Search NASA⌕ Search

SEARCH · Search NASA

Results for “APDs”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Temperature dependence of APD-based PET scanners

Purpose: Solid state detectors such as avalanche photodiodes (APDs) are increasingly being used in PET detectors. One of the disadvantages of APDs is the strong decrease of their gain factor with increasing ambient temperature. The light yield of most scintillation crystals also decreases when ambient temperature is increased. Both effects lead to considerable temperature dependence of the performance of APD-based PET scanners. In this paper, the authors propose a model for this dependence and the performance of the LabPET8 APD-based small animal PET scanner is evaluated at different temperatures.Methods: The model proposes that the effect of increasing temperature on the energy histogram of an APD-based PET scanner is a compression of the histogram along the energy axis. The energy histogram of the LabPET system was acquired at 21 °C and 25 °C to verify the validity of this model. Using the proposed model, the effect of temperature on system sensitivity was simulated for different detector temperature coefficients and temperatures. Subsequently, the effect of short term and long term temperature changes on the peak sensitivity of the LabPET system was measured. The axial sensitivity profile was measured at 21 °C and 24 °C following the NEMA NU 4-2008 standard. System spatial resolution was also evaluated. Furthermore, scatter fraction, count losses and random coincidences were evaluated at different temperatures. Image quality was also investigated.Results: As predicted by the model, the photopeak energy at 25 °C is lower than at 21 °C with a shift of approximately 6% per °C. Simulations showed that this results in an approximately linear decrease of sensitivity when temperature is increased from 21 °C to 24 °C and energy thresholds are constant. Experimental evaluation of the peak sensitivity at different temperatures showed a strong linear correlation for short term (2.32 kcps/MBq/°C = 12%/°C, R = −0.95) and long term (1.92 kcps/MBq/°C = 10%/°C , R = −0.96) temperature changes. Count rate evaluation showed that although the total count rate is consistently higher at 21 °C than at 24 °C for different source activity concentrations, this is mainly due to an increase in scattered and random coincidences. The peak total count rate is 400 kcps at both temperatures but is reached at lower activity at 21 °C. The peak true count rate is 138 kcps (at 100 MBq) at 21 °C and 180 kcps (at 125 MBq) at 24 °C. The peak noise equivalent count rate is also lower at 21 °C (70 kcps at 70 MBq) than at 24 °C (100 kcps at 100 MBq). At realistic activity levels, the scatter fraction is lower at higher temperatures, but at the cost of a strong decrease in true count rate.Conclusions: A model was proposed for the temperature dependence of APD-based PET scanners and evaluated using the LabPET small animal PET scanner. System sensitivity and count rate performance are strongly dependent on ambient temperature while system resolution is not. The authors’ results indicate that it is important to assure stable ambient temperature to obtain reproducible results in imaging studies with APD-based PET scanners.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Development of a novel depth of interaction PET detector using highly multiplexed G-APD cross-strip encoding

Purpose: The aim of this study was to develop a prototype PET detector module for a combined small animal positron emission tomography and magnetic resonance imaging (PET/MRI) system. The most important factor for small animal imaging applications is the detection sensitivity of the PET camera, which can be optimized by utilizing longer scintillation crystals. At the same time, small animal PET systems must yield a high spatial resolution. The measured object is very close to the PET detector because the bore diameter of a high field animal MR scanner is limited. When used in combination with long scintillation crystals, these small-bore PET systems generate parallax errors that ultimately lead to a decreased spatial resolution. Thus, we developed a depth of interaction (DoI) encoding PET detector module that has a uniform spatial resolution across the whole field of view (FOV), high detection sensitivity, compactness, and insensitivity to magnetic fields. Methods: The approach was based on Geiger mode avalanche photodiode (G-APD) detectors with cross-strip encoding. The number of readout channels was reduced by a factor of 36 for the chosen block elements. Two 12 × 2 G-APD strip arrays (25μm cells) were placed perpendicular on each face of a 12 × 12 lutetium oxyorthosilicate crystal block with a crystal size of 1.55 × 1.55 × 20 mm. The strip arrays were multiplexed into two channels and used to calculate the x, y coordinates for each array and the deposited energy. The DoI was measured in step sizes of 1.8 mm by a collimated {sup 18}F source. The coincident resolved time (CRT) was analyzed at all DoI positions by acquiring the waveform for each event and applying a digital leading edge discriminator. Results: All 144 crystals were well resolved in the crystal flood map. The average full width half maximum (FWHM) energy resolution of the detector was 12.8% ± 1.5% with a FWHM CRT of 1.14 ± 0.02 ns. The average FWHM DoI resolution over 12 crystals was 2.90 ± 0.15 mm. Conclusions: The novel DoI PET detector, which is based on strip G-APD arrays, yielded a DoI resolution of 2.9 mm and excellent timing and energy resolution. Its high multiplexing factor reduces the number of electronic channels. Thus, this cross-strip approach enables low-cost, high-performance PET detectors for dedicated small animal PET and PET/MRI and potentially clinical PET/MRI systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Si-APD linear-array x-ray detector with 10-100 μm spatial and sub-nanosecond time resolution

