Strain Ratio as a Quantification Tool in Strain Imaging

Abstract

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.

Strain Ratio of Ultrasound Elastography for the Evaluation of Tendon Elasticity

“…Furthermore, if the strain ratio is computed from the formula given by Yun et al (1), it should be positively correlated with shear wave velocity and kPa values considering the fact that they are measurements of similar objects. The abovementioned statement has been confirmed by an in vitro study that examined the strain ratios in phantoms demonstrating different degrees of elasticity (3). Their formula to calculate the strain ratio was "strain of the reference area/strain of the lesion," which was identical to that used in Yun's research (1).…”

Strain elastography for the assessment of skin nodules in dogs

“…It is the more objective, and more useful, SR parameter that expresses a momentary and relative difference in compressibility in two user‐selected areas within selected regions of interest in a strain elastogram. Computation of the SR does not require knowledge of the applied force and it is for this reason that SR is commonly used in clinical practice 16 …”

“…Computation of the SR does not require knowledge of the applied force and it is for this reason that SR is commonly used in clinical practice. 16 Some reports in veterinary medicine have evaluated the application of SR. 34,[39][40][41] However, based on our knowledge, no previous study has reported the use of this parameter to discriminate between several skin nodules of different origin. Using the machine's native software, twelve nodules obtained a value <1, displaying greater softness than the surrounding healthy tissue; surprisingly, five of these nodules were malignant.…”

“…In particular, SE allows a qualitative assessment of the examined tissue based on the distribution of colours, visual point scales and the quantification of hard areas 14,15 . In order to decrease interobserver variability, several clinical studies have focused mostly on the semiquantitative measurement of strain ratio (SR) to provide information on the relative stiffness of a target lesion in comparison with the surrounding healthy tissue 16 …”

“…14,15 In order to decrease interobserver variability, several clinical studies have focused mostly on the semiquantitative measurement of strain ratio (SR) to provide information on the relative stiffness of a target lesion in comparison with the surrounding healthy tissue. 16 Despite its widespread use in human medicine, few studies on the application of SE in veterinary medicine are available. For example, SE has been used to assess intraabdominal organs such as the liver, spleen, kidney, lymph nodes and malignant nodules of breast and spleen, yet only in one study has it been promoted as a complementary tool for differentiating lipomatosus from malignant subcutaneous neoplasms in dogs.…”