MRI RF Power Control via Subject Proximity Detection
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Solution Overview
Problem
Magnetic resonance imaging systems face challenges in ensuring that the specific absorption rate of radio frequency fields applied to subjects is kept within safe limits, as existing methods fail to reliably adjust for varying subject sizes and positions, potentially leading to hazardous exposure.
Innovation Solution
A method and system that determine position and lateral dimensions of the subject relative to the radio frequency transmit antenna, using proximity detectors, to adjust radio frequency power parameters such as duty cycle and amplitude, ensuring the specific absorption rate remains below the maximum tolerable level, thereby preventing hazardous exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If radio frequency power is increased to improve imaging quality and signal-to-noise ratio, then imaging performance is improved, but specific absorption rate may exceed safe limits causing hazardous exposure
Solution Approach 1:
The system dynamically adjusts radio frequency power parameters based on real-time detection of subject position and dimensions. The control unit continuously monitors proximity detector signals and modifies duty cycle and amplitude parameters accordingly, transitioning from static to dynamic power control to maintain safety while optimizing imaging quality
Solution Approach 2:
The system implements a feedback loop where proximity detectors continuously measure subject position and lateral dimensions, the control unit processes this information to calculate appropriate power parameters, and the radio frequency amplifier adjusts power delivery accordingly. This closed-loop feedback ensures specific absorption rate remains within safe limits while maintaining optimal imaging performance
2Ease of operation
If fixed radio frequency power parameters are used to simplify operation, then ease of operation is improved, but safety cannot be ensured for varying subject sizes and positions
Solution Approach 1:
The system performs self-adjustment by automatically detecting subject characteristics through proximity detectors and autonomously calculating and applying appropriate radio frequency power parameters. The control unit executes the method without requiring manual intervention, allowing the system to serve itself in adapting to different subjects while maintaining safety
Solution Approach 2:
The system changes radio frequency power parameters (duty cycle and amplitude) based on detected subject characteristics. The control unit calculates modified parameters according to the method, adjusting them in real-time to match subject size and position variations, thereby maintaining safety across diverse imaging scenarios
3Reliability
If manual adjustment of radio frequency power parameters is performed to ensure safety, then safety monitoring is improved, but human error may occur reducing reliability
Solution Approach 1:
The system eliminates the need for manual safety monitoring by implementing automatic detection and adjustment. The proximity detectors and control unit work together to autonomously determine safe power parameters based on subject characteristics, removing human operators from the safety-critical adjustment process and eliminating associated errors
Solution Approach 2:
The system replaces manual mechanical adjustment with automated electronic control. The control unit electronically adjusts radio frequency power parameters based on detector signals, substituting human manual operation with an automated electronic system that provides more reliable and consistent safety monitoring
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 reliable and automatic adjustment of the radio frequency excitation field to maintain a safe specific absorption rate, optimizing signal-to-noise ratio while ensuring subject safety across various subject sizes and positions.
Implementation Method 1
The term 'proximity detector', as used in this application, shall be understood particularly as a detector that is able to detect a position of an object without physical contact between the detector and the object. Preferably, the at least one proximity detector is selected out of a group formed by ultrasonic proximity detectors, optical (e.g. infrared) proximity detectors, in particular in proximity-sensing (diffused) arrangement
Implementation Method 2
at least one radio frequency transmit antenna that is configured for applying a radio frequency excitation field B1 to nuclei of or within the portion of the subject of interest for magnetic resonance excitation
Implementation Method 3
Safety requirements with regard to an upper limit of a specific absorption rate have to be observed
Data Source
AI summary
A method of operating a magnetic resonance imaging system (10) includes adjusting a radio frequency excitation field B1 to be applied to a subject of interest (20) to be imaged. At least one position parameter (d) that is indicative of a position of at least the portion of the subject of interest (20) relative to at least one radio frequency transmit antenna (36) of the magnetic resonance imaging system (10) is determined. At least one radio frequency power-related parameter of radio frequency power to be fed to the at least one radio frequency transmit antenna (36) is adjusted in dependence of the at least one of the determined at least one position parameter (d) and a determined geometric dimension (w) of the subject of interest (20).