Noninvasive Imaging of Colitis Using Multispectral Optoacoustic Tomography

Abstract

Currently, several noninvasive 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. Here, we assess the applicability and utility of multispectral optoacoustic tomography (MSOT) in evaluating the presence and severity of colitis. Methods: C57B/6 mice were untreated or treated with Bacteroides fragilis and antibiotic-mediated depletion of intestinal flora to initiate colitis. Mice were imaged using MSOT to detect intestinal inflammation. Intestinal inflammation identified with MSOT was also confirmed using both colonoscopy and histology. Results: Mice with bacterial colitis demonstrated a temporally associated increase in mesenteric and colonic vascularity with an increase in mean signal intensity of oxygenated hemoglobin (P = 0.004) by MSOT 2 d after inoculation. These findings were significantly more prominent 7 d after inoculation, with increased mean signal intensity of oxygenated hemoglobin (P = 0.0002) and the development of punctate vascular lesions on the colonic surface, which corresponded to changes observed on colonoscopy as well as histology. Conclusion: With improvements in depth of tissue penetration, MSOT may hold potential as a sensitive, accurate, noninvasive imaging tool in the evaluation of patients with inflammatory bowel disease.

Keywords: animal imaging; colitis; gastrointestinal; inflammatory bowel disease; molecular imaging; multispectral optoacoustic tomography; oxygenated hemoglobin.

FIGURE 1.

MSOT depicts inflammatory changes in murine colitis. Wild-type C57B/6 mice were orally inoculated with either phosphate-buffered saline alone (control) or ETBF. (A) MSOT imaging of mice before ETBF treatment (untreated). (B and C) Images of mice 2 and 7 d, respectively, after bacterial inoculation. Arrows indicate concentrated areas of oxyhemoglobin corresponding to colitis (B and C). Findings on MSOT were compared with colonoscopic findings (D–F) for each group of mice. Arrow indicates area of inflammation indicative of colitis (F).

FIGURE 2.

Mean MSOT signal intensity for oxyhemoglobin correlates with colitis severity score. Region of intensity measurements acquired for MSOT images were correlated to colitis severity score determined from colonoscopy images. (A) Mean signal intensity of oxyhemoglobin for each group (control, 2 d after ETBF inoculation, and 7 d after ETBF inoculation). ***P < 0.001. (B) Average colitis severity score for each group. ***P < 0.001. Error bars represent SD. (C) Correlation between mean signal intensity of oxyhemoglobin and mean colitis severity score for the 3 mice assessed using both MSOT and colonoscopy at all 3 time points (r = 0.82, P = 0.013). a.u. = arbitrary units.

FIGURE 3.

Histology findings demonstrate inflammatory changes consistent with colitis. Hematoxylin and eosin analysis of mouse colon demonstrated no evidence of inflammatory cell infiltrate in control mice (A and D) and progressively increasing polymorphonuclear leukocyte infiltrate 2 d (B and E) and 7 d (C and F) after ETBF inoculation as indicated by arrows. Histology images shown in C and F are from mouse represented in Figure 1.