Source: Alycia G. Berman, James A. Schaber, and Craig J. Goergen, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana Here we will demonstrate the fundamentals of single-photon emission computed tomography/computed tomography (SPECT/CT) imaging using mice. The technique involves injecting a radionuclide into a mouse, imaging the animal after it is distributed throughout the body, and then reconstructing the produced images to create a volumetric dataset. This can provide information about anatomy, physiology, and metabolism to improve disease diagnosis and monitor its progression. In terms of collected data, SPECT/CT provides similar information as positron emission tomography (PET)/CT. However, the underlying principles of these two techniques are fundamentally different since PET requires the detection of two gamma photons, which are emitted in opposite directions. In contrast, SPECT imaging directly measures radiation via a gamma camera. As a result, SPECT imaging has lower spatial resolution than PET. However, it is also less expensive because the SPECT radioactive isotopes are more readily available. SPECT/CT imaging provides both noninvasive metabolic and anatomical information that can be useful for a wide variety of applications.