In this study quantitation of the degree of deficiency of the blood-brain barrier (BBB) in patients with multiple sclerosis or brain tumors, by using MRI, is shown to be possible. As a measure of permeability of the BBB to Gadolinium-DTPA (Gd-DTPA) the flux per unit of distribution volume per unit of brain mass was used. This quantity was found by introducing the longitudinal relaxation rate (R1) as a measure of concentration of Gd-DTPA in the brain tissue in the mathematical model for the transcapillary transport over the BBB. High accordance between the observed data points and the model was found, and the results were comparable to results obtained from similar studies using positron emission tomography. The improved possibility of quantitating the defect of the BBB by MRI may give new information about pathogenesis or etiology, and leads to improved methods in monitoring the efficacy of treatments in intracranial diseases.

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The authors present an in vivo method for measuring the unidirectional influx constant (Ki) for gadolinium diethylenetriaminepentaacetic acid (DTPA) diffusion across the capillary membrane in the human myocardium with magnetic resonance imaging. Ki is related to the extraction fraction (E) and the perfusion (F) by the equation Ki = E.F.Ki was obtained by using the longitudinal relaxation rate (R1) as a measure of the myocardial concentration of Gd-DTPA in the mathematical model for transcapillary transport across capillary membranes. Myocardial enhancement after Gd-DTPA injection was followed by using inversion-recovery Turbo-FLASH (fast low-angle shot) images obtained in real time. The results were comparable to those obtained from studies with positron emission tomography in humans and invasive studies in animals. A method for obtaining the input function noninvasively is also presented. Comparison with direct arterial blood sampling showed that the noninvasive input function may be even more accurate with regard to timing and curve shape than the invasive input function. The procedure may therefore prove useful in clinical studies.