Magnetic Resonance Tomography Unit With Low-Frequency Field Compensation
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Solution Overview
Problem
Magnetic resonance tomography units are sensitive to variations in static or quasistatic B0 magnetic fields, particularly from low-frequency interference sources like streetcars and electric motors, which affect image quality by shifting the Larmor frequency and requiring precise tissue differentiation.
Innovation Solution
Incorporation of magnetic field sensors outside the MR unit to detect and compensate for low-frequency interference fields using a controller, adjusting gradient and quasistatic fields, and employing variable-frequency oscillators to maintain a constant center frequency during image capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic resonance tomography is performed with high magnetic fields, then imaging capability is improved, but sensitivity to low-frequency magnetic field interference increases
Solution Approach 1:
The system performs preliminary measurement of the ambient magnetic field environment before the actual MRI scan using the same sensor that will be used during imaging. This allows the system to capture low-frequency interference characteristics in advance, so that compensation can be applied during the actual scan without interrupting the imaging process.
Solution Approach 2:
The system continuously monitors the magnetic field environment during MRI scanning using the integrated field sensor, and dynamically adjusts the center frequency of the receiving system based on real-time feedback about interference conditions. This closed-loop control enables the system to adapt to changing interference levels while maintaining optimal imaging performance.
2Device complexity
If the bandwidth of the receiving system is limited, then signal processing is simplified, but sensitivity to static magnetic field variations increases
Solution Approach 1:
The system dynamically changes the center frequency parameter of the receiving system based on measured interference conditions. By adjusting the center frequency to track the Larmor frequency despite static field variations, the system maintains optimal signal reception within its limited bandwidth without requiring broader bandwidth or complex processing.
3Reliability
If frequency differences between protons in water and fat are very small, then tissue differentiation becomes more challenging, but chemical bond influence is minimized
Solution Approach 1:
The system uses an intermediary reference signal at the Larmor frequency that is dynamically adjusted based on measured interference conditions. This reference signal acts as a mediator between the transmitted RF pulses and the received MR signals, enabling precise frequency tracking and differentiation of water and fat protons even when their frequency differences are very small.
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
Effectively reduces the impact of low-frequency interference on MR images by compensating for shifts in the Larmor frequency and gradient fields, enhancing image quality without additional energy expenditure.
Implementation Method 1
A plurality of magnetic field sensors are arranged in the environment of the magnetic resonance tomography unit
Implementation Method 2
the controller ascertains a quasistatic magnetic field and/or a gradient field offset for compensation
Implementation Method 3
a quasistatic compensation magnetic field and/or gradient field offset for compensation of the captured interfering magnetic field
Implementation Method 4
employing variable-frequency oscillators to maintain a constant center frequency during image capture
Data Source
AI summary
A magnetic resonance tomography unit and a method for operating the magnetic resonance tomography unit are provided. The magnetic resonance tomography unit includes a plurality of magnetic field sensors arranged in an environment of the magnetic resonance tomography unit. The plurality of magnetic field sensors are configured to capture low-frequency magnetic fields in the environment of the magnetic resonance tomography unit and to transmit information about the magnetic fields to the controller via a signal connection. According to the method, fields for compensating the low-frequency magnetic fields are ascertained and output.