Flexible Resonant Trap Circuit for MRI B1 Coupling Suppression
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Solution Overview
Problem
In MRI systems, there is a need for flexible and form-fitting RF receive coils that can prevent coupling between the B1 field and transmission lines or inductive elements, ensuring safety and maintaining image uniformity while being mechanically compliant with patient anatomy.
Innovation Solution
A resonant trap circuit with a helical winding portion and a capacitor arranged between the winding segments, which is mechanically flexible and can be bent or twisted without compromising its frequency trap behavior, is integrated into the MRI system to prevent coupling with the B1 field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional rigid resonant trap circuits are used, then frequency filtering performance is achieved, but mechanical flexibility and form-fitting capability are lost
Solution Approach 1:
The resonant trap circuit is constructed using flexible printed circuit board (FPCB) technology, replacing traditional rigid PCB structures. This allows the circuit to be bent, twisted, and conform to complex anatomical surfaces while maintaining electrical connectivity and resonant frequency characteristics through the inherent flexibility of the FPCB substrate and conductor traces.
Solution Approach 2:
The circuit design incorporates dynamic mechanical properties by using flexible materials and structures that can adapt to different positions and orientations on the patient's body. The FPCB construction allows the resonant trap to maintain its electrical performance while dynamically conforming to various anatomical shapes during the MRI procedure.
2Measurement precision
If receive coils are positioned close to patient anatomy for better signal reception, then signal-to-noise ratio improves, but coupling with B1 field and antenna-like behavior increases
Solution Approach 1:
The resonant trap circuit acts as an intermediary element coupled to the receive coil and transmission lines. It provides frequency-selective filtering that blocks common mode currents at the Larmor frequency, preventing the transmission lines and inductive elements from coupling with the B1 excitation field while allowing the receive coil to maintain its close positioning for optimal signal reception.
Solution Approach 2:
The resonant trap extracts and removes the harmful common mode currents at the resonant frequency from the transmission lines and inductive elements. By creating a high impedance path specifically at the Larmor frequency, it separates the desired differential mode signals from the harmful common mode currents, preventing antenna-like behavior.
3Ease of operation
If transmission lines and inductive elements are present in the MRI system, then signal transmission is enabled, but antenna-like behavior and coupling with B1 field occur
Solution Approach 1:
The resonant trap circuit serves as a filtering intermediary inserted into the transmission line path. It allows normal signal transmission while selectively blocking common mode currents at the Larmor frequency, thereby preventing the transmission lines from exhibiting antenna-like behavior and coupling with the B1 field.
Solution Approach 2:
The resonant trap converts the potentially harmful antenna-like behavior of transmission lines into a beneficial frequency-selective filtering function. By designing the trap to resonate at the Larmor frequency, it transforms the transmission lines from unwanted radiating elements into controlled components that actively suppress common mode currents through resonant cancellation.
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
The resonant trap circuit effectively blocks common mode currents, preventing unwanted antenna-like behavior and ensuring spatial uniformity of the excitation and reception fields, thus enhancing image quality and patient safety.
Implementation Method 1
A capacitor is arranged to provide capacitance between the first helical winding segment and the second helical winding segment
Implementation Method 2
A resonant trap circuit with a helical winding portion and a capacitor arranged between the winding segments
Implementation Method 3
The precessing magnetization induces electric current in the receive coil via electromagnetic induction
Implementation Method 4
Impedance of a typical resonant trap circuit becomes very high at its resonant frequency
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A flexible resonant trap circuit is provided that includes a transmission line arranged to include a helical winding that has a first helical winding segment and a second helical winding segment; and a capacitor coupled between the first and second helical winding segments.