RF-Safe MRI Instrument Damping Element Design
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Solution Overview
Problem
Existing medical instruments used during MRI procedures face RF heating issues due to induced RF common mode currents, particularly pronounced at the distal tip, which can lead to tissue heating and safety concerns, especially for thin instruments and those introduced into the examination object.
Innovation Solution
Incorporating an electrically damping element, such as a resistive, reactive, or dielectric load, at the proximal end of the conductor, along with an RF trap circuit, to attenuate RF common mode currents by increasing energy loss and reducing RF field strength, thereby preventing tissue heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrically damping element is added to the conductor at the proximal end, then RF safety is improved by reducing induced RF common mode currents, but device complexity increases
Solution Approach 1:
The damping element is extracted as a separate, removable component rather than being integrated into the conductor itself. This allows the damping function to be added only when needed for RF safety without permanently increasing the complexity of the basic instrument design.
Solution Approach 2:
The damping element acts as an intermediary component that can be attached to the proximal end of the conductor to provide RF protection. This mediator approach allows the RF safety function to be added without modifying the fundamental design of the conductor or instrument.
2Device complexity
If the instrument remains simple without additional components, then device complexity is reduced, but RF heating of tissue occurs due to induced currents
Solution Approach 1:
The damping element is attached to the instrument before the MRI procedure begins, providing preliminary protection against RF heating. This preliminary action ensures that the protective function is in place before the harmful RF currents can be induced during the procedure.
Solution Approach 2:
The damping element changes the electrical parameters of the conductor system by introducing resistance or reactance at the proximal end. This parameter change increases energy loss and reduces the magnitude of RF common mode currents that can be induced in the conductor.
3Loss of energy
If a damping element is attached to the proximal end of the conductor, then energy loss increases to suppress RF currents, but this may affect signal transmission
Solution Approach 1:
The damping element is placed locally at the proximal end of the conductor where RF common mode currents are most problematic, rather than distributing damping throughout the entire conductor. This localized approach suppresses RF currents at the source while minimizing impact on the main signal transmission path.
Solution Approach 2:
The conductor system is segmented into different functional zones: the proximal end with the damping element for RF suppression, and the distal portion for signal transmission. This segmentation allows each segment to be optimized for its specific function without compromising the other.
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 solution effectively reduces RF-induced heating at the tissue level, enhancing RF safety without compromising instrument functionality or requiring modifications to the conductor, and can be applied to various medical instruments and structures.
Implementation Method 1
an electrically damping element in the form of at least one of a resistive, a reactive and a dielectric load, is effectively added to the conductor
Implementation Method 2
an RF trap circuit, connected at the proximal end of the conductor, for provoking at said proximal end said increased or maximum of the RF electric field strength or an increased or a maximum of the RF common mode current
Data Source
Figure 1~3
Figure 4
Figure 5~6
AI summary
An RF-safe interventional or a non-interventional instrument is disclosed for use during an MR imaging or MR examination of an examination object (A), which instrument is made of or comprises at least one longitudinal or elongated electrically conductive element (1, 3), especially in the form of a conductor or wire or line for feeding electrical signals, or in the form of the instrument itself or a component or a part thereof, which is not provided for feeding electrical signals but nevertheless electrically conductive, wherein all such elements are subject to RF common mode currents which are induced in the element when the instrument or element is exposed to an RF/MR excitation field generated during MR imaging or MR examination by means of an MR imaging apparatus. The instrument is made RF-safe by increasing the energy loss of an oscillator which is represented by the conductor (1, 3) by means of a damping element (4; 6) in order to prevent or limit RF heating of the examination object (A) at or surrounding the conductor (1, 3).