We developed a silicon avalanche photodiode (Si-APD) linear-array detector to be used for time-resolved X-ray scattering experiments using synchrotron X-rays. The Si-APD linear array consists of 64 pixels (pixel size: 100 × 200 μm{sup 2}) with a pixel pitch of 150 μm and a depletion depth of 10 μm. The multichannel scaler counted X-ray pulses over continuous 2046 time bins for every 0.5 ns and recorded a time spectrum at each pixel with a time resolution of 0.5 ns (FWHM) for 8.0 keV X-rays. Using the detector system, we were able to observe X-ray peaks clearly separated with 2 ns interval in the multibunch-mode operation of the Photon Factory ring. The small-angle X-ray scattering for polyvinylidene fluoride film was also observed with the detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Poster - 01: LabPET II Pixelated APD-Based PET Scanner for High-Resolution Preclinical Imaging

Purpose: LabPET II is a new generation APD-based PET scanner designed to achieve sub-mm spatial resolution using truly pixelated detectors and highly integrated parallel front-end processing electronics. Methods: The basic element uses a 4×8 array of 1.12×1.12 mm{sup 2} Lu{sub 1.9}Y{sub 0.1}SiO{sub 5}:Ce (LYSO) scintillator pixels with one-to-one coupling to a 4×8 pixelated monolithic APD array mounted on a ceramic carrier. Four detector arrays are mounted on a daughter board carrying two flip-chip, 64-channel, mixed-signal, application-specific integrated circuits (ASIC) on the backside interfacing to two detector arrays each. Fully parallel signal processing was implemented in silico by encoding time and energy information using a dual-threshold Time-over-Threshold (ToT) scheme. The self-contained 128-channel detector module was designed as a generic component for ultra-high resolution PET imaging of small to medium-size animals. Results: Energy and timing performance were optimized by carefully setting ToT thresholds to minimize the noise/slope ratio. ToT spectra clearly show resolved 511 keV photopeak and Compton edge with ToT resolution well below 10%. After correction for nonlinear ToT response, energy resolution is typically 24±2% FWHM. Coincidence time resolution between opposing 128-channel modules is below 4 ns FWHM. Initial imaging results demonstrate that 0.8 mm hot spots of a Derenzo phantom can be resolved. Conclusion: A new generation PET scanner featuring truly pixelated detectors was developed and shown to achieve a spatial resolution approaching the physical limit of PET. Future plans are to integrate a small-bore dedicated mouse version of the scanner within a PET/CT platform.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Pilot Readiness Development Program for Autonomous Pathogen Detection System (APDS) (Final Report)

The purpose of this CRADA was to develop, integrate, and test design changes to LLNL’s field prototype autonomous pathogen detection system (APDS). The desired result of this project was an improved design of the APDS, along with test data characterizing performance of the new hardware, software, and processes. This improved design was to be closer to the final production design for operation. The third amendment to the Statement of Work (SOW) significantly redefined the scope of the work from general improvements to creating a NGSS built system that included the improvements from before and prepared the system for head to head testing for the BioWatch Gen-3 program. All deliverables were met on time and on budget.

