X-ray CT Tube Voltage Modulation for Photon Energy Distribution Flattening
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Solution Overview
Problem
Photon counting X-ray CT systems face challenges in obtaining sufficient photons for diagnosis at low energy regions while avoiding excess exposure in high energy regions due to the large deviation in photon energy distribution, which requires widening the energy band and flattening the photon energy distribution.
Innovation Solution
An X-ray CT apparatus that includes an X-ray tube, detector, data acquisition system, tube voltage generator, and grid controller, where the tube voltage is changed in a predetermined cycle to synchronize with the rotation of the gantry, and the grid voltage is controlled to adjust the tube current, thereby flattening the photon energy distribution and maintaining a consistent dose rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the tube voltage is increased to obtain sufficient photons for diagnosis in low energy regions, then the photon count in diagnostic energy bands improves, but excess exposure occurs in high energy regions with large dose
Solution Approach 1:
The patent applies periodic action by changing the tube voltage in a predetermined cycle that synchronizes with the gantry rotation. The tube voltage is varied between a first voltage (producing photons with first energy distribution) and a second voltage (producing photons with second energy distribution) during the rotation period. This periodic voltage modulation allows the system to collect photons across different energy distributions over time, effectively widening the overall energy band and flattening the photon energy distribution without causing excess exposure in any single energy region.
2Object-affected harmful factors
If the tube voltage is decreased to reduce dose in high energy regions, then excess exposure is prevented, but insufficient photons are obtained in low energy regions for adequate diagnosis
Solution Approach 1:
The periodic action principle resolves this contradiction by alternating the tube voltage between higher and lower values during the gantry rotation cycle. When the tube voltage is set to the first voltage, sufficient photons are generated for low energy diagnostic regions. When the tube voltage is set to the second voltage, the dose in high energy regions is reduced. Over the complete rotation period, both requirements are satisfied through temporal separation of the voltage settings.
3Loss of energy
If the photon energy distribution is narrowed to concentrate photons in specific energy bands, then the dose efficiency improves, but the energy band coverage is insufficient for comprehensive diagnosis
Solution Approach 1:
The patent utilizes periodic action to achieve both dose efficiency and broad energy band coverage. By cycling the tube voltage between multiple discrete voltage levels during the gantry rotation, the system sequentially generates photons with different energy distributions. The temporal integration of these periodically varied photon streams results in a combined energy distribution that is both wide-ranging (providing comprehensive diagnostic coverage) and efficiently distributed (maintaining good dose efficiency across the entire energy spectrum).
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
The solution effectively widens the photon energy distribution, reduces X-ray dose variability, and prevents unnecessary exposure by synchronizing tube voltage changes with gantry rotation and adjusting tube current in response to voltage changes, ensuring a consistent X-ray intensity across different energy bands.
Implementation Method 1
X-rays radiated from an X-ray tube include characteristic X-rays and braking X-rays. Characteristic X-rays have an energy distribution which depends on the target material, while braking X-rays have a continuous energy distribution.
Implementation Method 2
X-rays radiated from an X-ray tube include characteristic X-rays and braking X-rays. Characteristic X-rays have an energy distribution which depends on the target material
Implementation Method 3
photon counting CTs using detectors of the photon counting method have been developed. The photon counting CTs are different from conventional X-ray CT apparatuses using integral-mode detectors in that the former classify and count the energy of X-rays (photons) incident on the detectors
Data Source
AI summary
X-ray CT apparatus is provided in which the photon energy distribution of X-rays to be radiated is flattened. X-ray CT apparatus includes an X-ray tube, a detector, a data acquisition system, a tube voltage generator, and a grid controller. The X-ray tube radiates X-rays onto a subject. The detector includes multiple detection elements for detecting photons forming the X-rays. The data acquisition system counts the number of the detected photons to acquire projection data based on the counted photons. The tube voltage generator applies the tube voltage to the X-ray tube while changing the tube voltage of the X-ray tube in a predetermined cycle. A tube current controller decreases the tube current upon an increase in the tube voltage, and increases the tube current upon a decrease in the tube voltage. Thus, the photon energy distribution of the X-rays radiated from the X-ray tube is flattened.