Preclinical Vibrational Shear Wave Elastography: effect of anaesthesia and tumour alignment on repeatability

Shear Wave Elastography (SWE) imaging provides a convenient method to study the mechanical properties of tumours. SWE needs to be reliable and robust in order to accurately detect changes in tissue properties in response to treatment. In preclinical tumours there are difficulties posed by their small size, and the need for sedation to reduce motion to capture imaging data in 3D. In this paper we report on the repeatability of Vibrational Shear Wave Elastography (VSWE) measurements in a preclinical tumour model. Tumours were grown subcutaneously on the flank of athymic nude mice (n=2) and imaged using our VSWE system which consists of an external vibrational source and a research ultrasound system with a high frequency probe. The probe was translated in the elevational directional to gather 3D data. Tumours were imaged on three consecutive days, and mice were sedated during separate sessions using either injectable or breathable anaesthetic. Tumors were imaged in both an "upright" and a more restrained "side" position where the mouse body was rotated ~45°. VSWE data was obtained at three vibration frequencies. Analysis of variance of mean SWS measurements revealed significant differences between the tumours (p<0.001), and between vibration frequencies (p<0.05). No significant differences in mean SWS values were found between choice of anaesthetic or tumour alignment. Appearance of SWS spatial distribution was found to be highly repeatable. Tumour motion amplitude was highest using breathable anaesthesia (<0.3 mm) in the upright alignment. Breathing rate was higher (~100 bpm) with injectable anaesthesia compared to breathable (~50 bpm). Side alignment reduced tumour motion approximately by a factor of 3 compared to the upright position. We conclude preclinical SWE using external vibration sources is repeatable, choice of anaesthetic and tumour alignment can mitigate potential issues with breathing motion, without impacting SWS measurements.