Converter Gain and Offset Estimation in X-ray Detectors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for estimating the gain and offset of converters in photon-counting detectors for x-ray imaging systems are inefficient and require individual calibration of each channel, leading to artifacts and reduced detection efficiency due to un-calibrated energy thresholds.
Innovation Solution
A method that selects a reference converter and a target converter, assigns different digital settings to generate reference and target voltages, and determines the gain and offset by measuring photon counts, allowing for relative calibration without a model or identifiable features in the x-ray spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual calibration of each channel is performed using conventional methods, then measurement precision of gain and offset is improved, but device complexity and calibration time increase significantly
Solution Approach 1:
The patent merges the calibration processes of multiple converters into a single unified procedure. By selecting one converter as reference and comparing other converters against it, the system performs relative calibration that simultaneously determines gain and offset for multiple channels in one process, rather than calibrating each channel separately through complex individual procedures
Solution Approach 2:
The calibration system uses the detectors themselves to perform the calibration measurements. The detectors measure photons generated by the converters, and these self-measurements provide the data needed to determine relative gain and offset, eliminating the need for external calibration equipment and complex external measurement procedures
2Measurement precision
If conventional calibration methods are used, then gain and offset can be determined, but ring artifacts appear in reconstructed images due to un-calibrated energy thresholds
Solution Approach 1:
The system establishes feedback relationships between converters by comparing their outputs against a reference converter. The measured photon counts from detectors provide feedback data that is used to calculate relative gain and offset values, which are then applied to correct the energy thresholds of all converters, ensuring consistent threshold positioning across channels and eliminating the conditions that cause ring artifacts
3Productivity
If the lowest threshold is placed lower to increase detection efficiency, then more photons can be counted, but noise counts increase and degrade the signal
Solution Approach 1:
The patent replaces mechanical trial-and-error threshold positioning with a physics-based calculation approach. By using the relative gain and offset values to precisely calculate the optimal threshold position in keV, the system can determine the exact threshold setting that maximizes photon detection while maintaining an appropriate signal-to-noise ratio, rather than relying on arbitrary or conservative threshold choices
4Measurement precision
If mono-energetic x-ray source or synchrotron beam is used for calibration, then accurate gain and offset can be obtained, but the method becomes impractical for clinical settings
Solution Approach 1:
The patent replaces expensive, complex calibration infrastructure (mono-energetic x-ray sources, synchrotrons) with simple, readily available components already present in clinical CT scanners (standard x-ray tube, detectors, converters). The method uses the existing system components to generate calibration data, making the calibration process practical and implementable in routine clinical settings without requiring specialized facilities
Solution Approach 2:
The patent introduces detectors as intermediaries between the converters and the calibration measurement process. The detectors measure photons generated by the converters, providing an indirect but sufficient means to determine relative gain and offset values without requiring direct access to mono-energetic x-ray beams or synchrotron facilities
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 provides accurate, fast, and efficient relative calibration of energy thresholds, improving image reconstruction and detection efficiency by eliminating ring artifacts and noise-related issues.
Implementation Method 1
The DAC converts a digital setting sent by a controller to an analog voltage with respect to which the heights of the photon pulses can be compared
Implementation Method 2
a photon counting x-ray detector determines the energy of a photon by comparing the height of the electric pulse generated by a photon interaction in the detector material to a set of comparator voltages
Implementation Method 3
Since some materials absorb a larger fraction of the x-rays than others, an image is formed of the subject or object
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Disclosed is methods, systems, apparatuses and computer programs for estimating a measure of the gain and offset of a converter (200). The converter is used for generating, based on digital settings, reference voltages to be used as thresholds by a comparator (10, 20) in a photon-counting detector in an x-ray imaging system. The method comprises the steps of selecting (S1 ) a first converter to act as a reference converter (100) and a second converter to act as a target converter (200). The method also comprises the step of assigning (S2) different digital settings to the reference converter (100), in order to generate at least two different reference voltages (R) to be used as thresholds by a comparator associated with the reference converter (100). The method also comprises the step of obtaining (S3), based on photon count measurements, information representing the number of photons registered in a photon counter associated with a comparator (20) whose reference voltage is generated by the target converter (200). Based on the obtained information representing the number of photons and the at least two digital settings, the method determines an estimate of the gain and offset of the target converter relative the reference converter.