Shielded Pixel Array for Dark Current Compensation in Photon Counting Detectors
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Solution Overview
Problem
Photon counting detectors based on direct conversion materials like Cadmium Zinc Telluride (CZT) suffer from unwanted dark current issues, leading to noise, resolution loss, and baseline shifts due to temperature variations, which current solutions like grid-switch sampling, pre-scan sampling, and AC coupling either require complex circuits or are not compatible with high integration needs.
Innovation Solution
A photon counting radiation detector with a shielded pixel array that measures dark current independently and applies compensation to irradiated pixels, using a radiation-absorbing coating or structure to isolate shielded pixels, allowing for accurate dark current determination and compensation during imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Baseline Restoration (BLR) circuits are used to compensate for dark current, then dark current compensation is improved, but device complexity increases and additional artifacts are introduced
Solution Approach 1:
The patent extracts the dark current measurement function from the irradiated detection pixels by designating specific shielded pixels that are isolated from radiation. This separation allows independent dark current measurement without the complexity of BLR circuits, as the shielded pixels naturally provide dark current signals free from radiation interference.
Solution Approach 2:
The patent introduces shielded pixels as intermediary elements that mediate between the radiation source and the detection pixels. These shielded pixels act as dedicated dark current sensors that do not directly detect radiation, providing clean dark current measurements for compensation purposes.
2Measurement precision
If grid-switch sampling is used to measure baseline shift, then dark current measurement is improved, but device complexity increases due to special X-ray tube and generator functionality requirements
Solution Approach 1:
The patent enables the detector array to self-measure dark current using its own shielded pixels during normal operation. The shielded pixels continuously provide dark current measurements without requiring external control mechanisms or special X-ray tube functionality, making the system self-sufficient for dark current compensation.
3Reliability
If pre-scan sampling is used to sample baseline before scan, then dark current compensation is improved, but measurement precision deteriorates due to temperature deviation during long scans
Solution Approach 1:
The patent implements continuous dark current measurement throughout the scan process using shielded pixels that operate continuously. Unlike pre-scan sampling which only measures before the scan, the shielded pixels provide ongoing dark current data that tracks temperature changes in real-time, maintaining measurement precision throughout the entire scan duration.
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 effectively reduces energy estimation errors caused by temperature-induced dark current drifts, maintaining high energy resolution and simplifying electronics by enabling digital compensation during image reconstruction.
Implementation Method 1
at least one pixel of the array of pixels is shielded from receiving radiation
Data Source
AI summary
The present invention is directed towards a photon counting radiation detector (10) comprising an array of pixels (13) comprising a plurality of detection pixels (131) for detecting imaging information. At least one pixel of the array of pixels (132) is shielded from receiving radiation. A dark current is determined from the shielded pixel (132) and is used to compensate for dark current in the other, non-shielded pixels (131). Embodiments are directed to integrating pixel shielding within an Anti Scatter Grid or in a mask.