Physicist Considerations for PET-CT and SPECT-CT

It is common to acquire contrast-enhanced CT scans. When both contrast and noncontrast scans are ordered, the noncontrast CT scan can be performed first (to also serve for PET attenuation correction), then the PET scan. After that, the contrast-enhanced CT is acquired. If only a single contrast-enhanced CT is requested, this scan could be used for PET attenuation correction, or a separate CTAC scan could be used. However, there is potential for contrast-induced correction artifacts in the former case. The degree to which these artifacts impact the PET images is not fully clear; the reader should investigate the literature for further details. For example:

SPECT-CT Implementation: Application and Radiation Dose

A SPECT system utilizes a gantry to rotate two gamma cameras, typically, around the patient. The earliest implementation of SPECT-CT mounted an X-ray source and detector onto the SPECT gantry. This limits the CT rotational speed to that of the SPECT gantry, so low-dose CT (low mAs, kVp) was implemented to prevent excessive radiation dose during the slow CT acquisition. Alternatively, the CT can be implemented on an independent gantry, similar to the typical PET-CT design; a “diagnostic” quality CT system can then be used. Design and operation of SPECT-CT systems are described in the following publications: