True coincidence count (TCC) and noise equivalent count (NEC) curves were measured with a standardized 20-cm-diameter nylon cylinder for five different CTI/Siemens PET (positron emission tomography) scanners with several scanner-collimator combinations: (1) 831/08-12 with 1-mm collimator septa; (2) 933/08-12 and 933/08-16 with 3 to 1-mm tapered collimator septa; and (3) 931/08-12 with 3 to 1-mm tapered and a 1-mm collimator septa and the 931/08-16 with 3 to 1-mm tapered collimator septa In addition, TCC and NEC curves on the 933/08-12 were compared with those from an Alderson brain phantom In general, it is found that the TCC curves indicated peak count rates and activity levels that were as much as 50% higher than the corresponding values from NEC curves The primary factor causing this difference is the noise effect of the randoms component It is demonstrated that, compared to the Alderson brain phantom, the standard 20-cm cylinder is a poor predictor of count rate performance for PET brain imaging >

Measuring PET scanner sensitivity: relating countrates to image signal-to-noise ratios using noise equivalents counts

A review and new data are presented on the absolute photon yield emitted by "classical" (NaI(Tl/sup +/), CsI(Tl/sup +/), CsI(Na/sup +/), CaF/sub 2/(Eu/sup 2+/), Bi/sub 4/Ge/sub 3/O/sub 12/, and CdWO/sub 4/) and "modern" (BaF/sub 2/, Gd/sub 2/SiO/sub 5/(Ce/sup 3+/), YAlO/sub 3/(Ce/sup 3+/), Lu/sub 2/SiO/sub 5/(Ce/sup 3+/), Lu/sub 3/Al/sub 5/O/sub 12/(Sc/sup 3+/), and K/sub 2/LaCl/sub 5/(Ce/sup 3+/)) scintillation crystals after absorption of X-rays and /spl gamma/-rays of energies ranging from 5 keV to 1 MeV. Factors influencing the energy resolution with which high energy photons can be detected with scintillator-photomultiplier combinations are reviewed. Attention is especially focused on the effects of nonproportionality in the scintillation response on the energy resolution.

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Non-proportionality in the scintillation response and the energy resolution obtainable with scintillation crystals

A review is presented of recent inorganic scintillator R&D. Attention is focused on Ce doped gamma-ray and thermal-neutron scintillators for counting applications.

Inorganic-scintillator development

Abbreviations: 
ACD, Annihilation coincidence detection; BGO, bismuth germanate; CBF, cerebral blood flow; CBV, cerebral blood volume; CMG, 3-(11C)-methyl-D-glucose; CMRGlc, cerebral metabolic rate for glucose; CMR02, cerebral metabolic rate for oxygen; CsF, cesium fluoride; CT, computed tomography; DG, deoxyglucose; FDG, 2-fluoro-2-deoxy-d-glucose; LC, lumped constant; OEF, oxygen extraction fraction; PCT, positron computed tomography; PETT, positron emission transaxial tomography; PT, physiological tomography.

Study of Cerebral Function with Positron Computed Tomography

Cerium‐activated phosphors are characterized by their fast luminescence decay. Gadolinium orthosilicate (Gd2SiO5) is a material possessing a high atomic number, and can also play host to the cerium activator. Cerium‐doped Gd2SiO5 single crystals were grown by the Czochralski technique, and their luminescence properties were examined. The light output was 1.3 times larger than that of the best Bi4Ge3O12, and the decay constant was 60 ns at room temperature.

Cerium‐activated Gd2SiO5 single crystal scintillator

A rotary positron emission computed tomography device is developed for human brain and animal studies. The device utilizes 64 rectangular BGO detectors arranged at unequal spacing on a circular ring. The detector ring is continuously rotated at a constant speed of 60 rpm or less. This single continuous motion of the ring with the detector array provides excellent sampling characteristics and high detector redundancy. The device has a field of view 24 cm in diameter with a slice thickness adjustable from 1 cm to 2 cm. Measured width of system response to a 2 mm diameter line source is 5.8 mm FWHM at the center and less than 9 mm FWHM within a circle 16 cm in diameter. Measured sensitivity including scattered coincidence events is about 17 kcps/pCi/ml for a 20 cm diameter water phantom and 2 cm thick slice.

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

This paper proposes a continuously rotating positron ECT system, in which the detectors are arranged on a circular ring with "non-uniform" spacing so as to provide much finer sampling interval in the projections than the conventional circular ring system. The address signals on the coincidence events are read out through a rotary photo-coupler, and the detector system can be rotated at a desired speed. Suitable detector arrangements are searched which provide sufficiently fine sampling interval with reasonable sampling density uniformity. Assuming about 50 detectors are arranged on a circle, the sampling characteristics of various detector arrangements have been examined. An iterative search method has also been applied to find a reasonable arrangement. The best arrangement has been obtained by the iterative method. It has an effective sampling interval of the order of (1/200)R, where R is the radius of the detector array, and the sampling density uniformity after 5-point smoothing is -7.8 ˜/spl I.chemo/18 % in the range of /spl I.chemo/ R/2.

"Positology"-the search for suitable detector arrangements for a positron ECT with continuous rotation

Characteristics of a gamma‐ray detector that utilizes a 24×24×15‐mm3 bismuth germanate (BGO) scintillator are measured. Fluorescent light output measured with a BGO crystal coupled to a R1306 photomultiplier (Hamamatsu TV) is found to be 15% that of a NaI(T1) scintillator for incident photons of a given energy. The FWHM of the time spectrum, measured with two BGO crystals coupled to R329‐2 photomultipliers, is equal to 2.0 ns for a 68Ge–68Ga source at room temperature.

Characteristics of a gamma‐ray detector using a bismuth germanate scintillator

Design consideration for a whole-body, multislice Positron CT having 3 detector rings, 160 BGO crystal/ring, and a continuously rotating scan is described. The one detector ring has 40 "BGO Quad-detectors", each of which consists of 4 BGO crystals and two photomultipliers. Improvements in the BGO crystal and the photomultiplier have been accomplished. Geometrical configuration of the collimator was determined through optimization of the main performances of both the inplane and cross-plane images, utilizing the formulae for a cylindrical phantom with uniform activity. A continuously rotating scan (0.5-1rps) with unequally spaced the Quad-detector units is used. Along with this scan, a 32-channel rotary photo-coupler was developed for contact-free data transmission.

Design Consideration for a Continuously Rotating Positron Computed Tomograph

An apparatus for a detecting the location of incident radiation comprises at least one pair of assembly comprised of a scintillation crystal consisting of a plurality of crystal segments, a pair of photo-multiplier tubes optically coupled to the scintillation crystal so as to be able to detect a scintillation produced in any one of these crystal segments. These plural crystal segments are coupled to each other in such manner that any scintillation produced in any single crystal segment will cause the photo-multiplier tubes to deliver substantially a same output irrespective of the illuminating position within this crystal segment, and also that scintillations produced in the respective crystal segments will cause the photo-multiplier tubes to deliver outputs which are different in level for the respective crystal segments.

Katsumi Takami

Papers

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

"Positology"-the search for suitable detector arrangements for a positron ECT with continuous rotation

Characteristics of a gamma‐ray detector using a bismuth germanate scintillator

Design Consideration for a Continuously Rotating Positron Computed Tomograph

Apparatus for detecting the location of incident radiation