Development of an emission-transmission CT system combining X-ray CT and SPECT

We describe the design and initial evaluation of a prototype emission-transmission imaging system which incorporates a third-generation X-ray CT scanner and a single-headed SPECT scanner. The two commercial imaging devices are juxtaposed such that the CT table can move the patient directly into the SPECT scanner prior to the X-ray scan. The integrated system is being used to investigate correlation of X-ray CT images with conventional SPECT images and to attempt correction of attenuation errors in the SPECT image. We have evaluated two potential sources of error in the acquisition and analysis of data from this system. First, the observed flux of scattered X-rays passing through the SPECT collimator into the gamma camera is 17,000 cps-well below the rated maximum of 180,000 cps. Second, attenuation correction of SPECT will be performed by generating an attenuation map from the CT image. Previous experience suggests that directly calculated values can be generated within 3% of actual attenuation values, but more complex approaches will be implemented if necessary. Preliminary results of applying CT-derived attenuation correction are presented for a myocardial perfusion phantom