-
[show abstract]
[hide abstract]
ABSTRACT: Radiation damage of amorphous silicon X-ray imagers leads to degradation of the detector's performance due to increased diode perimeter leakage. To reduce the effect of this damage, a novel pixel device based on a gated diode was fabricated. The additional gate metalization placed on the perimeter of the diode modulates the surface side-wall leakage and has been tested up to a 64 kGy absorbed dose in the diode. This new pixel design significantly reduces the increase in diode leakage and noise due to radiation damage, providing a more uniform performance and extending the lifetime of the imager.
IEEE Electron Device Letters 02/2008; · 2.85 Impact Factor
-
K.C. Burr,
A. Ivan,
J. LeBlanc, S. Zelakiewicz,
D.L. McDaniel,
C.L. Kim,
A. Ganin,
K.S. Shah,
R. Grazioso,
R. Farrell,
J. Glodo
[show abstract]
[hide abstract]
ABSTRACT: A gamma ray detector for PET, consisting of an array of mixed lutetium oxyorthosilicate (MLS) scintillator crystals coupled to a position sensitive avalanche photodiode (PSAPD), was evaluated. The scintillator array was constructed from individual MLS crystals with dimensions of 1.5 mm × 1.5 mm × 15 mm. The assembled 7 × 7 array, including intercrystal reflector material, had a pitch of 1.79 mm. The low noise, high gain PSAPD had dimensions of 14 mm × 14 mm. Peaks associated with each of the 49 scintillator crystals were readily identifiable in flood histograms, and most of the crystals demonstrated energy resolution in the range of 15% to 20% at 511 keV. Measurements of the timing of the PSAPD in coincidence with a fast-scintillator/PMT detector indicated a timing resolution of approximately 4 ns. The operating characteristics and design attributes, such as compactness and reduced readout channel requirements, of the PSAPD make it attractive for high resolution PET applications.
IEEE Transactions on Nuclear Science 09/2003; · 1.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A software suite for the modeling of medical imaging detectors has been constructed that uses GEANT4 for particle tracking and DETECT2000 for the optical modeling of scintillation photons. The Radiation Imager Virtual Laboratory (RIVL) is a collection of modular, stand-alone programs that are interfaced to each other via format conversion utilities and is intended to model the energy deposition, scintillation conversion, optical photon transport, signal sensing, electronics and pulse processing. RIVL makes use of a GEANT4 application developed at General Electric Global Research called the Virtual Radiation Imager (VRAI). VRAI is based on GEANT4, a sophisticated and mature collection of C++ libraries that are commonly used in nuclear and particle physics and is seeing an increased use in the medical imaging community. With GEANT4, the physical interactions of particles are well modeled in the energy regime relevant for medical imaging. Modeling of the optical transport of scintillation photons is performed with the program DETECT2000, which enables detailed control over optical properties and is better suited than GEANT4 for modeling the transport of optical scintillation photons. Interfacing GEANT with DETECT2000 harnesses the strengths of each of these programs to create a complete model for various medical imaging applications. The simulation of the response of the photosensor to scintillation photons, as well as the logic applied to the photosensor signals to reconstruct the hit position and energy are accomplished with custom software modules written at the GE Global Research Center.
Nuclear Science Symposium Conference Record, 2002 IEEE; 12/2002
-
[show abstract]
[hide abstract]
ABSTRACT: A new surface parameterization has been implemented in DETECT2000 that allows for the efficient representation of a thin film of reflector material with non-negligible transmission. Material is usually modeled in DETECT by specifying the optical attenuation and scatter lengths. For a material such as Teflon, commonly used as a reflector material for nuclear medicine scintillators, the scatter length can be very short. Modeling the propagation of photons in a material with a very short scattering length can be computationally intensive as there can be many scatter interactions before the photon either exits the material or is absorbed. In a detector design that makes generous use of Teflon, most of the computations can be spent simply transporting photons in the Teflon. To address this issue, a parameterized surface has been implemented which is specified not by the bulk optical scatter and attenuation lengths, but rather by a reflection and transmission coefficient. This allows computationally efficient modeling of thin film reflectors where surface properties and transmission are relevant.
Nuclear Science Symposium Conference Record, 2002 IEEE; 12/2002
-
K.C. Burr,
A. Ivan,
J. LeBlanc, S. Zelakiewicz,
D.L. McDaniel,
C.L. Kim,
A. Ganin,
K.S. Shah,
R. Grazioso,
R. Farrell,
J. Glodo
[show abstract]
[hide abstract]
ABSTRACT: A gamma ray detector for PET, consisting of an array of mixed lutetium oxyorthosilicate (MLS) scintillator crystals coupled to a position sensitive avalanche photodiode (PSAPD), was evaluated. The scintillator array was constructed from individual MLS crystals with dimensions of 1.5 mm×1.5 mm×15 mm. The assembled 7×7 array, including inter-crystal reflector material, had a pitch of 1.79 mm. The low noise, high gain PSAPD had dimensions of 14 mm×14 mm. Peaks associated with each of the 49 scintillator crystals were readily identifiable in flood histograms, and most of the crystals demonstrated energy resolution in the range of 15% to 20% at 511 keV. Preliminary measurements of the timing of the PSAPD in coincidence with a fast-scintillator/PMT detector indicated a timing resolution of approximately 4 ns. The operating characteristics and design attributes, such as compactness and reduced readout channel requirements, of the PSAPD make it attractive for high resolution PET applications.
Nuclear Science Symposium Conference Record, 2002 IEEE; 12/2002
-
[show abstract]
[hide abstract]
ABSTRACT: Extending, the lifetime of amorphous silicon based radiation imagers is necessary for numerous applications including industrial inspection and radiation therapy. To achieve a longer lifetime, a new pixel design has been fabricated. This design incorporates a gated diode that significantly increase mitigates the effect of radiation damage. Additionally, each pixel incorporates a storage capacitor to increase the dynamic range of the pixel and a reflective layer to maximize the light collection efficiency. We report on the device performance of this design and the imaging performance of the complete detector.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
-
[show abstract]
[hide abstract]
ABSTRACT: Recently, with the prospect of great improvement in image quality, the development of time of flight technology has become an exciting topic for positron emission tomography. The excitement was further accelerated by the introduction of various fast and high light output scintillators as well as photosensors. However, the development of improved time of flight detectors is not only about the selection of crystals and photosensors, but also about how detectors are assembled to optimize their performance. For example, depending on crystal block structure, photo-sensor layout, and coupling methods, a detector's timing resolution can be drastically different. Since the effect of block structure for timing resolution is complex and less understood it is essential to first dissect the block structure and understand the impact of its basic components on timing resolution. In this paper, we will present the dependence of timing resolution on varying the dimensions of the scintillator crystals that are the main component of a block detector.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
