Cadmium telluride (CdTe) is one of the materials used in photon-counting detectors for x-ray computed tomography. One challenge with this material is that it is susceptible to polarisation due to holes being trapped in impurities in the material. This can potentially lead to the buildup of bulk charge in the semiconductor, causing decreased charge collection efficiency and degraded energy resolution.
In this work, we develop a simulation model of CdTe detectors with polarisation and use it to study the effect of polarisation on the measured energy spectrum for different charge collection times. To this end, we use a theoretical model of charge buildup to find the critical charge in the detector’s bulk above which the detector can be considered completely polarised. We then simulate a 320-by-270-by-1600 μm CdTe detector used in CT clinical imaging, for varying degrees of polarisation (ratio between the actual charge and the critical charge) and charge collection time. Our results show that the measured spectrum gets heavily distorted for large degrees of polarisation or for short charge collection time. We also put these results in context by discussing how they relate to the critical fluence rate and the time of flight of the charge carriers. These results can lead to improved simulation models of CdTe detectors and a better understanding the factors affecting their imaging performance.
We provide an introductory overview of medical and industrial x-ray imaging applications and requirements for readers whose primary background is in quantum imaging. We discuss some opportunities for quantum X-ray imaging and related techniques such as ghost imaging to provide meaningful benefits in imaging and explain some of the key challenges that remain before practical applications can reach end users.
KEYWORDS: Sensors, Personal digital assistants, Gamma radiation, Global Positioning System, Field programmable gate arrays, Crystals, Calibration, Imaging systems, Signal detection, Data communications
The GE Intelligent Personal Radiation Locator (IPRL) system consists of multiple hand held radiation detectors and a
base station. Each mobile unit has a CZT Compton camera radiation detector and can identify isotopes and determine the
direction from which the radiation is detected. Using GPS and internal orientation sensors, the system continuously
transforms all directional data into real-world coordinates. Detected radiation is wirelessly transmitted to the base station
for system-wide analysis and situational awareness. Data can also be exchanged wirelessly between peers to enhance the
overall detection efficiency of the system. The key design features and performance characteristics of the GE IPRL
system are described.
A 4π direction-sensitive gamma imager is presented, using a 1 cm3 3D CZT detector from Yinnel
Tech and the RENA-3 readout ASIC from NOVA R&D. The measured readout system electronic noise is
around 4-5 keV FWHM for all anode channels. The measured timing resolution between two channels
within a single ASIC is around 10 ns and the resolution is 30 ns between two separate ASIC chips. After
3D material non-uniformity and charge trapping corrections, the measured single-pixel-event energy
resolution is around 1% for Cs-137 at 662 keV using a 1 cm3 CZT detector from Yinnel Tech with an 8 x 8
anode pixel array at 1.15 mm pitch. The energy resolution for two pixel events is 2.9%. A 10 uCi Cs-137
point source was moved around the detector to test the image reconstruction algorithms and demonstrate
the source direction detection capability. Accurate source locations were reconstructed with around 200
two-pixel events within a total energy window ±10 keV around the 662 keV full energy peak. The angular
resolution FWHM at four of the five positions tested was between 0.05-0.07 steradians.
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