Persistent Current Estimator for Photon Counting Detectors
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Solution Overview
Problem
Direct conversion materials in photon counting detectors, such as CdTe and CZT, produce persistent current that leads to baseline shifts in signal output, causing erroneous binning of detected radiation due to the dynamic and varying nature of this current, which cannot be effectively compensated by static bias correction.
Innovation Solution
A persistent current estimator is implemented, comprising circuitry with resistive, capacitive, and feedback elements to model and estimate the persistent current, generating a compensation signal that is injected back into the pre-amplifier to cancel out the persistent current, thereby mitigating baseline shifts and improving energy resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If static bias compensation is used to correct dark current, then dark current is compensated, but persistent current cannot be compensated because it dynamically changes
Solution Approach 1:
The patent applies dynamics by transitioning from static bias compensation to dynamic persistent current estimation. The system uses a persistent current estimator that continuously models and estimates the time-varying persistent current based on recent pulse data, allowing the compensation to adapt to changing conditions rather than using a fixed static value
Solution Approach 2:
The patent implements feedback by using the estimated persistent current to generate a compensation signal that is fed back to compensate for the persistent current in real-time. The system continuously monitors the detector output, estimates persistent current, and adjusts compensation based on this feedback loop, enabling adaptation to dynamic changes
2Measurement precision
If direct conversion material is used for photon counting detection, then energy resolution is achieved, but persistent current is generated causing baseline shifts
Solution Approach 1:
The patent extracts the harmful persistent current component from the total detector signal by modeling and estimating it separately. The persistent current estimator isolates this harmful factor so it can be compensated independently, allowing the useful energy resolution signal to remain intact
Solution Approach 2:
The patent converts the harmful persistent current into a beneficial compensation opportunity by modeling its behavior and using it to generate a compensation signal. Instead of simply rejecting the persistent current, the system characterizes it and uses this knowledge to actively compensate for its effects, turning a harmful factor into a manageable parameter
3Measurement precision
If persistent current compensation is implemented, then baseline shifts are reduced, but device complexity increases due to additional circuitry
Solution Approach 1:
The patent introduces a persistent current estimator as an intermediary component between the detector and the readout electronics. This intermediary models and estimates the persistent current, serving as a bridge that allows compensation without requiring complex direct intervention in the signal path
Solution Approach 2:
The patent changes parameters by modeling the persistent current using a mathematical model with specific parameters (trapping rate, lifetime). By estimating these parameters from recent pulse data and using them to generate compensation, the system achieves complex compensation functionality through parameter-based control rather than complex circuit architecture
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
The solution effectively compensates for persistent current, reducing erroneous binning and enhancing the accuracy of energy-resolved radiation detection, allowing for more precise reconstruction of volumetric image data in imaging modalities like CT scans.
Implementation Method 1
X-ray photons illuminate the cathode, transferring energy to electrons in the direct conversion material, which creates electron/hole pairs, with the electrons drifting towards the anode
Implementation Method 2
an integrator, including: an amplifier (304); and a feedback circuit (303), including a second resistive element (306) indicative of the trapped hole recombination rate of the direct conversion material; and a capacitive element (308), wherein the second resistive element and the capacitive element are electrically in parallel
Data Source
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AI summary
An imaging system (100) includes a direct conversion detector pixel (111) that detects radiation traversing an examination region and generates an electrical signal indicative thereof, wherein the signal includes a persistent current, which is produced by a direct conversion material of the pixel and which shifts a level of the signal. A persistent current estimator (116) estimates the persistent current and generates a compensation signal based on the estimate. A pre-amplifier (112) receives the signal and the compensation signal, wherein the compensation signal substantially cancels the persistent current, producing a persistent current compensated signal, and that amplifies the compensated signal, generating an amplified compensated signal. A shaper (114) generates a pulse indicative of energy of the radiation illuminating the direct conversion material based on the amplified compensated signal.