Abstract 2196: Noninvasive description of natural tumor evolution

Background: Our goal is to investigate how quantitative parameters of Contrast Enhanced Ultrasound (CEUS) and Shear Wave Elastography (SWE) change during tumor growth and link them with morphological and histological indexes. Methods: An ectopic model of murine colorectal carcinoma (CT26) was implanted in 46 mice (BALB/c ) at Day 0. On 5 subsequent days, data were acquired from subsets of these mice (D7, n=8 ; D10, n=9 ; D14, n=10 ; D16, n=9, D17, n=10) by scanning each tumor along its major, longitudinal axis in vivo to obtain conventional B-mode, SWE (SSI, Aixplorer, SL15-4 probe) and dynamic CEUS (Sequoia 512, 7-14 MHz probe, cadence contrast pulse sequencing) data. The ellipsoidal volume of each tumor was estimated from measurements of the width and thickness of the largest plane along the longitudinal and transversal plane using B-mode display on the Aixplorer device. Quantitative maps of tissue elasticity distribution in the tumor were obtained from SWE data. Average values and standard deviation of SWE data were calculated within regions selected to outline the tumor cross section on B-mode images. CEUS was performed after a syringe-pump-controlled bolus injection in the caudal vein of 40 μL of SonoVue (Bracco Suisse, Geneva, Switzerland) in a weight-adjusted volume of 0.5 mL/kg. A lognormal model was fit to the time intensity curve inside the tumor to estimate parameters related to microvascular volume and flow. All tumors imaged on a given day were excised and marked to conserve orientation and approximate position relative to the US imaging plane. Tumors were frozen with liquid nitrogen in an Optimal Cutting Temperature compound cube and stored at -80°C. Results: Significance of correlations were evaluated using the non-parametric Spearman correlation coefficient (RS). Average SWE parameters were not significantly correlated with the CEUS parameters (p > 0.03). Standard deviation of SWE in the tumor was well correlated with tumor volume (RS = 0.65 [p