NIMG-52DYNAMIC CONTRAST ENHANCED MR ESTIMATION OF PHARMACOKINETIC PARAMETERS OF GLIOBLASTOMA MULTIFORME TUMORS: A COMPARISON STUDY FOR PERITUMORAL AND GLOBAL ARTERIAL INPUT FUNCTIONS USING MODEL SELECTION TECHNIQUE

Abstract

Identification of Arterial Input Function (AIF) is one of the crucial steps for quantitative analysis of tissue vascular permeability in Dynamic Contrast Enhanced Magnetic Resonance Imaging studies. In practice, the global AIF is usually identified by experts, which never accounts for dispersion, delay, and partial volume effects. In this pilot study, it is hypothesized that embedded tumors are supplied by their surrounding tissue. This study compares the MR estimates of Pharmacokinetic parameters (PK) in Glioblastoma-Multiforme (GBM) tumors for Peritumoral-derived AIF (PTAIF) as opposed to the use of global AIF. Using the trace of the contrast agent concentration (∝ to relaxivity change, ΔR1) in seventeen treatment-naive GBM patients, a neuroradiologist manually picked the global AIF for each patient. A series of two-dimensional Region of Interests were drawn on the periphery of each tumor in each slice to generate a three-dimensional ROI for encompassing the whole tumor. Then the ΔR1 profile was averaged over the 3D-ROI to generate the PTAIF. For each patient, the global AIF and PTAIF profiles were normalized to the brain white matter. Using the Model-Selection technique and Maximum-Likelihood algorithm, all PK parameters of three Toft-derived models (models 1, 2 and 3), were estimated for two AIFs. The results revealed that PK analysis using PTAIF generates higher plasma volumes in model-1 and model-2 (20% and 60%) with 52% lower plasma volume in model-3 compared to global AIF. PK analysis using PTAIF generates lower transfer constants in models-2 and 3 (54% and 90% for outward-transfer-constant of model-2 and 3 respectively and 13% for backward-transfer-constant of model-3). Also, the extra-vascular-extra-cellular space estimated by the PTAIF compared to the AIF shows significant reduction. The results of this study imply that using Tissue Input Function such as PTAIF compared to the globally selected AIF may highly change the estimates of the PK parameters.