In vivo evaluation of remyelination in rat brain by magnetization transferimaging

The aim of this work was to assess quantitatively and qualitatively the abi lity of magnetization transfer imaging to follow in vivo remyelination. Dem yelination lesions were induced in rats by the injection of L-alpha-lysopho sphatidylcholine stearoyl into the corpus callosum and imaging was performe d in vivo on a 4.7-Tesla system at different time points. The percentage of magnetization transfer ratio (MTR) decrease was calculated for each animal . To evaluate the MTR findings for remyelination, myelin was quantitated by histological analysis of the lesion size and counting the number of remyel inating axons. An MTR decrease was observed when demyelination was present at 7 days after injection. During the remyelinating phase between day 30 an d 40 after injection, contralateral values almost complete returned to norm al, thus indicating remyelination. Histologically, at days 30 and 40 after injection, the lesion area was reduced in size and the axons were surrounde d by a thin myelin sheath, indicating the remyelination process. Statistica l analysis showed that the profile of MTR values was significantly correlat ed with the course of remyelination. All the MTR changes show a correlation with both myelin damage and repair. In conclusion, the study of the MTR pr ofile in this myelin lesion model demonstrates in vivo the loss of myelin a nd the presence of spontaneous remyelination. This methodological approach which can also be applied to multiple sclerosis patients to show demyelinat ion, should prove helpful to determine the degree of spontaneous and therap eutically induced remyelination in multiple sclerosis lesions, and thus to validate therapeutic treatments for myelin repair. (C) 2000 Elsevier Scienc e B.V, All rights reserved.