Wenze Xi

HelmetPET: A silicon photomultiplier based wearable brain imager

We are developing the HelmetPET, a wearable human PET brain imager which has the potential application of evaluating brain function utilizing PET based radiopharmaceuticals in standing, balancing or moving patients. The HelmetPET is composed of two rings of radiation detectors together providing a cylindrical reconstructed volume with an axial length of 5 cm. Each ring is composed of twenty 2.5 cm2 silicon photomultiplier (SiPM) based detector modules. Each detector module is composed of a 5×5 array of twenty-five Hamamatsu S10362-33-050P Multi Pixel Photon Counters (MPPCs). The 3 mm2 MPPCs are arranged on a 5mm step. Coupled to each of the MPPC modules is a LYSO scintillator crystal array coupled to the MPPC array using to two different LYSO pixel arrays: 1.0×1.0×10 mm3 and 1.5×1.5×10 mm3. The current phase of the project is to equip the forty 2.5 cm2 detector modules with resistive readout and assemble them in a helmet type head support and suspend from a flexible mechanical mount.

High-performance DIRC detector for the future Electron Ion Collider experiment

A radially-compact subsystem providing particle identification (e/π, π/K, K/p) over a wide momentum range is an essential requirement for the central detector of an Electron-Ion Collider (EIC). With a radial size of only a few cm, a detector based on Detection of Internally Reflected Cherenkov light (DIRC) principle is a very attractive solution. The R&D undertaken by the EIC PID consortium achieved the goal of showing feasibility of a high-performance DIRC that would extend the momentum coverage well beyond state-of-the-art allowing 3σ separation of π/K up to 6 GeV/c, e/K up to 1.8 GeV/c and p/K up to 10 GeV/c. A key component to reach such a performance is a special 3-layer spherical compound lens. This article describes the status of the design and R&D for the DIRC at EIC detector, with a focus on the detailed Monte Carlo simulation results for the high-performance DIRC.

Imaging corn plants with PhytoPET, a modular PET system for plant biology

PhytoPET is a modular positron emission tomography (PET) system designed specifically for plant imaging. The PhytoPET design allows flexible arrangements of PET detectors based on individual standalone detector modules built from single Hamamatsu H8500 position sensitive photomultiplier tubes and pixelated LYSO arrays. We have used the PhytoPET system to perform preliminary corn plant imaging studies at the Duke University Biology Department Phytotron. Initial evaluation of the PhytoPET system to image the biodistribution of the positron emitting tracer 11C in corn plants is presented. 11CO2 is loaded into corn seedlings by a leaf-labeling cuvette and translocation of 11C-sugars is imaged by a flexible arrangement of PhytoPET modules on each side. The PhytoPET system successfully images 11C within corn plants and allows for the dynamic measurement of 11C-sugar translocation from the leaf to the roots.

PhytoPET: Design and initial results of modular PET for plant biology

We have developed a positron emission tomography (PET) system designed specifically for plant imaging in Phytotron at Duke University. Initial evaluation of a PhytoPET system to image the biodistribution of the positron emitting tracer 11C in live plants is presented. The mechanical arrangement of the detectors is designed to accommodate the unpredictable and random distribution in space of the plant parts such as stems, leaves, and roots. Prototyping such a system requires a completely new PET system design strategy different from preclinical and clinical applications. This PhytoPET design allows flexible arrangements of PET detectors based on individual standalone detector modules built from single 5 cm × 5 cm Hamamatsu H8500 position sensitive photomultiplier tubes. Each H8500 is coupled to a L YSO:Ce scintillator array composed of 48 × 48 elements that are 10 mm thick with a 1 mm pitch. Initial results provide planar PET images from two different arrangements (1 × 4 or 2 × 2) for flexible imaging capability.

Ethernet-based flash ADC for a plant PET detector system

We have developed a flash analog to digital (ADC) based read out system to be used for a Positron Emission Tomography (PET) system. The custom designed 16 channel 12-bit Ethernet-based flash ADC (EFADC-16) unit operates at 250 MHzls/channel utilizing a gigabit Ethernet interface to parse time-stamped event signals. Each unit allows the user to define a custom coincidence table for triggering. Each EFADC-16 unit can digitize four H8500 position sensitive photomultiplier tubes (PSPMT) equipped with a Jefferson Lab designed 4 channel resistive readout (a total of 16 channels). We present initial performance results of the EFADC-16 with four PET detector modules in a plant biology application to acquire tomographic images of the translocation of 11C within an oak seedling.

