Multiband RF Refocusing Pulse for Reduced Field of View MRI Slice Coverage
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Solution Overview
Problem
Current reduced field of view (rFOV) MRI techniques have limited slice coverage due to partial saturation in slice locations that overlap with the periodic side lobes of the RF excitation profile, particularly in applications like axial DWI of the spine or breast, where sufficient coverage is not achieved.
Innovation Solution
A magnetic resonance imaging system and method utilizing a 2D echo-planar RF excitation pulse with multiple side lobes along the slice select axis and a multiband RF refocusing pulse to increase slice coverage by simultaneously acquiring and refocusing multiple slice locations, employing parallel imaging techniques to reconstruct reduced field-of-view MR images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a 2D echo-planar RF excitation pulse with multiple side lobes is used to reduce field of view, then the field of view is reduced, but slice coverage is limited due to partial saturation in slice locations overlapping with side lobes
Solution Approach 1:
The refocusing pulse is segmented into multiple frequency bands, each targeting a specific slice location. This multiband refocusing pulse simultaneously refocuses spins in multiple slices that would otherwise experience partial saturation from the excitation side lobes, thereby increasing slice coverage while maintaining the reduced field of view
Solution Approach 2:
The refocusing pulse parameters are modified to create a multiband pulse with distinct frequency components. Each frequency band is tuned to a specific slice location, allowing selective refocusing of multiple slices. This parameter change enables the system to overcome the partial saturation limitation and achieve broader slice coverage
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 solution significantly enhances slice coverage by allowing the acquisition and reconstruction of multiple slices per acquisition, effectively addressing the limitations of conventional rFOV techniques while maintaining acceptable imaging quality.
Implementation Method 1
MRI uses a powerful magnet to create a strong, uniform, static magnetic field (i.e., the 'main magnetic field')
Implementation Method 2
the nuclear spins that are associated with the hydrogen nuclei in tissue water become polarized. This means that the magnetic moments that are associated with these spins become preferentially aligned along the direction of the main magnetic field
Implementation Method 3
gradient coils that produce smaller amplitude, spatially varying magnetic fields when a current is applied to them... create a small ramp on the magnetic field strength, and concomitantly on the resonance frequency of the nuclear spins
Implementation Method 4
Radio frequency (RF) coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei. The RF coils are used to add energy to the nuclear spin system in a controlled fashion
Data Source
AI summary
A method for reduced field of view magnetic resonance (MR) imaging includes applying a pulse sequence using a plurality of gradient coils and at least one RF coil of a magnetic resonance imaging system. The pulse sequence includes a two dimensional (2D) echo-planar RF excitation pulse with a plurality of side lobes along a slice select axis and a multiband RF refocusing pulse. MR data is acquired in response to the application of the pulse sequence and at least one MR image is reconstructed based on the MR data. The at least one MR image may then be displayed.