Photon Counting Detector with Mixed Sensitivity Elements for X-ray CT
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Solution Overview
Problem
Photon counting CT systems face challenges with pile-up phenomena, leading to degraded signal-to-noise ratios and artifacts due to overlapping response waveforms at high X-ray doses, and reduced photon counting at low doses, which increases production costs with existing detectors requiring multiple detection elements and complex circuitry.
Innovation Solution
An X-ray CT apparatus with a detector comprising multiple detection elements of varying response characteristics, including high and low sensitive elements, arranged spatially to manage count rates and reduce pile-up, using a combination of direct and indirect conversion types, and employing count rate calculating and image reconstruction circuitry to select appropriate elements for image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If X-ray photons enter at a high frequency (high doses), then the photon counting capability is utilized, but response waveforms overlap causing pile-up and degrading measurement accuracy
Solution Approach 1:
The detector is divided into multiple detection elements (first, second, and third types) with different response characteristics. Each element type has distinct attenuation characteristics that allow them to handle different photon flux levels, preventing pile-up by distributing the counting load across segmented elements with varying temporal response properties.
Solution Approach 2:
Different regions of the detector utilize different types of detection elements optimized for local conditions. Elements with faster response characteristics are positioned where high photon flux occurs, while elements with slower response are used in regions with lower flux, matching the local quality of photon incidence to the appropriate detection characteristics.
2Measurement precision
If X-ray dose is decreased to low doses to avoid pile-up, then response waveforms do not overlap, but the number of counted photons is reduced degrading S/N ratio and causing artifacts
Solution Approach 1:
The system changes the effective detection parameters by selecting different types of detection elements based on the X-ray dose level. At low doses, elements with higher sensitivity are activated to maximize photon capture and maintain S/N ratio, while at high doses, elements with faster response characteristics are used to prevent pile-up, thus adapting the detection parameters to the current operating conditions.
3Reliability
If multiple detection elements are provided in an area corresponding to one pixel to reduce pile-up, then pile-up occurrence is reduced, but production cost increases due to microfabrication and switching circuitry
Solution Approach 1:
The detector area is segmented into multiple types of detection elements distributed across the detector surface. Instead of providing multiple elements within a single pixel area requiring complex microfabrication and switching circuitry, the patent uses spatially distributed element types that can be manufactured using standard fabrication processes, reducing production complexity and cost while maintaining pile-up reduction capability.
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 solution enables the reconstruction of high-quality X-ray CT images with a wide dynamic range, reducing production costs and pile-up occurrences by effectively managing count rates and selecting appropriate detection elements for image reconstruction, thereby maintaining high signal-to-noise ratios across varying X-ray doses.
Implementation Method 1
a detector which includes a plurality of detection elements and outputs a detection signal according to an incidence of an X-ray photon to each of the detection elements
Data Source
AI summary
An X-ray CT apparatus according to an embodiment includes a detector, counted result collecting circuitry, count rate calculating circuitry, control circuitry, and image reconstruction circuitry. The detector includes a plurality of detection elements including a plurality of types of detection elements with different response characteristics to an X-ray dose, and outputs a detection signal according to an incidence of an X-ray photon to each of the detection elements. The counted result collecting circuitry collects counted results obtained by counting X-ray photons from detection signals output by the detection elements. The count rate calculating circuitry calculates a count rate from the detection signals output by the detection elements. The control circuitry selects a detection element based on the count rate and respective response characteristics of the detection elements. The image reconstruction circuitry reconstructs X-ray CT image data using the counted result obtained from the detection element selected by the control circuitry.