Implanted coil MR microscopy of renal pathology.

Abstract

Inductively coupled implanted coils have been shown to provide up to a 10-fold increase in signal-to-noise ratio when compared to whole-body imaging of small animals. The current study was designed to extend the implanted coil imaging technique to a rodent model of renal pathology. Resonant radiofrequency (RF) coils were implanted around the left kidney of four rats and inductively coupled from within a birdcage body coil. All images were acquired at 2 T using a T1-weighted spin-echo sequence with TR = 500 ms and TE = 20 ms. In vivo MR microscopy with voxels of 117 x 117 x 2000 microns demonstrated cortex, inner and outer medulla, and major vascular structures on baseline images. Mercuric chloride-induced nephrotoxic acute tubular necrosis (ATN) diminished cortico-medullary contrast at 24 h after dosing with pathologic evaluation demonstrating nephrotoxic changes in the inner cortex. The kidney regained a baseline MR appearance 360 h after dosing and resolution of the damage was confirmed with histology. T1 data were gathered on excised kidneys as an adjunct to the images to help correlate the loss and return of cortico-medullary contrast with the pathology and pathophysiology of nephrotoxic ATN. With implanted RF coils we were able to demonstrate renal pathology and follow its subsequent resolution. Specifically, loss and return of cortico-medullary contrast as a result of nephrotoxic ATN were serially documented in four rats. Such serial in vivo studies performed on single animals should further the use of MR microscopy by minimizing the number of animals required for adequate biostatistics.