Variable Pitch Spiral CT Image Reconstruction
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Solution Overview
Problem
Current computed tomography (CT) imaging methods face challenges in efficiently reconstructing images with variable pitch during spiral scanning, leading to artifacts and suboptimal data utilization, especially when the examination object is moved at different speeds relative to the x-ray detector unit.
Innovation Solution
A method that involves spiral scanning with a variable pitch, filtering output data, and weighted back projection, where the non-constant pitch is accounted for using mathematical approximations to accurately reconstruct images, allowing for faster and more effective artifact-free imaging by considering the actual position and pitch of the spiral during back projection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If variable pitch spiral scanning is used to improve scanning efficiency and reduce recording time, then productivity increases, but image reconstruction accuracy deteriorates due to artifacts and suboptimal data utilization
Solution Approach 1:
The patent applies preliminary action by pre-calculating correction factors and weighting functions based on the variable pitch profile before image reconstruction. The system computes the actual table position as a function of projection angle in advance, determines the appropriate weighting for each projection data point, and prepares correction algorithms that account for the non-uniform sampling density. This preliminary preparation enables accurate reconstruction despite the variable pitch scanning, resolving the contradiction between scanning efficiency and reconstruction accuracy.
2Adaptability or versatility
If the examination object is moved at different speeds during spiral scanning to optimize contrast medium recording, then adaptability improves, but measurement precision deteriorates due to pitch variations
Solution Approach 1:
The patent implements dynamics by making the pitch parameter variable rather than fixed. The table feed speed is dynamically adjusted during scanning to optimize contrast medium visualization in different anatomical regions. The system continuously adapts the pitch based on the imaging requirements, allowing faster scanning in less critical areas and slower scanning where contrast detail is paramount. This dynamic adaptation is compensated through the weighting function that accounts for the instantaneous pitch value at each projection angle.
Solution Approach 2:
The patent applies parameter changes by modifying the pitch parameter throughout the scanning process. Different pitch values are used at different stages or regions of the scan to optimize image quality for specific anatomical structures or contrast phases. The system changes the table feed speed parameter dynamically, and the reconstruction algorithm compensates for these parameter changes using the recorded pitch profile and appropriate weighting functions, thereby maintaining measurement precision despite parameter variations.
3Device complexity
If conventional back projection methods are used for variable pitch scanning, then device complexity remains low, but image quality deteriorates due to artifacts
Solution Approach 1:
The patent introduces an intermediary element in the form of a weighting function that mediates between the simple back projection operation and the variable pitch scanning requirements. Rather than fundamentally changing the back projection algorithm, the system applies a weighting factor to each projection data point based on the local pitch value and sampling density. This intermediary weighting step corrects for the variable pitch effects while maintaining the computational simplicity of back projection, thus improving image quality without significantly increasing device complexity.
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 enables faster, more effective, and artifact-free image reconstruction in spiral CT imaging, allowing for variable pitch during data acquisition, improving image quality by accurately accounting for the spiral profile and pitch variations, thus enhancing the visualization of examination objects with varying levels of detail.
Implementation Method 1
the examination object is penetrated—starting from an x-ray source (x-ray tube, focus)—by a, for example, conical or pyramidal beam that is captured, more or less attenuated after penetration by a detector array of planar design. The measured values are filtered in a suitable way and back projected, as a result of which at least one slice image is obtained that, owing to the different absorption values of the respective x-rays, represents the anatomy in this slice region by different grey scale values.
Data Source
AI summary
An imaging method is disclosed for variable pitch spiral CT. In at least one embodiment, the method includes spiral scanning of an examination object lying on a patient table, with the aid of a beam emanating from at least one focus, and the aid of a detector arrangement of planar design lying opposite the focus, the detector arrangement supplying output data that represent the attenuation of the beams during passage through the examination object; filtering the output data; weighted back projection of the filtered output data; and visualizing a layer or a volume on a display unit on the basis of the back projected output data. In at least one embodiment, a non constant pitch of the spiral scanning is taken into account computationally during the back projection. In at least one embodiment, a CT machine is disclosed for carrying out the above named method.