RAPID TISSUE OXYGEN-TENSION MAPPING USING F-19 INVERSION-RECOVERY ECHO-PLANAR IMAGING OF PERFLUORO-15-CROWN-5-ETHER

Fluorine-19 inversion-recovery, echo-planar imaging (IR-EPI) was used in conjunction with a new PFC emulsion, perfluoro-15-crown-5-ether, to map the spatial distribution of oxygen tension in murine liver, spleen and radiation induced fibrosarcoma (RIF-1) tumors. Intravenously administered PFC emulsions were allowed to sequester in the liver, spleen, and tumor 3 to 7 days prior to imaging experiments. Seven, 64 x 64 IR-EPIs were acquired with successively increasing inversion times (TI). A nonlinear least-squares regression algorithm was used to fit the seven two-dimensional matrices, on a pixel-by-pixel basis, to solve for the relaxation rate, R(1), of the sequestered PFC. From in vitro calibration curves, the oxygen tension (pO(2)) was calculated from the measured R(1). Oxygen tension maps were then murine liver and spleen were produced (in 2.5 min) to demonstrate the technique and changes in tissue oxygenation as a function of breathing gas (air and carbogen (95% O-2 - 5% CO2)) are presented. Tissue pO(2) maps from RIF-1 tumors (n = 5) were obtained in less than 10 min and changes in tumor pO(2) were studied when the breathing gas was switched from air to carbogen. The results from tumor pO(2) maps were compared with F-19 MR spectroscopy measurements to check for consistency. Histogram analysis yielded an average liver and spleen pO(2) of 43 torr and 26 torr for RIF-1 tumors when the animals were breathing air. Statistically significant changes in tumor oxygenation as a function of breathing gas were obtained from both pO(2) maps (6 +/- 2 torr, P < 0.05) and F-19 MR spectroscopy (13 +/- 3 torr, P < 0.01) as evaluated using the Student's paired t test.