Magnetic Resonance Pilot Tone Signal Attenuation
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Solution Overview
Problem
Magnetic resonance systems face challenges in capturing patient movements due to weak pilot tone signals and low signal-to-noise ratios when both pilot tone and magnetic resonance signals are received by the same receiver, leading to artifacts from patient movements like heartbeat and respiration.
Innovation Solution
A magnetic resonance system with a pilot tone apparatus that decouples a high-frequency magnetic alternating field, interacting with the patient's body to generate a pilot tone signal, which is modulated by movements, and uses a frequency-dependent attenuator to enhance the signal-to-noise ratio of the pilot tone signal without affecting the magnetic resonance signal, allowing for shared signal processing resources and improved movement capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the pilot tone signal and magnetic resonance signal are received and evaluated at the same time by the same receiver, then shared signal processing resources are utilized, but the amplitude dynamic range of the receiver system is restricted and the signal-to-noise ratio of the pilot tone signal becomes too low
Solution Approach 1:
The receiver system is divided into two separate receivers: a first receiver dedicated to receiving the pilot tone signal and a second receiver dedicated to receiving the magnetic resonance signal. This segmentation allows each receiver to be optimized for its specific signal type without the dynamic range restrictions that would result from attempting to process both signals simultaneously in a single receiver.
Solution Approach 2:
While the patent uses separate receivers, both receivers are part of the same overall magnetic resonance system and share common components such as the transmitter, gradient system, and control unit. This multi-functionality approach allows the system to handle multiple signal types with dedicated processing paths while maintaining resource efficiency at the system level.
2Adaptability or versatility
If the maximum possible receive level of the pilot tone signal is limited to maintain amplitude dynamic range, then the receiver can handle both signals, but the effective amplitude dynamic range is restricted
Solution Approach 1:
The receiver system is segmented into two independent receiving paths, allowing each receiver to operate with its own optimized dynamic range settings. The first receiver can be configured for the specific amplitude range of pilot tone signals while the second receiver handles magnetic resonance signals, eliminating the need to compromise the overall amplitude dynamic range.
3Object-affected harmful factors
If the portion of the magnetic alternating field which penetrates the tissue moved by the heartbeat is too small, then the pilot tone signal generation is limited, but the demodulated receive signal has a signal-to-noise ratio which is too low
Solution Approach 1:
A dedicated pilot tone transmitter generates a continuous wave magnetic field that serves as an intermediary signal. This pilot tone field penetrates the patient's body and interacts with moving tissues to create modulated signals that can be detected by the first receiver. The intermediary pilot tone signal amplifies the otherwise too-weak effects of tissue movement on the main magnetic resonance field.
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 enables more reliable capture of patient movements by increasing the signal-to-noise ratio of the pilot tone signal, maintaining the amplitude dynamic range for magnetic resonance signals, and reducing noise, thus improving image quality by synchronizing image capture with patient movements.
Implementation Method 1
a continuous monofrequency magnetic alternating field originating from a small conductor loop at least partially through the body of the patient into the individual elements of a magnetic resonance local coil. Since most biological tissues are almost completely transparent to magnetic fields, the generated magnetic field penetrates the body of the patient almost unchanged. Most tissues are however (slightly) conductive and therefore the continuous wave magnetic field induces eddy currents.
Implementation Method 2
Most tissues are however (slightly) conductive and therefore the continuous wave magnetic field induces eddy currents. These eddy currents in turn generate a magnetic field which is superimposed on the excitation field, resulting in modulations in the received magnetic field in the receiving coil.
Implementation Method 3
a frequency-dependent attenuator for attenuating a received pilot tone signal relative to a received magnetic resonance signal
Implementation Method 4
By evaluating this signal, a movement phase of the heart or respiration can be inferred
Data Source
AI summary
A magnetic resonance system has a receiver designed to receive and evaluate a pilot tone signal and a magnetic resonance signal at the same time. The receiver additionally has a frequency-dependent attenuator to attenuate a received pilot tone signal relative to a received magnetic resonance signal.