In vivo quantitative mapping of cardiac perfusion in rats using a noninvasive MR spin-labeling method

Measurement of myocardial perfusion is important for the functional assessm ent of heart in vivo. Our approach is based on the modification of the long itudinal. relaxation time T1 induced by magnetic spin labeling of endogenou s water protons. Labeling is performed by selectively inverting the magneti zation within the detection slice, and longitudinal relaxation is measured using a fast gradient echo MRI technique, As a result of blood now, nonexci ted spins enter the detection slice, which leads to an acceleration of the relaxation rate. Incorporating this phenomenon in a mathematical model that describes tissue as two compartments yields a simple expression that allow s the quantification of perfusion from a slice-selective and a global inver sion recovery experiment. This model takes into account the difference betw een T1 in blood and T1 in tissue. Our purpose was to evaluate the feasibili ty and reproducibility of this technique to map quantitatively myocardial p erfusion in vivo in rats. Quantitative maps of myocardial blood now were ob tained from nine rats, and the reproducibility of the technique was evaluat ed by repeating the whole perfusion experiment four times. Evaluation of re gions of interest within the myocardium yielded a mean perfusion value of 3 .6 +/- .5 ml.min(-1).g(-1) over all animals, which is in good agreement wit h previously reported literature values.