IN-VIVO ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY IMAGING IN EXPERIMENTAL ONCOLOGY - THE HOPE AND THE REALITY

Purpose: Low frequency (280 MHz) electron paramagnetic resonance imagi ng is a new magnetic resonance technique, still being developed, that can map the in vivo spatial distribution of paramagnetic species such as nitroxide free radicals. The reduction rate of these molecules is a ffected by oxygen concentration. This paper gives some examples of the use of electron paramagnetic resonance imaging methodology in whole r ats in the framework of its possible use in experimental oncology. Met hods and Materials: The 280 MHz apparatus based on a cylindrical 16 po le magnet was developed and designed specifically for 50-200 g laborat ory animals. It generates the main field and the three field gradients required for three-dimensional (3-D) projections. A pyrrolidine nitro xyl (2,2,5,5,-tetramethylpyrrolidine- 1-oxyl-3-carboxylic acid) was in jected intravenously in rats to provide an electron paramagnetic reson ance signal for in vivo measurements. Electron paramagnetic resonance X-band spectrometer was used to monitor pyrrolidine nitroxyl decay in an external blood circuit during normoxia and moderate hypoxia (15% O- 2). Results and Conclusion: One-dimensional (1-D) transversal and long itudinal mapping of this nitroxide free radical distribution in rat wh ole body was obtained 7-9 min after injection. In circulating blood, n itroxide half-life decreased significantly during hypoxia. The present sensitivity (10(-4)-10(-5) M), spatial resolution (3-10 mm) and colle ction time (3-5 min) could be drastically improved by narrow linewidth paramagnetic probes and pulsed techniques.