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.

1. In Vivo Imaging Set-up

1. Open up the imaging software.
2. To set-up the CT portion of the scan, allow the X-ray tube to warm up by selecting the option on the software. The system will begin heating up the tube.
3. Anesthetize the mouse. To ensure that the mouse is unconscious, extend one leg and pinch the animal's paw. If the mouse does not produce a withdrawal reflex, the animal is sufficiently anesthetized.
4. Inject the mouse intravenously with the radionuclide. A common

Representative results using a ^99mTc-based tracer in a rat are demonstrated in Figure 2. Acquisition of SPECT/CT should display the SPECT data (shown as shades of yellow/orange in the figure) overlaid on CT data (shown as shades of gray). Within the SPECT model, the degree of physiological activity is demonstrated by the intensity of color. Thus, the areas of yellow show greater activity than areas of orange. The SPECT data in the figure was acquir

SPECT/CT was used to provide anatomical and functional information. The general procedure involved injection of a radionuclide, imaging, and then reconstruction of the data. This procedure, discussed within the context of small animal imaging, is similar to what is performed clinically. However, the use of small animals adds some additional technical nuances that should not be overlooked. Small animal models, as might be surmised, necessitate the use of higher resolution in imaging. In addition, small animals have increa