The response of human tumors to carbogen breathing, monitored by gradient-recalled echo magnetic resonance imaging

Purpose: Gradient-Recalled Echo (GRE) Magnetic Resonance Imaging (MRI), which detects changes in blood vessel deoxyhaemoglobin content, has been investigated as a noninvasive monitor of changes in human tumor oxygenation and blood flow, in response to carbogen (95% O2, 5% CO2) breathing. Methods and Materials: GRE images (TE = 60 ms, TR = 200 ms, α = 40 deg., 2562 matrix) were acquired from 31 patients with primary and metastatic disease, prior to and during carbogen breathing. Three patients underwent a follow-up examination after radiotherapy. Results: Seventeen out of 34 tumors showed enhanced image intensity, consistent with an improvement in tumor oxygenation and blood flow, while 11 showed no response; 6 studies were technical failures. In one patient a metastatic node that had eluded orthodox investigation was visualized. A reduction in response was observed in the three patients studied postradiotherapy. Conclusion: This method, which can be performed on a standard clinical MRI instrument, provides a noninvasive measurement of tumor response to oxygenation/blood flow modification. In principle, this should enable the clinician to optimize treatment protocols, such as carbogen breathing, for individual radiotherapy patients