Relaxation measurements at 300 MHz using MR microscopy.

Previous data on changes in tissue T1 with field have suggested the convergence of tissue T1 values toward a common value at high (greater than 4.0 T) fields. Measures of T2 dependence have suggested reduction of T2 with field. The purpose of this study was to observe the T1 and T2 at 85.5 and 300 MHz of microstructures in excised rat kidneys by employing MR microscopy. This study represents the first attempt of MR microscopy at 7.0 T with regard to the subject of magnetic field dependence of T1 and T2. As expected, T1 did increase with increasing field strength but not as dramatically as might be expected. Subtle differences in the microstructures of the kidney and the binding of water in those structures were discernible on the basis of T1 differences at 300 MHz. T2 values decreased, raising speculation concerning the mechanism for this dependence. The improved SNR permits smaller samples to be examined at much higher resolutions (greater than 30 X 30 X 200 microns), further extending the potentials for MR microscopy.