CT Motion Correction Using Radio-Opaque Markers
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Solution Overview
Problem
Patient movement during a CT scan can distort the resulting three-dimensional CT image, affecting diagnostic accuracy and treatment planning in medical applications.
Innovation Solution
A set of radio-opaque markers is attached to the patient's head, and a CT scanner captures two-dimensional x-ray projections, which are then processed to generate a motion data set by identifying and subtracting motion-blurred markers, allowing for the reconstruction of a high-quality three-dimensional CT image that corrects for patient movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a CT scan is performed without motion correction, then the scanning process is simple and fast, but the resulting three-dimensional CT image contains motion artifacts and reduced diagnostic accuracy
Solution Approach 1:
Markers are attached to the patient's head before the CT scan begins. These markers serve as reference points that will be used throughout the scanning process to detect and correct any motion that occurs during acquisition, allowing motion correction to be performed preliminarily rather than requiring complex real-time intervention
Solution Approach 2:
Radio-opaque markers are introduced as intermediary objects that mediate between the patient's motion and the CT imaging system. The markers are easily detectable in the x-ray projections and serve as reference points to calculate motion transformations, simplifying the motion correction process by providing clear, distinguishable features to track
2Reliability
If markers are attached to the patient for motion tracking, then motion artifacts are reduced, but the device complexity and processing time increase
Solution Approach 1:
The motion correction process extracts and isolates the markers from the rest of the anatomy by generating a mask of the markers and subtracting it from the simulated projections. This separation allows the system to focus computational resources only on tracking the markers rather than analyzing the entire complex anatomy, significantly reducing processing time
Solution Approach 2:
The image processing is segmented into distinct steps: generating a mask of the markers, simulating marker projections, subtracting simulated projections from actual projections to isolate marker positions, and then calculating motion transformations. This segmentation allows each step to be optimized independently and processed efficiently
3Measurement precision
If motion-blurred markers are removed from the CT image, then the marker positions can be accurately determined, but information about the patient's anatomy is lost
Solution Approach 1:
Instead of permanently removing marker information from the final CT image, the system creates a copy of the marker mask and uses it to generate simulated projections. The actual CT image data is preserved and combined with motion correction information derived from the marker positions, maintaining both anatomical information and motion correction capabilities
Solution Approach 2:
The motion-blurred markers are temporarily discarded from the three-dimensional CT image to enable accurate motion detection, but the marker information is recovered by using the determined motion transformations to correct the entire image dataset. This allows the markers to serve their motion-tracking function while their information is preserved in the corrected final image
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 method effectively reduces motion artifacts in CT images, resulting in more accurate and reliable diagnostic images by accounting for patient movement, thereby enhancing the precision of medical diagnoses and treatments.
Implementation Method 1
A CT scanner includes a gantry that supports and houses an x-ray source that generates x-rays and a complementary flat-panel detector
Implementation Method 2
A set of markers that are radio-opaque (i.e., are relatively opaque to x-rays) are attached to a patient's head
Data Source
AI summary
A method of correcting for motion of a patient during a CT scan includes observing positions of radio-opaque markers in a series of two dimensional x-ray projections taken by a scanner. The markers are positioned on a patient in a fixed and rigid relationship, a CT scan is performed to obtain a three dimensional CT image, and an actual projected position of each of the markers in each two dimensional projection is determined. A motion data set is obtained based on the actual projected positions of the plurality of the markers. A final three dimensional CT image is reconstructed employing the motion data set.