Evaluation of the effects of photoradiation therapy on brain tumors with in vivo P-31 MR spectroscopy.

In vivo phosphorus-31 magnetic resonance (MR) spectra were obtained by a surface coil method from rat glioma tissue inoculated subcutaneously in CD Fisher rats, and the effects of photoradiation therapy on tumors were evaluated by sequentially observing spectral changes. In the control group, the nucleoside triphosphate (NTP) and phosphomonoester peaks were large, the phosphocreatine peak was small, and the inorganic phosphate (Pi) peak was intermediate. In all eight cases in the group in which a dose of 10 mg/kg of hematoporphyrin derivatives (HpD) was given before photoirradiation, NTP peaks decreased, and the Pi peak increased remarkably within 1 hour after the 60-minute white-light irradiation. Spectral changes were observed before histologic changes were apparent. Histologic examinations 3 days after irradiation showed extensive necrosis in the tumor tissue. With preinjection of 5 mg/kg HpD, three of the eight cases showed spectrum changes after the irradiation. No spectrum changes were observed in the group with preinjection of 2.5 mg/kg. In vivo P-31 MR spectra measurements are useful not only to investigate the energy metabolism of tumor tissue in vivo but also to evaluate the effects of photoradiation therapy on tumors.