Implementation and applications of a combined CT/SPECT system

Combined radionuclide/radiographic (e.g., SPECT/CT, PET/CT) imaging systems are being developed for correlation of structure and function, primarily for assessment of patients with cancer. Another important aspect of these approaches is the possibility of using anatomical data from CT to derive patient-specific compensations for perturbations in the radionuclide data. For example, a patient-specific attenuation map can be derived from CT and incorporated into an iterative reconstruction algorithm to correct the radionuclide image for photon attenuation. In addition, the geometry, location, and configuration of anatomical regions can be determined using CT, from which recovery coefficients or other geometrical factors can be derived to compensate the radionuclide data for errors caused by the limited spatial resolution of radionuclide images. The use of CT to derive correction factors for these perturbations allows combined X-ray/radionuclide imaging techniques to achieve a high degree of accuracy in the absolute quantitation of radiopharmaceuticals.