Tunable RF Coil Resonant Frequency Adjustment for Portable MRI
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Solution Overview
Problem
Portable magnetic resonance imaging (MRI) devices face limitations in achieving high-quality images due to low-intensity main magnetic fields, which result in unfavorable signal-to-noise ratios and reduced magnetization, making it challenging to produce images of sufficient quality.
Innovation Solution
A magnetic resonance imaging device equipped with a radio frequency assembly that includes a tunable circuit and radio frequency coil, allowing dynamic adjustment of the resonant frequency within a broader working frequency range than the intrinsic bandwidth, enhancing the signal-to-noise ratio and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a portable MRI device uses a permanent magnet or electromagnets of limited capacity, then the mass and bulk of the device are reduced, but the main magnetic field intensity is limited to greater than 60 mT, which degrades image quality
Solution Approach 1:
The patent changes the resonant frequency parameter of the radio frequency assembly dynamically to match the Larmor frequency of hydrogen nuclei at low magnetic field strengths. By adjusting the resonant frequency within a broad range (e.g., 20-80 kHz) to cover the entire Larmor frequency spectrum, the system optimizes signal reception at each magnetic field intensity level, thereby maintaining image quality despite using lightweight permanent magnets.
2Reliability
If the main magnetic field intensity is increased to improve signal-to-noise ratio, then image quality improves, but the mass and bulk of the MRI device increase
Solution Approach 1:
The patent employs a dynamic resonant frequency adjustment mechanism that continuously adapts the radio frequency assembly's resonant frequency to match the instantaneous Larmor frequency during image acquisition. This dynamic tracking allows the system to extract maximum signal strength from low-intensity magnetic fields, achieving high signal-to-noise ratios without requiring heavy high-field magnets.
3Reliability
If a radio frequency coil with narrow bandwidth is used, then the quality factor is improved, but the working frequency range is limited, which reduces adaptability to different magnetic field strengths
Solution Approach 1:
The patent implements a dynamic resonant frequency adjustment system that allows the radio frequency assembly to track and adapt to varying Larmor frequencies across a broad spectrum. The resonant frequency is continuously adjusted to remain centered on the current operating frequency, enabling the narrow-bandwidth high-quality-factor coil to effectively operate across the entire frequency range by synchronizing with the instantaneous resonant condition.
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 solution improves image quality by dynamically adjusting the resonant frequency to cover all natural frequencies of hydrogen nuclei spins, effectively increasing the quality factor of the radio frequency coil and maintaining a consistent signal-to-noise ratio, even with low-intensity main magnetic fields.
Implementation Method 1
a radio frequency coil, which is characterized for an intrinsic bandwidth and an intrinsic resonant frequency and intended for transmitting and receiving radio frequency signals
Implementation Method 2
a tunable circuit, which is associated with the radio frequency coil and configured to make it possible to adjust the equivalent impedance of the radio frequency assembly within a given impedance range, the adjustment of the equivalent impedance making it possible to adjust the resonant frequency
Implementation Method 3
An MRI apparatus also comprises gradient coils configured to produce magnetic fields of small amplitude and varying in space when a current is applied thereto
Implementation Method 4
an MRI apparatus is provided with a magnet intended to impose on the body a static magnetic field (called 'main magnetic field'), under the effect of which the nuclear spins associated with the hydrogen nuclei contained in the water molecules forming part of this body polarize
Data Source
AI summary
A magnetic resonance imaging device includes a radio frequency assembly configured to transmit and receive radio frequency signals, the radio frequency assembly comprising: a radio frequency coil, which is characterized for an intrinsic bandwidth and an intrinsic resonant frequency and intended for transmitting and receiving radio frequency signals; a tunable circuit, which is associated with the radio frequency coil and configured to make it possible to adjust the equivalent impedance of the radio frequency assembly within a given impedance range, the adjustment of the equivalent impedance making it possible to adjust the resonant frequency, referred to as the adjusted frequency, and the bandwidth, referred to as the adjusted band, of the radio frequency assembly, the adjusted frequency and the adjusted band each being included in the intrinsic bandwidth so that the radio frequency assembly has a higher quality factor than the quality factor of the radio frequency coil alone.