Magnetic field dependence of 1/T1 of human brain tumors. Correlations with histology.

The authors have measured the magnetic field dependence of 1/T1 (nuclear magnetic relaxation dispersion, or NMRD profiles) of water protons of histologically characterized samples of astrocytomas, meningiomas, and lymphomas. The goal was to elucidate the determinants of 1/T1 of brain tumors at the cellular level and, in particular, to search for a possible correlation of the profiles with neoplastic properties, including degree of malignancy. Because of the recently demonstrated contribution of myelin to 1/T1 of white matter, careful histologic analyses were performed to correct for its presence. The range of magnitude of the profiles of differing types and grades of tumors correlates with the range of water content of these tumors; the correlation of water content with cellularity (density of cell nuclei in a histologic preparation), in turn, produces correlations of 1/T1 with tumor type. For all the tumors studied, 1/T1 is proportional to solids content; the constant of proportionality is relatively insensitive to tumor type and, for astrocytomas, grade of malignancy; and is about the same as that of normal gray matter. For low- and intermediate-grade astrocytomas that contain myelin, the myelin-specific contribution to 1/T1 has to be considered to make manifest the underlying correlations, which are best demonstrated at low fields, where the background contribution of water and dissolved oxygen is minimal. At high fields, where most imaging is done, a change in oxygen partial pressure, as for example from ischemia in very malignant tumors, is sufficient to alter 1/T1 significantly, reducing the intrinsic correlation between histology and 1/T1.