IN-VIVO QUANTIFICATION OF THE UNIDIRECTIONAL INFLUX CONSTANT FOR GD-DTPA DIFFUSION ACROSS THE MYOCARDIAL CAPILLARIES WITH MR-IMAGING

The authors present an in vivo method for measuring the unidirectional influx constant (K(i)) for gadolinium diethylenetriaminepentaacetic a cid (DTPA) diffusion across the capillary membrane in the human myocar dium with magnetic resonance imaging. K(i) is related to the extractio n fraction (E) and the perfusion (F) by the equation K(i) = E . F. K(i ) was obtained by using the longitudinal relaxation rate (R1) as a mea sure of the myocardial concentration of Gd-DTPA in the mathematical mo del for transcapillary transport across capillary membranes. Myocardia l enhancement after Gd-DTPA injection was followed by using inversion- recovery Turbo-FLASH (fast low-angle shot) images obtained in real tim e. The results were comparable to those obtained from studies with pos itron emission tomography in humans and invasive studies in animals. A method for obtaining the input function noninvasively is also present ed. Comparison with direct arterial blood sampling showed that the non invasive input function may be even more accurate with regard to timin g and curve shape than the invasive input function. The procedure may therefore prove useful in clinical studies.