Magnetic Resonance B1 Field Uniformity via Time-Varying Excitation
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Solution Overview
Problem
Magnetic resonance scanners face significant challenges in maintaining spatial uniformity of the B1 field at high static magnetic fields due to dielectric and conductivity effects from subjects, particularly with asymmetric subjects, leading to non-uniform tip angle distributions and image quality issues.
Innovation Solution
A magnetic resonance scanner system with at least one radio frequency coil and two independent amplifiers, controlled by a controller to generate a time-varying spatial B1 field distribution that time-integrates to achieve a more uniform spatial tip angle distribution, reducing spatial non-uniformity without requiring additional hardware or coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single radio frequency coil is used to maintain spatial uniformity of the B1 field, then device complexity is reduced, but spatial non-uniformity increases due to dielectric and conductivity effects at high fields
Solution Approach 1:
The patent applies dynamics by making the B1 field distribution time-varying rather than static. The system uses multiple amplifiers to generate different B1 field distributions at different time points, which when time-integrated produce a uniform tip angle distribution. This dynamic approach allows the system to overcome spatial non-uniformity without adding physical coil complexity.
Solution Approach 2:
The patent employs periodic action by using a sequence of radio frequency pulses with different amplitudes and/or phases applied at different time points. This temporal sequencing of excitation pulses creates a time-varying B1 field distribution that compensates for spatial non-uniformities when integrated over the pulse sequence duration.
2Manufacturing precision
If multiple independent amplifiers are used to tailor the B1 field distribution, then spatial uniformity of tip angle distribution is improved, but device complexity increases
Solution Approach 1:
The patent reduces device complexity by using dynamics in the time domain. Instead of requiring many spatially distributed amplifiers, the invention uses a smaller number of amplifiers to create time-varying field distributions that achieve uniformity through temporal integration, thereby reducing hardware complexity while maintaining precision.
Solution Approach 2:
The patent applies parameter changes by varying the amplitude and phase parameters of the radio frequency pulses applied at different time points. These parameter variations in the temporal domain compensate for spatial non-uniformities, achieving uniform tip angle distribution without requiring proportional increases in amplifier数量.
3Manufacturing precision
If adiabatic RF pulses are used to reduce the range of excited tip angles, then spatial uniformity is improved, but time consumption and RF exposure increase
Solution Approach 1:
The patent uses periodic action with a sequence of non-adiabatic RF pulses applied at different time points with different amplitudes and phases. This approach achieves uniform tip angle distribution through temporal integration without requiring the extended duration of adiabatic pulses, thereby reducing acquisition time while maintaining precision.
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 provides flexible and effective compensation for B1 field non-uniformity, leading to more accurate magnetic resonance data and improved image quality, reducing the effects of B1 non-uniformity and enhancing reconstructed images and spectra.
Implementation Method 1
A magnetic resonance excitation system including at least one radio frequency coil arranged to generate a time-varying spatial B1 field distribution in a subject in the examination region
Implementation Method 2
The time-varying spatial B1 field distribution time-integrates to define a spatial tip angle distribution in the subject having reduced spatial non-uniformity
Data Source
AI summary
In a magnetic resonance scanner, a main magnet (20, 22) generates a static magnetic field at least in an examination region. A magnetic field gradient system (30, 54) selectively superimposes magnetic field gradients on the static magnetic field at least in the examination region. A magnetic resonance excitation system (36, 36′) includes at least one radio frequency coil (30, 301, 302, 303) arranged to inject radio frequency B1 fields into the examination region and at least two radio frequency amplifiers (38, 40, 40′) coupled with different input ports of the at least one radio frequency coil. A controller (66, 70) controls the magnetic resonance excitation system to produce a time varying spatial B1 field distribution in a subject (16) in the examination region that time integrates to define a spatial tip angle distribution in the subject having reduced spatial non uniformity.