| 61. |
- Sundberg, Christel, et al.
(författare)
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1-µm spatial resolution in silicon photon-counting CT detectors
- 2021
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Ingår i: Journal of Medical Imaging. - : SPIE - International Society for Optical Engineering. - 2329-4302 .- 2329-4310. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Spatial resolution for current scintillator-based computed tomography (CT) detectors is limited by the pixel size of about 1 mm. Direct conversion photon-counting detector prototypes with silicon- or cadmium-based detector materials have lately demonstrated spatial resolution equivalent to about 0.3 mm. We propose a development of the deep silicon photon-counting detector which will enable a resolution of 1 ?? µ m , a substantial improvement compared to the state of the art. Approach: With the deep silicon sensor, it is possible to integrate CMOS electronics and reduce the pixel size at the same time as significant on-sensor data processing capability is introduced. A Gaussian curve can then be fitted to the charge cloud created in each interaction.We evaluate the feasibility of measuring the charge cloud shape of Compton interactions for deep silicon to increase the spatial resolution. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated deep silicon detector with a pixel size of 12 ?? µ m , we present a method for estimating the interaction position. Results: Using estimations for electronic noise and a lowest threshold of 0.88 keV, we obtain a spatial resolution equivalent to 1.37 ?? µ m in the direction parallel to the silicon wafer and 78.28 ?? µ m in the direction orthogonal to the wafer. Conclusions: We have presented a simulation study of a deep silicon detector with a pixel size of 12 × 500 ?? µ m 2 and a method to estimate the x-ray interaction position with ultra-high resolution. Higher spatial resolution can in general be important to detect smaller details in the image. The very high spatial resolution in one dimension could be a path to a practical implementation of phase contrast imaging in CT.
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| 62. |
- Sundberg, Christel, et al.
(författare)
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1-mu m spatial resolution in silicon photon-counting CT detectors
- 2021
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Ingår i: Journal of Medical Imaging. - : SPIE, the international society for optics and photonics. - 2329-4302 .- 2329-4310. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Spatial resolution for current scintillator-based computed tomography (CT) detectors is limited by the pixel size of about 1 mm. Direct conversion photon-counting detector prototypes with silicon- or cadmium-based detector materials have lately demonstrated spatial resolution equivalent to about 0.3 mm. We propose a development of the deep silicon photon-counting detector which will enable a resolution of 1 μm, a substantial improvement compared to the state of the art.Approach: With the deep silicon sensor, it is possible to integrate CMOS electronics and reduce the pixel size at the same time as significant on-sensor data processing capability is introduced. A Gaussian curve can then be fitted to the charge cloud created in each interaction.We evaluate the feasibility of measuring the charge cloud shape of Compton interactions for deep silicon to increase the spatial resolution. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated deep silicon detector with a pixel size of 12 μm, we present a method for estimating the interaction position.Results: Using estimations for electronic noise and a lowest threshold of 0.88 keV, we obtain a spatial resolution equivalent to 1.37 μm in the direction parallel to the silicon wafer and 78.28 μm in the direction orthogonal to the wafer.Conclusions: We have presented a simulation study of a deep silicon detector with a pixel size of 12 × 500 μm2 and a method to estimate the x-ray interaction position with ultra-high resolution. Higher spatial resolution can in general be important to detect smaller details in the image. The very high spatial resolution in one dimension could be a path to a practical implementation of phase contrast imaging in CT.
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| 63. |
- Sundberg, Christel, et al.
(författare)
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1 mu m Spatial Resolution in Silicon Photon-Counting CT Detectors by Measuring Charge Diffusion
- 2020
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Ingår i: MEDICAL IMAGING 2020: PHYSICS OF MEDICAL IMAGING. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510633926
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Konferensbidrag (refereegranskat)abstract
- One of the existing prototype detector systems for full-field photon-counting CT is a silicon detector developed by our group. Spatial resolution is clinically important to resolve small details and can enable more efficient phase-contrast imaging. However, improving the resolution is difficult as decreasing the pixel size is associated with technical challenges. By integrating CMOS electronics into the silicon sensor, it is possible to reduce the pixel size drastically while also introducing on-sensor data processing capabilities. In this work, we evaluate the feasibility of measuring the charge cloud shape of Compton interactions in a silicon strip detector to increase the spatial resolution. With an incident spectrum of 140 kVp, Compton interactions constitute 66.2% of the detected interactions. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated silicon strip detector with a pixel size of 12x500 mu m(2), we present a method in which the interaction position can be determined. For an ideal case without electronic noise an average absolute error of 0.65 mu m is obtained in the direction along the wafer and 13.08 mu m in the trans-wafer direction. With simulated electronic noise and a lowest threshold of 0.88 keV the corresponding values are 1.38 mu m and 122.83 mu m. Our results show that the proposed method has the potential to very significantly increase the spatial resolution in a full-field photon-counting detector for CT.
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| 64. |
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| 65. |
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| 66. |
- Sundberg, Christel, et al.
