THE DESIGN AND PERFORMANCE OF A SIMULTANEOUS TRANSMISSION AND EMISSION TOMOGRAPHY SYSTEM

A commercial three-detector single-photon emission computed tomography (SPECT) system that enables simultaneous acquisition of transmission and emission data without increasing patient scanning time has been de signed and manufactured. This system produces a reconstructed attenuat ion coefficient distribution that can be used to correct for photon at tenuation in the emission reconstruction. The three detectors with fan -beam collimators are mounted to the gantry in a triangular arrangemen t. A transmission line source assembly was mounted at the focal line o f one of the detectors and controlled to move in synchrony with the op posing fan-beam collimator, Data from transmission and emission source s at different energies were acquired in one detector, while the other two simultaneously acquired emission data. A transmission source of G d-153 was used with Tc-99m-labeled radiopharmaceuticals, and Co-57 was used with Tl-201. Algorithms were developed to subtract crosstalk bet ween transmission and emission energy windows in ail three detectors. A transmission maximum-likelihood iterative algorithm was used to reco nstruct the attenuation distribution, which was used in combination wi th an iterative maximum-likelihood expectation-maximization algorithm to compensate for the attenuation of the projection of the emission di stribution, The results in phantom studies displayed greater uniformit y of activity with attenuation-corrected reconstruction. This was demo nstrated visually and quantitatively by using anterior-to-inferior rat ios close to one and low spatial %rms error as a measure of improved u niformity.