X-Ray Calibration Phantom Layout for Accurate Material Decomposition
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Solution Overview
Problem
Existing x-ray imaging systems, particularly Photon-Counting Spectral Computed Tomography (PCSCT) systems, face challenges in accurately performing material basis decomposition due to the lack of effective calibration methods that can generate a mapping between different x-ray spectra and detector outputs, and conventional calibration phantoms are cumbersome and prone to errors from partial volume effects and uneven scatter profiles.
Innovation Solution
A novel calibration phantom comprising geometric objects such as cylinders of different materials and sizes is used, allowing for controlled movement and precise determination of path lengths, enabling accurate material basis decomposition by generating a mapping between path lengths and detector responses without requiring complex positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a step-wedge phantom with multiple material combinations is used to sample a large-enough part of the material space, then calibration accuracy is improved, but the size, weight, and manufacturing cost of the phantom increase significantly
Solution Approach 1:
The calibration phantom is divided into multiple separate cylindrical objects of different materials (first material, second material, third material) with different attenuation coefficients. These segmented cylindrical objects are arranged in different combinations and positions within the phantom holder, allowing comprehensive material space sampling without requiring a single large monolithic structure. This segmentation enables accurate calibration while keeping individual phantom components manageable in size and weight.
2Measurement precision
If a step-wedge phantom with fine step sizes is used to avoid partial volume effects, then measurement precision is improved, but the required phantom length in the z-direction becomes very large
Solution Approach 1:
Instead of using fine step sizes along the z-direction (one dimension), the invention distributes multiple cylindrical objects of different materials in radial and angular positions around the x-ray beam path. This transforms the problem from a one-dimensional step-wedge approach to a multi-dimensional arrangement where material combinations are achieved through spatial distribution in multiple dimensions (radial distance, angular position, depth), thereby avoiding the need for excessive phantom length while maintaining measurement precision.
3Quantity of substance
If a conventional step-wedge phantom is used, then material space sampling is achieved, but scatter profiles become uneven and calibration accuracy deteriorates
Solution Approach 1:
The phantom is designed with cylindrical objects of different materials positioned at specific locations to create locally optimized scatter profiles. By strategically placing cylindrical objects made of different materials (with different attenuation coefficients) at different radial distances and angular positions, the phantom produces more uniform scatter distributions across the detector compared to conventional step-wedge designs. This local quality optimization ensures that each region of the phantom contributes appropriately to the overall scatter profile, improving calibration accuracy while maintaining comprehensive material space sampling.
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
The novel phantom design allows for efficient, artefact-free material basis decomposition and image reconstruction by minimizing scatter bias and overcoming the limitations of conventional phantoms, facilitating improved calibration of PCSCT systems.
Implementation Method 1
an x-ray imaging system having an x-ray source and an x-ray detector
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
There is provided a calibration phantom for an x-ray imaging system having an x-ray source and an x-ray detector. The calibration phantom (5) comprises a combination of geometric objects (1, 2, 3) of at least three different types and/or compositions including: -a first object (1) located in the middle, comprising a first material; -a plurality of second objects (2) arranged around the periphery of the first object, at least a subset of the second objects comprising a second material different than the first material, wherein the first object is relatively larger than the second objects; -a plurality of third objects (3) arranged around the periphery of the first object and/or around the periphery of at least a subset of the second objects, at least a subset of the third objects comprising a third material different than the first material and the second material, wherein the third objects are relatively smaller than the second objects.