

PA Bottomley - Ann NY Acad Sci, 1987 - academia.edu
Ann NY Acad Sci, 1987academia.edu
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 …
Summary
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 solventsuppressed spectroscopy of proton ('H) metabolites using a combination of chemicalselective 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.
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