Quantification of the effect of water exchange in dynamic contrast MRI perfusion measurements in the brain and heart

Measurement of myocardial and brain perfusion when using exogenous contrast agents (CAs) such as gadolinium-DTPA (Gd-DTPA) and MRI is affected by the diffusion of water between compartments. This water exchange may have an im pact on signal enhancement, or, equivalently, on the longitudinal relaxatio n rate, and could therefore cause a systematic error in the calculation of perfusion (F) or the perfusion-related parameter, the unidirectional influx constant over the capillary membranes (K-j). The aim of this study was to quantify the effect of water exchange on estimated perfusion (F or K-j) by using a realistic simulation. These results were verified by in vivo studie s of the heart and brain in humans. The conclusion is that water exchange b etween the vascular and extravascular extracellular space has no effect on K-j estimation in the myocardium when a normal dose of Gd-DTPA is used. Wat er exchange can have a significant effect on perfusion estimation (F) in th e brain when using Gd-DTPA, where it acts as an intravascular contrast agen t. (C) 2001 Wiley-Liss, Inc.