X-ray Focus Position Correction Using Thermal Expansion Segmentation
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Solution Overview
Problem
The existing focus position estimation methods in X-ray CT apparatuses suffer from reduced prediction accuracy due to thermal expansion caused by X-ray irradiation, particularly when different portions of the X-ray tube and cooling characteristics change over time, leading to inaccuracies in determining the X-ray irradiation field and degrading image quality.
Innovation Solution
An X-ray imaging apparatus that includes an X-ray generation unit with distinct heat-induced change components, a detection unit for electrical signal conversion, a focus position detection mechanism, and a correction unit to estimate and adjust for focus position changes, ensuring accurate alignment of the X-ray irradiation region with the detection unit to maintain image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus position estimation uses last X-ray irradiation data, then prediction can be made, but prediction accuracy decreases due to thermal expansion from multiple heat sources with different temperature transmissions
Solution Approach 1:
The patent segments the thermal expansion problem by separating it into two distinct components: immediate thermal expansion from the X-ray tube and delayed thermal expansion from the gantry rotation unit. Each component is modeled and corrected independently using separate time constants, allowing accurate prediction of focus position changes despite multiple heat sources with different temperature transmission characteristics.
Solution Approach 2:
The patent performs preliminary characterization of thermal expansion behavior by measuring focus position changes at multiple time points after X-ray irradiation. This preliminary data collection enables the system to determine separate time constants for different thermal expansion components, which are then used for accurate real-time prediction and correction of focus position drift.
2Productivity
If X-ray irradiation range is not adjusted for thermal expansion, then imaging can proceed without delay, but image quality degrades due to focus position shifts
Solution Approach 1:
The patent implements a feedback mechanism where the estimated focus position change (calculated from thermal expansion models) is used to dynamically adjust the X-ray irradiation range. This closed-loop control ensures that the irradiation field remains accurately aligned with the detection elements despite thermal expansion, maintaining image quality without requiring imaging delays.
3Measurement precision
If multiple thermal expansion components are considered, then prediction accuracy can be maintained, but calculation complexity increases
Solution Approach 1:
The patent manages calculation complexity by using parameter separation - dividing the thermal expansion correction into distinct time constants (first time constant for immediate expansion, second time constant for delayed expansion). This parameterization allows the complex multi-component thermal behavior to be handled through systematic, modular calculations rather than requiring complex real-time simulations.
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 solution effectively eliminates and suppresses image quality degradation caused by focus shifts, maintaining accurate X-ray irradiation field determination without delaying imaging timing, even when thermal expansion occurs from multiple factors with different temperature transmissions.
Implementation Method 1
generates X-rays by accelerating thermal electrons, which are generated by the filament, with a high voltage
Implementation Method 2
some of the energy of the thermal electrons is converted into X-rays
Implementation Method 3
the temperature of the rotary shaft that supports the X-ray target is increased and this causes expansion and contraction (hereinafter, referred to as thermal expansion). As a result, the focus position changes
Implementation Method 4
the generated heat is directed to the outside by radiation or a cooler, the temperature of the rotary shaft of the X-ray target or the like falls
Data Source
AI summary
An X-ray imaging apparatus including: X-ray generation means that irradiates X-rays from the focus and that has a first portion changing so as to have a first change component and a second portion changing so as to have a second change component, which is different from the first change component; focus position detection means that detects a focus position when the X-rays are irradiated; focus position change amount estimation means that estimates the amount of change in the focus position at an arbitrary point of time with respect to the reference position of the focus using a first amount of change, which changes so as to have the first change component, and a second amount of change, which changes so as to have the second change component; and correction means that corrects the positions of the irradiation region of the X-rays so as to cancel the amount of change in the focus position estimated by the focus position change amount estimation means.