MAGNETIC-RESONANCE MICROSCOPY OF THE RAT CAROTID-ARTERY AT 300-MEGAHERTZ

RATIONALE AND OBJECTIVES. Magnetic resonance microscopy (MRM) has evol ved from a technical curiosity to a tool with which researchers can st udy important disease models. But MRM is not simply an extension of cl inical magnetic resonance imaging. In this article, the unique adaptat ions of MRM required in the study of carotid artery disease are outlin ed. The techniques of MRM are integrated into a specific model of caro tid artery disease in the rat to allow in vivo studies of vascular wal l thickening after removal of the vascular endothelium. METHODS. Imagi ng was performed at 300 MHz in 250-gm Sprague-Dawley rats using surgic ally implanted radiofrequency coils to localize the region of interest and to provide an increase in the signal-to-noise ratio over that of volume or surface coils. A three-dimensional Fourier encoding sequence was modified with flow-dephasing gradients to minimize signal and art ifacts from moving blood. RESULTS. In vivo images were acquired with s patial resolution of 25 X 25 X 400 mu m and signal-to-noise ratio more than sufficient to define the morphology of the vascular wall. Signif icant changes in the intensity and distribution of signal were visible in the area surrounding the vessel after angioplasty. CONCLUSIONS. Si gnal-to-noise improvements from surgically implanted coils coupled to a three-dimensional radiofrequency-refocused sequence with flow-dephas ing gradients were sufficient to define the wall of the carotid artery . The diffusion-weighted pulse sequence detects signal changes in the area surrounding the vessel after angioplasty. The MRM techniques desc ribed and the contrast observed allow us, for the first time, to follo w in vivo the early stage of developing atherosclerosis in the vessel wall and closely surrounding tissue.