New modular data acquisition electronics for cross-strip cadmium zinc telluride (CZT) detector readout were developed to lower the electronic noise and increase the applied voltage bias capabilities compared to previous designs. The modular data acquisition electronics will be utilized to develop a two-panel head and neck dedicated positron emission tomography (PET) system. Each panel will consist of 150 CZT crystals (4 × 4 × 0.5cm 3) covering an area of 20×15 cm2 in an edge-on configuration to achieve high detector efficiency at 511 keV. This paper presents the first characterization results of CZT detectors based on the new readout electronics system. Ge-68 and Cs-137 were used as the point source for measuring the energy spectra. Three individual CZT detectors (117 anode channels) were tested together with a full data acquisition chain. The mean FWHM energy resolution across all 117 anode channels is 8.36%±0.52% at 511 keV without any correction and the lower keV threshold of the energy spectra resides between 0 keV to 50 keV. For reference, the previous small animal system had a mean FWHM energy resolution of 10.78%±1.45% at 511 keV before correction and a lower keV threshold of 100 keV to 150 keV.

Organ-dedicated PET scanners are becoming more prevalent because of their advantages in higher sensitivity, improved image quality, and lower cost. Detectors utilized in these scanners have finer pixel size with depth of interaction (DOI) capability. This work presents a LYSO(Ce) detector module with DOI capability which has the potential to be scaled up to a high-resolution small animal or organ-dedicated PET system. For DOI capability, a submodule with one LYSO block detector utilizing PETsys TOFPET2 application-specific integrated circuit (ASIC) was previously developed in our lab. We scaled up the submodule and optimized the configuration to allow for a compact housing of the dual-readout boards in one side of the blocks by designing a high-speed dual-readout cable to maintain the original pin-to-pin relationship between the Samtec connectors. The module size is 53.8 × 57.8 mm2. Each module has 2 × 2 LYSO blocks, each LYSO block consists of 4 × 4 LYSO units, and each LYSO unit contains a 6 × 6 array of 1 × 1 × 20 mm3 LYSO crystals. The four lateral surfaces of LYSO crystal were mechanically ground to W14, and the two end surfaces were polished. Two ends of the LYSO crystal are optically connected to SiPM for DOI measurement. Eight LYSO blocks performance including energy, timing, and DOI resolution is characterized with a single LYSO slab. The in-panel and orthogonal-panel spatial resolution of the two modules with 107.4 mm distance between each other are measured at 9 positions within the field of view (FOV) with a 22Na source. Results show that the average energy, timing, and DOI resolution of all LYSO blocks are 16.13% ± 1.01% at 511 keV, 658.03 ± 15.18 ps, and 2.62 ± 0.06 mm, respectively. The energy and timing resolution of two modules are 16.35% and 0.86 ns, respectively. The in-panel and orthogonal-panel spatial resolution of the two modules at the FOV center are 1.9 and 4.4 mm respectively.

Cadmium zinc telluride (CZT) detectors are suitable for various applications due to the good energy resolution and the simple pixilation to achieve high spatial resolution. Our group is developing a two-panel head and neck dedicated positron emission tomography system based on CZT detectors. Each panel will consist of 150 CZT crystals (4×4×0.5 cm3) covering an area of 20×15 cm2 in an edge-on configuration to achieve high detector efficiency at 511 keV. In this work, we present the design and development of a full data acquisition chain that enables a low noise and compact readout for each panel. The initial results of the readout circuit were quantified using a 1 kHz square wave test pulse. The pulse amplitude was chosen to generate approximately the same amount of charges as a 511 keV photon would provide in CZT. The best-case FWHM electronic noise at 511 keV was measured to be 0.69% ± 0.16% (3.52 ± 0.81 in keV units after conversion). The FWHM electronic noise at 511 keV for a complete DAQ chain was 4.33% ± 0.30% (22.13 ± 1.53 in keV units).

Cadmium zinc telluride (CZT) radiation detectors are suitable for various applications, due to good energy performance at room temperature and simple pixilation to achieve high spatial resolution. Our group is developing a two-panel head-and-neck dedicated positron emission tomography (PET) system with CZT detectors. In this work, we present the back-end readout electronic design and the initial electronic noise results of our system. The back-end readout electronic incorporates RENA boards (a total 150 RENA boards for each panel), 30:1 fan-in boards connecting 30 RENA boards to the PicoZed 7010/7020 board (a total 5 fan-in boards for each panel). In each panel, 5:1 intermediate boards are used for biasing CZT detectors. The RENA board and the Picozed board are capable of data transmission of 50 Mbps and 6.6 Gbps, respectively. Electronic noise was also quantified using a square wave test pulse that provides charge injection into each channel of the RENA chip in the amount of 75fC/Volt. The pulse amplitude was chosen to generate approximately the same amount of charges as 511 keV photon would provide for each channels. The FWHM electronic noise at 511 keV was measured to be less than 1% (FWHM of 7.80 ± 1.47 ADC units or 4.89 ± 0.92 keV after conversion).

