X-ray CT Image Uniformity via Row-Specific Gain Adjustment
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Solution Overview
Problem
Conventional X-ray CT apparatuses with multi-column detectors or two-dimensional area detectors face challenges in achieving uniformity of tomographic images due to differences in detector characteristics across rows, leading to issues with exposure and CT value conversion, especially at increased cone angles.
Innovation Solution
The method normalizes the data range of projection data from each row and adjusts CT value conversion parameters based on the contribution rate of each detector row to ensure accurate CT value conversion, accounting for differences in detector quality and sensitivity across rows, and considers the three-dimensional position of pixels within the cone beam for precise CT value adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single row of CT value conversion parameters is used for three-dimensional back projection, then the processing is simplified, but the uniformity of tomographic image in z-axis deteriorates due to differences in detector characteristics across rows
Solution Approach 1:
The patent divides the CT value conversion process into row-specific segments, applying individual conversion parameters to each row of projection data before three-dimensional back projection. This segmentation allows each row with different detector characteristics to be processed independently, ensuring uniform tomographic image quality in the z-axis while maintaining manageable processing complexity through systematic parameter application.
2Area of stationary object
If the cone angle of X-ray cone beam is increased, then the coverage area is improved, but the exposure to unused X-ray aggravates
Solution Approach 1:
The patent applies local quality correction by determining contribution rates for each row of projection data based on the specific geometric relationship between that row and the object being imaged. This allows the system to account for varying exposure conditions across different rows caused by increased cone angle, adjusting CT values locally to compensate for unused X-ray exposure and maintain image quality throughout the coverage area.
3Device complexity
If CT value conversion is performed after three-dimensional back projection, then the reconstruction process is simplified, but the accuracy of CT value conversion deteriorates due to dispersion in data range of projection data
Solution Approach 1:
The patent performs preliminary CT value conversion on each row of projection data before three-dimensional back projection by determining row-specific contribution rates and applying appropriate conversion parameters. This preliminary action corrects for dispersion in data range early in the process, ensuring accurate CT values are maintained throughout the reconstruction while keeping the overall process manageable through systematic parameter determination.
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 uniform CT value conversion across the z-axis in X-ray CT imaging, improving image quality and reducing artifacts by accounting for the unique characteristics of each detector row, thereby achieving consistent and accurate tomographic images in axial, cinescan, or helical scans.
Implementation Method 1
an X-ray data acquisition means for acquiring X-ray projection data by revolving an X-ray generator and a two-dimensional X-ray area detector... for detecting X-ray in opposition, around a rotation center therebetween, and by transmitting through an object placed therebetween
Data Source
AI summary
The present invention provides the adjustment of CT value which is the pixel value of a tomographic image in the conventional scan (axial scan) or cinescan or helical scan by an X-ray CT apparatus incorporating a multi column X-ray detector or a two-dimensional X-ray detector of matrix arrangement represented by a flat panel X-ray detector. The gain and bias of the projection data of each row are adjusted prior to the three-dimensional back projection or prior to the reconstruction function convolution. Alternatively, the gain and bias are adjusted after determining the gain and bias value to adjust the CT value by taking into account the contribution rate of each row to the tomographic image after the three-dimensional back projection. Alternatively, the gain and bias are adjusted after determining the gain and bias value to adjust CT value by taking into account the contribution rate of each row to the tomographic image relying on the position of each row in z direction in case of axial scan after three-dimensional back projection.