REGIONAL TUMOR OXYGEN DYNAMICS - F-19 PBSR EPI OF HEXAFLUOROBENZENE

We demonstrate a novel approach to measuring regional tumor oxygen ten sion using F-19 pulse burst saturation recovery echo planar imaging (E PI) relaxometry of hexafluorobenzene. Hexafluorobenzene offers excepti onal sensitivity to changes in oxygen tension, and has a single resona nce making it ideal for imaging studies, By combining a pulse burst sa turation recovery preparation sequence with EPT, the relaxation experi ments were performed in similar to 20 min facilitating measurements of dynamic changes in pO(2) accompanying interventions, Direct intratumo ral administration of hexafluorobenzene permitted labeling of specific regions of interest, and imaging provided maps of pO(2), confirming d istinct intra tumoral heterogeneity, For a group of three Dunning pros tate adenocarcinoma R3327-AT1 tumors interrogation of the central tumo r region showed skewed pO(2) distributions with considerable radiobiol ogical hypoxia (similar to 90% voxels had pO(2) < 15 torr) when rats b reathed 33% O-2. Altering the inspired gas to pure oxygen caused distr ibutions to shift towards increased pO(2) with significant increases i n mean oxygen tension (p < 0.05) in two cases. Interrogation of both c entral and peripheral regions in a fourth tumor showed bimodal distrib ution for tumor oxygenation including similar to 75% voxels with pO(2) > 15 torr, EPI allows the fate of individual voxels to be traced: upo n altering the inspired gas to pure oxygen those voxels with baseline pO(2) > 30 torr showed significant changes (p < 0.05), whereas those w ith pO(2) < 16 torr showed minimal response. The precision of the meas urements, together with the ability to simultaneously examine dynamic changes in multiple regions should provide a useful technique for inve stigating tumor hypoxia with respect to therapy. (C) 1997 Elsevier Sci ence Inc.