Small Animal X-ray Computed Tomography

X-ray computed tomography (CT) systems with high resolution (also known as micro-CT systems) have been developed over the last two decades and have been used with great success in small animal studies. A micro-CT scanner is based on the same underlying physical principle as a clinical CT scanner, but it is designed for higher-resolution imaging. It produces three-dimensional (3D) tomographic data at microscopic resolution (voxel size ≤100 μm3) by taking hundreds of 2D projections from multiple angles around the animal (Holdsworth and Thornton 2002). The X-ray source produces a cone beam, which is projected through the specimen with the resultant radiographic density of the specimen projected onto a 2D detector. The projections are used by a reconstruction algorithm that is generally based on the filtered backprojection (Kak and Slaney 1988) (see Figure 36.1). The resultant micro-CT scan is a 3D matrix of voxels with values proportional to the mean linear attenuation coefficient of the material within each voxel; the 3D matrix can be sliced in any orientation to reveal different views of the anatomy. There are many commercially available micro-CT scanners for in vivo and ex vivo imaging. In vivo scanners are used to scan live animals (mostly mice and rats), while ex vivo scanners are used for imaging dead specimens and materials, such as bone and scaffolds. There are major differences between the two types of scanners. With in vivo micro-CT instruments, the animal remains alive and available for longitudinal studies, thus reducing the number CONTENTS