Development of quantitative imaging methods for the GE Hawkeye CT/SPECT system

Combined CT/SPECT systems enable absolute quantitation in SPECT images. To date, this ability has been limited to use on unique research systems such as that at the UCSF Physics Research Laboratory. However, the advent of commercially developed combined imaging systems (e.g. General Electric Medical Systems Hawkeye) could allow more widespread use of this technology. We have investigated several of the imaging properties of the Hawkeye and developed image reconstruction/quantitation algorithms for this system. First, we used a point source to measure the collimator resolution as a function of distance from the camera. These data allow us to characterize the point-spread function of the gamma camera for different isotopes and collimator types. The reconstruction projector incorporates this information to compensate the radionuclide data for camera-specific and depth-dependent collimator blur. Second, we scanned attenuation calibration phantoms to calibrate the Hawkeye´s CT values against a basis set of known material properties, attenuation coefficients, and standard CT numbers. Our data allow us to generate attenuation maps of the patient for any nuclear medicine photon energy