THE RESPONSE TO CARBOGEN BREATHING IN EXPERIMENTAL TUMOR-MODELS MONITORED BY GRADIENT-RECALLED ECHO MAGNETIC-RESONANCE-IMAGING

Gradient-recalled echo magnetic resonance imaging (GRE MRI), which giv es information on blood flow and oxygenation changes (Robinson SP, How e FA, Griffiths JR 1995, int J Radiat Oncol Biol Phys 33: 855), was us ed to observe the responses of six rodent tumour models to carbogen br eathing. In one transplanted rat tumour, the Morris hepatoma 9618a, an d a chemically induced rat tumour, the MNU-induced mammary adenocarcin oma, there were marked image intensity increases, similar to those pre viously observed in the rat GH3 prolactinoma. In contrast, the rat Wal ker carcinosarcoma showed no response. In two mouse tumours, the RIF-1 fibrosarcoma and the human xenograft HT29, carbogen breathing induced a transient fall in signal intensity that reversed spontaneously with in a few minutes. The rat GH3 prolactinoma was xenografted into nude m ice, and an increase in image intensity was found in response to carbo gen, suggesting that any effects that carbogen may have had on the hos t were not significant determinants of the tumour response, The increa ses in GRE image intensity of the MNU, H9618a and GH3 tumours during c arbogen breathing are consistent with increases in tumour oxygenation and blood flow, whereas the responses of the RIF-1 and HT29 tumours ma y be the result of a transient steal effect followed by homeostatic co rrection.