Strain Ratio as a Quantification Tool in Strain Imaging

Ultrasound-based strain imaging is available in several ultrasound (US) scanners. Strain ratio (SR) can be used to quantify the strain recorded simultaneously in two different user-selected areas, ideally exposed to the same amount of stress. The aim of this study was to evaluate SR variability when assessed in an in-vitro setup with a tissue-mimicking phantom on resected tissue samples and in live tissue scanning with endoscopic applications. We performed an in vivo retrospective analysis of SR variability used for quantification of elastic contrasts in a tissue-mimicking phantom containing four homogenous inclusion in 38 resected bowel wall lesions and 48 focal pancreatic lesions. Median SR and the inter-quartile range (IQR) were calculated for all external and endoscopic ultrasound (EUS) applications. The IQR and median provide a measure of SR variability focusing on the two percentiles of the data closest to the median value. The overall SR variability was lowest in a tissue-mimicking phantom (mean QR/median SR: 0.07). In resected bowel wall lesions representing adenomas, adenocarcinomas, or Crohn lesions, the variability increased (mean IQR/Median: 0.62). During an in vivo endoscopic examination of focal pancreatic lesions, the variability increased further (mean IQR/Median: 2.04). SR variability increased when assessed for different targets with growing heterogeneity and biological variability from homogeneous media to live tissues and endoscopic application. This may indicate a limitation for the accuracy of SR evaluation in some clinical applications.