MRI Excitation Angle Optimization for RF Uniformity
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Solution Overview
Problem
In high magnetic field MRI systems, the shortening of RF signal wavelength results in nonuniform RF magnetic fields, making it difficult to determine optimal RF signal transmit power for maximizing NMR signal strength, leading to degraded image quality.
Innovation Solution
A magnetic resonance imaging apparatus with an imaging area setting unit, excitation angle determination unit, and imaging unit that uses a pre-scan to determine optimal excitation angles for RF magnetic fields, adjusting RF transmit power based on collected magnetic resonance signals to ensure uniform image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high magnetic field strength is used to increase RF signal frequency, then imaging resolution and signal-to-noise ratio are improved, but RF magnetic field uniformity deteriorates due to wavelength shortening
Solution Approach 1:
The patent applies local quality by determining position-dependent optimal excitation angles tailored to each imaging location. The system divides the imaging space into different regions and assigns specific excitation angles to each region based on the local RF magnetic field characteristics, thereby compensating for the nonuniformity caused by high field strength while maintaining high resolution imaging.
Solution Approach 2:
The patent changes the excitation angle parameter as a function of position to compensate for RF field nonuniformity. By adjusting the excitation angle according to the local B1 field strength at different locations, the system maintains consistent signal intensity across the imaging area despite the wavelength shortening effect at high magnetic fields.
2Device complexity
If conventional RF transmit power adjustment is used in high magnetic field, then equipment simplicity is maintained, but determination of optimal transmit power becomes difficult due to nonuniform RF magnetic field
Solution Approach 1:
The patent performs preliminary measurement of the RF magnetic field distribution (B1 mapping) before actual imaging to characterize the nonuniformity. Based on this preliminary data, the system pre-calculates position-dependent optimal excitation angles and transmit power settings, allowing accurate power determination without adding complex real-time adjustment mechanisms.
Solution Approach 2:
The system uses the imaging data itself to determine optimal transmit power settings. By analyzing the signal intensity distribution from preliminary scans, the system automatically derives the excitation angle corrections needed, making the system self-calibrating without requiring external complex measurement equipment.
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
Enables the determination of appropriate RF signal transmit power for high magnetic field imaging regions, improving image quality by maximizing NMR signal strength and maintaining uniformity across the imaging area.
Implementation Method 1
a transmit RF coil capable of generating a uniform RF magnetic field (B1 magnetic field) in the imaging place
Implementation Method 2
magnetic resonance imaging is an imaging method which magnetically excites nuclear spins of a patient placed in a static magnetic field with an RF signal at the Larmor frequency to reconstruct an image using an NMR (nuclear magnetic resonance) signal
Data Source
AI summary
According to one embodiment, a magnetic resonance imaging apparatus includes; an imaging area setting unit configured to set an imaging area for a patient according to an imaging condition; an excitation angle determination unit configured to collect magnetic resonance signals from the imaging area by a pre-scan and to determine, on the basis of the collected magnetic resonance signal, an optimal excitation angle of a radio-frequency magnetic field for use in an imaging scan; and an imaging unit configured to acquire imaging data by carrying out the imaging scan of the set imaging area for the patient applying the radio-frequency magnetic field with the determined optimal excitation angle.