A 3-detector ring, 5-slice whole-body positron CT has been developed and is being tested. The PCT, POSITOLOGICA-II, has a total of 480 BGO's (160/ring), and employs continuous rotation scan (0.5rps). By using a 15mm wide BGO, a 9.2mm FWHM spatial resolution for reconstructed image is obtained at the center of FOV. Measured phantom diameter dependence of the true count rate shows good agreement with theoretically anticipated characteristics, including maximum sensitivity at around 30cm dia. Sensitivities for 20cm dia. phantom are 28 and 38 kcps/Â¿Ci/ml for in-plane and cross-plane, respectively, including scattered coincidences. Relative system detection efficiency measured with a line source at FOV center is 96% at 15ns time window (90% at 12ns), basing on 100% efficiency in 20-24ns.
[Show abstract][Hide abstract] ABSTRACT: A new dual rectangular photomultiplier tube (PMT) developed for the positron CT is discussed in comparison with the conventional small-diameter PMT. A matching in shape between the scintillator and the PMT is an important factor to obtain good time resolution. The new PMTs have coincidence time resolution less than 3 ns in FWHM coupled to 12 mm (wide) x 24 mm (high) x 24 mm (long) BGO scintillators for 511 keV annihilation Â¿-rays while resolution of the conventional small-diameter PMTs is around 5 ns in FWHM.
[Show abstract][Hide abstract] ABSTRACT: Experiments using three types of detectors for high spatial resolution positron CT have been carried out as follows : 1. One to one coupling between a BGO scintillator and a thin rectangular photomultiplier tube (PMT). 2. Combining a small position sensing PMT with two BGO scintillators. 3. Combining a large PMT with two or more BGO scintillators and using other detectors for scintillator identification -- a) small PMT's, b) silicon photodiodes (SiPD). The time resolution obtained in method 1 was poorer than that of the other methods due to the present status of thin PMT performance - poor cathode sensitivity. In method 2 and 3-a), good time resolution and position sensing were obtained. In method 3-b), the peak to valley ratio of 1.8 in pulse height spectrum was obtained with a cooled BGO scintillator and a SiPD.
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