MR Relaxometry and Perfusion of the Myocardium in Spontaneously Hypertensive Rat: Correlation with Histopathology and Effect of Anti-hypertensive Therapy

Objectives: To investigate myocardial relaxation times and perfusion values in spontaneously hypertensive rats (SHRs) at various stages of the disease, with or without anti-fibrotic therapy, and to correlate magnetic resonance imaging (MRI) findings with histopathological myocardial fibrosis and capillary density.

Methods: Five groups of rats underwent MRI at 4.7 T. They were either untreated or treated with an aldosterone-synthase inhibitor. T1, T2 and T2 relaxation times were determined and myocardial perfusion was quantified from an arterial spin labelling sequence. MR relaxation times and perfusion values were compared with the fibrotic content and capillary density of the myocardium obtained at histology after euthanasia.

Results: T1 values significantly increased during the course of hypertensive disease, and correlated with myocardial fibrosis (R = 0.71, P < 0.001); T2 values also increased but were weakly correlated with myocardial fibrosis (R = 0.27,P = 0.047). Myocardial perfusion and capillary density significantly decreased with hypertensive disease but they did not correlate. Following prolonged treatment, we observed a trend associating T1 decrease and improved perfusion compared with untreated SHRs.

Conclusions: Myocardial T1 and T2 values increase with hypertensive disease, whereas myocardial perfusion decreases. The correlation between T1 values and collagen density suggests that the former could be considered as a non-invasive marker of myocardial fibrosis.

Key Points: • MR is increasingly used to assess alteration in myocardial tissue content. • MR relaxometry and perfusion can be assessed in rats without exogenous contrast agents. • Myocardial T1 and T2 values significantly increase during the course of hypertensive heart disease. • T1 values correlate significantly with myocardial collagen content. • Myocardial perfusion values decrease with hypertensive disease.