CLINICAL APPLICATION OF SATURATION TRANSFER MRI FOR DIFFERENTIATING TUMOUR PROGRESSION FROM RADIATION NECROSIS IN BRAIN METASTASES

Stereotactic radiosurgery for the treatment of brain metastases delivers a high dose of radiation with excellent local control, but increases the likelihood of radiation necrosis. As shown in our previous work, saturation transfer MRI, consisting of quantitative magnetization transfer (qMT) and chemical exchange saturation transfer (CEST), is a promising technique for distinguishing radiation necrosis (RN) from tumour progression (TP) in brain metastases. A 3D qMT/CEST acquisition was recently implemented and over 100 patients have been scanned to date. The purpose of this work is to assess the ability of advanced MRI parameters, including qMT and CEST metrics, which are sensitive to macromolecules and metabolism. The specific metrics that were explored included the amide and NOE contributions of the magnetization transfer ratio (MTR), the MTR asymmetry, the apparent exchange-dependent relaxation (AREX), the qMT semi-solid pool fraction and the T1 and T2 relaxation times. For a subset of the patients, dynamic susceptibility contrast (DSC) perfusion images were acquired. Examples of confirmed tumour progression and radiation necrosis cases will be presented, comparing the structural images (pre- and post-contrast T1-weighted and FLAIR images) with parameter maps from qMT and CEST and also the relative cerebral blood flow (rCBF) from DSC perfusion imaging. Interim cohort results will be presented. Approaches for standardizing the parameters across multiple MRI vendors are also explored.