SPECT/CT physical principles and attenuation correction

Using nuclear medicine techniques, physiologic activity and processes can be identified in a way that is unique from other modalities. Oftentimes it is helpful to know the exact location of the physiologic uptake that is visualized on a scan. Knowing the exact location can sometimes help to distinguish normal from abnormal physiologic uptake. When an abnormality has been identified, knowing the exact location can then be helpful in treatment planning. The ability to provide precise localization of physiologic data from nuclear medicine studies is now possible with hybrid SPECT/CT systems. Additionally, these systems provide an accurate attenuation correction of the nuclear medicine image data. After reading this article, the technologist will be able to list and describe the inherent problems associated with SPECT image acquisition and reconstruction, briefly explain how data acquired from the CT scanner are used to provide attenuation correction data for SPECT and anatomic information for diagnostic purposes, list and briefly describe the different types of clinical SPECT/CT systems, and discuss the importance of accurate CT and SPECT image registration.