Quantitative detection of tumor O2 using the intratumoral fluorescent probe confirmed, using a different technique, that tumors with 64Cu-ATSM uptake also exhibit regions of very low oxygenation, ranging from 0.6 to 2.6 mmHg, which would be expected to have biologic consequences including radioresistance and HIF1α induction (Table 1). Here, HIF1A is linked to neoplasm.