The apparent diffusion constant measured by MRI correlates with pO2 in a RIF-1 tumor.

As tissue oxygen tension (PO 2 ) is an important variable in cancer therapy, it would be of major clinical benefit to be able to measure pO 2 noninvasively. Current methods for determining pO 2 in clinical settings are limited to superficial tumors. The authors measured the apparent diffusion constant (ADC) in an implanted murine fibrosarcoma (RIF-1) using magnetic resonance imaging and correlated the ADC with tissue pO 2 measured by electron paramagnetic resonance oximetry. The ADC correlates significantly with tissue pO 2 in this tumor (r = 0.89 ; n = 14) and so may provide a noninvasive index of pO 2 in tumors.