Abstract 2812: A multi-modality robotic ultrasound and bioluminescence system provides a low-cost alternative to magnetic resonance imaging for measurement of orthotopic pancreatic tumors
Authors: Rojas Juan , Joiner Jordan , Velasco Brian , De Lille Alexandra , Czernuszewicz Tomek J. , Pylayeva-Gupta Yuliya , Dayton Paul A. 
Published: July 2021

Abstract
Solid tumor models are widely used to evaluate efficacy of novel therapeutics. Calipers, a rapid but error-prone technique that is often used to measure volume in subcutaneous models, cannot measure orthotopic tumors, which have been proven to better represent clinical disease. Bioluminescence Imaging (BLI) on the other hand, is a well-established and non-invasive technique for tumor development. Yet several of factors should be carefully considered when interpreting BLI data (signal depth attenuation, hypoxia, necrosis, D-luciferin kinetics, luciferase expression, immune response, etc.). As a result, researchers often include an anatomical modality such as magnetic resonance (MR) or ultrasound (US). MR imaging is the gold standard but suffers from long and expensive acquisitions, while conventional US is fast but requires skilled users and lacks repeatability. Here, we compare BLI tumor cell viability measurements with volume measurements from robotic US and MRI and highlight the value of tracking both anatomical and molecular readouts for therapeutic efficacy assessment. Pancreatic tumor cells (KPC 4662) were injected into the pancreas tail of 10 C57BL/6 female mice and imaged weekly with BLI, US, and MRI starting 7 days after injection. Robotic US and BLI images were acquired with a Strata (SonoVol, Inc.) system, and MRI images with the 9.4 Tesla BioSpec MR scanner (Bruker Biospin). US and MR images were digitally segmented for volume and BLI signal was quantified using SonoEQ (SonoVol, Inc.). Tumor volumes obtained via robotic US and MRI had a strong correlation (R2 = 0.95). Bland-Altman analysis showed an insignificant mean bias of 12 mm3 (p = 0.28). The limits of agreement and coefficient of variation were 130 mm3 and 26%, respectively. BLI signal was detected on the first timepoint (7d), while tumors were not resolvable anatomically until 9d. BLI signal increased rapidly for the first 2 timepoints but remained stable after that. In comparison, tumor volume increased throughout the study and so, there was a poor correlation between molecular BLI and volumetric anatomical US measurements (R2 = 0.69). This work demonstrates the importance of multimodality imaging of tumor growth. BLI signal plateaus because dead tumor cells at the core do not produce light so while BLI is a valuable and highly sensitive tool for cell viability, initial growth, and drug efficacy, limitations mentioned above may bias assessment of response to therapy. Hence, a combined BLI signal and volume readout in orthotopic models may offer a more complete picture of tumor development and treatment efficacy. Robotic US provides similar measurements of orthotopic tumors to MRI while allowing faster scan times at a reduced cost. Therefore, robotic ultrasound with integrated BLI allows for a more holistic assessment of tumor development and response to therapy.
Citation Format: Juan Rojas, Jordan Joiner, Brian Velasco, Alexandra De Lille, Tomek J. Czernuszewicz, Yuliya Pylayeva-Gupta, Paul A. Dayton. A multi-modality robotic ultrasound and bioluminescence system provides a low-cost alternative to magnetic resonance imaging for measurement of orthotopic pancreatic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2812.