Photon Detection Device Ballistic Deficit Adjustment
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Solution Overview
Problem
Conventional gain calibration methods neglect pixel variations caused by differences in transient response, leading to gain differences and affecting spectral linearity in photon-counting based spectral CT systems using direct converting materials like CZT.
Innovation Solution
The detection device adjusts the ASIC operating point per pixel to compensate for ballistic deficit by iteratively evaluating and adjusting the feedback resistor or feedback current source to ensure consistent photo peak amplitudes across the pixel matrix, using a feedback discharge unit and energy determination unit with comparators to set appropriate energy thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gain calibration is used to adjust ASIC threshold levels, then energy calibration is improved, but pixel variations caused by transient response differences are neglected leading to gain differences and spectral linearity issues
Solution Approach 1:
The patent applies preliminary action by adjusting the ASIC operating point before performing energy calibration. The method first compensates for ballistic deficit by setting appropriate feedback resistor values or feedback current source levels for each pixel, then proceeds with conventional energy calibration. This preliminary compensation ensures that transient response variations do not undermine the spectral linearity achieved through energy calibration.
Solution Approach 2:
The patent utilizes parameter changes by modifying the ASIC operating point parameters, specifically the feedback resistor value or feedback current source level, for each pixel. By iteratively adjusting these parameters during a calibration phase, the system compensates for pixel-specific transient response variations and ballistic deficit, thereby improving spectral linearity while maintaining energy calibration accuracy.
2Measurement precision
If the feedback resistor value is increased to compensate for ballistic deficit, then photo peak amplitude is improved, but the feedback loop collection time is extended affecting count rate
Solution Approach 1:
The patent applies local quality by individually adjusting the feedback resistor value or feedback current source level for each pixel based on its specific transient response characteristics. Rather than using a uniform setting across all pixels, the system optimizes each pixel's operating point parameters to achieve appropriate photo peak amplitudes while minimizing the impact on count rate, acknowledging that different pixels may require different local optimizations.
Solution Approach 2:
The patent employs partial action by iteratively adjusting the feedback resistor or feedback current source to achieve sufficient photo peak amplitude without excessively extending the feedback loop collection time. The calibration process seeks an optimal compromise point where photo peak amplitude is adequate for accurate energy measurement while the count rate remains acceptable for clinical applications.
3Reliability
If per-pixel ASIC operating point adjustment is implemented to adjust ballistic deficit, then spectral linearity is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by implementing an automated calibration procedure that iteratively adjusts each pixel's ASIC operating point parameters without requiring manual intervention. The system automatically measures photo peak amplitudes, compares them to reference values, and adjusts feedback resistor or feedback current source settings accordingly. This automation reduces the complexity burden despite the increased number of parameters being managed.
Solution Approach 2:
The patent utilizes feedback by implementing an iterative calibration process where the system continuously monitors photo peak amplitudes and adjusts ASIC operating point parameters based on the measured performance. The feedback loop compares actual photo peak amplitudes with target values and modifies feedback resistor or feedback current source settings to minimize deviations, thereby achieving spectral linearity through closed-loop control.
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 equalizes ballistic deficit across pixels, improving spectral linearity and energy resolution by ensuring that each pixel operates with a predefined expected value, thereby enhancing the performance and accuracy of photon-counting systems.
Implementation Method 1
a radiation sensitive sensor (14) of the pixel detects photons emitted by a radiation source (2) and generates a corresponding electrical signal
Data Source
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Figure 2A
Figure 2B
AI summary
The present invention relates to a detection device (6) for detecting photons emitted by a radiation source (2) and capable of adjusting ballistic deficit. The detection device (6) comprises a pre-amplifying unit (11) (such as, e.g., a charge-sensitive amplifier), a shaping unit (60) comprising a feedback discharge unit (13, I) (such as, e.g., a feedback resistor or a feedback current source), and a feedback discharge control unit (50) coupled to the feedback discharge unit (13, I). The feedback discharge control unit (50) is adapted to, e.g., adjust a resistance of a feedback resistor (and/or to adjust the current value of the feedback current source) if an electrical pulse generated by the shaping unit (60) does not exceed at least one energy comparison value (X1, X2,..., XN). The feedback discharge control unit (50) is adapted to not adjust the parameter of the feedback discharge unit (13, I) if the electrical pulse exceeds the at least one energy comparison value (X1, X2,..., XN). By tuning the feedback resistor operating point (or the feedback current source operating point), the ballistic deficit can be adjusted to a predefined expected value.