X-ray Tube Current Profile Control via Preview Attenuation
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Solution Overview
Problem
Current automatic dose control systems for X-ray imaging fail to accurately account for patient attenuation variations and technical limitations of X-ray tubes, leading to sub-optimal X-ray dose delivery and potential overheating, especially when patients are not optimally positioned or move during scans.
Innovation Solution
A method involving a preview acquisition to determine three-dimensionally modulated X-ray attenuation, which allows for initial tube-current profile calculation and real-time adjustment within a defined tolerance band to prevent overheating and optimize patient dose, using a tube-current controller that includes an X-ray attenuation estimation unit, profile definition, and dose determination modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If real-time tube current control is implemented to achieve predefined image noise, then image quality is improved, but technical limitations such as tube inertia and overheating cannot be accounted for
Solution Approach 1:
The system performs a preview acquisition (topogram) before the actual CT scan to determine patient attenuation characteristics in advance. Based on this preliminary information, an initial tube current profile is calculated that accounts for patient-specific attenuation while considering tube thermal limitations. This preliminary action allows the system to plan the tube current modulation strategy before actual imaging, avoiding real-time control issues related to tube inertia and overheating.
Solution Approach 2:
The system dynamically adjusts the tube current profile during the CT scan based on the preliminary attenuation map. The tube current is modulated along the z-direction (longitudinal axis) according to patient attenuation characteristics determined from the preview acquisition. This dynamic adjustment maintains image quality while adapting to patient-specific anatomy and avoiding tube overheating by redistributing the dose temporally and spatially.
2Use of energy by moving object
If topograms are used to determine patient attenuation, then dose optimization is possible, but inaccuracies occur when patients are not optimally positioned or move during scans
Solution Approach 1:
A preview acquisition (topogram) is performed before the actual CT scan to capture patient attenuation characteristics. This preliminary measurement allows the system to calculate an initial tube current profile that is optimized for the patient's anatomy. The topogram is acquired when the patient is positioned on the table, and the resulting attenuation map is used to plan the tube current modulation for the subsequent scan.
Solution Approach 2:
The system uses the preview acquisition data as feedback to adjust and optimize the tube current profile for the actual CT scan. The attenuation characteristics measured during the preview are fed into the tube current calculation algorithm, which generates an optimized current profile that accounts for patient-specific attenuation. This feedback mechanism allows dose optimization based on actual patient anatomy while compensating for positioning variations.
3Measurement precision
If tube current is increased to ensure adequate image quality, then image quality is improved, but X-ray tube overheating occurs
Solution Approach 1:
The system dynamically modulates the tube current along the longitudinal axis during the CT scan based on patient attenuation characteristics. Instead of using a constant high current that would cause overheating, the current is adjusted in real-time according to the attenuating structures encountered at different z-positions. This dynamic adjustment maintains adequate image quality in high-attenuation regions while reducing current in low-attenuation regions, preventing tube overheating.
Solution Approach 2:
The tube current parameter is changed and modulated as a function of position along the patient's body and time during the scan. The system calculates an optimal current profile that varies the tube current magnitude based on patient attenuation characteristics determined from preview acquisition. This parameter modulation allows the system to use higher current only when and where necessary for image quality, while using lower current elsewhere to avoid overheating.
4Object-affected harmful factors
If tube current is reduced to minimize patient dose, then radiation exposure is reduced, but image quality deteriorates
Solution Approach 1:
The system applies local quality optimization by modulating the tube current according to patient attenuation characteristics at different positions along the longitudinal axis. High tube current is applied only in regions with high attenuation (e.g., thick body parts) where it is necessary for adequate image quality, while low tube current is used in regions with low attenuation where less dose is required. This localized approach minimizes overall patient dose while maintaining image quality where it matters most.
Solution Approach 2:
The tube current is dynamically adjusted during the scan based on patient-specific attenuation characteristics determined from preview acquisition. The system calculates an optimized current profile that varies the current magnitude along the z-direction to match patient anatomy. This dynamic modulation ensures adequate dose is delivered to high-attenuation regions for acceptable image quality while reducing dose to low-attenuation regions, achieving dose optimization without significant image quality deterioration.
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 enhances the accuracy of tube-current adjustments based on patient-specific attenuation, reducing overall patient dose and preventing X-ray tube overheating, thereby improving image quality while minimizing radiation exposure.
Implementation Method 1
an X-ray radiation source (8) for emitting X-ray radiation
Implementation Method 2
measuring an actual X-ray attenuation during acquisition of the at least one X-ray image
Data Source
AI summary
A method is described for controlling a tube current for acquiring at least one X-ray image. The method includes performing a preview acquisition of the region under examination; determining a three-dimensionally modulated X-ray attenuation of the region based upon the preview acquisition; determining initial tube-current profiles based upon the X-ray attenuation; defining a tolerance band for subsequent real-time modification of tube currents, a maximum permitted tube-current profile being determined for which an X-ray tube of the X-ray imaging apparatus does not overheat; determining an expected value and a maximum value of a potential patient dose based upon the initial tube-current profiles and the tolerance band; measuring an actual X-ray attenuation during acquisition of the at least one X-ray image; determining adjusted tube-current profiles based upon the actual X-ray attenuation and the initial tube-current profiles; and adjusting the tube current in accordance with the adjusted tube-current profiles determined.