In this paper, the room-temperature performance of different optical coupling materials post temperature exposure was tested. The tested couplers included OC431A-LVP, OG0010 optical grease, BLUESIL V-788, and SAINT-GOBAIN BC-630. This was done by subjecting the whole detector with newly applied optical coupling materials to a 2-h temperature exposure-ranging from -20 to 50 °C and then by letting it return to room temperature before collecting a spectrum from a Cs-137 source. The energy resolution at 662 keV was computed as the metric for evaluating the performance. Three trials were run at each coupler-temperature combination. Our results reveal that the performance of all coupling agents do indeed change with temperature after the 2-h exposure. Over all the tested temperature trials, the energy resolution ranged from 11.4 to 14.3% for OC431A-LVP; 10.2 to 14.6% for OG0010; 10 to 13.4% for BLUESIL V-788; and 9.8 to 13.3% for SAINT-GOBAIN BC-630. OC431A-LVP had the lowest variance over the full range, while BC-630 was the most constant for temperatures above 20 °C. Ultraviolet-visible (UV-Vis) spectra experiments were also performed on isolated optical coupling materials to measure the light absorption coefficient. The results show that the temperature-induced variance in light absorption coefficient of each optical coupling materials is one of the reasons for the variance in energy resolution performance. Our findings suggest the need for further investigation into this effect and the recommendation that optical coupling materials need to be selected for the task at hand with greater scrutiny.

Positron emission tomography (PET) suffers from limited spatial resolution in current head and neck cancer management. We are building a dual-panel high-resolution PET system to aid the detection of tumor involvement in small lymph nodes ([Formula: see text]10 mm in diameter). The system is based on cadmium zinc telluride (CZT) detectors with cross-strip electrode readout (1 mm anode pitch and 5 mm cathode pitch). One challenge of the dual-panel system is that the limited angular coverage of the imaging volume leads to artifacts in reconstructed images, such as the elongation of lesions. In this work, we leverage a penalized maximum-likelihood (PML) reconstruction for the limited-angle PET system. The dissimilarity between the image to be reconstructed and a prior image from a low-resolution whole-body scanner is penalized. An image-based resolution model is incorporated into the regularization. Computer simulations were used to evaluate the performance of the method. Results demonstrate that the elongation of the 6-mm and 8-mm diameter hot spheres is eliminated with the regularization strength γ being 0.02 or larger. The PML reconstruction yields higher contrast recovery coefficient (CRC) of hot spheres compared to the maximum-likelihood reconstruction, as well as the low-resolution whole-body image, across all hot sphere sizes tested (3, 4, 6, and 8 mm). The method studied in this work provides a way to mitigate the limited-angle artifacts in the reconstruction from limited-angle PET data, making the high-resolution dual-panel dedicated head and neck PET system promising for head and neck cancer management.

Optical property modulation induced by ionizing radiation is a promising approach for ultra-fast, lower time jitter detection of photon arrival time. If successful, this method can be utilized in time-of-flight positron emission tomography to achieve a coincidence time resolution approaching 10 ps. In this work, the optical property modulation based method is further developed with focus on a detection setup based on two crossed polarizers. Previous work demonstrated that such an optical setup could be utilized in radiation detection, though its detection sensitivity needed improvement. This work investigates the angle between polarizers and electric field distribution within the detection crystal to understand and improve the detection sensitivity of an optical polarization modulation based method. For this work, cadmium telluride (CdTe) was studied as the detector crystal . The magic angle (i.e. optimal working angle) of the two crossed polarizers based optical setup with CdTe were explored theoretically and experimentally. The experimental results show that the detection sensitivity could be improved by around 10% by determining the appropriate magic angle. We then studied the dependence of detection sensitivity on electric field distribution as well as on the bias voltage across the detector crystal using CdTe crystals. The experimental results show that a smaller electrode on the detector crystal, or a more concentrated electric field distribution could improve detection sensitivity. For CdTe, a detector crystal sample with 2.5 mm × 2.5 mm square electrode has twice the detection sensitivity of a detector crystal with 5 mm × 5 mm square electrode. Increasing the bias voltage before saturation for CdTe could further enhance the modulation strength and thus, the sensitivity. Our investigations demonstrated that by determining the proper working angle of polarizers and bias electrical distribution to the detector, we could improve the sensitivity of the proposed optical setup.

In a detector system where the number of channels exceeds the number of channels available on an application-specific integrated circuit (ASIC), there is a need to configure channels among multiple ASICs to achieve the lowest electronic noise and highest count rate. In this work, two board configurations were designed to experimentally assess which one provides the more favorable performance. In the half-half configuration, contiguous channels from one edge to the center of CZT detector are read by one ASIC, and the other half are read by the other ASIC. In the alternate configuration, the CZT channels are read by alternating ASICs. A lower electronic noise level, better FWHM energy resolution performance (5.35% ± 1.08% compared to 7.84% ± 0.98%), and higher count rate was found for the anode electrode strips with half-half configuration. Cross-talk between ASICs and deadtime play a role in the different performances, and the total count rate of the half-half configuration has a count rate 18.1% higher than that of the alternate configuration.

Currently, injection sites of probes, cannula, and optic fibers in stereotactic neurosurgery are typically located manually. This step involves location estimations based on human experiences and thus introduces errors. In order to reduce localization error and improve repeatability of experiments and treatments, we investigate an automated method to locate injection sites. This paper proposes a localization framework, which integrates a region-based convolutional network and a fully convolutional network, to locate specific anatomical points on skulls of rodents. Experiment results show that the proposed localization framework is capable of identifying and locatin bregma and lambda in rodent skull anatomy images with mean errors less than 300 μm. This method is robust to different lighting conditions and mouse orientations, and has the potential to simplify the procedure of locating injection sites.