OXYGEN-INDUCED MR SIGNAL CHANGES IN MURINE TUMORS

Breathing of 100% oxygen was used to challenge vascular autoregulation in 14 mice with either osteosarcomas (n = 6) or mammary carcinomas (n = 8). Reproducible and statistically significant signal intensity cha nges of -29 +/- 6% to +35 +/- 3% were observed on heavily T-2-weighte d images in the tumors during the oxygen challenge. No significant cha nges were observed in muscle. For the mammary carcinomas a higher perc entage of tumor voxels showed significant signal-intensity decrease (3 1 +/- 8%) compared to the percentage of voxels showing a signal-intens ity increase (22 +/- 3%). In contrast, for the osteosarcomas, a higher percentage of tumor voxels showed signal-intensity increase (52 +/- 9 %) compared to the percentage of voxels showing signal-intensity decre ase (27 +/- 9%). The regional distribution of these signal intensity c hanges did not correlate with the signal pattern on T-1-, T-2-,and T-2 -weighted and Gd-DTPA enhanced images acquired without breathing 100% oxygen. Most likely, the signal intensity changes represented the ina bility of the tumor's neovascularization for autoregulation during the oxygen challenge, particularly in hypoxic regions. Although further i nvestigation is needed, the findings that malignant tumor tissue showe d signal intensity changes, whereas normal muscle tissue did not, sugg ests that this technique may prove useful in distinguishing benign fro m malignant tissue. (C) 1998 Elsevier Science Inc.