T*(1e) and T*(2e) maps derived in vivo from the rat using longitudinally detected electron spin resonance phase imaging: Application to abdominal oxygen mapping

A novel imaging modality is introduced which uses radiofrequency longitudin ally detected electron spin resonance (RF-LODESR). It is capable of providi ng qualitative and semi-quantitative information on a variety of parameters reflecting physiological function, the most significant being tissue oxyge nation. Effective spin-lattice (T-1e*) and spin-spin (T-2e*) electronic rel axation time maps of the abdomen of living 200-g rats were generated after intravenous administration of a triarylmethyl free radical (TAM). These map s were used to evaluate oxygen distribution. Differences between the liver, kidneys, and bladder were noted. Conclusions were made regarding the distr ibution, perfusion, and excretion rate of the contrast medium. Ligature-ind uced anoxia in the kidney was also visualized. LODESR involves transverse E SR irradiation with a modulated excitation, and observing oscillations in t he spin magnetization parallel to the main magnetic field. The T-1e* and T- 2e* maps were calculated from a set of LODESR signal phase images collected at different detection frequencies. Each phase image also provides qualita tive information on tissue oxygen levels without any further processing. Th is method presents an alternative to the conventional transverse ESR linewi dth-based oximetry methods, particularly for animal whole-body imaging appl ications. (C) 2001 Wiley-Liss, Inc.