<title>Tumor oximetry: a comparison between near-infrared frequency-domain spectroscopy of hemoglobin saturation and <formula><sup><roman>19</roman></sup></formula>F MRI of hexafluorobenzene</title>

Abstract

Studies have shown that hypoxic tumor cells are relatively more resistant to radiotherapy, chemotherapy, and photodynamic therapy. Tumor oximetry, e.g., measurement of oxygen tension (PO2) of tissue and/or blood oxygenation (S02) of the vascular bed, could be valuable for optimizing treatment plans. In this study, we employed a recently developed homodyne system to measure changes in hemoglobin saturation (S02) and concentration in the vascular bed of rat prostate and breast tumors. For comparison, tissue p02 values were measured using 19F MR EPI of hexafluorobenzene, providing a map of regional tumor oxygenation tension. Both S02 and p02 measurements were taken while the inhaled gas was alternated between 33% oxygen, 100% oxygen and carbogen (95% oxygen, 5% C02). The results obtained for both techniques showed significant changes in tumor oxygenation accompanying respiratory challenge, with changes in vascular S02 preceding tissue p02 change. The combined use of these two techniques provides new insight into the dynamics of tumor oxygenation by making available a method of obtaining regional information of the state of the tissue, as well as a non-invasive, real-time method for determining changes in the vascular bed.