In vivo surface localized phosphorous nuclear magnetic resonance spectroscopy with a slotted crossover surface coi

The development of a technique for noninvasive in vivo phosphorous (31P) nuclear magnetic resonance (NMR) spectroscopy of skin tissue is presented. Tissue viability is often difficult to evaluate clinically. In vitro NMR of skin flaps and grafts completed by other authors via acid extractions has shown predictive correlates for clinical applications. Problems making in vivo non-invasive surface localized spectroscopy impractical for studying intact skin tissue involved inadequate SNR and localization effects. The development of the conventional crossover surface coil and its modification to form the slotted crossover surface coil has made experiments of this nature feasible for the first time. In vivo spectra have been acquired in as little as 5 minutes at 2 Tesla with localization depths from 1 to 4mm. The crossover surface coil is constructed with two turns of copper foil using a unique transposition construction that incorporates an explicit center tap ground of the widened bottom layer. The coil reduces dielectric and inductive losses by effective shielding of electric fields and uniform distribution of magnetic fields for minimum quality factor (Q) losses upon coil loading. Flexible, copper foil construction permits easy conformation to tissues of interest enhancing coil performance. Construction details of the crossover coil and Q data for coils of various sizes at a number of frequencies are given. The slotted crossover surface coil incorporates advances of the conventional crossover surface coil with a modified shape format. Enhanced signal-to-noise ratios (SNR) are achieved via reduced coil-samples loses a smaller coil radius, close probe-to-sample conformation, increased copper surface area, and maximized region-of-interest (ROI) tissue presentation to the probe. The slotted shape effectively reduces the coil diameter, thus, minimizing B1 field penetration and producing an innate localization effect. Utilization of single broad band pulse followed by acquisition eliminates SNR losses associated with pulse sequence localization schemes. Surface localized depth selection is achieved using different predetermined pulse widths. Preliminary in vivo experiments using the slotted crossover surface coil at 2 Tesla to characterize normal and burned rat skin tissue demonstrated its research and clinical implications. It appears that burn severity and tissue viability determinations are possible using PCr/Pi ratios. These rations show significant reduction proportional to burn severity. Hypermetabolic processes were also observed in a partial-thickness burn via increasing rations and PCr metabolite concentrations. This technique may provide a noninvasive tool for the collection of clinical information relevant to diagnoses, physiological status, treatment efficacy, and prognostic indices.