MR OF WALLERIAN DEGENERATION IN THE FELINE VISUAL-SYSTEM - CHARACTERIZATION BY MAGNETIZATION-TRANSFER RATE WITH HISTOPATHOLOGIC CORRELATION

PURPOSE: To examine the utility of measuring magnetization transfer ra tio for delineating the dynamic changes of wallerian degeneration whic h occur after controlled injury in a feline model in which anatomic pa thways are well understood. METHODS: Using standard neurosurgical tech niques, discrete lesions were made to ablate the visual cortex. Gradie nt imaging was performed serially at 1.5 T, with and without a saturat ion pulse to create a magnetization transfer effect. At varying interv als, the animals were killed for histologic analysis. RESULTS: Within the first 2 weeks there is a statistically significant increase in mag netization transfer ratio relative to the control hemisphere within th e white matter connections between the lateral geniculate nucleus and the visual cortex at a time when no effects are visually detectable on spin-echo images. Between 16 and 28 days, this reverses to a decrease in magnetization transfer ratio in both the lateral geniculate nucleu s itself and the adjacent superolateral white matter. More remote whit e matter tracts remained stable, without significant change. CONCLUSIO NS: Magnetization transfer ratio seems to be more sensitive for early detection of degeneration than conventional spin-echo imaging. Moreove r, temporal changes in magnetization transfer ratio seem to correspond well with known histologic phases of wallerian degeneration.