CT High-Voltage Switching for Constant Dual-Energy Separation
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Solution Overview
Problem
High voltage generators in CT imaging systems face challenges in maintaining consistent energy separation between high-kV and low-kV levels during dual energy scans, especially when tube current modulation is used, leading to non-ideal waveforms and inconsistent image reconstruction due to varying fall times caused by HV capacitance discharge.
Innovation Solution
A control system is implemented to activate the high voltage generator during fall transitions, supplying an equalization current to maintain a constant fall time between energy levels, ensuring equal energy distribution and consistent image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If tube current modulation is used during dual energy scan, then X-ray exposure can be adjusted for different parts of the body, but fall time between high-kV and low-kV becomes inconsistent creating disproportionate energy separation
Solution Approach 1:
The system measures the actual fall time between high-kV and low-kV transitions and uses this feedback to calculate and apply a correction current to the HV capacitance discharge, ensuring consistent energy separation despite tube current modulation
Solution Approach 2:
The system dynamically adjusts the discharge current parameter of the HV capacitance based on the measured fall time and tube current conditions, changing the electrical parameters to maintain constant energy separation across varying exposure conditions
2Speed
If HV capacitance discharge is used for voltage transition, then rapid switching between high-kV and low-kV is achieved, but fall time varies with tube current creating non-ideal waveforms
Solution Approach 1:
The system continuously monitors the fall time of voltage transitions and uses this information to adjust the equalization current applied during subsequent transitions, maintaining consistent fall times despite variations in tube current
Solution Approach 2:
An equalization current is introduced as an intermediary element that modifies the HV capacitance discharge process, acting as a mediator between the rapid switching requirement and the consistency requirement by controlling the discharge rate
3Reliability
If calibration is performed at different temperatures, then environmental conditions are accounted for, but HV capacitance variation with temperature still creates inconsistent fall times
Solution Approach 1:
The system measures the actual fall time under current environmental conditions and adjusts the equalization current accordingly, providing real-time compensation for temperature-induced HV capacitance variations without requiring recalibration
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 ensures substantially equal energy separation between high-kV and low-kV levels, improving the effectiveness of CT image reconstruction and maintaining consistency under varying environmental conditions.
Implementation Method 1
a high voltage generator switches between 'low-kV' and 'high-kV' in order to emit low energy X-rays and high energy X-rays, respectively, from an X-ray tube
Implementation Method 2
the high voltage generator typically includes a high voltage (HV) capacitance which may include a filtering capacitor and/or parasitic capacitance
Implementation Method 3
The low energy and high energy X-rays emitted, after being attenuated by the patient or object, impinge upon an array of radiation detectors
Data Source
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AI summary
The present inventors have recognized that fall times between high-kV to low-kV levels (during a "dual energy" or "fast-kV" energy scan) are linked to the discharge of HV (high voltage) capacitance. In an embodiment of the invention, a high voltage generator may be activated during fall transitions from first to second energy levels in order to substantially maintain a predetermined fall transition time. Accordingly, substantially equal energy distributions between high-kV and low-kV levels may be achieved.