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Bias-free positioning estimators for scintillation cameras are investigated. A linear correlation coefficient (LCC) and Chi square error (CSE) method are evaluated with respect to linearity and spatial resolution performance. The LCC method uses correlation information between the true function (i.e., light response function) and measured data in mapping an event characterization vector to the associated position. The CSE method estimates the position where the Chi square error between two functions becomes minimized. In order to determine true statistics as a function of position, the light response function (LRF) was estimated based on sample measurements by using a cubic spline interpolation technique which provides smooth first-order and continuous second-order derivative of the LRF. Both methods have superior linearity properties compared to the weighted centroid. Each method can be considered as a bias-free positioning estimator within the effective field of view of the detector. The spatial resolution performance of the CSE method is ~7% and ~16% better than the weighted centroid method for a 16- and 25-mm-thick crystal, respectively. The spatial resolution performance of the LCC method is comparable to that of the weighted centroid method. Index Terms--Positioning algorithm, scintillation camera.

Operation of PET in 3-D mode, without internal septa results in increased sensitivity but at the cost of increased scatter fraction. Significant amounts of scattered events in 3-D PET either originate from activity outside the FOV (OFOV) or scatter from matter outside the FOV, complicating scatter correction methods. We performed 3-D PET simulations with scanner geometry based on the GE Advance with several phantom geometries designed to characterize all scatter with particular attention to that from out- side the FOV. Scatter from OFOV matter was deduced by performing simulations with matter and activity within the FOV only (short phantom). Studies were repeated with phantoms with identical characteristics inside the FOV but with additional OFOV material (long phantom) but no activity outside the FOV. The incremental effect of OFOV activity was then determined by repeating the long phantom studies with additional activity. Scatter was also classified as single or multiple. In summary, the data allow extraction of yields from unscattered and all types of scattered events. The effect of source position, both within and external to the FOV, on scatter was determined by performing a series of simulations with point sources and techniques similar to those described above. The effect of energy discriminator setting (with BGO detectors) was also studied and data sets were generated for five settings from 300 to 425 keV. Using a Zubal phantom with the lungs and heart in the FOV and the abdomen outside the FOV and with a 300 keV discriminator, we find a total scatter fraction of 57%. Of the total scatter, 7.4% comes from OFOV matter, and 24% from OFOV activity. If the discriminator is increased to 425 keV the scatter fraction drops to 36%. OFOV scatter, particularly from OFOV activity, becomes relatively less important with the OFOV matter contribution dropping to 5.3% and OFOV activity contribution to 17%. [ABSTRACT FROM AUTHOR]

A data acquisition system for a single-ring, high-resolution, small-animal PET scanner is described. This single-ring test system is part of the development of a multiring scanner. The system was designed to be as simple (short development cycle, and low cost) and as flexible as possible while maintaining high performance standards necessary for high-resolution quantitative studies. Unlike the multiring system electronics under development, the test system does not use a clock, but identifies coincidences by overlapping logic signals. The ring consists of up to 18 multicrystal MiCE modules, each of which is coupled to a resistive summing board that produces two X and two Y position signals. These are sent to the inputs of an analog multiplexer circuit. Total energy signals are also produced and used as inputs to NIM discriminators. A field programmable gate array (FPGA) is used for all system logic functions. This allows software development, testing, implementation, and modification of logic circuitry without hardware modification. Inputs to the FPGA are the outputs of the 18 discriminators. The FPGA logic produces and locks an event signal whenever two modules along allowed lines of response trigger within a preset resolving time. The FPGA also produces detector codes identifying the detectors involved in the event. These are recorded and also sent to the multiplexer to switch the position signals from the modules involved in the event to a buttered CAMAC ADC system for digitization. A "not busy" signal from the ADC is used to reset the FPGA releasing the locked signals allowing further event acquisition. [ABSTRACT FROM AUTHOR]

This work presents a row/column summing readout electronics for an 8×8 silicon photomultiplier array. The summation circuit greatly reduces the number of electronic channels, which is desirable for pursuing higher resolution positron emission tomography scanners. By using a degenerated common source topology in the summation circuit, more fan-in is possible and therefore a greater reduction in the number of electronic channels can be achieved. The timing signal is retrieved from a common anode, which allows the use of a single fast-sampling analog to digital converter (ADC) for the timing channel and slower, lower power ADCs for the 64 spatial channels. Preliminary results of one row summation of the 8×8 readout electronics exhibited FWHM energy resolution of 17.8% and 18.3% with and without multiplexing, respectively. The measured timing resolution is 2.9ns FWHM.