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This study introduces a depth-encoding PET detector inserting a glass plate between the pixilated scintillation crystal layers. The principle of the proposed design was that the relative amount of light received by each photosensor will be altered by using the glass plate. This change in the light distribution can generate a pattern diagram of the 2D flood histogram that identifies depth position as well as X-Y position of \gamma–ray interaction. A Monte Carlo simulation was conducted for the assessment of the DOI-PET detector of 4 \times 4 array photosensor coupled with 2-layers of LSO arrays which consist of 4 \times 4 arrays of 3 \times 3 \times 10~\mm^3 discrete crystals. The traced light distribution for each event was converted by the modified resistive charge division networks into the 2D flood histogram. Optical glass plates with 11 different thicknesses that range from 0 to 10 mm with a 1 mm step were modeled. This was done, to estimate the thickness which allows the extraction of the depth information from the 2D flood histogram. An experimental study was performed to acquire the flood histograms of the DOI-PET detectors with 3 and 5 mm thick glass plate. The effect of glass plate on light loss and count rate loss were assessed for two detector configurations with and without glass plate. The simulation results showed that the flood histogram without overlapping of each crystal position can be generated for the detectors by inserting the glass plates with thickness of 3\sim 10~\mm. They were also demonstrated in the acquired representative flood histograms which were obtained by the experimental study. The light and count rate losses measured from DOI-PET detector with 3 mm thick glass plate was \sim 5\% and \sim 2\%, respectively. This study demonstrated that the proposed DOI-PET detector can extract the 3D \gamma -ray interaction position without considerable performance degradations of PET detector from the 2D flood histogram. [ABSTRACT FROM AUTHOR]

Recently, we reported a hybrid positron emission tomography-magnetic resonance imaging (PET-MRI) approach involving the transmission of a photo-sensor charge signal to a preamplifier using a long cable. However, in this application, pulse distortions may degrade the performance of the PET detector. The purpose of this study is to further extend the charge signal transmission (CST) approach and to design a PET detector module capable of transmitting the photo-sensor charge signal to PET electronics remotely located outside the MRI room for the hybrid PET-MRI. To achieve this, we developed a pulse restoration circuit (PRC) compensating the performance degradations caused by using the long cable from Geiger-mode avalanche photodiode (GAPD) to PET electronics. The effect of the cable length on the PET detector performance was examined using different lengths of flexible flat cable ranging from 0 to 21 m. Rise time, fall time and amplitude of the GAPD output were measured as a function of the cable length. Photopeak position, energy resolution and time resolution were also measured using a 100 MS/s data acquisition unit. PRC based on the filtering and shaping networks consisted of amplitude, and rise and fall restorations. The amplitude restoration was designed using op-amp and resistors. The rise time-fall time restoration was designed using RC shaping filter. The measured pulse shapes passing through the long cable with PRC were similar to the output of GAPD with the cable length of 0 m (amplitude 169 mV, rise time 35 ns and fall time 210 ns), and the degrading PET detector performance caused by long cable were restored (energy resolution 16%, photopeak position 400 ch and time resolution 1.3 ns). There were no significant changes in the PET detector module performance using the CST approach with PRC as a function of the cable length, both outside and inside the MRI room. There were no obvious artifacts or changes in the MR phantom images. These results show that the proposed approach using extended charge signal transmission method with long cable and simple pulse restoration circuit is reliable and useful for the development of a hybrid PET-MRI system. [ABSTRACT FROM AUTHOR]

This paper presents the development of filtering methods for positron emission tomography (PET) signals contaminated by radio frequency (RF) pulses for combined PET and clinical 3-T magnetic resonance imaging (MRI). The filtering methods include software, hardware, and hybrid correction methods. In the software correction method, PET signals are assessed, and valid signals are identified based on the characteristics of a typical PET signal using Field-Programmable Gate Array (FPGA)-based programming. The hardware correction method makes use of differential-to-single-ended and low-pass filter circuits for PET analog signals. The hybrid correction method involves the sequential application of both the hardware and software methods. Both valid and contaminated PET signals are measured with an oscilloscope. An evaluation is then made of the performance (energy resolution, photopeak channel, total counts, and coincidence timing resolution) of the PET detector modules with and without various MR sequences (gradient echo, spin echo T1 sequence). For all correction methods, the energy resolution, photopeak position, and coincidence timing resolution with MR sequences are similar (< 3\%) to those without MR sequences. However, the total count of each module depends greatly on the method applied. The hybrid correction method displays an ability to preserve (< 1\%) the total counts of the modules during various MR sequences. The results show that this filtering method, which can reject noise signals and reduce count loss while preserving the valid analog signals of MR sequences, is reliable and useful for the development of simultaneous PET-MRI. [ABSTRACT FROM AUTHOR]