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Dynamic Contrast-Enhanced T 1-Weighted Perfusion MRI differentiates Tumor Recurrence from Radiation Necrosis : relative Cerebral Blood Volume Measurements and FDG-PET Validation

INTRODUCTION: Magnetic resonance imaging plays an important role in the detection and evaluation of brain tumors. Conventional contrast-enhanced MRI delineates areas of blood brain barrier (BBB) leakage, but is less reliable in assessing tumor grade and distinguishing radiation-induced necrosis (RN) from tumor recurrence. The gold standard for distinguishing RN from tumor recurrence is F fluorodeoxyglucose positron emission tomography (FDG-PET), which provides a measure of the rate of glucose metabolism. A high metabolic rate of glucose indicates active tumor tissue. Since MRI is used for the routine evaluation of brain tumors and is less expensive and less time-consuming than FDG-PET, the development of a MR technique that could help distinguish RN from tumor recurrence would be an advance. It is generally agreed that there is an association between microvascular density and tumor energy metabolism meaning estimates of cerebral blood volume (CBV) provided by MR perfusion imaging should provide information similar to FDG-PET. Dynamic susceptibility contrast (DSC) perfusion imaging is confounded by the BBB deficiency of brain tumors, due to a change of T1 and T2* relaxation and sampling of the extravascular space. Recently, a T1 weighted MR perfusion imaging method has been developed (1), where the BBB deficiency can be readily incorporated in the tracer kinetic modelling (2,3). Thus, T1 weighted perfusion imaging can estimate the CBV of brain tumors, without a pre-bolus of contrast (4) or additional corrections for contrast agent extravasation (5). Here, we investigate whether T1 weighted perfusion is able to distinguish RN from tumor recurrence using FDG-PET as a reference.