Time-dependent diffusion MRI for differentiating gliomas from brain metastases and identifying brain metastasis origin

Purpose To evaluate the diagnostic efficacy of time-dependent diffusion MRI (t _d -dMRI)-based cell size imaging to distinguish gliomas from brain metastases (BrMs) and identify BrM origins. Methods 89 patients (31 males; mean age, 52.47 ± 12.32 years), including 21 patients with isocitrate dehydrogenase (IDH)-wildtype gliomas, 12 with IDH-mutant gliomas, 33 with breast cancer BrMs, and 23 with lung cancer BrMs, were prospectively recruited for t _d -dMRI examinations. Microstructural parameters, including mean cell diameter (C_d), volume fraction of the intracellular space (V _in ), extracellular diffusivity, and cellularity, were estimated from t _d -dMRI using the IMPULSED model and compared across different tumors. Diagnostic performance was assessed using the area under the receiver operating characteristic curve (AUC). The microstructural parameters were validated with pathologic measurements. Results Gliomas and BrMs had significantly different microstructural parameters. Lung cancer BrMs had significantly higher C_d and V _in values compared with breast cancer BrMs, IDH-wildtype gliomas, and IDH-mutant gliomas ( P  < 0.001 - P  = 0.004). C_d performed well in distinguishing between IDH-wildtype gliomas and lung cancer BrMs (AUC = 0.866), IDH-mutant gliomas and lung cancer BrMs (AUC = 0.923), and breast cancer BrMs and lung cancer BrMs (AUC = 0.907). IDH-wildtype and IDH-mutant gliomas had no significant differences in all microstructural parameters ( P  > 0.05). C_d correlated well with pathologically average cell diameter ( P  = 0.013, r  = 0.770) and total cell area ( P  = 0.039, r  = 0.673) of brain tumors. Conclusion t _d -dMRI-based microstructural imaging can be used to differentiate gliomas and BrMs and determine BrM origins.