The Quantitative Study Of Skeletal Muscle Function During Exercise Using Dynamic Phosphorus MRS.

PrefacePhosphorus MR spectroscopy has special capabilities in the analysis of in vivo energy metabolism of human tissue and cell.The concentration of phosphide is correlated well with energy metabolism,determination of concentration and distribution of phosphorus metabolism can reflect cellular energy status.Therefore,phosphorus MR spectroscopy,which can detect content of both energy-rich phosphate and phospholipids, plays an important role in the study of in vivo energy metabolism of tissues and should be an important tool in the study of diseases associated with muscle.Dynamic phosphorus MR spectroscopy can measure the change of cellular energy-rich phosphate compounds during rest,systolic phase,and restoration process;evaluate the efficiency of energy conversion during working of skeletal muscle.It is useful tool to study of muscle function.In addition,dynamic phosphorus MR spectroscopy is also an important tool to study of mitochondria function due to its capacity of detection of disturbance of intra-cellular glycogenolysis and oxidative phosphorylation in vivo.However,in the past,the ratios of every metabolite peaks to the peak of PCr were used in similar abroad study to indirectly evaluate the muscular energy metabolism,lack of methods and approach of direct quantitative assessment.Domestic similar study of phosphorus MR spectroscopy is just recently on the way,and most in the experimental and unsolved status.The quantitative method of phosphorus MR spectroscopy and phosphorus MR spectroscopy characteristic of normal muscle have not been systematical studied.Especially,the study of dynamic phosphorus MR spectroscopy is vacant which is limited by evaluated index.Our studies are to quantitatively evaluate phosphorus MR spectroscopy of quadriceps muscle of thigh in adult and adolescent age groups,to evaluate the energy metabolism of normal muscle in different age group,therefore,it can establish the basis for further study of pathophysiology characteristic of both muscle diseases and systematic diseases.Meanwhile,our studies are to evaluate skeletal muscle function of health volunteers using in vivo dynamic phosphorus MR spectroscopy,to quantitative study of energy metabolism of skeletal muscle in physiological state during exercise.It is the attempt to noninvasively evaluate the skeletal muscle function using living cell imaging technique.PurposeOur studies are to evaluate the energy metabolism of normal muscle.In resting state in adult and adolescent age groups,in order to investigate individual energy metabolism feature in different age group,which can establish the basis for further study of pathophysiology characteristic of both muscle diseases and systematic diseases. Meanwhile,our studies are to evaluate skeletal muscle function of health volunteers using in vivo dynamic phosphorus MR spectroscopy(³¹P-MRS),to quantitative study of energy metabolism of skeletal muscle in physiological state during exercise.It is the attempt to noninvasively evaluate the skeletal muscle function using living cell imaging technique.Materials and MethodsNoninvasive 31P-MRS was acquired from quadriceps muscles in healthy people including 10 adults and 6juvenile,the ages range from 22 to 55 years old(median age 38±12),and from 7 to 16 years old(median age 11±3).All subjects haven't received systematical physical training and all 16 subjects have received ³¹P-MRS data collection and quantitative analysis on 1.5T Philips Achieva magnetic resonance system which equipped with polynucleation analysis system.³¹P-MRS data collection was using surface coil with capacity of both reception and emission surface coil.The surface coil was fixed on the surface of thigh.Imaging was firstly acquired using proton frequency to observe the scope of acquisition of ³¹P-MRS;and then automatic shimming,further shimming and acquisition of spectral lines were performed respectively.Volume acquisition sequence was used in the course of acquisition of spectral lines.Acquisition parameters were:TR =2500ms,excitation=64 times,total acquisition time=3min. Calculation of the area under every metabolite peak when presence of infinity TR was performed using fitting of exponential function,and standardization of difference of longitudinal relaxation of phosphorus compounds was also performed.Correction factor was calculated by measuring of signal effect of different intramusculary compounds with different layers of subcutaneous fat in order to perform standardized correction of heterogeneity of field strength for surface coil.Content of ATP was 5.5mmol/kg as standard to perform half absolutely quantitive analysis of every phosphorus compound in our study(unit:mmol/kg).Maximum voluntary contraction(MVC) testing of musculus quadriceps fexoris was performed before dynamic ³¹P-MRS study.25%of MVC(low-load) and 50%of MVC(high-load) were used respectively during acquisition of ³¹P-MRS on moving state. Imaging at resting state was firstly acquired using proton frequency to observe the scope of acquisition of ³¹P-MRS;and then automatic shimming,further shimming and acquisition of spectral lines were performed respectively.Volume acquisition sequence was used in the course of acquisition of spectral lines.Total acquisition time for every spectral line was 1min.Six spectral lines at resting state were acquired.Meanwhile, materials with equivalent weight of 25%MVC was strained to ankle,and the subjects were asked to kick one time every 5s in order to contract musculus quadriceps,total six spectral lines at moving state were acquired.And then,loading