Multi-Slice MRI Using Slice-Encoding Gradient Blips
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Solution Overview
Problem
Current parallel MRI techniques fail to significantly reduce scan time for advanced imaging methods like diffusion weighted imaging and functional MRI, particularly for echo planar imaging (EPI) sequences, due to limitations in separating aliased pixels and increasing noise amplification, which degrades image quality and resolution.
Innovation Solution
A method for simultaneous multi-slice MRI that shifts aliased pixels by a selected percentage of the imaging field-of-view (FOV) to achieve more reliable separation, reducing scan time and improving signal-to-noise ratio (SNR), applicable to EPI and other pulse sequences that sample multiple lines of k-space after a single RF excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If simultaneous multi-slice acquisition is implemented using conventional parallel MRI techniques, then scan time is reduced, but noise amplification increases and image quality degrades due to difficulty in separating aliased pixels
Solution Approach 1:
The patent introduces a slice-encoding dimension by applying magnetic field gradient blips along the slice-encoding direction during EPI readout. This creates a fourth dimension (slice position encoding) that enables separation of simultaneously acquired slices in k-space, resolving the aliasing problem without increasing noise amplification. The gradient blips encode slice position information that allows subsequent separation of aliased pixels through Fourier transformation along this new dimension.
2Speed
If conventional parallel imaging methods are used to accelerate EPI sequences, then imaging speed increases, but separation of aliased pixels becomes unreliable and pixel tilt and blurring occur
Solution Approach 1:
The patent applies slice-encoding gradient blips during the EPI readout process to pre-encode slice position information into the k-space data before acquisition is complete. This preliminary encoding of slice position allows for accurate separation of aliased pixels during reconstruction without requiring post-acquisition estimation of coil sensitivities, thereby maintaining pixel separation accuracy while achieving accelerated imaging speed.
3Productivity
If multiple slices are acquired simultaneously to reduce scan time, then productivity increases, but device complexity increases due to need for additional gradient blips and reconstruction processing
Solution Approach 1:
The slice-encoding gradient blips serve multiple functions: they encode slice position information, enable separation of simultaneously acquired slices, and maintain compatibility with standard EPI readout. This multi-functionality allows the system to acquire multiple slices simultaneously using existing hardware capabilities without requiring additional specialized components, thereby increasing productivity while limiting the increase in device complexity.
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 reduces scan time by 2-6 fold for EPI acquisitions, enhances imaging speed and sensitivity, and allows for clinically acceptable durations for modern diffusion imaging methods like Q-ball imaging and high angular resolution diffusion imaging, while minimizing pixel tilt and blurring.
Implementation Method 1
magnetic field gradient blips are played out along the slice-encoding direction during the application of each phase encoding gradient blip
Implementation Method 2
Magnetic resonance imaging ('MRI') uses the nuclear magnetic resonance ('NMR') phenomenon to produce images
Data Source
AI summary
A method for multi-slice magnetic resonance imaging, in which image data is acquired simultaneously from multiple slice locations using a radio frequency coil array, is provided. By way of example, a modified EPI pulse sequence is provided, and includes a series of magnetic gradient field “blips” that are applied along a slice-encoding direction contemporaneously with phase-encoding blips common to EPI sequences. The slice-encoding blips are designed such that phase accruals along the phase-encoding direction are substantially mitigated, while providing that signal information for each sequentially adjacent slice location is cumulatively shifted by a percentage of the imaging FOV. This percentage FOV shift in the image domain provides for more reliable separation of the aliased signal information using parallel image reconstruction methods such as SENSE. In addition, the mitigation of phase accruals in the phase-encoding direction provides for the substantial suppression of pixel tilt and blurring in the reconstructed images.