X-ray Tube Focal Spot Deflection for CT Cone Beam Artifacts
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Solution Overview
Problem
Computed tomography (CT) imaging systems face incomplete projection sampling due to the cone beam effect and longitudinal truncation, leading to image artifacts, especially when imaging larger regions, as exact reconstruction is not possible except at the center plane.
Innovation Solution
An x-ray tube with multiple focal spots along the z-direction is used, where the focal spots are deflected and switched on/off alternately to irradiate each voxel from different cone angles at the same projection view angle, reducing cone beam and truncation artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single focal spot is used in step-and-shoot mode CT imaging, then the device complexity is reduced, but cone beam and longitudinal truncation artifacts occur leading to incomplete reconstruction
Solution Approach 1:
The single focal spot is segmented into multiple focal spots (at least two) spaced along the z-direction. Each focal spot independently irradiates the imaging volume from slightly different longitudinal positions, enabling complete coverage and eliminating truncation artifacts while maintaining a relatively simple x-ray tube structure.
Solution Approach 2:
The invention adds the z-direction dimension to focal spot positioning by spacing multiple focal spots along the longitudinal axis. This dimensional expansion allows the x-ray beam to cover the entire imaging volume from multiple longitudinal perspectives, resolving the cone beam effect and enabling exact reconstruction throughout the volume.
2Manufacturing precision
If multiple focal spots spaced along the z-direction are used, then cone beam and truncation artifacts are reduced, but the device complexity increases
Solution Approach 1:
Multiple focal spots are merged into a single x-ray tube structure rather than using separate tubes. The electron beam is deflected to strike different positions on the anode target, creating multiple focal spots that function as an integrated unit within one tube, thereby reducing overall system complexity.
Solution Approach 2:
The x-ray tube employs dynamic electron beam deflection to switch between multiple focal spots. The deflection mechanism allows the electron beam to be dynamically redirected to different target positions, enabling the tube to operate with multiple focal spots on demand without requiring multiple static tube structures.
3Manufacturing precision
If focal spots are switched on and off alternatively, then complete voxel irradiation from different cone angles is achieved, but the scanning time increases
Solution Approach 1:
The multiple focal spots are activated in periodic alternation during the scanning process. Each focal spot is turned on and off in sequence, creating a periodic irradiation pattern that ensures complete voxel coverage from different cone angles while maintaining a controlled scanning timeline.
Solution Approach 2:
The focal spot switching is designed to maintain continuous useful action throughout the scan. By carefully timing the alternation between focal spots and coordinating with the gantry rotation and table movement, the system ensures that irradiation of the imaging volume continues without interruption, minimizing additional scan time.
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 allows for reduced cone beam and truncation artifacts, enabling complete reconstruction of imaging volumes and improving image quality by ensuring all voxels are exposed to x-ray radiation, even for larger imaging regions.
Implementation Method 1
a cathode configured to emit electrons
Implementation Method 2
The emitted electrons are deflected onto the target surface
Implementation Method 3
an x-ray tube with multiple focal spots along the z-direction
Implementation Method 4
projection data acquired by rotating the gantry with the x-ray source and detector array about an object to be imaged
Data Source
AI summary
Methods and apparatus for x-ray imaging with focal spot deflection are provided. The apparatus includes an x-ray tube having a cathode configured to emit electrons and an anode having a target with a target surface defining a target angle. The emitted electrons are deflected onto the target surface with the target surface substantially aligned with a z-axis parallel to a gantry rotation axis.