Fast kV-switching CT pre-reconstruction decomposition
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Solution Overview
Problem
Current dual energy computed tomography (CT) systems face challenges in achieving accurate temporal and spatial registration of high and low energy data sets, leading to image quality issues such as noise and misregistration, and are not cost-effective due to the need for additional equipment like dual X-ray sources or specialized detectors.
Innovation Solution
A method of pre-reconstruction decomposition for fast kV-switching acquisition in dual energy CT, involving fast switching of the X-ray tube between high and low energy levels, acquiring dual energy data sets at a predetermined number of projections per rotation, and symmetrically matching these data sets to perform pre-reconstruction decomposition, generating dual energy computed tomography images without the need for additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fast kV-switching techniques are used to alternate voltages between projections, then dual energy data acquisition speed is improved, but temporal and spatial registration accuracy deteriorates leading to view misregistration
Solution Approach 1:
The patent applies preliminary action by performing decomposition in the data domain before image reconstruction. The dual energy decomposition is executed on the raw projection data while it is still in the data domain, prior to the reconstruction step. This preliminary decomposition allows the system to separate the high and low energy components before any misregistration artifacts can propagate into the final image, thereby maintaining both fast acquisition speeds and registration accuracy.
Solution Approach 2:
The patent introduces an intermediary processing step - the pre-reconstruction decomposition algorithm - that acts as a mediator between the fast kV-switching acquisition and the final image reconstruction. This intermediary decomposition process in the data domain corrects for temporal and spatial misregistration by separating the energy components before they can cause view misregistration artifacts in the reconstructed images.
2Measurement precision
If dual source CT scanners or sandwich detectors are used to achieve dual energy imaging, then energy separation is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies the copying principle by using a single X-ray source that alternates between high and low kV settings to create two separate energy data sets. Instead of requiring two physical X-ray sources (dual source CT) or complex sandwich detectors, the system creates copies of the imaging process at different energy levels using one source, thereby achieving dual energy separation without the associated complexity and cost of multiple sources or specialized detectors.
Solution Approach 2:
The patent demonstrates universality by making a single X-ray source perform multiple functions - it alternates between generating high energy X-rays and low energy X-rays. This single source multi-functionality replaces the need for separate dedicated high energy and low energy sources, thereby achieving dual energy imaging capability with simpler, more cost-effective equipment while maintaining proper energy separation.
3Measurement precision
If slow kV-switching with alternating rotations is used, then energy separation is improved, but temporal registration deteriorates by at least one rotation period
Solution Approach 1:
The patent applies preliminary action by performing the energy decomposition in the data domain before reconstruction. This preliminary decomposition of the alternating rotation data allows the system to properly associate high and low energy projections that were acquired at different times, correcting for the temporal delay that would otherwise cause misregistration. The decomposition happens before the temporal misalignment can propagate into the final image.
Solution Approach 2:
The patent replaces the mechanical synchronization approach (where slow kV-switching relies on precise mechanical timing between alternating rotations) with a data processing approach. Instead of mechanically ensuring temporal alignment, the system uses pre-reconstruction decomposition in the data domain to mathematically correct for the temporal offset, substituting mechanical precision requirements with computational correction.
Data Source
AI summary
Fast kV-switching is a dual energy acquisition technique in computed tomography (CT) in which alternating views correspond to the low and high tube voltages. Its high temporal resolution and its suitability to a variety of source trajectories make it an attractive option for dual energy data acquisition. Its disadvantages include a one-view misregistration between the data for high and low voltages, the potentially poor spectrum separation due to the more-like a sine wave rather than the desired square wave in fast kV-switching, and the higher noise in the low voltage data because of the technical difficulty in swinging the tube current to counter the loss of x-ray production efficiency and loss of penetration at lower tube voltages. Despite the disadvantages, symmetric view matching according to the current invention substantially improves streaks and other artifacts due to the view misregistration, sufficient spectrum separation even in a sinusoidal waveform swinging between 80 kV and 135 kV, and contrast-to-noise for the simulated imaging task maximized at monochromatic energy of 75 keV.