Application Of Diffusion Tensor Imaging In Polymyositis And Dermatomyositis

Objective To explore the characteristics of thigh muscles of patients withpolymyositis and dermatomyositis on diffusion tensor imaging.Subjects and Methods12patients from our hospital with PM/DM were collectedas patient group.10of them were proved as PM/DM with muscle biopsy, and the other2patients were diagnosed as dermatomyositis according to typical symptom, physicalsign and laboratory examination.10healthy volunteer were involved as control group.Both conventional MR imaging and diffusion tensor imaging of hibateral thighmuscles were performed on all the patients and healthy volunteer subjects. All theoriginal data were inported to the GE adw4.4work station. The following parametersof each muscle were calculated from DT images: average diffusion coefficient （ADC），fractional anisotropy （FA） and three Eigenvalues （λ1>λ2>λ3）. To compare theADC value and FA value of each muscle in control group, one-factor analysis ofvariance was used. The comparison between edema muscles and normal muscles,unaffected muscles and normal muscles were analyzed respectively using Student’st-test.Results The total mean ADC value and FA value of normal muscles were（1.71±0.03）×10^-3mm²/s，0.285±0.02respectively. Vastus medialis showed highest ADCvalue and Gracilis showed lowest ADC value with statistical differences from the othermuscles. Gracilis，Semitendinosus and Semimembranosus showed higher FA valuethen the others with statistical differences. Three eigenvalues of combined normal muscles were （2.25±0.02）×10^-3mm²/s，（1.64±0.03）×10^-3mm²/s，（1.24±0.03）×10^-3mm²/s respectively. The total mean ADC value、FA value and eigenvalues foredema muscles were（1.97±0.05）×10^-3mm²/s,0.285±0.02,（2.56±0.07）×10^-3mm²/s,（1.90±0.05）×10^-3mm²/s and（1.44±0.04）×10^-3mm²/s respectively.ADC and three eigenvalues of each edema muscle were statistically increasedcompared with normal muscle. There was no statistical difference of FA valuvebetween edema muscles and normal muscles. For unaffected muscles, the ADC value,FA value and eigenvalues showed no statistical difference from normal muscles.Conlusion For healthy volunteers, ADC value and FA value were different for eachthigh muscles. Gracilis，Semitendinosus and Semimembranosus showed higher FAvalue then others. For PM/DM, Edema muscles showed significantly higher diffusivitythan normal muscles along three basic directions in the ellipsoidal globe model ofdiffusion tensor. This differences can be explained by the pathology of PM/DM. Therewas no statistical difference of FA value between edema muscles and normal muscles,and this result suggests that the regularity of muscle fiber arrangement was notdestructed by inflammation. In short, DTI can be used to evaluate the anisotropicdiffusion characteristics of muscles of PM/DM patients quantitatively and to analyzethe muscles on the level of pathology, And this study provided a reference for DTI tobe used in other myopathies.