Magnetic resonance imaging analysis of left ventricular function in normaland spontaneously hypertensive rats

1. We have used magnetic resonance imaging (MRI) to examine acute morpholog ical changes in the left ventricle throughout the cardiac cycle in normal W istar Kyoto rats (WKY) and also to follow the development of chronic change s in spontaneously hypertensive rats (SHR). This involved the development o f MRI and quantitative analysis techniques for characterizing contractile c hanges during the cardiac cycle. 2. Images of the cardiac anatomy in two age groups (8 and 12 weeks old) of young anaesthetized adult normal WKY and SHR were acquired in planes both p arallel and perpendicular to the principal cardiac axis. 3. Complete coverage of the heart by imaging planes was achieved with high time resolution (13 ms), with typically 12 time frames in the cardiac cycle , using a short echo time (5 ms) multislice gradient-echo imaging sequence. Imaging was synchronized to the R wave of the electrocardiogram. 4. The image slices could be reconstructed into complete geometrically and temporally coherent three-dimensional data sets. Left ventricular (LV) volu mes were thus reconstructed throughout the cardiac cycle by combining trans verse cardiac image sections. This volume analysis revealed structural and functional differences between the normal WKY and SHR in both age groups of 8 and 12 weeks. Measurements from the cardiac images were additionally val idated against histological measurements. 5. The SHR showed a raised LV end-systolic volume and a correspondingly poo rer ejection fraction as well as LV hypertrophy when compared with the cont rols. Left ventricular function in the SHR appeared stable between the two age groups. 6. We developed a simple geometrical model of the left ventricle based on a single longitudinal image section and successfully used this to describe s ome functional parameters of the left ventricle in the WKY and SHR. This ge ometrical model has the potential to greatly reduce the imaging time needed to study the beating heart in future serial investigations of cardiac phys iology in rats. 7. Our experimental and analytical methods together form a powerful set of quantitative techniques which combine both imaging and functional analysis and will be applicable for future studies of chronic physiological changes in animal disease models.