Quantitative diffusion measurements in focal multiple sclerosis lesions: Correlations with appearance on TI-weighted MR images

OBJECTIVE. Relative hypointensity on T1-weighted MR imaging has been sugges ted as a putative disability marker. The purpose of our study was to determ ine if there are quantifiable diffusion differences among focal multiple sc lerosis lesions that appear differently on conventional T1-weighted MR imag es. We hypothesized that markedly hypointense lesions on unenhanced T1-weig hted images would have significantly increased diffusion compared with othe r lesions, and enhancing portions of lesions would have different diffusion compared with nonenhancing lesions. SUBJECTS AND METHODS. Average apparent diffusion coefficient (ADC) was calc ulated fur 107 lesions identified on T2-weighted images in 16 patients with multiple sclerosis and was compared with the ADC of normal white matter in 16 age- and sex-matched control subjects. Seventy-five nonenhancing lesion s (29 isointense, 46 hypointense) and 32 enhancing lesions (6 isointense, 2 6 hypointense) were categorized on the basis of unenhanced T1-weighted MR i maging. RESULTS. Hypointense and isointense nonenhancing lesions both showed signif icantly higher ADC than normal white matter (p < 0.0001). Hypointense nonen hancing lesions showed higher ADC values than isointense nonenhancing lesio ns (p < 0.0001). Diffusion in enhancing portions of enhancing lesions was d ecreased when compared with nonenhancing portions. CONCLUSION. Quantitative diffusion data from MR imaging differ among multip le sclerosis lesions that appear different From each other on T1-weighted i mages. These quantitative diffusion differences imply microstructural diffe rences, which may prove useful in documenting irreversible disease.