of ankle was rapidly increased to 50%MVC,above-mentioned procedures were repeated,another six spectral lines at moving state were acquired.Finally,six to ten spectral lines at convalescence stage were acquired after removal of ankle loading.Processing of spectral lines were performed using package basis on Matlab software.Through the procedure of Fourier transformation,baseline modulation,and phase correction,spectral line with different frequency domain was acquired.Four spectral lines were selected from six spectral lines in every stage and superimposed to form spectral line of stage.The absolute concentration of PME,Pi,PDE,CP and ATP were determined from spectra,and the value of ADP,phosphorylation potential(PP),and enzymatically active Mg-ATP complex were calculated.The work / cost ratios were derived from weight /(Pi / CP) to compare muscle efficiency between adults and young subjects. Results1.³¹P-MRS can directly measure concentration of some of chemical compoundsThe content of intramusculary metabolite greater than 1mmol can be detected directly by ³¹P-MRS when it was without macromolecular binding.Seven resonance peaks of metabolism products were observed:from left to fight one by onehosphomonoesterase (PME),inorganic phosphate(Pi),phosphodiesterase(PDE), phosphocreatine(CP),γ-adenosine triphosphate(ATP),α-ATP,andβ-ATP.Quantitative analysis can be performed by calculation of the area of under every peak,the content of PDE for adolescent was obviously decreased compared with that for adult;while the content of ATP was obviously increased.There was no significant difference for other chemical compounds.2.³¹P-MRS can indirectly measure concentration of chemical compounds which were related with energy metabolismMost of ADP were combined with myofibrillae,therefore,free dissolvable ADP in cytoplasm was less and impossible to detect.However,the content of ADP could be calculated according to equilibrium reaction of enzymatic creatinkinase.The level of PH value,Mg-ATP,and total Mg for adolescent was obviously decreased compared with that for adult,while there were no significant difference for the contents of ADP,PP, free Mg iron,and free ATP when different age group was compared.3.Comparison of dynamic ³¹P-MRS results in adolescent group and adult groupThe peak of Pi was increased and the peak of CP was decreased when low-load(25 %of MVC) movement was performed;The peak of Pi was continually increased and the peak of CP was obviously decreased when high-load(50%of MVC) movement was performed;The peak of Pi was decreased and the peak of CP was approximately returned to the level of rest state at convalescence stage.However,the level of ATP was approximately constant at rest stage,at moving stage,and at convalescence stage. Quantitative observation of dynamic changes of Pi,CP,andβ-ATP of different age group at moving stage showed that the level of Pi was increased and the level of CP was decreased during the movement for both two groups,and the levels of both Pi and CP were approximately returned to the levels of rest state after the cessation of movement. Among them,the increase of Pi in adult group was greater during high-load movement. However,the level of ATP was approximately constant in these two groups,the level of ATP in adolescent group greater in different stage compared with that in adult group. The total intra-cellular phosphoric content remained constant for two groups of subjects.Comparison of phosphoric contents in different stage for adolescent group and adult group:There were no significant longitudinal change of PME and PDE.And there was no significant difference of PME for two age group when transversal comparison was performed.Only in high load moving stage,the mean value of PME for adolescent group was lower than that for adult group.Comparison of the content of ADP,PP,Mg ionic compound in musculus quadriceps fexoris and working efficiency of muscle in different stage for two age groups:The content of ADP was increased and the content of PP was decreased during the movement;and return to the level of rest stage after the cessation of movement.There was no statistical difference for two different age groups.While the content of Mg-ATP and total Mg iron remains constant,though slightly increased in adolescent group.There was no statistical difference of free Mg iron and free ATP for two different age groups. Muscle efficacy was depend on loading weight/(Pi/CP),muscle efficacy was increased during high loading.There was no statistical difference for two different age groups, though slightly increased in adult group.ConclusionPhosphorus MR spectroscopy has special capabilities in the quantitative study of many kinds of chemical compounds which participate in the course of energy metabolism,and it can non-invasively detect intracellular microenvironment.Our studies are to evaluate the energy metabolism of normal muscle in adult and adolescent age groups, and successfully investigate individual energy metabolism feature in different age group, which can establish the basis for further study of pathophysiology characteristic of muscle diseases.High energy compounds which can be directly utilized in skeletal muscle in juvenile subjects were slightly higher,while capabilities of energy reservation and working efficiency in juvenile subjects were similar with those in adult.Intra-cellular interconversion of energy-rich phosphate plays an important role in the maintaining of normal function of skeletal muscle during exercise.Dynamic ³¹P-MRS can reflect energy metabolism of skeletal muscle during exercise and provides valuable information to evaluate muscle functional imaging.