MR properties of excised neural tissue following experimentally induced inflammation

Changes in the MR parameters of inflamed neural tissue were measured in vitro. Tumor necrosis factor-alpha (TNF-alpha) was injected into rat sciatic nerves to induce inflammation with negligible axonal loss and demyelination. The MR parameters, such as T1/T2 relaxation and magnetization transfer (MT), were measured 2 days after TNF-alpha injection and were found to be substantially different from those of normal nerves. The average T1/T2 relaxation times increased, whereas the MT ratio (MTR) and the quantitative MT parameter M0B (which describes the semisolid pool of protons) decreased. The MR parameters correlated very well with the extracellular volume fraction (EM) of neural tissue evaluated by quantitative histopathology. The multicomponent T2 relaxation was shown to provide the best quantitative assessment of changes in neural tissue microstructure, and allowed us to distinguish between the processes of inflammation and demyelination. In comparison, the MT measurements were less successful due to competing contributions of demyelination and pH-sensitive changes in the MT effect.