Measurements of a dual-energy fast photon counting CdTe detector with integrated charge sharing correction

2013 ◽  
Author(s):  
Christer Ullberg ◽  
Mattias Urech ◽  
Niclas Weber ◽  
Anders Engman ◽  
Anna Redz ◽  
...  
Keyword(s):  
Photon Counting ◽  
Dual Energy ◽  
Charge Sharing ◽  
Cdte Detector

Measurements of charge sharing in a hybrid pixel photon counting CdTe detector

2021 ◽  
Vol 16 (12) ◽  
pp. C12027
Author(s):  
A. Krzyzanowska
Keyword(s):  
Spatial Resolution ◽  
Single Photon ◽  
Spectral Response ◽  
Photon Counting ◽  
Radiation Detectors ◽  
Charge Sharing ◽  
Single Photon Counting ◽  
X Ray ◽  
Cdte Detector ◽  
Wide Range

Abstract Hybrid pixel radiation detectors working in a single-photon counting mode have gained increasing attention due to their noiseless imaging and high dynamic range. Due to the fact that sensors of different materials can be attached to the readout circuit, they allow operation with a wide range of photon energies. The performance of the single photon counting detectors is limited by pile-up. To allow a detector to work under high flux conditions, the pixel size is reduced, which minimizes detector dead time. However, with smaller pixel sizes the charge sharing effect, a phenomenon that deteriorates both detection efficiency and spatial resolution is more profound. The influence of charge sharing on the detector performance can be quantified using parameterization of the s-curve obtained in the spectral response measurements. The article presents the measurements of the response function of a hybrid pixelated photon counting detector for certain primary energy, which corresponds to the probability of detecting a photon as a function of its energy deposition. The measurements were carried out using an X-ray tube by performing a threshold scan during illumination with X-ray photons of a 1.5 mm and 0.75 mm thick CdTe detector with 100 µm pixel pitch. The charge size cloud depends on the sensor material, the bias voltage, and the sensor thickness. Therefore, the experimental data from a sensor biased with different bias voltages are compared to the theoretical results based on a cascaded model of a single-photon counting segmented silicon detector. The study of the charge sharing influence on the spatial resolution of the CdTe detector will serve for a further study of the possible implementations of the algorithms achieving subpixel resolution, in which the charge sharing becomes the desired effect since the charge division in the pixels is used to interpolate the photon interaction position.

Application of the dual energy technique by using a photon counting CdTe detector

2008 ◽  
Author(s):  
Wenjuan Zou ◽  
Takuya Nakashima ◽  
Yoshiaki Onishi ◽  
Hisashi Morii ◽  
Yoichiro Neo ◽  
...  
Keyword(s):  
Photon Counting ◽  
Dual Energy ◽  
Cdte Detector

scholarly journals Charge Sharing and Charge Loss in High-Flux Capable Pixelated CdZnTe Detectors

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 3260
Author(s):  
Kjell A. L. Koch-Mehrin ◽  
Sarah L. Bugby ◽  
John E. Lees ◽  
Matthew C. Veale ◽  
Matthew D. Wilson
Keyword(s):  
Carrier Transport ◽  
Hole Transport ◽  
Uniform Electric Field ◽  
Photon Flux ◽  
High Flux ◽  
Charge Sharing ◽  
Cdte Detector ◽  
Charge Loss ◽  
Cdznte Detectors ◽  
Detector Model

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field.

scholarly journals Threshold-dependent iodine imaging and spectral separation in a whole-body photon-counting CT system

2021 ◽  
Author(s):  
S. Sawall ◽  
L. Klein ◽  
E. Wehrse ◽  
L. T. Rotkopf ◽  
C. Amato ◽  
...  
Keyword(s):  
Image Quality ◽  
Photon Counting ◽  
Dual Energy ◽  
Whole Body ◽  
Dual Energy Ct ◽  
Post Mortem ◽  
Tube Voltage ◽  
Spectral Separation ◽  
Dual Source ◽  
Noise Ratio

