Assessment of vessel permeability by combining dynamic contrast-enhanced and arterial spin labeling MRI

The forward volumetric transfer constant (K-trans), a physiological parameter extracted from dynamic contrast-enhanced (DCE) MRI, is weighted by vessel permeability and tissue blood flow. The permeabilityxsurface area product per unit mass of tissue (PS) in brain tumors was estimated in this study by combining the blood flow obtained through pseudo-continuous arterial spin labeling (PCASL) and K-trans obtained through DCE MRI. An analytical analysis and a numerical simulation were conducted to understand how errors in the flow and K-trans estimates would propagate to the resulting PS. Fourteen pediatric patients with brain tumors were scanned on a clinical 3-T MRI scanner. PCASL perfusion imaging was performed using a three-dimensional (3D) fast-spin-echo readout module to determine blood flow. DCE imaging was performed using a 3D spoiled gradient-echo sequence, and the K-trans map was obtained with the extended Tofts model. The numerical analysis demonstrated that the uncertainty of PS was predominantly dependent on that of K-trans and was relatively insensitive to the flow. The average PS values of the whole tumors ranged from 0.006 to 0.217min(-1), with a mean of 0.050min(-1) among the patients. The mean K-trans value was 18% lower than the PS value, with a maximum discrepancy of 25%. When the parametric maps were compared on a voxel-by-voxel basis, the discrepancies between PS and K-trans appeared to be heterogeneous within the tumors. The PS values could be more than two-fold higher than the K-trans values for voxels with high K-trans levels. This study proposes a method that is easy to implement in clinical practice and has the potential to improve the quantification of the microvascular properties of brain tumors. Copyright (c) 2015 John Wiley & Sons, Ltd.