Multi-Frequency Pilot Tone Transmitter for MRI Movement Detection
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in detecting patient movements due to weak and unreliable pilot tone signals, leading to artifacts in generated images, especially when using continuous wave magnetic fields that induce eddy currents and result in low signal-to-noise ratios.
Innovation Solution
A narrowband pilot tone signal with discrete frequency components is generated, stabilized by a frequency stabilization unit, and transmitted through spatially separated magnetic field loops to create additional coupling paths, allowing individual evaluation and improving the signal-to-noise ratio (SNR) without interfering with MRI image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous wave magnetic field is used to generate pilot tone signals, then the magnetic field penetrates the patient's body and induces eddy currents for movement detection, but the induced eddy currents generate interfering magnetic fields that reduce the signal-to-noise ratio
Solution Approach 1:
The continuous wave magnetic field is segmented into multiple discrete frequency components (e.g., first frequency component at 62.5 MHz, second frequency component at 62.6 MHz). This segmentation allows the receiving system to process different frequency components separately, extracting movement information from each while filtering out interfering signals, thereby improving the signal-to-noise ratio while maintaining reliable movement detection
Solution Approach 2:
The system changes the frequency parameter of the pilot tone signal from a single continuous frequency to multiple discrete frequencies. By transmitting signals at different frequencies and processing them separately in the receiving system, the method enables discrimination between the pilot tone signals and interfering magnetic resonance signals, improving both reliability and signal-to-noise ratio
2Device complexity
If a monofrequency pilot tone signal is transmitted, then the system structure is simple, but the received signal amplitude fluctuations are very weak and difficult to evaluate
Solution Approach 1:
The single frequency signal is segmented into multiple discrete frequency components. Each frequency component interacts with different tissue paths, creating distinct coupling paths through the patient's body. The receiving system processes these segmented frequency components separately, combining the information to achieve stronger and more reliable movement detection signals while maintaining relatively simple device structure
Solution Approach 2:
The system transitions from a one-dimensional monofrequency signal to a multi-dimensional frequency spectrum approach. By adding the frequency dimension and transmitting multiple discrete frequency components, the system creates additional measurement dimensions that improve movement detection precision without significantly increasing overall system complexity
3Reliability
If the pilot tone signal frequency is placed at the edge of the receiver's frequency range, then the signal can be received simultaneously with magnetic resonance signals without overlapping, but the signal-to-noise ratio becomes too low
Solution Approach 1:
Instead of placing a single pilot tone frequency at the edge of the receiver's frequency range, the system segments the signal into multiple discrete frequency components distributed across the frequency spectrum. This segmentation allows the receiver to process each frequency component with optimal filtering, improving the signal-to-noise ratio while maintaining the capability for simultaneous reception with magnetic resonance signals
Solution Approach 2:
The system changes the frequency distribution parameter from a single edge-frequency signal to multiple frequencies distributed across the available bandwidth. This parameter change enables the receiver to utilize its full frequency response characteristics, improving signal-to-noise ratio while avoiding overlap with magnetic resonance signals through careful frequency selection
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
The solution enhances the reliability and accuracy of patient movement detection by increasing the SNR in the demodulated received signal, ensuring stable frequency components that do not overlap with MRI signals, thus reducing image artifacts.
Implementation Method 1
most tissues are (weakly) conductive, and therefore the continuous wave magnetic field induces eddy currents. These eddy currents, in turn, generate a magnetic field that overlays the excitation field
Implementation Method 2
a continuous, monofrequency alternating magnetic field from a small conductor loop, at least partially through the patient's body, into the individual elements of an MR local coil
Implementation Method 3
The transmitting device has a frequency stabilization unit. The frequency stabilization unit is configured to stabilize a frequency difference between a plurality of frequency components
Implementation Method 4
By evaluating this signal, a phase of movement of the heart or breathing can be determined
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a transmitter for a pilot tone signal with a plurality of discrete frequency components and a magnetic resonance imaging scanner with such a transmitter. The transmitter has a frequency stabilization unit configured to maintain a constant frequency difference between the plurality of frequency components.