Knee Joint Loading Assembly for Reproducible MRI Scans
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Solution Overview
Problem
Existing MRI systems lack the ability to consistently and reproducibly apply mechanical loads to a subject's knee joint during imaging, which is crucial for accurate analysis of cartilage deformation and progression over time.
Innovation Solution
A system is developed that secures a subject's knee joint within an MRI scanner, allowing for the application and maintenance of a predetermined load, using a force sensor assembly, mobile unit, and stationary base, ensuring consistent positioning and load application across multiple scans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a load is applied to the knee joint during MRI scanning, then cartilage deformation can be measured, but the positioning and load application cannot be reproduced across multiple scans
Solution Approach 1:
The system applies a predetermined load to the knee joint before the MRI scan begins and maintains this load throughout the scanning process. The load application is prepared in advance with specific force magnitudes (e.g., 25%, 50%, 75% of body weight) and the knee joint is positioned in a standardized manner before scanning, ensuring that the same conditions can be reproduced in follow-up scans.
Solution Approach 2:
The system controls and standardizes key parameters including the magnitude of applied load (as percentage of body weight), the position of the knee joint, and the duration of load application before scanning. By controlling these parameters consistently across multiple scans, the system enables reproducible measurement of cartilage deformation under identical loading conditions.
2Measurement precision
If the knee joint is restrained to prevent motion artifacts, then image quality improves, but the ability to apply controlled mechanical load is reduced
Solution Approach 1:
The system separates the functions of motion restraint and load application by using distinct components: a restraining apparatus (shoulder harness, waist strap, ankle restraint) that prevents unwanted body movements, and a separate load application mechanism (force sensor assembly with mobile unit) that applies controlled mechanical load to the knee joint. This segmentation allows both functions to operate simultaneously without interference.
Solution Approach 2:
The system introduces a force sensor assembly as an intermediary device between the subject's lower extremity and the applied load. This intermediary component measures the actual force applied and provides feedback to ensure the predetermined load is maintained, while the restraining apparatus independently manages motion control. The intermediary force sensor enables precise load control without compromising motion restraint effectiveness.
3Reliability
If multiple scans are performed to track cartilage progression, then longitudinal data can be collected, but inconsistent loading conditions reduce data reliability
Solution Approach 1:
The system standardizes critical scanning parameters including the applied load magnitude (expressed as a percentage of the subject's body weight), the position of the knee joint, and the timing of load application relative to the scan. By controlling these parameters consistently across multiple time points, the system ensures that changes in cartilage morphology observed in longitudinal studies are due to actual progression rather than variations in loading conditions.
Solution Approach 2:
The force sensor assembly provides real-time feedback on the actual load applied to the knee joint during each scan. This feedback mechanism allows the system to verify that the predetermined load was successfully applied and maintained, and to make adjustments if necessary. The recorded load data is stored and can be compared across multiple scans to ensure consistency, thereby validating the reliability of longitudinal comparisons.
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
Enables reproducible MRI scans of the knee joint under controlled load conditions, facilitating longitudinal studies of cartilage degeneration and response to surgical interventions, providing detailed cartilage deformation measurements.
Implementation Method 1
a force sensor assembly adapted to monitor a load as applied on a subject's knee joint when the force sensor assembly remains in direct contact with the subject's lower extremity
Implementation Method 2
MRI provides soft-tissue images with superior contrast. Thus, MRI has become a widely-used modality for joint imaging
Data Source
AI summary
A system that includes: a force sensor assembly adapted to monitor a load as applied on a subject's knee joint when the force sensor assembly remains in direct contact with the subject's lower extremity and the load is monitored from inside a main magnet of an MRI scanner; a mobile unit comprising tracks configured to adjust a position of the force sensor assembly; a stationary base on which the mobile unit and the force sensor assembly are located, the mobile unit translatable solely axially on the stationary base; and a processor coupled to the force sensor assembly and programmed to read information encoding the load being monitored by the force sensor assembly, wherein an MRI scan of the knee joint is initiated only when a pre-determined load has been applied to the subject's knee joint for a pre-determined period of time.