Spectral CT Local Tomography with Fixed Photon-Counting Detectors
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Solution Overview
Problem
CdTe/CZT-based photon-counting detectors suffer from polarization in non- or low-attenuated beams near the edges of the scan field of view and after scanning low-attenuation regions, such as the lung, due to fast CT gantry rotation speeds and high centrifugal forces, making dynamic bowtie filters or collimators unreliable.
Innovation Solution
A method for spectral reconstruction in CT imaging using a combined third- and fourth-generation CT scanner with fixed photon-counting detectors, where the detectors are turned on and off based on the size and location of the region of interest (ROI), and slow kVp switching or dual-source, dual-detector scanners are employed to obtain and process data sets for improved image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If dynamic bowtie filters or collimators are used to attenuate beams, then detector polarization is reduced, but system reliability and feasibility deteriorate due to fast gantry rotation speeds and high centrifugal forces
Solution Approach 1:
The patent employs dynamic switching of fixed bowtie filters based on the detected position of the X-ray source. As the gantry rotates, the system automatically selects appropriate fixed filters to match the current scan position, achieving dynamic attenuation adjustment without mechanical moving parts during scanning. This resolves the contradiction by providing the benefits of dynamic filtration while eliminating the reliability issues of mechanically dynamic systems.
Solution Approach 2:
The patent introduces fixed bowtie filters as intermediary elements positioned between the X-ray source and the detector array. These fixed filters serve as a static mediation solution that replaces the need for dynamic mechanical filters, thereby reducing detector polarization through appropriate beam attenuation while maintaining system reliability by eliminating moving parts subject to centrifugal forces.
2Loss of information
If all photon-counting detectors remain on during scanning, then complete data acquisition is achieved, but detector polarization increases due to exposure to non- or low-attenuated beams
Solution Approach 1:
The patent applies local quality by selectively activating only those photon-counting detectors that are currently required for the scan position. Instead of uniformly keeping all detectors on, the system determines which specific detectors should be active based on the X-ray source position and patient anatomy, thereby reducing overall detector exposure to high-flux beams while maintaining complete data acquisition for the region of interest.
Solution Approach 2:
The patent implements periodic switching of detector states based on the periodic rotation of the gantry. As the X-ray source rotates around the patient, detectors are turned on and off in a periodic manner that synchronizes with the gantry rotation, ensuring that each detector is active only during the brief period when it is needed for data acquisition, thus minimizing cumulative exposure and polarization.
3Reliability
If fixed bowtie filters are used instead of dynamic filters, then system reliability improves, but adaptability to different scan positions and regions of interest deteriorates
Solution Approach 1:
The patent achieves adaptability with fixed filters by implementing dynamic switching logic that selects among multiple fixed bowtie filters based on real-time gantry position and scan parameters. This allows the system to adapt to different scan positions and regions of interest by appropriately selecting which fixed filter to use, thereby maintaining high system reliability while achieving the necessary versatility.
Solution Approach 2:
The patent segments the filtration system into multiple discrete fixed bowtie filters, each optimized for specific scan positions or anatomical regions. By dividing the filtration function across multiple fixed elements rather than using a single static filter, the system can selectively activate appropriate segments (filters) to match different scanning scenarios, thus achieving adaptability while maintaining the reliability benefits of fixed filters.
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 allows for accurate spectral imaging of ROIs while mitigating detector polarization and reducing radiation dose, enabling efficient spectral reconstruction and protecting detector elements from high flux beams.
Implementation Method 1
CdTe/CZT-based photon-counting detectors
Implementation Method 2
an X-ray source that rotates in a trajectory about the object
Implementation Method 3
Radiographic imaging, in its simplest expression, is an X-ray beam traversing an object and a detector relating the overall attenuation per ray
Data Source
AI summary
A method for performing reconstruction for a region of interest (ROI) of an object is provided. The method includes designating the ROI within the object, the ROI being located within a scan field of view (FOV) of a combined third- and fourth-generation CT scanner, the CT scanner including fixed photon-counting detectors (PCDs), and an X-ray source that rotates about the object in synchronization with a rotating detector. Further, the method includes determining, for each PCD, as a function of view angle, an on/off timing schedule, based on a size and location of the designated ROI, and performing a scan to obtain a first data set from the rotating detector and a second data set from the plurality of PCDs, while turning each PCD on and off according to the determined schedule. Finally, the method includes performing reconstruction using the first and second data sets to obtain ROI spectral images.