Magnetization transfer characterization of hypertensive cardiomyopathy: significance of tissue water content.

Magnetization transfer measurements offer the potential for specific noninvasive tissue characterization. The goal of the present study was to determine if changes in magnetization transfer would accompany the myocardial remodeling that occurs with hypertrophic cardiomyopathy. Using 40-week spontaneously hypertensive rat (SHR) myocardium, T1, T2, and T1 in the presence of off-resonance irradiation (T1sat) were found to be greater compared to Wistar-Kyoto (WKY) controls. The pseudo-first order rate constant of magnetization transfer (kfor) was less in 40-week SHR compared with WKY while the ratio of equilibrium magnetization in the presence and absence of off-resonance irradiation (MsIM0) was not different. The extent to which observed interspecies differences in tissue water content affected these parameters was investigated by dehydrating normal and hypertrophic myocardium. Significant correlations found between tissue water content and T1, T2, T1sat and kfor, but not MsIM0, suggested changes in tissue water dominated the observed interspecies differences in relaxation parameters. Thus, ventricular remodeling in hypertrophic cardiomyopathy does not alter magnetization transfer though the accompanying change in tissue water content influences water proton relaxation.