Photon Counting CT's are increasingly being used in many countries across the World. Photon-Counting Computed Tomography (PCCT) is a new technology that enables higher spatial resolution compared to conventional CT techniques, energy resolved imaging and spectral post-processing. This leads to improved contrast-to-noise ratio, artifact and potential dose reduction as well as elimination of electronic noise. Since the introduction of clinical PCCT in 2021, a shift has been observed from solely pre-clinical studies, clinical research to clinical use.
It's a Quantum Leap in Computed Tomography. The purest Cadmium Telluride crystal in the world laid the basis for this technology. (Also note that CdTe in thin film can be used in flexible Solar Panels and the US leads the research & production on these)
All medical CT systems today are equipped with solid‐state scintillation detectors. In a two‐step conversion process, the absorbed X‐rays are first converted into visible light in the scintillation crystal. The light is then converted into an electrical signal by a photodiode attached to the backside of each detector cell.
The low‐level analog electric signal of the photodiodes is susceptible to electronic noise, which sets an ultimate limit to potential further radiation dose reduction.
At the same time, it is problematic to significantly increase the spatial resolution of solid‐state scintillation detectors beyond today’s performance levels.
As part of this two‐step conversion process, the light created by thousands of X-ray photons is accumulated over the integration time and measured as a whole, thereby losing the spectral information of the incoming signal.
Photon-counting detectors, by contrast, can directly transform X‐ray photons into electrical signals.
In a direct conversion process, the absorbed X‐rays create electron‐hole pairs in the semiconductor. The charges are separated in a strong electric field between cathode on top and pixelated anode electrodes at the bottom of the detector.
Compared to solid‐state scintillation detectors, photon-counting detectors have several advantages. The individual detector cells are defined by the strong electric field between common cathode and pixelated anodes (Fig. 2), and there is no need for additional septa between the detector pixels to avoid optical cross talk inherent to scintillation detectors. The geometrical dose efficiency is, therefore, better than that of scintillation detectors and only reduced by the anti‐scatter collimator blades or grids that are also present in scintillation detectors. Furthermore, each “macro” detector pixel confined by collimator blades may be divided into smaller detector sub‐pixels which are read‐out separately to significantly increase spatial resolution.
With a photon-counting detector being able to count the charges created by individual x‐Ray photons as well as measuring their energy level, we now have a detector that has intrinsic spectral sensitivity in every scan.
Many major manufacturers like Siemens, Philips, Canon, GE & Toshiba have their own models available. Canon uses Cadmium Zinc Telluride (CZT). The addition of Zinc to Cadmium Telluride increases the detector’s ability to effectively capture photons, for greater dose efficiency.
Perhaps it's easily explained by these short videos by Siemens.
Part 1
Part 2
It's a Quantum Leap in Computed Tomography. The purest Cadmium Telluride crystal in the world laid the basis for this technology. (Also note that CdTe in thin film can be used in flexible Solar Panels and the US leads the research & production on these)
All medical CT systems today are equipped with solid‐state scintillation detectors. In a two‐step conversion process, the absorbed X‐rays are first converted into visible light in the scintillation crystal. The light is then converted into an electrical signal by a photodiode attached to the backside of each detector cell.
The low‐level analog electric signal of the photodiodes is susceptible to electronic noise, which sets an ultimate limit to potential further radiation dose reduction.
At the same time, it is problematic to significantly increase the spatial resolution of solid‐state scintillation detectors beyond today’s performance levels.
As part of this two‐step conversion process, the light created by thousands of X-ray photons is accumulated over the integration time and measured as a whole, thereby losing the spectral information of the incoming signal.
Photon-counting detectors, by contrast, can directly transform X‐ray photons into electrical signals.
In a direct conversion process, the absorbed X‐rays create electron‐hole pairs in the semiconductor. The charges are separated in a strong electric field between cathode on top and pixelated anode electrodes at the bottom of the detector.
Compared to solid‐state scintillation detectors, photon-counting detectors have several advantages. The individual detector cells are defined by the strong electric field between common cathode and pixelated anodes (Fig. 2), and there is no need for additional septa between the detector pixels to avoid optical cross talk inherent to scintillation detectors. The geometrical dose efficiency is, therefore, better than that of scintillation detectors and only reduced by the anti‐scatter collimator blades or grids that are also present in scintillation detectors. Furthermore, each “macro” detector pixel confined by collimator blades may be divided into smaller detector sub‐pixels which are read‐out separately to significantly increase spatial resolution.
With a photon-counting detector being able to count the charges created by individual x‐Ray photons as well as measuring their energy level, we now have a detector that has intrinsic spectral sensitivity in every scan.
Many major manufacturers like Siemens, Philips, Canon, GE & Toshiba have their own models available. Canon uses Cadmium Zinc Telluride (CZT). The addition of Zinc to Cadmium Telluride increases the detector’s ability to effectively capture photons, for greater dose efficiency.
Perhaps it's easily explained by these short videos by Siemens.
Part 1
Part 2
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