Ablation Probe Position Sensor for MRI Thermometry
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Solution Overview
Problem
Magnetic resonance thermometry during cardiac ablation therapy is challenging due to the difficulty in accurately measuring temperature in moving tissues, such as a beating heart, as phase changes in MRI images can be attributed to tissue movement rather than temperature changes.
Innovation Solution
A system that uses a combination of MRI thermometry and position sensors to track the ablation site's position and orientation, allowing for the acquisition of synchronized MRI thermometry images by determining if the site has moved within a predefined limit, enabling accurate temperature measurement using PRF-based phase imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MRI thermometry is used to measure temperature in moving cardiac tissue, then temperature monitoring capability is improved, but measurement precision deteriorates due to tissue movement causing phase changes
Solution Approach 1:
A position sensor is introduced as an intermediary device to track the location and orientation of the ablation probe. This position information serves as a mediator that allows the system to distinguish between phase changes caused by tissue movement and those caused by temperature changes, thereby resolving the measurement reliability issue while maintaining temperature monitoring capability
Solution Approach 2:
The system implements feedback by continuously monitoring position sensor data and using it to adjust or compensate for movement artifacts in the MRI thermometry measurements. The position information feeds back into the temperature measurement process, enabling real-time correction of movement-induced errors and maintaining measurement precision
2Reliability
If radiofrequency energy is applied at high power to create sufficient lesion size, then ablation effectiveness is improved, but temperature control deteriorates due to excessive local heating
Solution Approach 1:
The MRI thermometry system provides real-time temperature feedback during the ablation procedure. This feedback allows the operator to monitor local tissue temperature and adjust the radiofrequency power accordingly, ensuring that sufficient lesion size is achieved while preventing excessive heating that could cause charring and functional barriers
Solution Approach 2:
The system uses periodic MRI imaging to monitor temperature at the ablation site during the procedure. By acquiring temperature data at regular intervals, the system enables controlled heating cycles that achieve effective ablation while allowing for cooling periods, thus maintaining temperature within safe limits
3Temperature
If slower heating is used to improve temperature control, then temperature management is improved, but procedural efficiency deteriorates due to prolonged procedure time
Solution Approach 1:
The system enables continuous monitoring of temperature during the ablation procedure through real-time or near-real-time MRI thermometry. This continuous feedback allows for optimized heating rates that maintain effective temperature control while minimizing procedure time, as the operator can confidently apply higher power when temperature readings confirm safe conditions
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 precise temperature monitoring at the ablation site, enabling controlled and effective cardiac ablation procedures by distinguishing between temperature changes and tissue movement, thus avoiding overheating and improving procedural efficiency.
Implementation Method 1
measuring magnetic fields generated at the distal tip by coils external to the subject
Implementation Method 2
Magnetic resonance thermometry based on the proton resonance frequency (PRF), has been proposed for intrabody temperature measurements. A phase shift in the PRF is linear over a wide temperature range
Data Source
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AI summary
Thermography of an ablation site can be carried out by navigating (73) a probe into contact with target tissue in the heart, obtaining (77) a first position of a position sensor in the probe and acquiring (75) a first magnetic resonance thermometry image of the target tissue. The method can be carried out during ablation (79) by iteratively reading (83) the position sensor to obtain second positions and acquiring (87) a new magnetic resonance thermometry image of the target tissue when the distance between the first position and one of the second positions is less (85) than a predetermined distance. The images can be analyzed to determine (89) the temperature of the target tissue.