In vivo X-Ray Computed Tomographic Imaging of Soft Tissue with Native, Intravenous, or Oral Contrast

Abstract

X-ray Computed Tomography (CT) is one of the most commonly utilized anatomical imaging modalities for both research and clinical purposes. CT combines high-resolution, three-dimensional data with relatively fast acquisition to provide a solid platform for non-invasive human or specimen imaging. The primary limitation of CT is its inability to distinguish many soft tissues based on native contrast. While bone has high contrast within a CT image due to its material density from calcium phosphate, soft tissue is less dense and many are homogenous in density. This presents a challenge in distinguishing one type of soft tissue from another. A couple exceptions include the lungs as well as fat, both of which have unique densities owing to the presence of air or bulk hydrocarbons, respectively. In order to facilitate X-ray CT imaging of other structures, a range of contrast agents have been developed to selectively identify and visualize the anatomical properties of individual tissues. Most agents incorporate atoms like iodine, gold, or barium because of their ability to absorb X-rays, and thus impart contrast to a given organ system. Here we review the strategies available to visualize lung, fat, brain, kidney, liver, spleen, vasculature, gastrointestinal tract, and liver tissues of living mice using either innate contrast, or commercial injectable or ingestible agents with selective perfusion. Further, we demonstrate how each of these approaches will facilitate the non-invasive, longitudinal, in vivo imaging of pre-clinical disease models at each anatomical site.

In Vivo Quantitative Microcomputed Tomographic Analysis of Vasculature and Organs in a Normal and Diseased Mouse Model

“…The x-rays of the micro-CT only allow for the examination of density contrast with respect to the surrounding environment, like the lungs, fat and bones. Soft tissues are less dense and often have similar densities or contrast to the surrounding tissues, leading to difficulties in differentiating between them [ 13 ]. To increase the contrast between different soft tissues, contrast agents have been developed and their differential distribution can be leveraged to help discern other organs and vessels within experimental mouse disease models.…”

Correlation of X-Ray Computed Tomography with Quantitative Nuclear Magnetic Resonance Methods for Pre-Clinical Measurement of Adipose and Lean Tissues in Living Mice

“…In general, whole mouse data sets have a minimum voxel size (maximum resolution) in the range of 100 μm. This value provides an optimum balance of radiation dose, data size, and field-of-view, and can meet the majority of application demands to image fat, as well as lung, liver, kidney, GI, and other soft tissues [ 12 ]. However, some scanners, due mostly to technical hardware limitations, may not provide images suitable for all applications.…”

“…Fortuitously for obesity researchers, adipose tissue maintains a unique HU range of approximately −300 to −50 HU, which may be leveraged for quantitative measurement. Computational segmentation tools may be used to selectively extract the adipose volume into a separate data set using its innate contrast properties [ 12 ]. Studies have also been conducted in which lean tissue volumes were segmented and quantified using a different HU range from that used for adipose tissue [ 14 , 28 ].…”

“…Briefly, the technology relies on the acquisition of a series of planar X-ray images captured at various angles around a given specimen using a gantry based system. This data is input into a filtered back projection algorithm to yield a three dimensional array of radiodensity values and computational segmentation tools may be used to selectively extract the adipose volume using its innate contrast properties [ 12 ].…”

Small Animal X-ray Computed Tomography

“…Figure 36.11 presents examples of GI imaging using micro-CT with BaSO 4. (Wathen et al 2013). Polyps in the colon can also be detected by using an administration of BaSO 4 followed by air used as a negative contrast agent for the bowel space (Boll et al 2011a).…”