Pilot Tone Signal Extraction for Cardiac Motion Detection

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Solution Overview

Problem

Existing methods for detecting cardiac movement during magnetic resonance (MR) scans face challenges due to interference from high magnetic fields and limitations in resolving small movements, particularly with pilot tone navigation methods that rely on larger wavelengths, which may not accurately capture cardiac motion.

Innovation Solution

A method using a pilot tone signal acquired by a magnetic resonance receiver coil arrangement with multiple channels, employing independent component analysis (ICA) to calculate a demixing matrix and separate cardiac movement signals from other components, followed by adaptive filtering to extract reliable cardiac motion signals in real-time or retrospectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If ECG leads are used to detect cardiac movement during MR scans, then cardiac motion can be detected for triggering, but the high magnetic fields cause interference in the ECG leads reducing signal reliability

Engineering Contradiction:

Improvecardiac movement detection accuracyVSAvoidsignal reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces a pilot tone signal as an intermediary carrier wave that is modulated by cardiac motion. Instead of directly measuring ECG leads in the magnetic field, the system uses this intermediary RF signal that can be transmitted through the body and detected by coil elements, converting the measurement problem into a frequency modulation detection task that is less susceptible to magnetic field interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the electrical measurement system (ECG leads and electrodes) with an electromagnetic field-based detection system using pilot tone signals and coil elements. This substitution moves from direct electrical contact measurements to field-based measurements, eliminating the interference problems associated with ECG leads in high magnetic fields.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If pilot tone navigation is used to detect physiological motion, then movement can be detected without ECG leads, but the larger wavelengths (4.7m or 2.3m) cannot resolve small cardiac movements

Engineering Contradiction:

Improveoperation simplicityVSAvoidsmall movement resolution

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent segments the detection system into multiple independent coil elements arranged in an array. By using multiple spatially distributed sensors rather than a single measurement point, the system can detect local variations in the pilot tone signal that correspond to small cardiac movements, effectively segmenting the measurement space to improve resolution.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from scalar amplitude detection to vector-based phase and amplitude analysis across multiple spatial dimensions. By analyzing the pilot tone signal across multiple coil elements in different spatial positions and processing both amplitude and phase information, the system extracts detailed cardiac motion information that would be invisible to simple amplitude-based detection.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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

This approach allows for robust and reliable extraction of cardiac movement signals, reducing interference and improving triggering reliability, enabling ECG-free cardiac imaging with better patient comfort and reduced preparation time, while being applicable across various imaging modalities.

Implementation Method 1

a pilot tone signal emitted by a pilot tone emitter (14) is received by a magnetic resonance receiver coil arrangement (28)

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

From a calibration portion of the Pilot Tone signal, a demixing matrix is calculated using an independent component analysis (ICA) algorithm, where the demixing matrix calculates the independent components from the plurality of signal components

Methodology Applied

Scientific EffectIndependent component analysis:

Implementation Method 3

An adaptive, stochastic, or model-based filter is applied to the at least one movement signal representing one particular movement type

Methodology Applied

Scientific EffectAdaptive filtering: Filter (electronic)

Data Source

PatentUS11096630B2Generating a movement signal of a part of the human or animal body

Publication Date: 2021.08.24 SIEMENS HEALTHINEERS AG

AI summary

A method for generating a movement signal of a body part, of which at least a portion is undergoing a cardiac movement, includes providing a pilot tone signal acquired from the body part by a magnetic resonance receiver coil arrangement. A demixing matrix is calculated from a calibration portion of the Pilot Tone signal using an independent component analysis algorithm. The independent component corresponding to the cardiac movement is selected. The demixing matrix is applied to further portions of the pilot tone signal to obtain a movement signal representing the cardiac movement. An, adaptive stochastic, or model-based filter is applied to the signal representing the cardiac movement, to obtain a filtered movement signal.