Combining the two modalities has great advantages: The CT, based on imaging with X-rays is able to visualize the anatomy of the organ whereas SPECT shows the currently running processes. Both systems, X-ray unit and gamma camera are combined in one unit, their image data are combined in the common computer system. It produces very plastic 3D images that offer a wide range of information.
In clinical routine as well as basic research, this is of great use, for example during a planned lymph node surgery: The position, size and potential outbreaks can be represented as accurately before surgery that you can virtually rely on a 3D navigation device in the subsequent operation.
Furthermore the SPECT/CT system provides researchers with the ability to not only image diseases, but also to leverage the high resolution to see the unseen for more confident interpretations. Its unique quantitative capabilities provide the ability to monitor and adjust treatments earlier by accurately measuring even small differences.