Development of PhytoPET: A plant imaging PET system

The development and initial evaluation of a high-resolution positron emission tomography (PET) system to image the biodistribution of positron emitting tracers in live plants is underway. The positron emitting 11CO2 tracer is used in plant biology research investigating carbon sequestration in biomass, optimization of plant productivity and biofuel development. This PhytoPET design allows flexible arrangements of PET detectors based on individual standalone detector modules built from single 5 cm × 5 cm Hamamatsu H8500 position sensitive photomultiplier tubes. Each H8500 is coupled to a LYSO:Ce scintillator array composed of 48×48 elements that are 10 mm thick arranged with a 1.0 mm pitch. An Ethernet based 12-bit flash analog to digital data acquisition system with onboard coincident matrix definition is under development to digitize the signals. The detector modules of the PhytoPET system can be arranged and stacked to accommodate various sized plants and plant structures.

A positron projection imager for whole-body mouse imaging

Certain experimental questions in molecular imaging can be answered with projection imaging systems rather than tomographs. Accordingly, we have designed, assembled and are now testing a projection imaging system able to visualize the whole-body distribution of positron-emitting compounds in mouse-size animals. When completed, this positron projection imager (PPI) will plug into the MONICA portable dual gamma camera system to provide the user with a positron projection imaging capability and all of the data acquisition and analysis features available with MONICA for single photon projection imaging.

Externally-Modulated Electro-Optically Coupled Detector Architecture for Nuclear Physics Instrumentation

A new laser-based externally-modulated electro-optically coupled detector (EOCD) architecture is being developed to enable high-density readout for radiation detectors with accurate analog radiation pulse shape and timing preservation. Unlike digital conversion before electro-optical modulation, the EOCD implements complete analog optical signal modulation and multiplexing in its detector front-end. The result is a compact, high performance detector readout that can be both radiation tolerant and immune to magnetic fields. In this work, the feasibility of EOCD was explored by constructing a two-wavelength laser-based externally-modulated EOCD, and testing analog pulse shape preservation and wavelength-division multiplexing (WDM) crosstalk. Comparisons were first made between the corresponding initial pulses and the electro-optically coupled analog pulses. This confirmed an excellent analog pulse preservation over ~ 29% of the modulators switching voltage range. Optical spectrum analysis revealed less than -14 dB crosstalk with 1.2 nm WDM wavelength bandgap, and provided insight on experimental conditions that could lead to increased inter-wavelength crosstalk. Further discussions and previous research on the radiation tolerance and magnetic field immunity of the candidate materials were also given, and quantitative device testing is proposed in the future.

Calibration methodology for a dual-ended readout silicon photomultiplier based depth-of-interaction PET detector module

We developed a novel calibration methodology for a PET detector with dual-ended readout of an LYSO array by two silicon photomultipliers (SiPMs). By introducing a detector gain balancing step in the calibration process, improved depth-of-interaction calibration uniformity and accuracy can be achieved. The entire calibration process has four steps: scintillation crystal array mappings for two SiPM readouts, detector gain balancing, energy calibration, and depth-of-interaction calibration. This document provides a detailed description on the detector calibration system setup.

Radiation tolerance survey of selected silicon photomultipliers to high energy neutron irradiation

A key feature of silicon photomultipliers (SiPMs) that can hinder their wider use in medium and high energy physics applications is their relatively high sensitivity to high energy background radiation, with particular regard to high energy neutrons. Dosages of 1010 neq/cm2 can damage them severely. In this study, some standard versions along with some new formulations are irradiated with a high intensity 241AmBe source up to a total dose of 5 × 109 neq/cm2. Key parameters monitored include dark noise, photon detection efficiency (PDE), gain, and voltage breakdown. Only dark noise was found to change significantly for this range of dosage. Analysis of the data indicates that within each vendors product line, the change in dark noise is very similar as a function of increasing dose. At present, the best strategy for alleviating the effects of radiation damage is to cool the devices to minimize the effects of increased dark noise with accumulated dose.