Magnetic Resonance SAR Control via Anatomical Positioning
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Solution Overview
Problem
Magnetic resonance examinations for whole-body screening face challenges in maintaining uniform contrast and preventing specific absorption rate (SAR) exceedance across different bed positions, leading to potential heating of biological tissue and flawed image combinations.
Innovation Solution
A method that automatically determines the anatomical structure of the examination subject at each bed position and calculates the specific absorption rate (SAR) for each position before generating electromagnetic fields, comparing it with a threshold value to prevent SAR exceedance, allowing for uniform contrast and slice thickness in combined images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electromagnetic fields are generated according to a predetermined magnetic resonance measurement protocol at several different bed positions, then magnetic resonance images can be acquired for whole-body screening, but the specific absorption rate (SAR) may be exceeded leading to tissue heating
Solution Approach 1:
The system performs a preliminary localizer examination to determine the anatomical structure of the examination subject before the actual magnetic resonance measurement. Based on this preliminary information, the SAR is calculated in advance for each bed position, allowing parameter adjustments to be made before the harmful effect (SAR exceedance) can occur during the main examination
Solution Approach 2:
The system calculates the SAR based on the determined anatomical structure and provides feedback by comparing the calculated SAR with a threshold value. This feedback mechanism allows the system to identify potential SAR exceedances and trigger appropriate responses (parameter adjustments or notifications) before the actual measurement begins
2Object-affected harmful factors
If the magnetic resonance measurement protocol parameters are adjusted at individual bed positions to prevent SAR exceedance, then tissue heating is prevented, but the contrast uniformity across combined images deteriorates
Solution Approach 1:
The system applies local quality adjustments by modifying measurement parameters (such as reduction of the number of slices or changes in sequence parameters) only at specific bed positions where SAR exceedance is predicted, while maintaining standard parameters at other positions. This localized approach prevents tissue heating at critical positions while preserving contrast uniformity in regions where SAR is not exceeded
Solution Approach 2:
The system changes physical parameters of the measurement protocol (number of slices, sequence parameters) based on the calculated SAR values and anatomical structure. By dynamically adjusting these parameters according to the specific anatomical conditions at each bed position, the system prevents SAR exceedance while maintaining optimal image quality and contrast uniformity
3Productivity
If different protocols use different fields of view to minimize acquisition time, then productivity increases, but the probability of examination subject movement between measurements increases
Solution Approach 1:
The system performs a preliminary localizer examination that captures the entire examination region, establishing a reference framework before the actual measurements begin. This preliminary action allows the system to plan and coordinate different protocols at different bed positions while maintaining spatial reference, thereby reducing the likelihood of misalignment due to subject movement
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
Ensures that magnetic resonance images can be combined with uniform contrast and slice thickness, preventing SAR exceedance and reducing the need for parameter adjustments during the examination, thereby enhancing image quality and safety.
Implementation Method 1
The absorption of electromagnetic field energy may result in heating of the tissue and is therefore to be restricted during the implementation of a magnetic resonance examination. The specific absorption rate SAR is used as a measure of the absorption of electromagnetic field energy in biological tissue.
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for implementing an MR examination of an examination subject with a predetermined MR measurement protocol at several different bed positions of the bed of the MR apparatus, a respective anatomical structure of the examination subject is determined for each of the several bed positions and a respective specific absorption rate is determined for each of the several bed positions as a function of the respective anatomical structure of the examination subject at the corresponding bed position and the predetermined MR measurement protocol. The specific absorption rates for the several bed positions are determined before electromagnetic fields are generated according to the respective predetermined MR measurement protocol. The specific absorption rates are compared with an absorption rate threshold value and a notification is output if at least one of the specific absorption rates exceeds the absorption rate threshold value.