Tumour response to hypercapnia and hyperoxia monitored by FLOOD magnetic resonance imaging

Flow and oxygenation dependent (FLOOD) MR images of GH3 prolactinomas displ ay large intensity increases in response to carbogen (5% CO2/95%O-2) breath ing. To assess the relative contributions of carbon dioxide and oxygen to t his response and the tumour oxygenation state, the response of GH3 prolacti nomas to 5% CO2/95% air, carbogen and 100% O-2 was monitored by FLOOD MRI a nd pO(2) histography. A 10-30% image intensity increase was observed during 5% CO2/95% air breathing, consistent with an increase in tumour blood flow , as a result of CO2-induced vasodilation, reducing the concentration of de oxyhaemoglobin in the blood. Carbogen caused a further 40-50% signal enhanc ement, suggesting an additional improvement due to increase blood oxygenati on. A small 5-10% increase was observed in response to 100% O-2, highlighti ng the dominance of CO2-induced vasodilation in the carbogen response. Desp ite the large FLOOD response, non-significant increases in tumour pO(2) wer e observed in response to the three gases. Tissue pO(2) is determined by th e balance of oxygen supply and demand, hence increased blood flow/oxygenati on may not necessarily produce a large increase in tissue pO(2). The FLOOD response is determined by the level of deoxygenation of blood, the size of this response relating to vascular density and the potential of high-oxygen content gases to improve the oxygen supply to tumour tissue. Copyright (C) 1999 John Wiley & Sons, Ltd.