Photon Counting Pixelated Detector Charge Sharing
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Solution Overview
Problem
Photon counting in pixelated detectors suffers from charge sharing, leading to double counting and reduced image contrast due to the expansion of charge clouds across multiple pixels, which complicates achieving high spatial resolution and energy spectroscopy.
Innovation Solution
Implementing a method where each pixel registers charges with a delay dependent on the charge received, designating a 'master' pixel for each event and inhibiting neighboring 'slave' pixels from counting, allowing for accurate single-event registration without increasing the trigger threshold, thus preventing double counting and maintaining high detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the trigger threshold is increased to prevent double counting from charge sharing, then false counting is reduced, but detection efficiency decreases because more valid photons fall below the threshold
Solution Approach 1:
The detector is divided into multiple pixels, each with its own counter and discriminator. This segmentation allows independent evaluation of charge in each pixel, enabling the system to identify when charge from a single photon is shared across multiple pixels and count it only once, thereby maintaining high detection efficiency while preventing double counting
Solution Approach 2:
The system uses feedback from the discriminator output to control the counter incrementing process. When a photon deposits charge in multiple pixels, the feedback mechanism ensures that only the first pixel to exceed the threshold increments its counter, while subsequent pixels are inhibited from counting the same event, thus preventing double counting without requiring a higher threshold
2Measurement precision
If pixel size is reduced to improve spatial resolution, then image detail improves, but charge sharing increases causing more double counting events
Solution Approach 1:
The detector is divided into multiple pixels, each with its own counter and discriminator. This segmentation allows independent evaluation of charge in each pixel, enabling the system to identify when charge from a single photon is shared across multiple pixels and count it only once, thereby maintaining high detection efficiency while preventing double counting
Solution Approach 2:
The system uses feedback from the discriminator output to control the counter incrementing process. When a photon deposits charge in multiple pixels, the feedback mechanism ensures that only the first pixel to exceed the threshold increments its counter, while subsequent pixels are inhibited from counting the same event, thus preventing double counting without requiring a higher threshold
3Quantity of substance
If charge integration is used instead of photon counting, then more signal is collected, but electronic noise and detector leakage current are integrated with the signal reducing image contrast
Solution Approach 1:
The system uses periodic sampling at the photon arrival level rather than continuous integration. Each photon event is detected and counted individually as it occurs, with the counter updating in real-time. This periodic event-based approach collects signal without integrating noise, maintaining high image contrast while still achieving high signal collection through the high count rate capability of photon counting
Solution Approach 2:
The system replaces the mechanical charge integration process with an electronic photon-by-photon counting mechanism. Instead of integrating charges over time in a capacitor and then digitizing, the system uses discriminators to detect each photon event individually and increments a digital counter. This substitution eliminates the integration of electronic noise and leakage current while maintaining signal collection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures that each event is counted only once, enhancing image contrast and spatial resolution while allowing for small pixel sizes without compromising detection efficiency, thereby overcoming the limitations of charge sharing in photon counting systems.
Implementation Method 1
When highly energetic photons are 'detected' in a semiconductor detector, electron-holes are created. The electrons and holes move in opposite directions towards the electrodes because of a bias voltage applied.
Implementation Method 2
Because of the bias voltage, this charge cloud starts to drift to the detector electrode and during this drifting time, the transverse size of the charge cloud expands according the diffusion formula of Fick's law.
Data Source
AI summary
A method for photon counting for pixels in a pixelated detector is disclosed, wherein for each of the pixels, one or more neighbouring pixels are defined. The method comprises receiving a charge in one or more of the pixels and comparing for each of the pixels the charge with a trigger threshold. If the charge in a pixel is above the trigger threshold, the charge is registered in the pixel after a registration delay, wherein the registration delay is dependent on the level of the charge received in the pixel in such a way that a registration delay decreases with increasing charge. A counter for a pixel is incremented when the charge is registered and an increment of a counter of the neighbouring pixels is inhibited. Pixelated semiconductor detectors are also disclosed.