Balanced Slice-Selective Gradients for Multiband MRI Artifact Reduction
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Solution Overview
Problem
Conventional multiband MRI techniques are inefficient for sequences like spin echo, turbo spin echo, and gradient echo with long TRs, as they require inefficient single-band reference scans and are not compatible with sequences that acquire multiple k-space lines after one excitation, leading to noise amplification and residual aliasing artifacts.
Innovation Solution
A generalized process for simultaneous multi-slice MRI using multiband RF excitation, which involves a low-resolution fast multi-dimensional reference scan to obtain coil sensitivity maps and applies balanced slice-selective gradients for phase modulation, allowing for efficient separation of aliased signals across various 2D and 3D MR pulse sequences, including spin-echo, turbo spin-echo, and echo planar imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-band reference scan is used for multiband imaging, then coil sensitivity profiles can be obtained for parallel imaging reconstruction, but acquisition time is significantly increased and imaging efficiency is reduced
Solution Approach 1:
The patent applies partial action by acquiring only a subset of k-space lines (e.g., every other line or a reduced number of lines) for the reference scan instead of the complete k-space. This partial acquisition provides sufficient coil sensitivity profile information for parallel imaging reconstruction while dramatically reducing the reference scan time and improving overall imaging efficiency.
2Object-affected harmful factors
If blipped CAIPIRINHA method is used for phase modulation, then FOV shift and reduced aliasing artifacts are achieved, but it is incompatible with sequences using refocusing RF pulses and balanced SSFP sequences
Solution Approach 1:
The patent inverts the conventional blipped CAIPIRINHA approach by applying slice-selective gradient blips during the readout period rather than during the excitation period. This inversion makes the phase modulation compatible with refocusing RF pulses and balanced SSFP sequences while still achieving FOV shift and reduced aliasing artifacts, thus resolving the compatibility issue.
Solution Approach 2:
The patent changes the timing parameter of the gradient blip application from the excitation period to the readout period. This parameter change enables compatibility with multiple MRI sequences including those with refocusing RF pulses and balanced SSFP sequences, while maintaining the beneficial effects of FOV shift and artifact reduction.
3Productivity
If multiple k-space lines are acquired after one excitation (as in EPI and TSE sequences), then imaging efficiency is improved, but conventional multiband techniques cause noise amplification and residual aliasing artifacts
Solution Approach 1:
The patent applies preliminary action by implementing phase modulation through gradient blips before the readout of each k-space line. This preliminary phase modulation separates the aliased slices in the phase-encoding direction, preventing noise amplification and residual aliasing artifacts during the efficient multiple k-space line acquisition of EPI and TSE sequences.
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 significantly reduces acquisition time and minimizes noise amplification and aliasing artifacts, enabling efficient multiband slice accelerated imaging for diverse MRI sequences while maintaining high image quality.
Implementation Method 1
simultaneous multi-slice or multi-slab Magnetic Resonance Imaging (MRI) using multiband RF excitation
Implementation Method 2
slice-selective gradients
Implementation Method 3
the signals from all slices are acquired simultaneously by multiple receive coils
Data Source
AI summary
A computer-implemented method for performing multi-band slice accelerated imaging includes performing a low-resolution fast multi-dimensional reference scan to obtain a coil sensitivity map. A multiband imaging scan is performed to acquire a plurality of k-space lines representative of an anatomical area of interest. A multi-band signal corresponding to the plurality of k-space lines is separated into a plurality of image slices using a parallel imaging reconstruction technique and the coil sensitivity map.