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In Vitro Ultrasound Biomicroscopic Imaging of Colitis in Rats

Division of Gastroenterology, Endoscopy Unit (M.S.) and Department of Internal Medicine (C.Z.), Clementino Fraga Filho University Hospital, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; and Department of Surgery, Center of Experimental Surgery, School of Medicine (A.S.), Multidisciplinary Research Laboratory, Pathologic Anatomy (K.M.), and Biomedical Engineering Program, Graduate Engineering Program Coordination (J.C.), Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

Address correspondence to João C. Machado, PhD, Cidade Universitária, 2030 Horácio Macedo Ave, Center of Technology, Block H, Room 327, 21941-914 Rio de Janeiro-RJ, Brazil. E-mail: jcm{at}peb.ufrj.br

Objective. The purpose of this study was to show the feasibility of 50-MHz ultrasound biomicroscopy (UBM) to image the rat colon. Methods. B-mode images were obtained from ex vivo colon samples (n = 4) collected from Rattus norvegicus (Berkenhout, 1769) rats, with 2,4,6-trinitrobenzene sulfonic acid–induced colitis in 3 of them. Left colon rectangular fragments (5 x 5 mm) were obtained after necropsy, and UBM images were acquired with the samples immersed in saline at 37°C. All layers of the normal intestinal wall were analyzed according to their thickness and the presence of uneven bowel mucosa (ulcers). The folds and layers detected by UBM were correlated with histopathologic analysis. Results. The 4 layers of the normal colon were identified on the UBM images: the mucosa (hyperechoic), muscularis mucosae (hypoechoic), submucosa (hyperechoic), and muscularis externa (hypoechoic). On 2 UBM images, superficial ulcers were detected, approximately 0.5 mm in size, with intestinal involvement limited to the mucosa. The histopathologic analysis verified enlargement of submucosa layers due to an edema associated with sub-mucosa leukocyte infiltration. On 1 UBM image, it was possible to detect a deep ulcer, which was confirmed by the light microscopic analysis. Conclusions. An ultrasound imaging system was scaled and optimized to visualize the rat colon. Ultrasound biomicroscopy provided axial and lateral resolutions close to 25 and 45 µm, respectively, and adequate penetration depth to visualize the whole thickness of an inflamed colon. The system identified the colon layers and was able to detect mural changes and superficial ulcers on the order of 500 µm.

Key Words: experimental colitis • high-frequency ultrasound • image • rat • ultrasound biomicroscopy

Abbreviations: micro-CT, micro–computed tomography • MRI, magnetic resonance imaging • OCT, optical coherence tomography • PET, positron emission tomography • PVC, polyvinyl chloride • RF, radio frequency • TNBS, 2,4,6-trinitrobenzene sulfonic acid • UBM, ultrasound biomicroscopy