MRI Motion Sensing Using RF Intermodulation Beat Pilot Tones
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Solution Overview
Problem
Current MRI systems face challenges in managing patient motion during scans, particularly cardiac and respiratory motion, which can corrupt scan data, and existing motion sensing methods cause patient discomfort or have limited sensitivity, especially for pediatric patients and those with uncontrollable disorders.
Innovation Solution
A flexible sensing method using Beat Pilot Tones (BPT) that transmits two independent frequencies f1 and f2, creating intermodulation products at the receiver coil, allowing for high sensitivity motion detection without additional on-patient hardware, and can be implemented through software changes in the MRI system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Pilot Tones are used for motion detection, then the method is simple to implement, but the sensitivity to motion within the body is limited
Solution Approach 1:
The patent changes the frequency parameters by transmitting two independent frequencies (f1 and f2) instead of a single Pilot Tone frequency. This creates intermodulation products that enable detection of smaller motions while the frequencies can be configured through software, maintaining implementation simplicity while dramatically improving sensitivity.
Solution Approach 2:
The patent introduces intermodulation products as an intermediary mechanism. By transmitting two frequencies that interact through the receiver coil's nonlinear response, the system creates new frequency components that are highly sensitive to motion, effectively using the intermodulation effect as a mediator to amplify motion signals.
2Measurement precision
If hardware is placed on the patient's body for motion sensing, then motion signals can be obtained, but patient discomfort occurs and setup time increases
Solution Approach 1:
The patent makes the MRI scanner itself serve the dual purpose of imaging and motion detection. The scanner's existing transmit and receive systems are used to generate and detect motion signals, eliminating the need for external sensors on the patient. This self-service approach maintains motion detection capability while removing hardware that causes discomfort.
Solution Approach 2:
The patent enables the MRI scanner to perform multiple functions simultaneously - standard imaging and motion detection - using the same hardware components. The transmit system generates both imaging RF pulses and motion detection tones, while the receiver coils process both types of signals, making the system universal and eliminating separate motion sensing hardware.
3Measurement precision
If ECG and flexible sensors are used for motion monitoring, then cardiac and respiratory motion can be detected, but patient discomfort and motion artifacts in ECG waveform occur
Solution Approach 1:
The patent uses intermodulation products as an intermediary to detect cardiac and respiratory motion without direct contact with the patient. The two transmitted frequencies interact through the receiver coil to create beat frequencies that modulate according to patient motion, allowing detection of cardiac and respiratory patterns without ECG electrodes or flexible sensors that cause discomfort and artifacts.
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
Enhances motion detection sensitivity by 20× compared to traditional Pilot Tones, improving scan accuracy and comfort by reducing setup time and avoiding hardware-related discomfort, while maintaining signal-to-noise ratio.
Implementation Method 1
transmits two independent frequencies f1 and f2, creating intermodulation products at the receiver coil
Data Source
AI summary
A method of sensing motion in an MRI scanner includes transmitting at least two tones having different frequencies, using intermodulation to combine the two tones, transmitting the two tones as a combined signal during an MRI scan of a patient, receiving the combined signal using a receiver in the MRI scanner, demodulating the combined signal to produce a demodulated signal, and analyzing the demodulated signal to detect motion of the patient during the MRI scan.