MRI RF Receive Coil Circuit for Dog-Ear Noise Suppression
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Solution Overview
Problem
MRI systems face increased noise and instability due to mutual inductance between RF receive coils, leading to degraded image quality and signal distortion, despite efforts to minimize noise through baluns and preamplifiers, which often result in oscillations and poor signal extraction at frequencies other than the MR frequency.
Innovation Solution
Incorporating resonant circuits in the RF receive coil circuit to increase source impedance at specific frequencies, thereby reducing preamplifier gain at dog-ear frequencies and maintaining stability at the MR frequency, using resonant circuits tuned to match the dog-ear frequencies and adjusting impedance values to achieve higher blocking impedance and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple RF receive coils are overlapped to fit in the MRI system, then the system can process more signal channels, but mutual inductance between coils increases causing signal distortion and noise
Solution Approach 1:
The patent introduces preamplifiers with low input impedance as intermediary components between the RF receive coils and the signal processing system. These preamplifiers act as mediators that convert the high-impedance coil signals to low-impedance signals, thereby reducing mutual inductance effects and allowing more coils to be overlapped without excessive interference
Solution Approach 2:
The patent changes the impedance parameter of the signal path by using preamplifiers with low input impedance (e.g., 2 ohms) instead of traditional high-impedance inputs. This parameter change fundamentally alters how the coils interact electromagnetically, enabling higher coil density while maintaining signal integrity
2Reliability
If low input impedance preamplifiers are used to isolate RF receive coils, then blocking impedance increases and coil isolation improves, but dog-ear peaks appear at frequencies other than MR frequency causing oscillation and instability
Solution Approach 1:
The patent employs feedback mechanisms in the form of resonant circuits that are tuned to the dog-ear frequencies. These resonant circuits provide negative feedback at the problematic frequencies, canceling out the dog-ear peaks and stabilizing the preamplifier gain across the frequency spectrum while maintaining the low input impedance for isolation
Solution Approach 2:
The patent dynamically adjusts the impedance parameters of the preamplifier system by adding resonant circuits that modify the frequency response. The resonant circuits are tuned to create impedance peaks at the dog-ear frequencies, effectively suppressing the unwanted gain peaks while maintaining the low input impedance at the MR frequency
3Stability of the object's composition
If resonant circuits are added to reduce preamplifier gain at dog-ear frequencies, then stability at MR frequency is maintained, but device complexity increases
Solution Approach 1:
The patent segments the frequency control function by adding separate resonant circuits for each dog-ear frequency rather than using a single complex broadband solution. Each resonant circuit is independently tuned to a specific problematic frequency, allowing modular design and simplifying the overall system architecture despite the added components
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 enhances the signal-to-noise ratio by stabilizing the preamplifier and reducing noise interference, allowing for clearer and more accurate MRI image extraction without compromising the gain at the MR frequency, thus improving image quality.
Implementation Method 1
Incorporating resonant circuits in the RF receive coil circuit to increase source impedance at specific frequencies
Implementation Method 2
The resonance or vibration of the hydrogen nuclei in the slice increases and they absorb extra energy from the pulse. When the pulse ends, the hydrogen nuclei release the extra energy, which induces an electrical signal or MRI signal in the RF receive coil.
Data Source
AI summary
An apparatus and method for receiving a magnetic resonance (MR) signal for imaging a patient. The MR signal includes a MR frequency. A radio frequency (RF) coil has first and second end portions. An impedance converter is in electrical communication with the RF coil. A preamplifier in electrical communication with the impedance converter, the preamplifier having a gain. At least one resonant circuit electrically connected to at least one end portion of the RF coil.