Phosphorus MR spectroscopy in the treatment of human extremity sarcomas

The application of 31P MR spectroscopy in the characterization and treatment of malignant human extremity tumors is reviewed and placed in the perspective of results obtained in murine sarcomas. Despite the now widespread acquisition of gradient localized spectral maps, the low spatial resolution that can be achieved at 1.5 or 2 T with 31P MRS, greatly limits its use in the study of tumor heterogeneity. The potential of 31P MRS is in the evaluation and monitoring of large inoperable extremity tumors. There are early spectral changes in human extremity sarcomas monitored after therapy, and recent studies have shown that the 31P MR spectra measured before treatment, and the changes in phosphate metabolites measured shortly thereafter, correlate with the clinical response after 2 or 3 months. Larger clinical studies are needed to confirm whether correlations of, for instance, pretreatment tumor pH with necrosis at resection and Pi decrease with tumor regression, can be used as a predictive test for clinical response.