Dyke Award paper. 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 ratio for for delineating the dynamic changes of wallerian degeneration which occur after controlled injury in a feline model in which anatomic pathways are well understood.

METHODS Using standard neurosurgical techniques, discrete lesions were made to ablate the visual cortex. Gradient imaging was performed serially at 1.5 T, with and without a saturation pulse to create a magnetization transfer effect. At varying intervals, the animals were killed for histologic analysis.

RESULTS Within the first 2 weeks there is a statistically significant increase in magnetization transfer ratio relative to the control hemisphere within the 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 nucleus itself and the adjacent superolateral white matter. More remote white matter tracts remained stable, without significant change.

CONCLUSIONS Magnetization transfer ratio seems to be more sensitive for early detection of degeneration than conventional spin-echo imaging. Moreover, temporal changes in magnetization transfer ratio seem to correspond well with known histologic phases of wallerian degeneration.