||Ultrasonographic and biomechanical properties in muscle injury after over-stretch
||Department of BioMedical Engineering
muscle strain injury
本實驗採用小鼠之腓腸肌之肌肉-肌腱組織進行體外被動拉伸測試之壓力-鬆弛現象測量，同一小鼠之左側直接用於測量，右側之組織則先經過40% 應變量之過度拉伸5分鐘後再進行測量。一開始將長度固定於原始長度並每次調整應變量10%直至達40%，於機械特性測試時亦同時利用高頻超音波系統搭配30MHz之探頭進行超音波訊號之截取。利用超音波探頭於Z軸之深度改變並拼接聚焦區之訊號以降低待測組織之影像失真情形，超音波訊號之擷取方向包含截面及縱切面，輸出之超音波影像分別以灰階值及 Nakagami 參數表示。機械特性之測試結果以應力鬆弛現象達一穩定狀態後之平均荷重或壓力表示，而超音波參數則計算於影像中固定四個區域之平均灰階值及Nakagami參數，再利用這些數據進一步分析機械特性與超音波參數之關係。此外，為了分析肌肉組織之結構改變與力學特形及超音波參數之相關性，組織學研究亦使用於本研究於了解肌肉纖維及膠原蛋白纖維之表現。
Musculoskeletal system plays an important role in body movement, and it was responsible to force generation and loading. The mechanical properties of material were indicated to the response during loading, and these properties were often seen as the key factors to evaluate the functions of skeletal muscle tissue. Hence, Comparing the subjective method in clinical to evaluate the strain injury in skeletal muscle tissue, it is better to provide the accuracy and objective information about strain injury by detecting the mechanical behavior. But, there are some limitations in this kind of evaluation due to the mechanical properties were difficult to measure in vivo. Therefore, how to measure the mechanical force noninvasively is an important issue in developing the technique. The ultrasonic imaging system was one of common tool for diagnosis used in clinical because the advantages such as noninvasive and convenient. Besides, the wave transmission, reflection, and scattering of ultrasound can be used to reflect the physical parameters in the tissue, and as well advanced to help evaluate the biomechanical properties, such as elastic or stiffness. The objectives of this study were to investigate the correlation between ultrasonic parameters from ultrasonographys and mechanical behavior of muscle tissue, and developed an objective method to help assess the injury level in strain injury muscle.
The gastrocnemius muscle-tendon units from mice were use to proceed the stress-relaxation tests, at the same time, the images were recorded by high-frequency ultrasound with 30 MHz transducer. The left tissue was tested directly, and right one was tested post 40 % strain overstretch 5 minutes. To modulate the length of muscle to measure the static stress, from original length to 40% strain with the 10% increments each time. The way of scanning was the brightness/depth (B/D) mode, which can be used to reduce the adverse effects of beam diffraction on the image resolution. The ultrasonic signals were recorded in cross section and longitudinal section, and the results of ultrasonic signals were displayed as ultrasonography in types of echogenicity and Nakagami parameter. The results of mechanical force were showed as the mean value of stress or load in static state, and the ultrasonic parameters were expressed as the mean value from four stationary areas, and then, according to these results, the correlation coefficient between them was analyzed. Moreover, the histological study was also used to evaluate the appearance changes of muscle and collagen fibers to realize the relationship between the mechanical and ultrasonic properties.
The results showed that the strong correlation between echogenicity and mechanical force in both normal and damaged tissue, and the echogenicity also could reflect the phenomenon, decreased load in damaged tissue. And there was a strong correlation between Nakagami and Mechanical force except the results from ultrasonography of damaged tissue in the mode of cross section. The Nakagami parameter in damaged ultrasonography of cross image didn’t correlate to stress increase, but related to the lost scatterer in the region of interest moderately. The results of histographys showed the density of muscle fibers related to echogenicity and Nakagami, and the collagen fiber in the muscle tissue could be observed the rupture in damaged tissue to result in lowering the mechanical behavior and concentration of scatterer.
In conclusion, this study established a relationship between mechanical and ultrasonic properties which can be applied in normal and injured tissue. Through correlating the different factors in ultrasonography, mechanical behavior and microstructure changes to verify that the ultrasonic can be an appropriate method to reflect the biomechanical properties in skeletal muscular tissue. In the future, this system can be effectively developed as a noninvasive and accurate method to diagnose the muscle injury applied in clinical.
Figure Content VII
Table Content X
Skeletal muscular structure 1
Mechanical properties of skeletal muscular tissue 3
Strain muscle injury 6
High frequency ultrasound 8
Mechanical properties detected by ultrasound 9
SPECIFIC AIMS 12
MATERIALS and METHODS 13
Muscles preparation 13
Mechanical testing of muscle tissue 13
High frequency ultrasound 15
Region of interest quantification 17
Biomechanical Properties for normal and injured muscles 19
Histological Analysis 20
Over-stretching changed the mechanical properties of muscle 25
The changes of ultrasonographic parameters in post-damaged muscle 26
Correlation of ultrasonic characteristics with biomechanical properties in normal and injured muscles 27
Structure changes in muscle fibers during different strains 34
Immediate follow over-stretching did not induce inflammatory response in the injured muscle 38
To distinguish the factor cause different Nakagami outcomes in post-damaged muscle between cross and longitudinal sections 39
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