Glutathione is essential for the maintenance of cellular redox homeostasis, and is often upregulated in cancer cells in response to elevated levels of ROS . Subsequently, elevated expression and activity of system x C -can increase the antioxidant capacity of cancer cells, resulting in resistance to chemotherapy . In mouse models of ovarian cancer, [ 18 F]FSPG was shown to predict resistance to chemotherapy through the measurement of tumor antioxidant capacity . Outside of cancer imaging, [ 18 F]FSPG has been investigated for the imaging of multiple sclerosis and cerebral ischemia .