LAUSR

Brain metastasis is a common characteristic of late-stage lung cancers. High doses of targeted radiation can control tumor growth in the brain but can also result in radiation-induced necrosis. Current methods are limited for distinguishing whether new parenchymal lesions following radiotherapy are recurrent tumors or radiation-induced necrosis, but the clinical management of these two classes of lesions differs significantly. Here we developed, validated, and evaluated a new MRI technique termed selective size imaging using filters via diffusion times (SSIFT) to differentiate brain tumors from radiation necrosis in the brain. This approach generates a signal filter that leverages diffusion time dependence to establish a cell-size-weighted map. Computer simulations in silico, cultured cancer cells in vitro, and animals with brain tumors in vivo were used to comprehensively validate the specificity of SSIFT for detecting typical large cancer cells and the ability to differentiate brain tumors from radiation necrosis. SSIFT was also implemented in patients with metastatic brain cancer and radiation necrosis. SSIFT showed high correlation with mean cell sizes in the relevant range of less than 20 μm. The specificity of SSIFT for brain tumors and reduced contrast in other brain etiologies allowed SSIFT to differentiate brain tumors from peri-tumoral edema and radiation necrosis. In conclusion, this new, cell size-based MRI method provides a unique contrast to differentiate brain tumors from other pathologies in the brain.