MODIFICATION OF TUMOR PERFUSION AND OXYGENATION MONITORED BY GRADIENTRECALLED ECHO MRI AND P-31 MRS

Gradient recalled echo (GRE) H-1 images can be used to monitor changes in blood oxygenation via the dephasing effects of paramagnetic deoxyh aemoglobin (Hb). We have modulated the blood flow/oxygenation of GH3 r at tumours by i.v. calcitonin gene-related peptide (CGRP) or carbogen (95% O-2, 5% CO2) inhalation, and obtained GRE H-1 images interleaved with P-31 spectra before, during and after the insult, With CGRP the G RE image intensity decreased (6/10) by > 10% with a concomitant 40% de crease (4/4) in beta NTP/P-i and a small decrease in pH. Both the imag e intensity and P-31 spectra returned to near their pre-CGRP levels af ter 50 min, consistent with a transient episode of hypoxia, Carbogen b reathing (5/5) caused > 40% increases in average GRE image intensity, with no significant changes in the P-31 spectra (4/4), Three-dimension al GRE images were obtained to confirm that a T-2 increase, rather th an just an 'in-flow' effect due to increased blood flow, was responsib le for the GRE enhancement, Increases in average image intensity > 40% were observed for the three-dimensional GRE images (2/2), indicating a T-2 increase, Using Hb as an endogenous contrast agent, the high se nsitivity of the GRE technique may provide a method of monitoring hete rogeneous tumour perfusion and oxygenation, both in the laboratory and the clinic.