Imaging the Gastrointestinal Tract of Small Animals

Abstract

Animal models of human diseases are increasingly available and are invaluable for studies of organ pathophysiology. Megacolon, abnormal dilatation of the colon not caused by mechanical obstruction, involves the destruction of the autonomic nervous system innervating the colon. Animal models of megacolon include mouse models of Chagas disease and Hirschprung's disease. Small animal imaging has become an important research tool and recent advances in preclinical imaging modalities have enhanced the information content available from longitudinal studies of animal models of human diseases. While numerous applications of imaging technologies have been reported to study the brain and heart of mouse models, fewer studies of the gastrointestinal system have been undertaken due to technical limitations caused by peristaltic and respiratory motion. Various imaging modalities relevant to study of the gastrointestinal tract of intact live animals are reviewed herein.

Figure 1

MRI images in grey scale with a color overlay indicating the intestines and (in yellow) and the bladder in grey. Panel A shows an uninfected normal mouse and panel B shows an infected mouse. Note the enlargement of the intestine in the infected mouse.

Figure 2

Photograph of the mouse studied with demarcation of the region imaged and corresponding 3D spatial and 2D spectral-spatial image data. (A) A photograph of the mouse with a ruler for scale. The area imaged is shown between black lines. The mouse was fed with the charcoal probe for 1 day. (B) Spatial EPR 3D image visualizing the location of the charcoal probe in the GI tract. (C) Spectral-spatial 2D image data along the longitudinal axis from the proximal to the distal GI tract. From G. He, R. A. Shankar, M. Chzhan, A. Samouilov, P. Kuppusamy, and J. L. Zweier, Noninvasive measurement of anatomic structure and intraluminal oxygenation in the gastrointestinal tract of living mice with spatial and spectral EPR imaging, Proc Natl Acad Sci USA, 96(1999), pp. 4586–4591. “Copyright (1999) National Academy of Sciences, USA.”

Figure 3

Ungated coronal microCT images of normal chow-fed (A) and low-density, bowel-prepped (B) mice. Although fecal pellets (A, arrows) are distinguishable by virtue of their relatively high density, the lumen of the Intestinal tract is much easier to map after low-density bowel preparation (B). From P. J. Pickhardt, R. B. Halberg, A. J. Taylor, B. Y. Durkee, J. Fine, F. T. Lee, Jr., and J. P. Weichert, Microcomputed tomography colonography for polyp detection in an in vivo mouse tumor model. Proc Natl Acad Sci USA, 102(2005), pp. 3419–3422. “Copyright (2005) National Academy of Sciences, USA.”

Figure 4

In vivo microPET imaging of ⁶⁴Cu-PTSM-labeled lymphocytes post i.v. injection into a mouse. The mouse was microPET-scanned 0.12 h (A. 11.2 μCi), 3.12 h (B, 9.48 μCi), and 18.9 h (C, 4.01 μCi) postinjection of lymphocytes. Each microPET image shown here (A–C) is an average of 5–6 coronal slices. After the last microPET scan, this mouse was killed for DWBA (20.7 h). The location of activity In the last microPET image (C) clearly correlates with the DWBA image (E). The photo (D) provides the anatomic map necessary to resolve the source of activity in the microPET image from the DWBA section. Note that splenic lymphocytes initially traffic through lungs (A) and then accumulate in liver and spleen (B and C). The %ID/g scale quantifies the magnitude of signal observed in each microPET image, Lu, lungs; Li, liver; Sp, spleen; In, intestine. From N. Adonai, K. N. Nguyen, J. Walsh, M. Iyer, T. Toyokuni, M. E. Phelps, T. McCarthy, D. W. McCarthy and S. S. Gambhir, Ex vivo cell labeling with 64Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone) for imaging cell trafficking in mice with positron-emission tomography. Proc Natl Acad Sci USA, 99(2002), pp. 3030–3035. “Copyright (2002) National Academy of Sciences, USA.”