Background: Currently, several non-invasive modalities, including MRI and PET, are being investigated to identify early intestinal inflammation, longitudinally monitor disease status, or detect dysplastic changes in patients with inflammatory bowel disease (IBD). Currently, multispectral optoacoustic tomography (MSOT; often in combination with ultrasound) has been used to effectively image tumor xenografts as well as several orthotopic tumor models, including pancreatic adenocarcinoma, but not to specifically assess inflammatory or dysplastic changes in the bowel in murine models. Here, we assess the applicability and utility of (MSOT) in evaluating the presence and severity of colitis.

Methods: Nine 6-7 week old C57B/6 mice underwent antibiotic depletion of gastrointestinal flora before inoculation with enterotoxic Bacteroides fragilis to induce colitis. Mice were then anesthetized, depilated, imaged from their superior thorax to inferior pelvis using MSOT. Mice were evaluated prior to bacterial inoculation, 2 days after inoculation, and 7 days after inoculation. MSOT values for oxygenated and deoxygenated hemoglobin were determined using MSOT imaging software and compared using linear regression. At each timepoint, three mice underwent colonoscopy prior to euthanasia and colon processing for histology.

Results: Mice with bacterially-induced colitis demonstrated a temporally-associated increase in mesenteric and colonic vascularity, with an increase in mean signal intensity of oxygenated hemoglobin (1.150 vs. 2.716 MSOT a.u. compared to controls; p=0.004) by MSOT two days after inoculation. These findings were significantly more prominent 7 days after inoculation, with increased mean signal intensity of oxygenated hemoglobin (1.150 vs. 2.716 vs. 3.422 MSOT a.u. for controls vs. 2 days post-ETBF vs. 7 days post-ETBF, p=0.0002) and the development of punctate vascular lesions on the colonic surface. Compared to untreated controls, mice at 2 days and 7 days post ETBF inoculation demonstrated an increased colitis score on colonoscopy (1.5 vs. 2.5 vs. 5.5), which correlated well with MSOT findings of mean oxygenated hemoglobin signal intensity (r=0.82, p=0.013). These findings were also associated with inflammatory changes observed on histologic analysis.

Conclusions: MSOT represents a non-invasive diagnostic modality that effectively identifies colitis in a murine model. With improvements in depth of tissue penetration, MSOT may hold potential as a sensitive, accurate, non-invasive imaging tool in evaluation of both disease status and early detection of malignancy in patients with IBD.

Citation Format: Neal Bhutiani, William Grizzle, Susan Galandiuk, Dennis Otali, Gerald Dryden, Nejat Egilmez, Lacey R. Mcnally. Non-invasive imaging of colitis using multispectral optoacoustic tomography [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1863. doi:10.1158/1538-7445.AM2017-1863