In vivo relaxation times and hydrogen density at 0.063-4.85 T in rats with implanted mammary adenocarcinomas.

Magnetic resonance (MR) imaging at 0.063 T, 0.17 T, 0.35 T, 2.94 T, and 4.85 T was performed in rats with implanted mammary adenocarcinomas (and in control rats) to study hydrogen density and the effects of magnetic field strength on T1 and T2 relaxation times in vivo. T1 increased by an order of magnitude and T2 decreased by a factor of two between the lowest and highest field strengths. Only about half of the increased water content of tumor, compared with that of muscle, was reflected in increased hydrogen density. The sensitivity of relaxation time change was increased at the lower field strengths. These results are of significance in understanding the effects of field strength on lesion detectability, contrast, and signal-to-noise ratio.