MTR and TI provide complementary information in MS NAWM, but not in lesions

MTR and TI relaxation times ore abnormal in MS lesions and NAWM, and may re flect tissue damage such as demyelination and axonal loss. Their relationsh ip and potential to provide complementary information in tissue characteris ation is explored The aim of this study was to document the relationship be tween magnetisation transfer ratio (MTR) and TI relaxation time in Multiple Sclerosis (MS) lesions and normal appearing white matter (NAWM) in order t o determine whether the combination provides a more comprehensive tissue ch aracterisation than either parameter in isolation. Ten Patients with relaps ing remitting MS and la age matched healthy controls underwent imaging usin g a protocol which included the measurement of both MTR and TI relaxation t imes. The MTR and TI values were compared statistically using a commonly ad opted correlation approach and a mixed-model regression approach. There was a strong correlation between MTR and TI in MS lesions (r=0.74). The correl ation was seen equally in TI hypointense and isointense lesions. The relati onship was much weaker in MS NAWM (r=0.24) and no correlation was found in control while matter (r=0.06). Mixed-model regression analysis confirmed th at the relationship between TI and MTR is strongly dependent upon tissue ty pe (MS lesion, MS NAWM, or control white matter). The relationship between MTR and TI relaxation time measurements varies markedly between Pathologica l and normal tissue types In MS, the complementary information obtained fro m MTR and TI is most apparent in NAWM. The results emphasise the Potential for combinations of MR parameters to improve tissue characterisation, which in turn should improve understanding of disease pathology and treatment mo nitoring.