Dyke Award paper. MR of wallerian degeneration in the feline visual system: characterization by magnetization transfer rate with histopathologic correlation

Abstract

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.