Flexible RF/Shim Coil Coupling Reduction in MRI Systems
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Solution Overview
Problem
Integrated RF/shim coil arrays in MRI systems experience unwanted magnetic coupling with gradient coils, leading to image artifacts, safety concerns, and reduced image quality, especially in head-only MRI systems where gradient coils are close to RF coils.
Innovation Solution
A pre-scan procedure measures and reduces coupling between gradient coils and integrated RF/shim coils by determining excessive coupling along each gradient axis and adjusting the orientation or disabling specific coil elements to minimize interference, thereby improving field homogeneity and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If gradient coils are placed close to RF coils in head-only MRI systems, then space utilization is improved, but magnetic coupling between coils increases causing image artifacts
Solution Approach 1:
A coupling compensation unit is introduced as an intermediary component between the gradient coils and RF coils. This unit includes compensation gradients that can be adjusted to counteract the harmful magnetic coupling effects, allowing the gradient coils to remain close to the RF coils while eliminating the image artifacts caused by coupling.
Solution Approach 2:
The system dynamically adjusts gradient waveform parameters including amplitude, duration, and timing to minimize coupling effects. By changing these parameters, the system optimizes the balance between maintaining close coil placement for space efficiency and reducing magnetic coupling interference that causes image artifacts.
2Device complexity
If integrated RF/shim coil arrays are used, then system complexity is reduced, but unwanted magnetic coupling with gradient coils increases
Solution Approach 1:
The integrated RF/shim coil array is segmented into independently controllable elements. This allows selective activation and individual optimization of each coil element's coupling characteristics, reducing overall magnetic coupling interference while maintaining the benefits of integration.
Solution Approach 2:
The coupling compensation unit serves as a mediator that specifically addresses the magnetic coupling between the integrated RF/shim coil array and gradient coils. By providing compensatory gradients, it enables the use of integrated arrays without suffering from the unwanted coupling effects.
3Productivity
If gradient waveform amplitude is increased to improve imaging speed, then productivity increases, but coupling between gradient sub-system and flexible coil assembly increases
Solution Approach 1:
The system dynamically adjusts gradient waveform parameters including amplitude, duration, and timing to minimize coupling effects. By changing these parameters, the system optimizes the balance between maintaining high imaging speed and reducing magnetic coupling interference.
Solution Approach 2:
The system uses measurement results from the flexible coil assembly to provide feedback on coupling levels. Based on this feedback, the control unit adjusts the gradient waveform parameters in real-time to maintain high imaging speed while keeping coupling interference below acceptable thresholds.
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 pre-scan procedure effectively reduces unwanted coupling, enhancing image quality and safety by optimizing the orientation and operation of RF/shim coils relative to gradient coils, ensuring accurate B0 shimming and minimizing artifacts.
Implementation Method 1
a main magnet enclosed by said housing and configured to generate a substantially uniform magnet field within the bore
Implementation Method 2
a gradient sub-system comprising gradient coils to apply a gradient waveform that provides a magnetic field gradient as perturbations to the substantially uniform magnet field
Implementation Method 3
receive radio frequency (RF) signals from the subject in response to a portion of the subject being scanned
Data Source
AI summary
Some implementations provide an MRI system that includes: a housing having a bore accommodating a portion of a subject; a main magnet enclosed by said housing and configured to generate a substantially uniform magnet field within the bore; a gradient sub-system to provide perturbations to the substantially uniform magnet field; a flexible coil assembly configured to (i) receive radio frequency (RF) signals from the subject in response to the portion of the subject being scanned, and (ii) generate and apply B0 shimming to improve a field homogeneity of the substantially uniform magnetic field; and a control unit configured to: drive the gradient sub-system using a gradient waveform; and receive measurement results responsive to the gradient waveform such that a coupling between the gradient sub-system and the flexible coil assembly is determined and subsequently reduced in response to the determined coupling exceeding a pre-determined threshold.