Does size matter? A secondary analysis of the effect of region-of-interest size on muscle echotexture features of the gastrocnemius medialis in stroke

The analysis of muscle echotexture using ultrasound imaging is attracting increasing interest for assessing muscle tissue across different health conditions. However, variability in the size of the region of interest (ROI) can affect echotexture assessment. This study examines how varying ROI sizes may impact the quantification of echotexture in the gastrocnemius medialis of post-stroke individuals. A secondary analysis was performed on 130 ultrasound images from 22 post-stroke individuals. We extracted 21 echotexture features, including echovariation (EV) and mean echointensity (EI), from five ROI sizes: whole-muscle (maximum muscle tissue area), 300 × 300, 200 × 200, 100 × 100, and 50 × 50 pixels. Friedman tests, Bland-Altman analyses, and linear regression models were employed to evaluate the influence of ROI size on feature variability and measurement agreement. EV values decreased significantly as ROI size decreased ( p < 0.001), whereas EI showed the opposite trend, increasing significantly with progressively smaller ROIs. Results for the remaining features were more heterogeneous, although variability generally increased as ROI size decreased. The 300 × 300-pixel ROI showed the highest agreement with the whole-muscle ROI, minimizing variability while minimizing the inclusion of non-muscular structures. ROI size substantially influences quantitative echotexture measurements, particularly EV and EI values. As ROI size decreased, greater variability and lower agreement with the original whole-muscle ROI approach were observed. These findings highlight the methodological importance of ROI selection and delineation in quantitative muscle ultrasound research and may facilitate more consistent interpretation and potential clinical translation. Analysis of the Correlation Between Ultrasound Imaging and Functional Parameters in the Medial Gastrocnemius Muscle in Post-stroke Patients With Spasticity in the Lower Limb (US-function), https://clinicaltrials.gov/study/NCT06411587, NCT06411587, 2024-05-07.