Multimodal Imaging Quantitative Analysis Of Age-Related Changes In Skeletal Muscle And Cross-Sectional Study Of Comorbidity With Muscle,Bone And Fat

Objective:Sarcopenia is the age-related progressive decline in muscle mass,strength and physical function.It is accompanied by intermuscular fat accumulation,muscle fibrosis,selective atrophy of type 2 fibers,and perfusion changes that lead to deterioration in muscle force,decline in exercise capacity,and increase the risk of falls,fractures and disability among middle-aged and elderly people.While,muscle quality is closely related to muscle strength and body function,and may become an important indicator for the diagnosis and screening of sarcopenia.Imaging examination is considered to be the gold standard for evaluating body composition.It can not only measure muscle area and fat fraction,but also provide pathophysiological information about muscle edema,inflammation,fibrosis,and fat infiltration.This study is first to evaluate the age-related MRI parameters and to establish a standard for these parameters and age-related characteristics,and to explore biological markers for evaluating muscle in healthy thigh skeletal muscles using multiparametric quantitative MRI.Because of the interdependence and interaction between muscle,bone and fat,then we will study the prevalence rate of sarcopenia,osteoporosis and obesity among the middle-aged and elderly people in Shenyang,and to analyze the contributing factors and prediction models of related diseases;at the same time,to discover the changing patterns and variability with aging or gender of the Quantitative Computed Tomography(QCT)-derived muscle-bone-fat parameters and their interactions,therefore to evaluate QCT's clinical application of the age-related muscle-bone-fat diseases.Methods:This research were divided into two parts:1.A quantitative study of the age-related changes in thigh skeletal muscles using the multiparametric magnetic resonance imaging150 healthy volunteers(75 males,75 females;average age 45.6±15.6 years old,range22-69 years)were recruited and put into 5 groups according to their age:20-29 years(n=30),30-39 years(n=30),40-49 years(n=30),50-59 years(n=30),and 60-69 years(n=30).The multiparametric MR imaging(T₁-mapping,T₂-mapping,m Dixon-Quant,IVIM-DWI,and DTI)was performed on the mid-section of the right thigh on all volunteers employing a 3.0T MR system.Two radiologists measured the parametric maps of the quadriceps femoris,medial muscles and hamstrings of the thigh respectively.One-way ANOVA and post-hoc Dunnett T3 test were chosen to analyze the MR multi-parameters(T₁ and T₂ relaxation times,true diffusion coefficients(D),pseudo diffusion coefficients(D^*),perfusion fraction(f),apparent diffusion coefficients(ADC),fractional anisotropy(FA),and fat fraction(FF))in the thigh muscles among different age groups.Pearson or Spearman correlation coefficient(r)was applied to determine the correlation between MR multi-parameters and age,with the adjustment of the gender effect and the body mass index(BMI).Interrater reliability was also assessed with intraclass correlation coefficients(ICC).2.A cross-sectional study on the comorbidities of sarcopenia,osteoporosis and obesity among middle-aged and elderly people in Shenyang540 community populations were recruited in this study,including 186 males and 354females.Abdominal QCT was used to measure the muscle area and muscle density of L3lumbar vertebra,the average bone mineral density(BMD)of L2-L4 lumbar vertebra,and the visceral fat area in the intervertebral space of L4/5.The research subjects were grouped into 3 according to their age.The number of sarcopenias,osteoporosis,obesity and comorbidities among the overall and each age group was counted.The general linear model was applied to analyze the trends of the QCT-derived muscle-bone-fat parameters in age and gender among the groups,followed by Person or Spearman correlation analysis.With sarcopenia,osteoporosis and obesity as two dependent variables respectively,the logistic linear regression analysis was conducted of these variables and factors that may affect the value.Results:1.There were significant differences among the age groups in T₂ values(P<0.05)and FF(P<0.05)of the quadriceps,medial muscles and hamstrings,and FA(P<0.05)of the hamstrings.T₂ values(r=0.413,0.313,and 0.624,respectively,P<0.001)and FF(r=0.764,0.608,and 0.669,respectively,P<0.001)in all three muscles and FA(r=0.377,P<0.001)in the hamstrings were positively associated with age.These differences remained significant after adjustment for sex and BMI.Interrater reliability of all three muscles was excellent(ICC:0.759-0.938).2.The prevalence rate of sarcopenia in men and women in their over 40s were 26.3%and27.7%in Shenyang;the rate of osteoporosis were 11.3%and 28%;and the rate of abdominal obesity were 32.3%and 25.4%.These rates were also increasing with aging.The density and area of muscle,BMD were decreasing with age,while the visceral fat area was increasing with age.The correlation analysis showed that in male subjects,the muscle area was weakly correlated with age(r=-0.178)and BMD(r=0.265);the muscle density was moderately correlated with age(r=0.-437)and BMD(r=0.498);while BMD was strongly correlated with age(r=-0.548).The visceral fat area in males was weakly correlated with age(r=0.180)as well.In female subjects,the muscle area was weakly correlated with age(r=-0.234)and BMD(r=0.216);while the muscle density was strongly correlated with age(r=-0.521)and BMD(r=0.521);BMD was strongly correlated with age(r=-0.613);however,the visceral fat area was moderately correlated with age(r=0.311).The logistic regression analysis showed that the risk factors in sarcopenia were age(OR=1.045)and the difficulty in lifting weights(OR=3.566);whilst the protective factors in sarcopenia were body mass index(OR=0.488)and the muscle density(OR=0.845).The risk factors in osteoporosis were age(OR=1.139),the waist circumference(OR=1.085),the history of fracture(OR=2.584),and the history of thyroid disease(OR=2.512);the protective factors in osteoporosis were muscle density(OR=0.881)and the history of daily milk drinking(OR=0.804).The risk factors in obesity were age(OR=1.040)and the waist circumference(OR=1.102).Conclusion:1.The quantitative multiparametric MR imaging is a non-invasive method to evaluate the age-related structure and their dynamic changes of thigh skeletal muscles at the micro level.2.T₂ and FF of the all three muscle groups and FA of the hamstrings significantly change with aging.T₂ and FF can be used as biomarkers to evaluate the changes of skeletal muscles in aging.3.Abdominal QCT shows its clinical importance when applied to study the muscle-bone-fat diseases opportunity screening and their interaction.4.The prevalence rate of sarcopenia,osteoporosis and obesity in the community population?40 years old in Shenyang rises with aging.The comorbidities of these three diseases are highly likely and they can affect each other.5.BMD,the muscle area and the muscle density decreased with aging,while visceral fat dimensions increased with aging.6.The muscle density was more closely related to BMD and age than the muscle areas.Therefore,the muscle density can be a vital marker when evaluating sarcopenia.