CBCT Metal Artifact Reduction via Adaptive Trajectories
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Solution Overview
Problem
Cone Beam Computed Tomography (CBCT) imaging systems face challenges in generating diagnostic-quality images due to image artifacts caused by highly dense metal objects, which lead to image degradation and reduced quality, particularly in dental imaging where complex structures and varying densities are common.
Innovation Solution
A CBCT imaging system with a movable gantry center-of-rotation that performs an initial low-dose scan to determine metal locations, allowing for a second scan to minimize artifacts and optimize image quality by calculating X-ray source and detector trajectories that maximize angular range through regions-of-interest not blocked by metal, thereby reducing reconstruction artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard CBCT scan trajectory is used, then the scan can be completed quickly and efficiently, but metal artifacts severely degrade image quality and obscure diagnostic information
Solution Approach 1:
The system performs a preliminary low-dose scout scan before the main diagnostic scan to identify metal locations and calculate an optimized scan trajectory that avoids metal-induced artifacts. This preliminary action enables the main scan to proceed along artifact-minimizing paths while maintaining diagnostic image quality.
Solution Approach 2:
The scan trajectory is made dynamic and adaptive rather than fixed. The system calculates optimal source-detector orbits in real-time based on detected metal locations, allowing the scan path to dynamically adjust around metal objects. This dynamic trajectory optimization resolves the contradiction by enabling complex artifact-avoiding paths while maintaining scan efficiency.
2Productivity
If the X-ray source and detector follow a fixed circular orbit, then the scanning process is simple and fast, but metal objects cause photon starvation and severe streak artifacts
Solution Approach 1:
The system transitions from a fixed circular orbit to a dynamic, adaptive scan trajectory. Based on metal detection from scout scans, the system calculates optimized source-detector orbits that dynamically adjust to avoid metal-induced photon starvation. This dynamic approach maintains scan speed while eliminating the harmful effects of fixed trajectories passing through metal.
Solution Approach 2:
The system changes the scan trajectory parameters (source-detector orbit positions and angles) based on metal locations detected in preliminary scans. By adjusting these parameters to create artifact-minimizing paths, the system maintains high scan productivity while avoiding the photon starvation and streak artifacts caused by fixed circular orbits intersecting metal objects.
3Measurement precision
If a high-dose scan is performed to overcome photon starvation from metal, then image noise is reduced, but patient radiation exposure increases and metal artifacts persist
Solution Approach 1:
The system extracts and removes the problematic scan trajectories that pass through metal objects by calculating optimized orbits that specifically avoid metal-induced photon starvation. This extraction of harmful paths allows the scan to proceed along clean trajectories without needing excessive radiation dose, thereby reducing patient exposure while maintaining acceptable image noise levels.
Solution Approach 2:
A preliminary low-dose scout scan is performed to identify metal locations before the main diagnostic scan. This preliminary action enables the system to plan optimized trajectories that avoid metal, allowing the main scan to achieve adequate image quality with reduced radiation dose compared to brute-force high-dose scanning that would be required without trajectory optimization.
4Device complexity
If conventional reconstruction methods are used, then the reconstruction process is computationally efficient, but metal artifacts such as streaks and bands are generated that mask diagnostic structures
Solution Approach 1:
The system performs preliminary metal detection and trajectory optimization before the main scan and reconstruction process. By pre-identifying metal locations and calculating artifact-minimizing trajectories, the system reduces the severity of metal-induced artifacts in the projection data, thereby reducing the complexity required for artifact correction during reconstruction while still achieving diagnostic image quality.
Solution Approach 2:
The system uses the known locations of metal objects (detected from scout scans) to its advantage by calculating scan trajectories that strategically avoid metal-induced artifacts. This converts the harmful presence of metal into a beneficial opportunity for optimized trajectory planning, reducing reconstruction complexity by preventing artifacts at the data acquisition stage rather than requiring complex post-processing correction.
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 effectively minimizes metal-induced artifacts, enhancing image quality and allowing for accurate assessment and treatment planning by optimizing scan trajectories and weighting projection pixels to account for X-ray redundancies.
Implementation Method 1
The cone beam CT system directs, from various points along its orbit around the subject, a divergent cone beam of X-rays through the subject and to the detector
Implementation Method 2
Dense objects, having a high atomic number, attenuate X-rays in the diagnostic energy range much more strongly than do soft tissue or bone features, so that far fewer photons reach the imaging detector through these objects
Implementation Method 3
high-speed imaging detectors, such as digital radiography (DR) detectors that enable multiple images to be taken in rapid succession
Data Source
AI summary
The present disclosure describes a Cone Beam Computed Tomography (CBCT) imaging system and methods of operating the system to minimize the degradation of projection images by metal in a scanned object. The methods determine the location of metal in the scanned object by making an initial low dose scan and then, using information obtained from the low dose scan, perform a second scan that may be used to create a reconstruction with reduced artifacts. The methods also calculate X-ray source and detector scan trajectories which minimize reconstruction artifacts and optimize image quality, especially when a region-of-interest is near metal in the scanned object. Additionally, the methods of the present invention calculate X-ray source and detector scan trajectories that maximize the angular range of X-rays which pass through the region-of-interest that are not blocked by metal in the scanned object.