Arterial spin-labeling-based exchange time mapping for differentiation of high-grade glioma and brain metastases.

BACKGROUND: To evaluate whether blood-brain barrier (BBB) mapping via arterial spin-labeling (ASL)-derived exchange time (T ex) can differentiate high-grade gliomas from brain metastases and to compare regional BBB alterations with dynamic susceptibility contrast (DSC)-derived leakage parameters (K2). METHODS: A total of 18 patients with therapy-naive cerebral masses (11 gliomas, 7 metastases) underwent multi-echo-ASL and DSC perfusion MRI. T ex maps were obtained using a validated extended two-compartment model. K2 maps were derived from single-echo DSC. T ex and absolute K2 (|K2|) were quantified in contrast-enhancing tumor (CET), peritumoral T2/FLAIR hyperintense region (PTR), gray matter (GM), and white matter (WM). Regional differences were assessed using Wilcoxon signed-rank and Mann-Whitney U tests. Receiver operating characteristic (ROC) analyses evaluated discrimination between gliomas and metastases. RESULTS: T ex was significantly lower in PTR of gliomas versus metastases (P = 0.046). In receiver operating characteristic analysis, T ex slightly outperformed |K2| alone (area under the curve [AUC] = 0.792, 95% confidence interval [CI] [0.535, 0.986] vs. AUC = 0.760, 95% CI [0.508, 0.959]), with further improvement upon combination (AUC = 0.833, 95% CI [0.577, 1.000]). In gliomas, T ex was significantly lower in CET than in GM and WM (both P < 0.01) and PTR showed significantly lower T ex than WM (p < .01). |K2| was significantly higher in CET than all other regions (all p < .01) but did not differ between PTR and GM/WM. CONCLUSION: In this exploratory study, ASL-derived T ex suggests stronger BBB alterations in peritumoral tissue of high-grade gliomas compared with brain metastases. Adding |K2| further improved discrimination. This supports ASL-based BBB mapping as a complement to DSC leakage imaging. Validation in larger multicenter cohorts is warranted.