Biexponential Apparent Diffusion Coefficients In Polymyositis And Glycogen Storage Disease

Objective The purpose of this study was to investigate the need for biexponentialsignal decay modeling for muscle diffusion signal decays over an extended b-factorrange.The characteristic of edema muscle from PM and GSD was estimated bybiexponential apparent diffusion coefficients and their value of differential diagnosiswas discussed. The fast and slow diffusion compartments was also tried to explain.Subjects and Methods Eleven healthy volunteers，nine patients in the stage ofactive （cause of disease＜6months） with biopsy-proven PM and5patients withbiopsy-proven GSD were included in this study. Patients were selected using thefollowing criteria:（1） No fat infiltration and fat replacement were shown on T1images.（2） Edema muscle was shown on T2images, both as determined from visual inspectionby an experienced radiologist.All studies were performed with a3.0-T MR scanner operating at the9.1hardware/software configuration（Signa Excite HD, General Electric Healthcare,Milwaukee, WI, USA） using an eight-channel torso array coil. The scan range wasfrom the line of alaossisillii to popliteal space of the thigh. All examinations includedaxial T1-and T2-weighted images and echo-planar DWI with b-values of0，20，50，100，200，300，400,500，600，700，800，900，1000，1100，1200s/mm².Statistical analysis of the data was performed with the SPSS18.0，SPSS，Chicago，III，software package. The means and standard deviations （SD） of thebiexponential parameters Fast ADC, Slow ADC, and Fraction of Fast ADC wereobtained for each ROI. In the control，PM group and GSD group, data from CM and EM were taken into consideration. A statistical comparison among three group muscleswas made using ANOVA. p＜0.005in the F test was considered statisticalsignificance.Result Biexponential fits to the CM, EM decay curves are seen. Summarizes themeans±SD of the biexponential parameter that characterize the diffusion decay curvesfrom EM ROIs in9PM and5GSD and CM ROIs in11volunteers. The fraction of theFast ADC in CM and EM of PM and EM of GSD are quite comparable,0.76±0.33×10^-2mm²/s,0.81±0.12×10^-2mm²/s,1.11±0.24×10^-2mm²/s,respectively. Theslow ADC in EM of PM are approximately larger than those in ＣＭ，0.18±0.03×10^-2mm²/s versus0.14±0.09×10^-2mm²/s. The slow ADC in EM of GSD areless than those in ＣＭ,0.12±0.01×10^-2mm²/s versus0.14±0.09×10^-2mm²/s.Significantstatistical difference of the mean value of slow ADC in the three groups was existed（p<0.05）.Conclusion Biexponential fits to the muscle decay curves. Edema muscle wasanalyzed quantitatively and more information about the characteristic of edema musclewas provided by biexponential apparent diffusion coefficients which played a role indistinguishing between poliomyelitis and glycogen storage disease. Through this studywe guess that the slow diffusion compartment was concerned with intracellular watermolecule, binding state of water and the shift of intracellular and extracellular and thefast diffusion compartment was related with blood perfusion closely.