(författare)
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Increased count-rate performance and dose efficiency for silicon photon-counting detectors for full-field CT using an ASIC with adjustable shaping time
- 2019
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Ingår i: MEDICAL IMAGING 2019. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510625440
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Konferensbidrag (refereegranskat)abstract
- Photon-counting silicon strip detectors are attracting interest for use in next generation CT scanners. For silicon detectors, a low noise floor is necessary to obtain a good dose efficiency. A low noise floor can be achieved by having a filter with a long shaping time in the readout electronics. This also increases the pulse length, resulting in a long deadtime and thereby a degraded count-rate performance. However, as the flux typically varies greatly during a CT scan, a high count-rate capability is not required for all projection lines. It would therefore be desirable to use more than one shaping time within a single scan. To evaluate the potential benefit of using more than one shaping time, it is of interest to characterize the relation between the shaping time, the noise, and the resulting pulse shape. In this work we present noise and pulse shape measurements on a photon-counting detector with two different shaping times along with a complementary simulation model of the readout electronics. We show that increasing the shaping time from 28.1 ns to 39.4 ns decreases the noise and increases the signal-to-noise ratio (SNR) with 6.5% at low count rates and we also present pulse shapes for each shaping time as measured at a synchrotron source. Our results demonstrate that the shaping time plays an important role in optimizing the dose efficiency in a photon-counting x-ray detector.
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| 67. |
- Sundberg, Christel, et al.
(författare)
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Silicon photon-counting detector for full-field CT usingan ASIC with adjustable shaping time
- 2020
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Ingår i: Journal of Medical Imaging. - : SPIE - International Society for Optical Engineering. - 2329-4302 .- 2329-4310. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Photon-counting silicon strip detectors are attracting interest for use in next-generation CT scanners. For CT detectors in a clinical environment, it is desirable to have a low power consumption. However, decreasing the power consumption leads to higher noise. This is particularly detrimental for silicon detectors, which require a low noise floor to obtain a good dose efficiency. The increase in noise can be mitigated using a longer shaping time in the readout electronics. This also results in longer pulses, which requires an increased deadtime, thereby degrading the count-rate performance. However, as the photon flux varies greatly during a typical CT scan, not all projection lines require a high count-rate capability. We propose adjusting the shaping time to counteract the increased noise that results from decreasing the power consumption.Approach: To show the potential of increasing the shaping time to decrease the noise level, synchrotron measurements were performed using a detector prototype with two shaping time settings. From the measurements, a simulation model was developed and used to predict the performance of a future channel design.Results: Based on the synchrotron measurements, we show that increasing the shaping time from 28.1 to 39.4 ns decreases the noise and increases the signal-to-noise ratio with 6.5% at low count rates. With the developed simulation model, we predict that a 50% decrease in power can be attained in a proposed future detector design by increasing the shaping time with a factor of 1.875.Conclusion: Our results show that the shaping time can be an important tool to adapt the pulse length and noise level to the photon flux and thereby optimize the dose efficiency of photon-counting silicon detectors.
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| 68. |
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| 69. |
- Sundberg, Christel, et al.
(författare)
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Timing resolution in double-sided silicon photon-counting computed tomography detectors
- 2023
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Ingår i: Journal of Medical Imaging. - : SPIE-Intl Soc Optical Eng. - 2329-4302 .- 2329-4310. ; 10:02
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Our purpose is to investigate the timing resolution in edge-on silicon strip detectors for photon-counting spectral computed tomography. Today, the timing for detection of individual x-rays is not measured, but in the future, timing information can be valuable to accurately reconstruct the interactions caused by each primary photon. Approach: We assume a pixel size of 12 x 500 mu m(2) and a detector with double-sided readout with low-noise CMOS electronics for pulse processing for every pixel on each side. Due to the electrode width in relation to the wafer thickness, the induced current signals are largely dominated by charge movement close to the collecting electrodes. By employing double-sided readout electrodes, at least two signals are generated for each interaction. By comparing the timing of the induced current pulses, the time of the interaction can be determined and used to identify interactions that originate from the same incident photon. Using a Monte Carlo simulation of photon interactions in combination with a charge transport model, we evaluate the performance of estimating the time of the interaction for different interaction positions. Results: Our simulations indicate that a time resolution of 1 ns can be achieved with a noise level of 0.5 keV. In a detector with no electronic noise, the corresponding time resolution is similar to 0.1 ns. Conclusions: Time resolution in edge-on silicon strip CT detectors can potentially be used to increase the signal-to-noise-ratio and energy resolution by helping in identifying Compton scattered photons in the detector.
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| 70. |
- Svensson, Christer, 1941-, et al.
(författare)
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X-ray detector system based on photon counting
- 2018
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Patent (populärvet., debatt m.m.)abstract
- Disclosed is an x-ray detector system including a multitude of detector elements, each connected to a respective photon counting channel for providing at least one photon count output, and a read-out unit connected to the photon counting channels for outputting the photon count outputs. Each one of at least a subset of the photon counting channels includes at least two photon counting sub-channels, each photon counting sub-channel providing at least one photon count output and having a shaping filter, wherein the shaping filters of the photon counting sub-channels are configured with different shaping times, and wherein the photon counting sub-channels, having shaping filters with different shaping times, are adapted for counting photons of different energy levels. Furthermore, the read-out unit is configured to select, for each photon counting channel, photon count outputs from the photon counting sub-channels.
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