Exchange time from time-dependent diffusion-weighted MRI as a potential biomarker for treatment response in human brain metastasis.

Motivation: Previous studies linking exchange time Τex in brain metastases to treatment response have been dependent on the usage of Gadolinium contrasts agents for DCE-MRI. Goal(s): Determine whether Τex estimated using diffusion time dependent kurtosis from diffusion-weighted MRI before and after stereotactic radiosurgery (SRS) is correlated with treatment response for brain metastases. Approach: Estimating changes in Τex from time dependent kurtosis in a pilot cohort of 16 patients with brain metastases from multiple primary cancers before and after SRS and correlate them with treatment response using RANO-BM criteria. Results: All patients in the good/poor response groups (RANO-BM=1-2/3-4) had negative/positive changes in Τex, respectively. Impact: We provide evidence that estimates of exchange time in brain metastases using diffusion time dependent kurtosis is a potential biomarker to characterize treatment response using endogenous water contrast.