Magnetic Field Probe Positioning via Reference Tones in MRI
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Solution Overview
Problem
Existing methods for determining the position of magnetic field probes in MRI or spectroscopy measurements are cumbersome, requiring separate calibration and cannot be performed concurrently with MR sequences, especially for probes that are subject to displacement or used in flexible arrangements.
Innovation Solution
A method involving the application of a spatially and temporally variable magnetic reference field, known as 'reference tones,' during the MR pulse sequence to acquire probe MR signals and determine the position of magnetic field probes within a pre-defined volume of interest, allowing for high temporal resolution and independent position determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate calibration step is used to determine probe positions, then position measurement is achieved, but the scan protocol is extended and field monitoring with flexible probes is precluded
Solution Approach 1:
The patent combines the probe position measurement function with the main MR imaging/spectroscopy sequence by integrating reference tone application and probe signal acquisition into the existing pulse sequence timeline. This merging eliminates the need for separate calibration steps while maintaining continuous field monitoring capability.
Solution Approach 2:
The patent enables continuous position determination throughout the MR sequence by applying reference tones continuously during the acquisition window and continuously acquiring probe signals. This continuous action replaces discrete calibration steps and enables real-time tracking of flexible probes throughout the entire measurement process.
2Measurement precision
If unipolar or bipolar gradient pulses are used for position determination, then position measurement is achieved, but the intended spin manipulation of the MR sequence is altered and disturbed
Solution Approach 1:
The patent introduces reference tones as an intermediary mechanism for position determination. These reference tones are applied through the gradient coils but are designed to be orthogonal to the encoding gradients, serving as a mediator that enables probe tracking without directly interfering with the spin manipulation intended by the main sequence.
Solution Approach 2:
The patent changes the parameters of the gradient application by using high-frequency reference tones that are orthogonal to the encoding gradients. This parameter change allows position determination through probe signal modulation while maintaining the integrity of the original spin manipulation sequences.
3Speed
If position determination is performed during MR sequence acquisition, then temporal resolution is improved, but the reference field may interfere with the encoding gradients
Solution Approach 1:
The patent uses asymmetric, non-sinusoidal reference tone waveforms that are specifically designed to be orthogonal to the sinusoidal encoding gradients. This asymmetry in waveform shape creates a distinction between the reference tones and encoding gradients, enabling their simultaneous application without mutual interference.
Solution Approach 2:
The patent employs periodic reference tones applied at specific frequencies that do not overlap with the encoding gradient frequencies. This periodic action at distinct frequencies allows for clear separation and independent detection of position information without interfering with the image encoding process.
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
Enables automatic and precise position calibration of magnetic field probes, even in flexible arrangements, without disrupting the MR sequence, and allows for continuous field monitoring, improving image reconstruction and motion tracking capabilities.
Implementation Method 1
these so-called MR-type magnetic field probes are rigidly mounted in the periphery of the imaging volume
Implementation Method 2
small magnetic field detectors exploiting the magnetic field dependence of a magnetic resonance transition
Implementation Method 3
gradient and optionally shim coils for generating gradient and shim magnetic fields, respectively, superimposed to the static magnetic field
Implementation Method 4
A method involving the application of a spatially and temporally variable magnetic reference field, known as 'reference tones,' during the MR pulse sequence
Data Source
AI summary
A method of determining the position of at least one magnetic field probe located within a pre-defined volume of interest within a magnetic resonance (MR) imaging or spectroscopy arrangement comprises applying a spatially and temporally variable magnetic reference field having a unique time-course at every point in said volume of interest during a preselected time window. An MR signal is ac-quired from said magnetic field probe during said time window, and the position of the probe is determined from the probe MR signal.