Fast high-resolution magnetic resonance imaging demonstrates fractality ofmyocardial perfusion in microscopic dimensions

The fractal nature of heterogeneity of myocardial blood flow and its implic ations for the healthy and diseased heart is not yet understood. The main h indrance for investigation of blood flow heterogeneity and its role in phys iology and pathophysiology is that conventional methods for determination o f myocardial perfusion have severe limitations concerning temporal and spat ial resolution and invasiveness. In isolated rat hearts, we developed a nuc lear magnetic resonance technique that does not depend on contrast agents a nd in which the apparent longitudinal relaxation time is made perfusion sen sitive by selective preparation of the imaging slice. This perfusion-sensit ive relaxation time is determined within 40 seconds as a map with a high sp atial in-plane resolution of 140x140 mum(2) and a thickness of 1.5 mm. Perf usion imaging was validated with the established microsphere technique. Add itionally, the congruence between perfusion-sensitive T-1 maps and first-pa ss perfusion imaging was demonstrated. As an application of high-resolution perfusion imaging, fractal analysis of the spatial distribution of perfusi on was performed. We were able to demonstrate that the fractality of this d istribution exists even in microscopic dimensions. Vasodilation by nitrogly cerin modulated the fractal pattern of perfusion, and the decrease of the f ractal dimension indicated a shift toward homogeneity. This implies that pa rameters of the fractal distribution depend on the microvascular tone rathe r than on anatomic preformations; ie, fractality is a functional characteri stic of perfusion.