Rapid Measurement of Capillary Permeability Using the Early Part of the Dynamic Gd-DTPA MRI Enhancement Curve

Three fast, simple methods for measuring the permeability surface area product per unit volume, k, from the early part of the gadolinium-DTPA enhancement curve in blood-brain barrier and blood-retina barrier lesions are presented and evaluated by computer simulation. All use a minimum of scanning time, and the scanning and computing procedures are easy to implement. The first, using the initial slope of the enhancement vs time curve, is subject to errors of 17-26% from failure of the signal to rise linearly with time, caused by decay of plasma concentration, filling of leakage space, T2 losses, and signal nonlinearity with 1/T1. The second, the early enhancement method, takes account of all nonlinearities, and its accuracy is limited only by lack of prior knowledge of the size of the leakage space; some iterative computation is required. For brain lesions the error is 11%, with an imaging time of 3-10 minutes. The third, the simplified early enhancement method, appropriate for retinal lesions, takes account of plasma decay only and requires simpler computation. The maximum error is 10%, with an imaging time of 12-45 minutes.