In situ magnetic resonance microscopy.

Recent developments in MR permit imaging at microscopic resolution. Efforts have focused on small samples that fit entirely in the imaging probe. Extension of the techniques to imaging of individual organs in small animals is complicated by both the need to acquire an excessive number of phase encodings and limited signal to noise. Implantable radiofrequency coils described in this work eliminate both problems, permitting MR microscopy in the kidney of a live 200-g rat with spatial resolution of 117 X 117 X 1250 mu (.02 mm3). Inductive coupling permits complete freedom from external leads. A phantom designed to evaluate dielectric losses is described. Both phantom and in vivo comparison of live kidney images demonstrate the tenfold improvement in signal to noise obtained with the implantable coil.