VARIATION OF THE MAGNETIC-RELAXATION RATE-1-T1 OF WATER PROTONS WITH MAGNETIC-FIELD STRENGTH (NMRD PROFILE) OF UNTREATED, NON-CALCIFIED, HUMAN ASTROCYTOMAS - CORRELATION WITH HISTOLOGY AND SOLIDS CONTENT

The magnetic relaxation rate 1/T1 of tissue water protons was measured over a wide range of magnetic field strengths (NMRD profile) for 92 f resh surgical specimens of astrocytomas to search for correlations of 1/T1 with tumor histology, as determined by light microscopy, and to a ssess the diagnostic potential of NMRD profiles for grading astrocytom as. A third goal was to elucidate the molecular determinants of lin. E ach specimen was histologically graded and inspected for evidence of m ineral deposits (Ca, Fe); its dry weight was determined and expressed in % of original wet weight. To minimize variability not directly rela ted to tumor grade, this initial report is limited to NMRD profiles of 47 non-calcified, non-mehorrhagic, untreated astrocytomas. For these, the mean value of 1/T1 at very low magnetic field sterilants was foun d to increase with increasing grade of malignancy; no clear correlatio n could be demonstrated at high fields where most imaging is done. The spread of 1/T1 for different grades of malignancy is large, however, and the overlap significant, even at the lowest field, so that astrocy tomas can not be graded by NMRD profiles alone. Average 1/T1 and avera ge dry weight increase with grade of malignancy; but the variability o f lin among specimens of the same dry weight is large, indicating that at least one other cellular parameter, not variable in normal tissue, influences 1/T1 strongly. We hypothesize that this parameter reflects changes at the molecular level in size distribution, mobility, or int ermolecular interaction of cytoplasmic proteins. Which specific change s are induced by malignant transformation in astrocytomas remains to b e investigated.