Test-retest repeatability of ultrasonographic shear wave elastography in a rat liver fibrosis model: toward a quantitative biomarker for preclinical trials

Myofibroblasts: A New Factor Affecting the Hyperlipidemia-Induced Elastic Abnormality of Corpus Cavernosum in Rabbits Detected by 2-D Shear Wave Elastography

OBJECTIVE

Two-dimensional shear wave elastography (2-D SWE) has been proven to detect hyperlipidemia-induced elastic abnormality in the corpus cavernosum. This study investigated cytological factors affecting the elasticity of the corpus cavernosum in rabbits with hyperlipidemia using single-cell RNA sequencing (scRNA-seq).

METHODS

Male New Zealand white rabbits were randomly divided into a hyperlipidemia group (high-cholesterol diet) and a control group (standard diet). Penile 2-D SWE was performed to detect the elastic abnormality in the corpus cavernosum. ScRNA-seq was performed to observe cellular changes in the corpus cavernosum of rabbits with hyperlipidemia. Immunohistochemistry, immunofluorescence and histological examinations were conducted to verify the results of scRNA-seq.

RESULTS

Two-dimensional SWE revealed that the Young's modulus of the corpus cavernosum was significantly greater in the hyperlipidemia group than that in the control group (p < 0.001). Histological findings revealed extracellular matrix accumulation within the corpus cavernosum, with stronger staining of collagen types I and Ⅲ. ScRNA-seq revealed that fibroblasts, smooth muscle cells, and endothelial cells were the major cell types in the corpus cavernosum. A novel subtype of fibroblasts (myofibroblast) was discovered in the hyperlipidemia group, which was verified by immunofluorescence staining and gene ontology analysis. Fibroblasts, smooth muscle cells and endothelial cells were three cellular sources for myofibroblasts.

CONCLUSION

Myofibroblasts are activated and proliferate and secrete large amounts of collagen fibers in the corpus cavernosum during hyperlipidemia, leading to abnormal Young's modulus detected by 2-D SWE and their recognition as a new factor affecting the hyperlipidemia-induced elastic abnormality of the corpus cavernosum.

Preclinical Three-Dimensional Vibrational Shear Wave Elastography for Mapping of Tumour Biomechanical Properties In Vivo

Preclinical investigation of the biomechanical properties of tissues and their treatment-induced changes are essential to support drug-discovery, clinical translation of biomarkers of treatment response, and studies of mechanobiology. Here we describe the first use of preclinical 3D elastography to map the shear wave speed (cs), which is related to tissue stiffness, in vivo and demonstrate the ability of our novel 3D vibrational shear wave elastography (3D-VSWE) system to detect tumour response to a therapeutic challenge. We investigate the use of one or two vibrational sources at vibrational frequencies of 700, 1000 and 1200 Hz. The within-subject coefficients of variation of our system were found to be excellent for 700 and 1000 Hz and 5.4 and 6.2%, respectively. The relative change in cs measured with our 3D-VSWE upon treatment with an anti-vascular therapy ZD6126 in two tumour xenografts reflected changes in tumour necrosis. U-87 MG drug vs vehicle: Δcs = −24.7 ± 2.5 % vs 7.5 ± 7.1%, (p = 0.002) and MDA-MB-231 drug vs vehicle: Δcs = −12.3 ± 2.7 % vs 4.5 ± 4.7%, (p = 0.02). Our system enables rapid (<5 min were required for a scan length of 15 mm and three vibrational frequencies) 3D mapping of quantitative tumour viscoelastic properties in vivo, allowing exploration of regional heterogeneity within tumours and speedy recovery of animals from anaesthesia so that longitudinal studies (e.g., during tumour growth or following treatment) may be conducted frequently.

Development of a Robotic Shear Wave Elastography System for Noninvasive Staging of Liver Disease in Murine Models

Shear wave elastography (SWE) is an ultrasound-based stiffness quantification technology that is used for noninvasive liver fibrosis assessment. However, despite widescale clinical adoption, SWE is largely unused by preclinical researchers and drug developers for studies of liver disease progression in small animal models due to significant experimental, technical, and reproducibility challenges. Therefore, the aim of this work was to develop a tool designed specifically for assessing liver stiffness and echogenicity in small animals to better enable longitudinal preclinical studies. A high-frequency linear array transducer (12-24 MHz) was integrated into a robotic small animal ultrasound system (Vega; SonoVol, Inc., Durham, NC) to perform liver stiffness and echogenicity measurements in three dimensions. The instrument was validated with tissue-mimicking phantoms and a mouse model of nonalcoholic steatohepatitis. Female C57BL/6J mice (n = 40) were placed on choline-deficient, L-amino acid-defined, high-fat diet and imaged longitudinally for 15 weeks. A subset was sacrificed after each imaging timepoint (n = 5) for histological validation, and analyses of receiver operating characteristic (ROC) curves were performed. Results demonstrated that robotic measurements of echogenicity and stiffness were most strongly correlated with macrovesicular steatosis (R²  = 0.891) and fibrosis (R²  = 0.839), respectively. For diagnostic classification of fibrosis (Ishak score), areas under ROC (AUROCs) curves were 0.969 for ≥Ishak1, 0.984 for ≥Ishak2, 0.980 for ≥Ishak3, and 0.969 for ≥Ishak4. For classification of macrovesicular steatosis (S-score), AUROCs were 1.00 for ≥S2 and 0.997 for ≥S3. Average scanning and analysis time was <5 minutes/liver. Conclusion: Robotic SWE in small animals is feasible and sensitive to small changes in liver disease state, facilitating in vivo staging of rodent liver disease with minimal sonographic expertise.