Abstract Objective To evaluate the dual-energy (DE) performance and spectral separation with respect to iodine imaging in a photon-counting CT (PCCT) and compare it to dual-source CT (DSCT) DE imaging. Methods A semi-anthropomorphic phantom extendable with fat rings equipped with iodine vials is measured in an experimental PCCT. The system comprises a PC detector with two energy bins (20 keV, T) and (T, eU) with threshold T and tube voltage U. Measurements using the PCCT are performed at all available tube voltages (80 to 140 kV) and threshold settings (50–90 keV). Further measurements are performed using a conventional energy-integrating DSCT. Spectral separation is quantified as the relative contrast media ratio R between the energy bins and low/high images. Image noise and dose-normalized contrast-to-noise ratio (CNRD) are evaluated in resulting iodine images. All results are validated in a post-mortem angiography study. Results R of the PC detector varies between 1.2 and 2.6 and increases with higher thresholds and higher tube voltage. Reference R of the EI DSCT is found as 2.20 on average overall phantoms. Maximum CNRD in iodine images is found for T = 60/65/70/70 keV for 80/100/120/140 kV. The highest CNRD of the PCCT is obtained using 140 kV and is decreasing with decreasing tube voltage. All results could be confirmed in the post-mortem angiography study. Conclusion Intrinsically acquired DE data are able to provide iodine images similar to conventional DSCT. However, PCCT thresholds should be chosen with respect to tube voltage to maximize image quality in retrospectively derived image sets. Key Points • Photon-counting CT allows for the computation of iodine images with similar quality compared to conventional dual-source dual-energy CT. • Thresholds should be chosen as a function of the tube voltage to maximize iodine contrast-to-noise ratio in derived image sets. • Image quality of retrospectively computed image sets can be maximized using optimized threshold settings.

scholarly journals Optimization of a dual-energy contrast-enhanced technique for a photon-counting digital breast tomosynthesis system: I. A theoretical model

2010 ◽  
Vol 37 (11) ◽  
pp. 5896-5907 ◽  
Author(s):  
Ann-Katherine Carton ◽  
Christer Ullberg ◽  
Karin Lindman ◽  
Raymond Acciavatti ◽  
Tom Francke ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Photon Counting ◽  
Digital Breast Tomosynthesis ◽  
Dual Energy ◽  
Breast Tomosynthesis ◽  
Contrast Enhanced

scholarly journals Feasibility of unconstrained three-material decomposition: imaging an excised human heart using a prototype silicon photon-counting CT detector

2020 ◽  
Vol 30 (11) ◽  
pp. 5904-5912 ◽  
Author(s):  
Fredrik Grönberg ◽  
Johan Lundberg ◽  
Martin Sjölin ◽  
Mats Persson ◽  
Robert Bujila ◽  
...  
Keyword(s):  
Photon Counting ◽  
Rate Capability ◽  
Silicon Detector ◽  
Dual Energy ◽  
Material Decomposition ◽  
Clinical Value ◽  
Photon Counting Detector ◽  
Tomography System ◽  
Iodinated Contrast ◽  
Iodinated Contrast Agent

Abstract Rationale and objectives The purpose of this study was to evaluate the feasibility of unconstrained three-material decomposition in a human tissue specimen containing iodinated contrast agent, using an experimental multi-bin photon-counting silicon detector. It was further to evaluate potential added clinical value compared to a 1st-generation state-of-the-art dual-energy computed tomography system. Materials and methods A prototype photon-counting silicon detector in a bench-top setup for x-ray tomographic imaging was calibrated using a multi-material calibration phantom. A heart with calcified plaque was obtained from a deceased patient, and the coronary arteries were injected with an iodinated contrast agent mixed with gelatin. The heart was imaged in the experimental setup and on a 1st-generation state-of-the-art dual-energy computed tomography system. Projection-based three-material decomposition without any constraints was performed with the photon-counting detector data, and the resulting images were compared with those obtained from the dual-energy system. Results The photon-counting detector images show better separation of iodine and calcium compared to the dual-energy images. Additional experiments confirmed that unbiased estimates of soft tissue, calcium, and iodine could be achieved without any constraints. Conclusion The proposed experimental system could provide added clinical value compared to current dual-energy systems for imaging tasks where mix-up of iodine and calcium is an issue, and the anatomy is sufficiently small to allow iodine to be differentiated from calcium. Considering its previously shown count rate capability, these results show promise for future integration of this detector in a clinical CT scanner. Key Points • Spectral photon-counting detectors can solve some of the fundamental problems with conventional single-energy CT. • Dual-energy methods can be used to differentiate iodine and calcium, but to do so must rely on constraints, since solving for three unknowns with only two measurements is not possible. Photon-counting detectors can improve upon these methods by allowing unconstrained three-material decomposition. • A prototype photon-counting silicon detector with high count rate capability allows performing unconstrained three-material decomposition and qualitatively shows better differentiation of iodine and calcium than dual-energy CT.

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