PCCT Phantom Calibration for Small-Value Projection Correction
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Solution Overview
Problem
Existing PCCT apparatuses face decreased correction accuracy of projection values due to pile-up effects in high X-ray doses, leading to deteriorated image quality, particularly in ranges where projection values are smaller.
Innovation Solution
A PCCT apparatus and control method that utilize a scanner with a photon counting detector and a controller to calculate a conversion expression for converting projection values into transmission lengths using a phantom with known material, shape, and size, disposed not to overlap the scanner's rotation center, to improve correction accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photon counting detector is used to detect X-ray photons, then detection capability is improved, but pile-up effects occur in high X-ray dose ranges causing decreased correction accuracy
Solution Approach 1:
The patent segments the correction process into multiple correction values corresponding to different projection value ranges. Instead of using a single correction function, the system divides the correction into multiple segments where each segment has its own correction value, allowing accurate correction across the entire range including high dose regions where pile-up effects occur.
Solution Approach 2:
The patent changes the correction approach by calculating multiple correction values based on different assumptions about the relationship between projection values and transmission lengths. By varying the correction parameters and selecting appropriate correction values for different projection value ranges, the system maintains accuracy across all X-ray dose levels.
2Reliability
If beam hardening correction is applied to improve image quality, then non-linearity is reduced, but correction accuracy decreases in ranges where projection values are smaller
Solution Approach 1:
The patent applies local quality by providing different correction values for different projection value ranges. Instead of using a uniform correction approach, the system tailors the correction to the specific characteristics of each range, with specialized correction values for small projection value ranges where accuracy was previously insufficient.
Solution Approach 2:
The patent introduces dynamics by making the correction value variable rather than fixed. The system dynamically selects appropriate correction values based on the projection value range, allowing the correction to adapt to different measurement conditions and maintain accuracy across varying X-ray doses.
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
Enhances correction accuracy of projection values even in smaller ranges, thereby improving the image quality of tomographic images generated by the PCCT apparatus.
Implementation Method 1
a photon counting detector which detects X-rays transmitted through the subject for each of a plurality of energy bins
Implementation Method 2
an X-ray source which irradiates a subject with X-rays
Data Source
AI summary
Provided are a PCCT apparatus and a control method thereof capable of improving correction accuracy of a projection value even in a range in which the projection value is smaller.A PCCT apparatus includes a scanner that rotates an X-ray source which irradiates a subject with X-rays and a photon counting detector which detects X-rays transmitted through the subject for each of a plurality of energy bins, around the subject, an image generation unit that generates a tomographic image by using projection data calculated based on an output of the photon counting detector, and a controller that controls each unit, in which the controller calculates a conversion expression for converting a projection value of the subject into a transmission length by using a plurality of projection values acquired by performing rotational imaging on a phantom which is disposed not to overlap a rotation center of the scanner and of which a material, a shape, and a size are known, along with a plurality of transmission lengths of the phantom.