Feasibility study of imaging a living murine tumor by electron paramagnetic resonance.

An electron paramagnetic resonance image was measured for the first time from in vivo field gradient spectra of a living murine tumor (Cloudman S-91 melanoma in the tail of a DBA-2J mouse) using the paramagnetic nitroxide imaging agent 3-carboxamido-2,2,5,5-tetramethylpyrroline-1-oxyl injected into the tail vein. The experiments were accomplished at L-band frequency (1.55 GHz) with a single-turn flat-loop coil. A cross-sectional image was obtained perpendicular to the tail axis, which clearly distinguished features to the submillimeter resolution level.