Adiabatic RF Pulse Pair for Inner-Volume Selection in 3D MRI
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Solution Overview
Problem
Conventional 3D-TSE/FSE magnetic resonance imaging techniques face challenges with high sensitivity to off-resonance effects and geometric distortions due to limited RF pulse bandwidth, especially when using inner-volume selection schemes, leading to artifacts like chemical-shift misregistration and aliasing.
Innovation Solution
Replacing the conventional single refocusing RF pulse with a pair of adiabatic RF pulses for inner-volume selection in the phase-encoding direction, which increases the RF pulse bandwidth and reduces off-resonance artifacts, allowing for higher bandwidths and more efficient data acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a single refocusing RF pulse is used for inner-volume selection in 3D-TSE/FSE, then the pulse duration can be extended, but the RF pulse bandwidth becomes limited, resulting in high sensitivity to off-resonance effects
Solution Approach 1:
The patent divides a single refocusing RF pulse into multiple refocusing RF pulses with different flip angles. This segmentation allows the total refocusing effect to be achieved while using shorter individual pulses with higher bandwidth, thereby reducing sensitivity to off-resonance effects while maintaining the necessary pulse duration for inner-volume selection
Solution Approach 2:
The patent changes the flip angle parameter across multiple refocusing RF pulses instead of using a single pulse with fixed parameters. By varying the flip angles (e.g., using a train of pulses with decreasing flip angles), the system achieves the desired refocusing effect with higher bandwidth pulses, resolving the contradiction between pulse duration and bandwidth
2Manufacturing precision
If the field of view is reduced in the phase-encoding direction using inner-volume selection, then aliasing artifacts are avoided, but off-resonance artifacts such as chemical-shift misregistration and geometric distortion increase due to limited RF pulse bandwidth
Solution Approach 1:
By segmenting the refocusing pulse into multiple pulses with different flip angles, the patent achieves inner-volume selection with higher bandwidth, thereby maintaining image accuracy while reducing off-resonance artifacts like chemical-shift misregistration and geometric distortion
Solution Approach 2:
The patent converts the limitation of conventional single-pulse methods into an advantage by using multiple pulses with varying flip angles. This approach transforms what would be a source of artifacts (limited bandwidth) into a solution that actually reduces artifacts while maintaining the benefits of inner-volume selection
3Ease of manufacture
If conventional RF pulses are used with limited bandwidth, then the system operates within technical limitations of the RF transmission system, but data acquisition efficiency is reduced due to need for oversampling
Solution Approach 1:
By changing the pulse parameters from a single conventional pulse to a train of pulses with varying flip angles, the patent achieves higher effective bandwidth that is compatible with conventional RF transmission systems while eliminating the need for oversampling, thereby improving data acquisition efficiency
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 achieves at least 70% higher RF pulse bandwidth compared to non-adiabatic pulses, significantly reducing off-resonance-related artifacts and enabling faster data acquisition with reduced oversampling.
Implementation Method 1
radiating at least a pair of adiabatic RF pulses, instead of a conventional single refocusing RF pulse, for inner-volume selection in the phase-encoding direction
Implementation Method 2
The adiabatic RF pulses allow a high RF pulse bandwidth, for a given limit on the peak B1 field, to be achieved. Tests conducted using an adiabatic pulse pair in a 3D-TSE/FSE pulse sequence have shown that at least 70% higher bandwidth can be achieved, compared to the best non-adiabatic RF pulse
Implementation Method 3
Rapidly switched (activated) magnetic gradient fields may be superimposed on the basic field for spatial encoding of the magnetic resonance data (measurement data)
Implementation Method 4
the examination subject, in the opening of a magnetic resonance apparatus, is positioned in a strong, static, homogeneous basic magnetic field (also called a B0 field) with a field strength of 0.2 to 7 Tesla or more, such that nuclear spins in the subject orient preferentially along the basic magnetic field
Data Source
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AI summary
In a method and apparatus for magnetic resonance data acquisition, data are acquired according to a single-slab three-dimensional turbo or fast spin-echo pulse sequence, wherein the inner volume selection in the phase-encoding direction takes place by radiating a pair of adiabatic RF pulses, instead of the single refocusing RF pulse that is conventional. The radiation of the adiabatic RF pulses allows a high RF pulse bandwidth to be achieved, for a given limit on the peak radio-frequency field strength. Such a high RF pulse band-width reduces off-resonance-related artifacts.