PET Photosensor Circuit Dark Current Filtering
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Solution Overview
Problem
In PET scanners, the timing resolution is compromised by dark current signals, which obscure the onset of gamma ray-induced signals and reduce the overall signal quality and resolution, especially when summing signals from multiple photosensor regions.
Innovation Solution
The implementation of regional circuits with delay units and switches that selectively allow signals corresponding to gamma ray impingement to contribute to the summed output, while excluding dark current signals by setting a threshold for signal transmission, thereby preserving photon detection efficiency and maintaining improved timing resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If signals from multiple photosensor regions are summed to reduce cost and heat generation, then device complexity and power consumption are reduced, but dark current signals are also summed which degrades timing resolution
Solution Approach 1:
The patent applies preliminary action by evaluating and filtering signals before they are summed. Each regional circuit portion assesses its input signal to determine if it represents a valid gamma ray event or dark current, and only valid signals are transmitted to the summing circuit. This pre-filtering prevents dark current from degrading timing resolution while still allowing cost-effective signal summation.
Solution Approach 2:
The patent introduces intermediary components (delay units and switch circuits) between the photosensor regions and the summing circuit. These intermediaries act as gatekeepers that selectively transmit or block signals based on their validity, thereby mediating between the need for signal summation and the requirement to maintain timing resolution.
2Use of energy by moving object
If a beveled lightguide is used to achieve direct coupling between crystal array and SiPM array, then light collection efficiency is improved, but timing for crystals located at beveled edge is degraded
Solution Approach 1:
The patent applies local quality by implementing region-specific processing circuits that are tailored to the characteristics of each photosensor region. Each regional circuit portion is configured to handle signals from its specific region, applying appropriate delay and filtering tailored to local conditions, thereby compensating for position-dependent timing variations while maintaining overall system performance.
3Measurement precision
If direct coupling between crystal array and SiPM array is implemented, then timing resolution is improved, but optimization for various timing parameters becomes more difficult
Solution Approach 1:
The patent applies segmentation by dividing the photosensor array into multiple independent regional circuits, each with its own delay unit and switch circuit. This segmentation allows independent optimization of each region's timing parameters without affecting other regions, thereby simplifying the overall optimization process while maintaining high timing resolution through direct coupling.
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 enhances the timing resolution and reduces the impact of dark current on photosensor performance, leading to improved detector performance and reduced costs by minimizing the need for complex timing-related electronic components.
Implementation Method 1
The scintillator crystals receive the annihilation photons and generate light photons in response to the annihilation photons
Implementation Method 2
a photosensor configured to convert the light energy from the light photons to electrical energy used to reconstruct an image
Data Source
AI summary
A positron emission tomography (PET) photosensor output circuit configured to be operably coupled to a PET photosensor system is provided that includes a plurality of regional circuit portions and a summing portion. Each regional circuit portion is configured to be operably coupled to a corresponding photosensor system region and includes an input portion, a first branch, and a second branch. The first branch includes a delay unit and a switch. The second branch includes a sensor unit configured to place the switch in a closed position when a signal received via the input portion satisfies a threshold and to place the switch in an open position when the signal received via the input portion does not satisfy the threshold. The summing portion is configured to receive corresponding regional circuit outputs from the regional circuit portions, and to combine the regional circuit outputs to provide a summed output.