Comparison between MRI Blood-to-Brain Transfer Rate Constants from Individual MRI and Population Averaged Quantitative Autoradiographic Arterial Input Functions

Introduction: An arterial input function (AIF), plasma concentration versus time curve, for an MR contrast agent (MRCA) is used to estimate the blood–brain barrier (BBB) permeability of microvessels and several other vascular related parameters. In dynamic contrast-enhanced MRI (DCE-MRI), an intravenous step-down infusion (SDI) procedure that maintains a constant gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) blood concentration, has been shown to localize and quantify BBB opening more accurately than the bolus injection method commonly used. The direct blood sampling technique employed by quantitative autoradiography (QAR) methods produces a better signal-to-noise ratio for determining the AIF than routine DCE-MRI methods. Furthermore, an acceptable AIF may not always be obtained using DCE-MRI. The present study investigates the possibility of using an average AIF (AIFavg) obtained from a number of QAR experiments to estimate BBB permeability to Gd-DTPA for SDI procedure instead of using the individual MRI derived AIF (AIFind).