X-Ray CT Tube-Current Control for Synchronized Voltage Switching
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Solution Overview
Problem
In X-ray CT apparatuses using spectral scan methods, the tube-current feedback-control becomes unstable due to asynchronous switching of tube voltage, leading to inconsistent tube current, which affects image quality and causes unnecessary radiation exposure.
Innovation Solution
An X-ray CT apparatus with a filament control circuit that adjusts filament current based on characteristic data, synchronizing tube voltage switching and tube current modulation to stabilize the tube current during high and low voltage periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If tube-current feedback-control is performed during both high and low tube-voltage periods, then tube current can be controlled continuously, but the tube current becomes unstable due to asynchronous switching of tube voltage and tube current command signal
Solution Approach 1:
The control period is segmented into high tube-voltage periods and low tube-voltage periods. Tube-current feedback-control is performed only during high tube-voltage periods, while during low tube-voltage periods, the filament current value commanded at the end of the high tube-voltage period is maintained. This segmentation resolves the instability caused by asynchronous switching by ensuring feedback control occurs only when tube voltage is stable and high.
2Reliability
If tube-current feedback-control is performed only during high tube-voltage period, then tube current stability is improved, but tube current modulation cannot be effectively performed during low tube-voltage period
Solution Approach 1:
The filament current value is predetermined and stored in memory before the low tube-voltage period begins. During the low tube-voltage period, this pre-determined filament current value is maintained without changing, ensuring that when the high tube-voltage period resumes, the tube current can quickly return to the command value. This preliminary preparation enables effective tube current modulation while maintaining stability.
3Speed
If tube voltage switches to low tube-voltage before tube current reaches command value, then scanning speed is maintained, but tube current becomes unstable and affects image quality
Solution Approach 1:
The filament current value is pre-determined and stored in memory before the low tube-voltage period begins. During the low tube-voltage period, this pre-determined filament current value is maintained without changing, ensuring that when the high tube-voltage period resumes, the tube current can quickly return to the command value. This preliminary preparation enables effective tube current modulation while maintaining stability.
4Reliability
If filament current value is maintained during low tube-voltage period, then tube current stability is improved, but tube current decreases due to lowered tube voltage
Solution Approach 1:
The filament current value is changed based on the tube voltage level. During high tube-voltage periods, feedback control adjusts the filament current to maintain stable tube current. During low tube-voltage periods, a predetermined filament current value is maintained that corresponds to the high tube-voltage conditions, compensating for the reduced tube voltage and maintaining consistent tube current magnitude.
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
Stabilizes tube current, ensuring consistent image quality and reducing unnecessary radiation exposure by synchronizing tube voltage and current modulation.
Implementation Method 1
a spectral scan method is known as a technique in which image data are acquired by alternately switching a tube voltage to be applied to an X-ray tube between a high tube-voltage and a low tube-voltage during rotation of the X-ray tube inside a gantry
Data Source
AI summary
In one embodiment, an X-ray CT apparatus can perform a tube-current modulation scan. The X-ray CT apparatus includes an X-ray tube, a memory, an X-ray tube power supply, processing circuitry, and a filament control circuit. The memory stores, for each tube voltage to be applied to the X-ray tube, characteristic data in which a filament current flowing through a filament in the X-ray tube and the tube current are associated with each other. The X-ray tube power supply applies the tube voltage to the X-ray tube by periodically switching the tube voltage between a first value and a second value lower than the first value. The processing circuitry updates the command value of the tube current at a predetermined timing according to switching of the tube voltage. The filament control circuit specifies a filament-current command-value corresponding to the command value of the tube current based on the characteristic data.