Ex Vivo Characterization of Canine Liver Tissue Viscoelasticity Following High Intensity Focused Ultrasound (HIFU) Ablation

摘要

Elasticity imaging has shown great promise in detecting High Intensity Focused Ultrasound (HIFU) lesions based on their distinct biomechanical properties. However, quantitative mechanical properties of the tissue and the optimal intensity for obtaining the best contrast parameters remain scarce. In this study, fresh canine livers were ablated using combinations of ISPTA intensities of 5.55, 7.16 and 9.07 kW/cm² and time durations of 10 and 30 s ex vivo; leading to six groups of ablated tissues. Biopsy samples were then interrogated using dynamic shear mechanical testing within the range of 0.1-10 Hz to characterize the post-ablation tissue viscoelastic properties. All mechanical parameters were found to be frequency dependent. Compared to the unablated cases, all six groups of ablated tissues showed statistically-significant higher complex shear modulus and shear viscosity. However, among the ablated groups, both complex shear modulus and shear viscosity were found to monotonically increase in groups 1-4 (5.55 kW/cm² for 10 s, 7.16 kW/cm² for 10 s, 9.07 kW/cm² & 10 s, and 5.55 kW/cm² & 30 s, respectively), but decrease in groups 5 and 6 (7.16 kW/cm² for 30 s, and 9.07 kW/cm² for 30 s, respectively). For groups 5 and 6, the temperature was expected to exceed the boiling point, and therefore, the decreased stiffening could be due to the compromised integrity of the tissue microstructure. Future studies are needed to estimate the tissue mechanical properties in vivo and perform real-time monitoring of tissue alterations during ablation.