# Quantitative Ultrasound Texture Analysis to Assess the Spastic Muscles in Stroke Patients
## 4 Discussion
### In-Homogenous Muscle Texture  
In the present study, we found that the LBP operator provided a quantifying method related to the differences in muscle quality between paretic and non-paretic BBM while considering the specific size of ROI and muscle scanning planes. Because the interactions of ultrasonic signals between structure and composition of soft tissue are changed poststroke, it is quite straightforward to explain that paretic BBM shows different echotexture features than normal muscle. The spastic muscles are characterized by increased variability in the size and type of muscle fiber, decreased sarcomeres, muscle fiber morphology changes, and shortened muscle fiber length [2]. Furthermore, increased fat infiltration and an increased collagen concentration in the extracellular matrix have been reported post-stroke [17]. Increased local fibrosis or IMF may cause local changes in sound speed, density, and muscle stiffness, causing scatter in paretic muscle to exhibit higher variability. Considering these possible relations among textural features, tissue composition, and scatter distribution, the inhomogeneous echotexture in spastic BBM may indicate that localized heterogeneity causes muscle stiffness. After the stroke, prolonged immobilization and reduced extremity activity are commonly seen in stroke patients and result in muscle stiffness. The ultrasound is convenient for bedside use. Therefore, it is recommended to intervene as early as possible for monitoring muscle echotexture change and response to treatment. In this study, we used SWV to confirm the muscle stiffness of BBM. The results showed that SWV was greater in the spastic muscle, which represented that the paretic muscle in stroke is stiffer. This result is consistent with a previous study reporting 69.5% greater muscle stiffness in stroke survivors [17]. Previous ultrasonography study also reported a strong correlation (r\({}^{2}\) = 0.703) between muscle stiffness and echo intensity of paretic muscles [2]. This evidence showed that the interactions between muscle composition and wave reflections were changed post-stroke. It further supported that the altered muscle composition changes the muscle properties. Texture descriptors, such as LBP and high order, have recently been used to distinguish muscle type and sex in the healthy population and those with neuromuscular disorders [10; 24]. In the present study, ENT and ENG, which are powerful texture features of the LBP descriptor, were used to distinguish the echotexture features between paretic and non-paretic BBM. Because ultrasonic signals are interactions between structure and composition, pathological muscle shows different echotexture features than normal muscle. Increased local fibrosis or IMF may cause local changes in sound speed, density, and muscle stiffness, causing scatter in spastic muscle to exhibit higher variability. Considering these possible relations among textural features, tissue composition, and scatter distribution, the inhomogeneous echotexture in spastic BBM may indicate that spasticity causes localized heterogeneity. Interestingly, ENT texture (ENT1) was negatively correlated with muscle stiffness in the longitudinal plane. Our results also showed that ENG (ENG3) texture (homogeneity) was positively correlated with time factors (duration from stroke onset) in the transverse plane. These patterns could occur because alterations in muscle quality are progressive. [PERSON] et al. [25] proposed a simulated model to obtain the relationship between texture inhomogeneity and the arrangement of scatters in various tissues. In a homogeneous medium, such as liver or breast, as the density of the scatter increases, increased interaction of theacoustic waves with scatter causes high ENT. By contrast, in the non-homogeneous medium such as muscle, the local variability in tissue composition is relatively high.