Henderer, Bruce D.↗
DOE OSTI2018

Pilot Readiness Development Program for Autonomous Pathogen Detection System (APDS) Final Report CRADA No. TC02115.0

The purpose of this CRADA was to develop, integrate, and test design changes to LLNL’s field prototype autonomous pathogen detection system (APDS). The desired result of this project was an improved design of the APDS, along with test data characterizing performance of the new hardware, software, and processes. This improved design was to be closer to the final production design for operation. The third amendment to the Statement of Work (SOW) significantly redefined the scope of the work from general improvements to creating a NGSS built system that included the improvements from before and prepared the system for head to head testing for the BioWatch Gen-3 program. All deliverables were met on time and on budget.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

A new APDS approach - alarm processing based on alarm prioritization - 201

We take for granted that the advances in technology bring improvements to the conditions in which humans perform activities associated to them. Is that the case for digital alarm systems in nuclear power plants? The answer is not that simple. A review of the related literature, shows that still, the single most significant problem with alarm systems, is the large number of alarm messages presented to the operator at once. This is an issue that affects analog I and C control rooms with conventional annunciators and gets aggravated in digital I and C based control rooms. Digital alarm systems present the alarms in the form of lists in computer screens. This kind of presentation forces the operator to scroll or navigate pages to review the active alarms. Also, the alarm lists do not allow the operator to apply the pattern recognition practices acquired during training when using with fixed position alarm systems. An Alarm Processing and Diagnostic System (APDS) facilitates the alarm monitoring task by applying alarm reduction techniques based on alarm priorities. It allows the operators to focus on the most important alarms during plant upsets. A new generation of APDS should be based in an improved alarm analysis methodology. To develop such methodology, Tecnatom reviewed applicable standards and our own alarm analysis experiences. This paper documents the process and conclusions of the methodology development. (authors)

42 ENGINEERING↗
DOE OSTI2017

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd 3 O 4 (A = Ca, Sr)

The cubic semiconducting compounds APd 3 O 4 (A = Ca, Sr) can be hole-doped by Na substitution on the A site and driven toward more conducting states. This process has been followed here by a number of experimental techniques to understand the evolution of electronic properties. While an insulator-to-metal transition is observed in Ca 1–x Na x Pd 3 O 4 for x ≥ 0.15, bulk metallic behavior is not observed for Sr 1–x Na x Pd 3 O 4 up to x = 0.20. Given the very similar crystal and (calculated) electronic structures of the two materials, the distinct behavior is a matter of interest. We present evidence of local disorder in the A = Sr materials through the analysis of the neutron pair distribution function, which is potentially at the heart of the distinct behavior. Solid-state 23 Na nuclear magnetic resonance studies additionally suggest a percolative insulator-to-metal transition mechanism, wherein presumably small regions with a signal resembling metallic NaPd 3 O 4 form almost immediately upon Na substitution, and this signal grows monotonically with substitution. Here, some signatures of increased local disorder and a propensity for Na clustering are seen in the A = Sr compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Two-dimensional APDs and SPADs and related methods

Avalanche photodiodes (APDs) and single photon avalanche detectors (SPADs) are provided with a lateral multiplication region that provides improved amplification through increased impact ionization.

36 MATERIALS SCIENCE↗
DOE OSTI2013

PHENIX Muon Piston Calorimeter (MPC) APD and Prototype MPC Extension (MPC-EX) Tests

This is a technical scope of work (TSW) between the Fermi National Accelerator Laboratory (Fermilab) and the experimenters of Muon Piston Calorimeter Extension (MPC-EX) Collaboration who have committed to participate in beam tests to be carried out during the 2013- 2014 Fermilab Test Beam Facility program.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Photon-counting Properties of SAPHIRA APD Arrays

We measure the ability of the Leonardo Selex Advanced Photodiode HgCdTe Infrared Array (SAPHIRA) avalanche photodiode array to perform photon counting. The current SAPHIRA arrays achieve >90% single-photon efficiency (independent of quantum efficiency expected to be also >90%) and a time resolution of 125 μs with a dark current of 21e {sup −} s{sup −1} pix{sup −1}. Our characterization of several iterations of the SAPHIRA detector over the past 3 years of its development have also revealed a broader pulse height distribution than was originally expected.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Characterization of Large Area APDs for the EXO-200 Detector

EXO-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of scintillation light in an ultra-low-background liquid xenon (LXe) detector. We describe initial measurements of dark noise, gain and response to xenon scintillation light of LAAPDs at temperatures from room temperature to 169 K - the temperature of liquid xenon. We also describe the individual characterization of more than 800 LAAPDs for selective installation in the EXO-200 detector.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