Impact of transvascular and cellular-interstitial water exchange on dynamic contrast-enhanced magnetic resonance imaging estimates of blood to tissue transfer constant and blood plasma volume

Purpose: To examine the effect of transvascular (kbe) and cellularinterstitial water protons exchange (kie) in estimates of the blood-to-tissue contrast agent transfer rate constant (Ktrans), interstitial volume fraction (ve), and blood plasma volume fraction (vp) using a full three-site two exchange (3S2X) model. Materials and Methods: Using the Bloch-McConnell equations, magnetic resonance imaging (MRI) signal arising from a 3S2X system was derived for the T1-weighted spoiled gradient-recalled echo (SPGR) pulse sequence. To model the effects of kbe and kie on estimates of R1, the MRI-measured arterial input function, the different sets of values of kinetic parameters: Ktrans, ve, and vp and water protons exchange rates, kbe and kie, were used. To calculate the tissue water protons R1, the signal evolving from a 3S2X model was set to a monoexponential function. By comparing the estimated Ktrans, ve, and vp with their simulated model truth values, the impact of kbe and kie on Ktrans, ve, and vp was evaluated. Results: vp was strongly underestimated and Ktrans and ve were much less influenced by kbe, when kie was held constant. When kbe was held constant, the kie had a significant effect on Ktrans and ve and less effect on vp. Conclusion: The full 3S2X model allows accurate estimation of Ktrans, ve, and vp and rates of water proton exchange. J. Magn. Reson. Imaging 2013;37:435444. (C) 2012 Wiley Periodicals, Inc.