Skeletal muscle stiffness as measured by magnetic resonance elastography after chronic spinal cord injury:a cross-sectional pilot study

Skeletal muscle stiffness is altered after spinal cord injury(SCI).Assessing muscle stiffness is essential for rehabilitation and pharmaceutical interventions design after SCI.The study used magnetic resonance elastography to assess the changes in stiffness after chronic SCI compared to matched able-bodied controls and determine its association with muscle size,spasticity,and peak torque in persons with SCI.Previous studies examined the association between muscle stiffness and spasticity,however,we are unaware of other studies that examined the effects of muscle composition on stiffness after SCI.Ten participants(one female)with chronic SCI and eight(one female)matched able-bodied controls participated in this cross-sectional study.Magnetic resonance elastography was utilized to monitor stiffness derived from shear waves propagation.Modified Ashworth scale was used to evaluate spasticity scores in a blinded fashion.Peak isometric and isokinetic torques were measured using a biodex dynamometer.Stiffness values were non-significantly lower(12.5%;P=0.3)in the SCI group compared to able-bodied controls.Moreover,stiffness was positively related to vastus lateralis whole muscle cross-sectional area(CSA)(r2=0.64,P<0.005)and vastus lateralis absolute muscle CSA after accounting for intramuscular fat(r2=0.78,P<0.0007).Stiffness was also positively correlated to both isometric(r2=0.55-0.57,P<0.05)and isokinetic peak(r2=0.46-0.48,P<0.05)torques.Our results suggest that larger clinical trial is warranted to confirm the preliminary findings that muscle stiffness is altered after SCI compared to healthy controls.Stiffness appeared to be influenced by infiltration of intramuscular fat and modestly by the spasticity of the paralyzed muscles.The preliminary data indicated that the relationship between muscle stiffness and peak torque is not altered with changing the frequency of pulses or angular velocities.All study procedures were approved by the Institutional Review Board at the Hunter Holmes McGuire VA Medical Center,USA(IRB#:02314)on May 3,2017.

Comparative analysis of indentation and magnetic resonance elastography for measuring viscoelastic properties

Measurement the viscoelastic properties is important for studying the developmental and pathological behavior of soft biological tissues.Magnetic resonance elastography(MRE)is a non-invasive method for in vivo measurement of tissue viscoelasticity.As a flexible method capable of testing small samples,indentation has been widely used for characterizing soft tissues.Using 2nd-order Prony series and dimensional analysis,we analyzed and compared the model parameters estimated from both indentation and MRE.Conversions of the model parameters estimated from the two methods were established.We found that the indention test is better at capturing the dynamic response of tissues at a frequency less than 10 Hz,while MRE is better for describing the frequency responses at a relatively higher range.The results provided helpful information for testing soft tissues using indentation and MRE.The models analyzed are also helpful for quantifying the frequency response of viscoelastic tissues.

Progressive changes in platelet counts and Fib-4 scores precede the diagnosis of advanced fibrosis in NASH patients

BACKGROUND Cirrhosis and its complications develop in a subgroup of patients with nonalcoholic fatty liver disease(NASH).Early detection of liver fibrosis represents an important goal of clinical care.AIM To test the hypothesis that the development of cirrhosis in nonalcoholic fatty liver disease patients is preceded by the long-term trends of platelet counts and Fib-4 scores.METHODS We identified all patients in our healthcare system who had undergone fibrosis staging by liver biopsy or magnetic resonance elastography(MRE)for nonalcoholic fatty liver disease during the past decade(n=310).Platelet counts,serum glutamic-pyruvic transaminase and serum glutamic oxalacetic transaminase values preceding the staging tests were extracted from the electronic medical record system,and Fib-4 scores were calculated.Potential predictors of advanced fibrosis were evaluated using multivariate regression analysis.RESULTS Significant decreases in platelet counts and increases in Fib-4 scores were observed in all fibrosis stages,particularly in patients with cirrhosis.In the liver biopsy group,the presence of cirrhosis was best predicted by the combination of the Fib-4 score at the time closest to staging(P<0.0001),the presence of diabetes(P=0.0001),and the correlation coefficient of the preceding timedependent drop in platelet count(P=0.044).In the MRE group,Fib4 score(P=0.0025)and platelet drop(P=0.0373)were significant predictors.In comparison,the time-dependent rise of the Fib-4 score did not contribute in a statistically significant way.CONCLUSION Time-dependent changes in platelet counts and Fib-4 scores contribute to the prediction of cirrhosis in NASH patients with biopsy-or MRE-staged fibrosis.Their incorporation into predictive algorithms may assist in the earlier identification of high-risk patients.

Noninvasive Fibrosis Assessment in Chronic Hepatitis C Infection: An Update

Liver biopsy is historically the gold standard for liver fibrosis assessment of chronic hepatitis C patients.However,with the introduction and validation of noninvasive tests(NITs)to evaluate advanced fibrosis,and the direct-acting antiviral agents for treatment of chronic hepatitis C virus(HCV),the role of NITs have become even more complex.There is now need for longitudinal monitoring and elucidation of cutoff values for prediction of liver-related complication after sustained virological response.The aim of this report is to provide a critical overview of the various NITs available for the assessment of liver fibrosis in HCV patients.