Arterial spin labeling perfusion MRI differentiates between radiation necrosis and tumor in brain metastases treated with stereotactic radiosurgery

Abstract

Background. Accurate differentiation between radiation necrosis (RN) and tumor in brain metastases (BM) treated with stereotactic radiosurgery (SRS) can be challenging, but it is important because an accurate diagnosis impacts clinical management. In this study, we evaluated the utility of arterial spin labeling perfusion MRI (ASL-MRI) to ac¬complish this task. Methods. We retrospectively evaluated 45 patients with 52 previously irradiated BM who had ASL-MRI prior to surgical resection. Histopathology served as the ground truth diagnosis of tumor and RN. Maximum cerebral blood flow (CBF) values were obtained within the contrast-enhancing lesions of interest and the pons (for nor¬malization) on quantitative ASL-MRI CBF maps. In a subgroup analysis, patients with both pre-SRS and post-SRS ASL-MRIs were included, and CBF values were obtained at both timepoints. Results. Compared with RN, tumor had increased mean absolute and normalized CBF (P < .0001). In the subgroup analysis of patients with pre-SRS and post-SRS ASL-MRIs, change in absolute CBF (ΔCBF) and normalized CBF (ΔnCBF) of tumor showed higher absolute and percent differences between both timepoints (P < .02). Performance of ΔCBF and ΔnCBF (area under the receiver operating characteristic curve [AUROC] 0.80-0.89) acquired from 2 ASL-MRIs was comparable but not superior to CBF and nCBF (AUROC 0.90) acquired from single timepoint post-SRS ASL-MRI. Conclusions. Increased CBF, whether absolute or normalized, on post-SRS ASL-MRI performed well to differen¬tiate tumor from RN in BMs treated with SRS. Addition of pre-SRS CBF measurements did not improve the perfor¬mance. ASL-MRI is a promising imaging tool to distinguish RN from tumor in this patient population.