MRI Array Coil for Uniform RF Field Distribution
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges with non-uniform radio-frequency magnetic field distribution and sensitivity issues due to increasing static magnetic field intensities, leading to inadequate image contrast and uniformity, particularly when using separate transmission and reception array coils, which are inefficient and may increase specific absorption rate (SAR).
Innovation Solution
A magnetic resonance imaging apparatus that generates and allocates transmission radio-frequency pulse signals to multiple signal paths, selectively connects transmission and reception signal paths to radio-frequency coils, and controls the allocation to optimize the use of one or more coils for both transmission and reception, allowing for flexible application of the radio-frequency magnetic field and improved image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a birdcage type transmission coil is used to achieve uniform radio-frequency magnetic field distribution, then the radio-frequency magnetic field becomes non-uniform due to increased frequency at higher static magnetic field intensities, resulting in insufficient image contrast or uniformity
Solution Approach 1:
The array coil is designed to perform both transmission and reception functions. The same coil elements that detect magnetic resonance signals also generate the radio-frequency magnetic field for excitation, eliminating the need for separate transmission and reception coils and enabling uniform field distribution at high field intensities
Solution Approach 2:
The transmission coil is divided into multiple array coil elements arranged in a specific pattern. Each element can be independently controlled to generate radio-frequency pulses with specific amplitudes and phases, allowing precise control over the overall magnetic field distribution to achieve uniformity across the imaging region
2Manufacturing precision
If separate transmission array coil and reception array coil are used, then both coils must be disposed in the gantry around the subject, increasing device complexity and requiring large transmission power
Solution Approach 1:
The array coil serves dual purposes as both transmission and reception coil. The same physical coil structure and signal processing system are used for both generating the excitation radio-frequency field and detecting the magnetic resonance signals, significantly reducing the number of required components
Solution Approach 2:
The transmission and reception functions are merged into a single array coil system. The coil elements and their associated signal processing channels are shared between transmission and reception operations, simplifying the overall system architecture and reducing the number of discrete components
3Adaptability or versatility
If a large transmission array coil is prepared to cover the subject and enable imaging at various positions in a wide region, then a large transmission power is required which is not economical
Solution Approach 1:
The array coil system applies radio-frequency magnetic fields locally to specific regions of interest rather than uniformly across the entire subject. By controlling the amplitude and phase of individual coil elements, the system can concentrate the radio-frequency energy only where imaging is required, reducing overall power consumption
Solution Approach 2:
The system dynamically adjusts which coil elements are active and their respective power levels based on the imaging region and protocol requirements. This dynamic control allows the system to adapt power distribution to match the actual imaging needs, avoiding unnecessary power consumption in regions not being imaged
4Adaptability or versatility
If radio frequency is applied to a wide region of the subject, then the specific absorption rate (SAR) of the subject increases
Solution Approach 1:
The array coil enables selective application of radio-frequency magnetic fields to specific local regions of the subject. By independently controlling each coil element, the system can confine the radio-frequency energy to only the region being imaged, minimizing SAR in other parts of the subject
Solution Approach 2:
The system uses the received magnetic resonance signals from the same array coil to monitor and adjust the transmitted radio-frequency power in real-time. This feedback mechanism allows dynamic optimization of the radio-frequency field distribution to maintain image quality while minimizing SAR exposure
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 enables more efficient and uniform radio-frequency magnetic field application, reducing the need for multiple coils, minimizing SAR, and improving image quality by allowing for flexible field application and utilization of coils for both transmission and reception, thus addressing the limitations of existing systems.
Implementation Method 1
a magnetic resonance imaging apparatus which applies a gradient magnetic field and a radio-frequency magnetic field to a subject in a static magnetic field to image the subject based on magnetic resonance signals emitted from the subject
Implementation Method 2
magnetic resonance imaging (which will be referred to as an MRI apparatus hereinafter) and a magnetic resonance imaging method that perform imaging of a subject based on a magnetic resonance signal generated in the subjected by applying a gradient magnetic field and a radio-frequency pulse
Data Source
AI summary
A magnetic resonance imaging apparatus that applies a gradient magnetic field and a radio-frequency magnetic field to a subject in a static magnetic field to image the subject based on magnetic resonance signals emitted from the subject, includes a unit which generates K transmission radio-frequency pulse signals required to produce the radio-frequency magnetic field, an allocation unit which allocates the K transmission radio-frequency pulse signals to K in M transmission signal paths, a connection unit to which at most M radio-frequency coils are attachable and which selectively connects the M transmission signal paths and M reception signal paths to the radio-frequency coils, a selection unit which selects N in magnetic resonance signals which are respectively received by the at most M radio-frequency coils and transmitted through the at most M reception signal paths, and a unit which performs reception processing for each of the selected N magnetic resonance signals.