Non-invasive Assessment Of Acute Muscle Injury And Repair By Using Ultrasound Shear Wave Elastography:an Experimental Study

Objective:Muscle contusion is one of the common muscle injury.Imaging diagnosis is an important guarantee for early treatment of muscle contusion.Timely evaluation of muscle function and damage status can provide useful and reliable inspection data for clinicians,which has important guiding significance for the choice of treatment plan.Among various imaging methods,conventional ultrasound is often used for real-time and dynamic assessment of muscle injury due to its advantages of safety,no radiation,low price and repeatability.Ultrasonic elastic imaging can provide elastic information of tissues.At present,there are few reports on the application of ultrasonic elastic imaging in muscle injury and repair.In our study,a rabbit model of acute blunt contusion of hind leg muscles was established.By conventional ultrasound,contrast echocardiography and shear wave elastography(SWE),we observed the changes of ultrasonic parameters in muscle contusion and repair,summarized the change law of SWE measured value combined with pathology.We explore the value of SWE technique in the diagnosis,treatment and follow-up of muscle contusion,which provide experimental basis for the application and popularization of this technique in clinical practice.Methods:A total of 54 healthy adult male New Zealand white rabbits were recruited in this study.The rabbits were randomized into 3 groups(n=18 per group):(i)the control group: as a control without any injury or therapy;(ii)the contusion group: without any therapy after muscle contusion;(iii)the treatment group: the injured sites were treated with both topical icing and Yunnan Baiyao after contusion.The characteristics of ultrasound images of the hind leg muscles of normal rabbits were observed by using different ultrasound methods(traditional B-mode ultrasound,CDFI,contrastenhanced ultrasound and SWE),and the advantages and disadvantages of each ultrasound method were compared.SWE was performed at pre-injury,0.5,1,3,5,7,14,and 28 d after injury.At these time points,a rabbit in each group was selected randomly for histopathological observation.At the end of the experiment,all the experimental animals were killed.All muscle tissues were collected and stained with Masson to compare the content of collagen fibers in the muscle tissues.Finally,the correlation between the percentage of collagen fiber area and elastic modulus was analyzed by Spearman.Results:The SWE image of normal rabbit hind leg muscle was stable and uniform blue,but ROI sampling diameter,scanning section and other factors affected the SWE value of normal rabbit hind leg muscle.There were significant differences in SWE values between the control group,the contusion group and the treatment group at different time points(P < 0.05).The SWE values of the contusion group was the highest,and the control group was the lowest.After muscle contusion 1-3 days,the SWE values of the contusion group and the treatment group increased gradually,and then decreased gradually.The maximum value of SWE in contusion group and treatment group was about 66.70 kpa and 53.0 kpa respectively.Histopathology showed that muscle necrosis and rupture,bleeding,edema,inflammatory cell infiltration after muscle contusion 1-3 days.The changes of muscle fiber regeneration and repair were mainly observed at 5-28 d after injury.The changes of SWE values were consistent with the pathological changes after injury.On the 28 th day after muscle injury,there was the correlation between SWE values and collagen fiber content in Masson staining(P < 0.001).The Emax correlation coefficient was the largest,which was 0.761.Conclusion:The changes of SWE in the course of acute muscle contusion and repair were consistent with the pathological process.During the period of muscle injury,the SWE values of injured muscle increased gradually,and the SWE values decreased gradually during the period of muscle repair and remodeling.On the 28 th day after injury,there was the correlation between SWE value and collagen fiber content in Masson staining.SWE could provide real-time,non-invasive,quantitative information on the changes of stiffness in different stages of muscle injury,which provides an objective reference for the diagnosis of acute muscle contusion,tracking and follow-up,and is expected to provide an objective imaging index for the clinical evaluation of the therapeutic effect of muscle injury.