Iterative Tomographic Reconstruction with Fourier Filtering
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Solution Overview
Problem
Conventional tomographic imaging techniques face limitations in achieving rapid convergence and high-quality reconstruction, particularly in noise sensitivity and computational efficiency, especially in high-resolution nano CT applications.
Innovation Solution
An iterative reconstruction method employing Back Projection followed by mathematical filtering in Fourier space, with optional multi-grid processing, to accelerate convergence and enhance image quality by manipulating frequency spectra and optimizing filter forms at each iteration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional tomographic imaging techniques are used, then the imaging process can be completed, but the reconstruction process is slow and computationally inefficient
Solution Approach 1:
The patent divides the reconstruction process into multiple iterative steps, where each iteration performs a simplified reconstruction followed by filtering operations. This segmentation allows the complex reconstruction to be broken down into manageable computational tasks that can be processed progressively, improving overall speed while maintaining image quality.
Solution Approach 2:
The patent applies filtering operations in Fourier space during intermediate iterations to pre-condition the data before the final reconstruction. This preliminary processing of frequency components accelerates convergence by removing high-frequency noise and enhancing structural information early in the process, reducing the computational burden of subsequent iterations.
2Measurement precision
If conventional reconstruction methods are used, then the imaging can be performed, but the image quality is degraded due to noise sensitivity
Solution Approach 1:
The patent introduces filtering operations as intermediary steps between the back-projection and the final reconstruction. These filters act as mediators that process the frequency components of the intermediate images, suppressing noise while preserving essential structural information. The filters operate in Fourier space to selectively enhance or attenuate specific frequency bands, improving image quality without amplifying noise.
Solution Approach 2:
The patent dynamically adjusts filtering parameters during iterative reconstruction, adapting the filter characteristics to the current state of the reconstruction. By changing filter parameters such as cutoff frequencies and smoothing strengths based on iteration number and image content, the method optimizes noise suppression while maintaining sharpness of structural features throughout the reconstruction process.
3Productivity
If iterative reconstruction with filtering is applied, then convergence is accelerated and image quality is improved, but the computational complexity increases
Solution Approach 1:
The patent employs periodic filtering operations at regular intervals during the iterative reconstruction process. Rather than applying complex filtering at every iteration, the method uses periodic filtering at strategically selected steps, maintaining convergence acceleration while reducing overall computational complexity. The periodic application of filters creates a rhythm of processing that balances image quality improvement with computational efficiency.
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 significantly accelerates the reconstruction process while improving image quality by sharpening back-projected imagery and reducing noise, with the potential for substantial computational efficiency gains through progressive resolution refinement.
Implementation Method 1
a source, for producing a beam of radiation that can be directed at the specimen... the employed radiation will generally comprise X-rays
Implementation Method 2
a detector, for detecting a flux of radiation transmitted through the specimen from the source
Implementation Method 3
the CPM's charged-particle beam is used to irradiate a metal target, causing production of the Bremsstrahlung X-rays used to perform the desired tomography
Data Source
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AI summary
A method of investigating a specimen (S) using a tomographic imaging apparatus comprising: - A specimen holder, for holding the specimen; - A source (Sx), for producing a beam (B) of radiation that can be directed at the specimen (S); - A detector (D), for detecting a flux of radiation transmitted through the specimen (S) from the source (Sx); - A stage apparatus (A), for producing relative motion of the source (Sx) with respect to the specimen (S), so as to allow the source (Sx) and detector (D) to image the specimen (S) along a series of different viewing axes (Vi); - A processing apparatus, for performing a mathematical reconstruction step whereby output from the detector is compiled into a tomographic image of at least part of the specimen (S), wherein said reconstruction step is performed in multiple iterations, which comprise the following steps: (i) Using a Back Projection technique to produce an initial tomogram from a set of initial images; (ii) Subjecting said initial tomogram to a mathematical filtering operation, thereby producing an adjusted tomogram; (iii) Using a Forward Projection technique on said adjusted tomogram to dissociate it into a set of calculated images; (iv) Repeating steps (i)-(iii) until said calculated images satisfy an acceptance criterion. It is also provided a scanning electron microscope (1) including an in-situ computerised tomography (CT) module (7'') for performing CT inspection in-situ inside the chamber of the microscope (1).