Reference Detector Normalization via Generator Feedback
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Solution Overview
Problem
Existing CT systems face challenges in maintaining detector calibration due to radiation damage and aging, particularly in reference detectors located outside the field-of-view, which experience increased radiation doses and accelerated aging.
Innovation Solution
A method is introduced where x-rays are generated at a given high-voltage towards a subset of detector pixels without an object, measuring their output and determining a calibration factor based on the generator feedback current, using centermost detector modules for stability and reduced radiation exposure, to normalize projection data and update calibration factors periodically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reference detector is located outside the field-of-view to avoid blockage from the patient, then the reference detector provides convenient calibration data, but the reference detector experiences increased radiation dose and accelerated aging
Solution Approach 1:
The patent uses the generator feedback current as a proxy or copy of the reference detector signal. Instead of physically placing a reference detector outside the FOV (which would be damaged), the system copies the essential calibration information from the generator's current measurement, which is not subject to radiation damage.
Solution Approach 2:
The generator feedback current acts as an intermediary that provides the calibration reference information without being exposed to the harmful radiation environment. The mediator (feedback current) transfers the necessary calibration data from the x-ray generation process to the reconstruction system without suffering the adverse effects that would affect a physical detector placed in the high-radiation zone.
2Measurement precision
If a reference detector is placed outside the field-of-view to measure unattenuated x-rays, then calibration can be performed without patient blockage, but the detector is subject to accelerated aging and radiation damage
Solution Approach 1:
The patent replaces the mechanical/physical reference detector system with an electrical measurement system (generator feedback current). Instead of using a physical detector that would be damaged by radiation, the system uses electrical current measurements from the generator, which are not subject to radiation damage while still providing the necessary calibration information about unattenuated x-ray intensity.
Solution Approach 2:
The feedback current serves as a copy of the reference signal that would otherwise be obtained from a damaged detector. It replicates the essential calibration information (unattenuated x-ray intensity proportional to mAs) without requiring a physical detector in the harmful radiation environment.
3Manufacturing precision
If detector calibration is performed using traditional reference detectors, then calibration factors can be determined, but operational costs increase and image quality may degrade due to radiation damage to reference detectors
Solution Approach 1:
The system uses its own existing components (the generator's feedback current measurement capability) to perform the calibration function. Instead of requiring a separate reference detector subsystem that incurs additional costs and maintenance, the system serves its own calibration needs through the feedback current already being measured during normal operation.
Solution Approach 2:
The generator feedback current serves multiple functions: it controls the x-ray tube operation and simultaneously provides the reference signal for calibration. This multi-functionality eliminates the need for dedicated reference detector hardware, reducing operational costs while maintaining calibration accuracy.
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 stabilizes detector output, reduces radiation damage, and maintains accurate calibration without the need for separate reference detectors, enhancing image quality and reducing operational costs by utilizing the most stable and linear detector modules within the CT system.
Implementation Method 1
a high-voltage generator, an x-ray tube positioned on the gantry to generate x-rays
Implementation Method 2
a pixelated detector positioned on the gantry to receive the x-rays... the detector typically includes a photodiode-scintillator array of pixelated elements that convert the attenuated x-rays into photons within the scintillator, and then to electrical signals within the photodiode
Implementation Method 3
a calibration factor is determined based on the measured output and based on a generator feedback current measured during the total integration time
Data Source
AI summary
A CT system includes a rotatable gantry having an opening to receive an object to be scanned, a high-voltage generator, an x-ray tube positioned on the gantry to generate x-rays through the opening, and a pixelated detector positioned on the gantry to receive the x-rays. The system includes a computer programmed to cause the x-ray tube to generate x-rays, at a given high-voltage generator voltage (kV), toward a sub-set of detector pixels when no object is present within the opening, measure an output of the sub-set of detector pixels for a given number of views during the x-ray generation and for a total integration time, and determine a calibration factor based on the measured output and based on a generator feedback current measured during the total integration time.