Passive RFID Tracking in MR Apparatuses
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Solution Overview
Problem
Existing magnetic resonance (MR) tracking systems face challenges in accurately tracking the position and orientation of objects within MR apparatuses due to the need for signal transmission means like wires or active wireless transmitters, which are undesirable, and the sensitivity issues of ferromagnetic markers in strong magnetic fields, limiting continuous and accurate tracking.
Innovation Solution
A system comprising an MR apparatus with magnet, encoding, RF transmitter, and acquisition means, and a tracking device with a tracker structure, retransmitter, and electrical circuitry that operates at distinct resonance frequencies, allowing uninterrupted tracking by maintaining electromagnetic decoupling from the MR system's components, ensuring continuous operation and high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal wires or active wireless transmitters are attached to the field sensor for signal transmission, then position and orientation tracking can be achieved, but the device complexity increases and the object becomes more vulnerable to interference
Solution Approach 1:
The patent extracts the tracking function from the MR imaging system by using a separate passive RFID tag and dedicated reader system. The tag is simply attached to the object without any active electronics or signal transmission components, while the reader system handles all signal processing independently from the MR scanner.
Solution Approach 2:
The patent introduces an intermediary passive RFID tag that does not actively transmit signals but rather modulates the electromagnetic field in response to reader interrogation. This intermediary enables tracking without requiring complex signal transmission means attached to the object.
2Measurement precision
If ferromagnetic elements are used in markers for MR tracking, then the markers can be detected by the MR system, but the sensitivity of the markers is reduced in strong magnetic fields
Solution Approach 1:
The patent replaces ferromagnetic markers with passive RFID tags that operate on electromagnetic induction principles rather than magnetic susceptibility. This substitution eliminates the sensitivity reduction problem in strong magnetic fields while maintaining detectability through the MR system's electromagnetic environment.
Solution Approach 2:
The patent changes the operating parameters of the tracking marker by using RFID technology that operates at different frequency ranges than traditional ferromagnetic resonance. The passive tag responds to electromagnetic fields at frequencies where it maintains high sensitivity even in the presence of strong static magnetic fields.
3Adaptability or versatility
If the tracking system uses the same frequency as the MR sequence, then the tracking signals can be integrated with the MR system, but the tracking becomes interrupted during MR operation
Solution Approach 1:
The patent segments the electromagnetic spectrum into distinct frequency bands: the MR system operates at its characteristic Larmor frequency for imaging, while the RFID tracking system operates at a different frequency band. This frequency segmentation allows both systems to operate simultaneously without interference, enabling continuous tracking during MR acquisition.
Solution Approach 2:
The patent implements a dynamic frequency allocation strategy where the RFID reader continuously interrogates tags at frequencies independent of the MR pulse sequence timing. This dynamic operation allows tracking to proceed without interruption regardless of the MR sequence being executed.
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 continuous and accurate tracking of object position and orientation without interfering with the MR system, improving image quality and data integrity by avoiding signal transmission issues and maintaining sensitivity in strong magnetic fields.
Implementation Method 1
retransmitter means firmly attached to said tracker structure, said retransmitter means having at least one retransmitter resonance frequency
Implementation Method 2
transmitter means configured to transmit an electromagnetic field with at least one of said retransmitter resonance frequencies; receiver means configured to receive an electromagnetic field retransmitted by said retransmitter means
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a system and a method for tracking position and orientation of an object in a magnetic resonance (MR) apparatus. The system comprises a tracking device for electromagnetic measurements of position and orientation with a) a tracker structure (2) that is firmly attachable to the object (4) of which the position and orientation are to be measured; b) retransmitter means (6; 8a, 8b, 8c) firmly attached to said tracker structure, said retransmitter means having at least one retransmitter resonance frequency; and c) electrical circuitry means including: i) transmitter means (10) for transmitting an electromagnetic field with at least one of said retransmitter resonance frequencies; ii) receiver means (12; 14a,14b) for receiving an electromagnetic field retransmitted by said retransmitter means; said receiver means converting said electromagnetic field into a proportional voltage; and iii) calculating means for determining, from said proportional voltages obtained from said receiver means, a position and orientation of said retransmitter means, and concomitantly of said object. The tracking device can be used in an operating MR imaging or spectroscopy apparatus.