THE CHARACTERIZATION OF EXPERIMENTAL GLIOSIS BY QUANTITATIVE NUCLEAR MAGNETIC RESONANCE IMAGING

Abstract

Quantitative nuclear magnetic resonance imaging techniques were used to study the development of astrocytic gliosis following a cortical freezing injury in 4 cats, and the findings compared with the histological and ultrastructural appearances of the affected white matter. In the first week after lesioning, the acutely oedematous white matter was apparent as a region of signal abnormality with very prolonged T₁′ and T₂′ relaxation times. Following resolution of this oedema, the images remained normal for a period of approximately three months. After this latent period they became abnormal once again, and the abnormal signal was most evident in images emphasizing differences between tissues in T₁′ and proton density, but not T₂′. The light and electron microscopic appearances of the corresponding tissue were of astrocytic gliosis in each animal. Measurement of the relaxation times, T₁′ and T₂′ of the abnormal regions revealed an increase in T₁′ without a corresponding change in T₂′. The T₂′ magnetization decay characteristics were consistently monoexponential, in contrast to the clearly biexponential T₂ decay which has previously been demonstrated in the presence of acute vasogenic oedema. These findings suggest that the pattern of change of the relaxation times and T₂ magnetization decay might provide a means of distinguishing between lesions in multiple sclerosis which are predominantly gliotic, and those containing significant amounts of oedema.