Simultaneous Multi-Slice MRI Using Phase Modulation Gradients
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Solution Overview
Problem
Conventional MRI scans, particularly cine MR scans, are inefficient due to the need for multiple breath-holds, leading to prolonged scan times and discomfort for patients, especially those with breathing difficulties, and require additional reference scans for slice separation, increasing scan duration.
Innovation Solution
A system and method for simultaneous multi-slice (SMS) MRI that applies phase-encoding steps with phase modulation magnetic field gradients to acquire echo signals from multiple slice locations simultaneously, reconstructing aliasing images and reference slice images without additional reference scans, using techniques like auto-calibrated multiband imaging and compressed sensing to accelerate data acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cine MR scan scans one or two slices per breath-hold, then the MRI scanner can maintain simple acquisition sequence, but the scan time is prolonged and patient comfort deteriorates
Solution Approach 1:
The patent segments the imaging task into multiple slice groups, where each breath-hold acquires a specific group of slices simultaneously using multi-band excitation. This segmentation allows the scanner to cover the entire heart in fewer breath-holds (e.g., 3-4 breath-holds for 12-16 slices) compared to conventional sequential scanning, thereby reducing total scan time while maintaining manageable acquisition sequences
Solution Approach 2:
The patent merges multiple slice acquisitions into a single simultaneous multi-slice acquisition using multi-band RF excitation pulses. By combining the excitation of multiple slices into one pulse sequence executed during a single breath-hold, the system achieves higher productivity without proportionally increasing sequence complexity, as the additional slices are handled through parallel processing in the acceleration factor
2Ease of operation
If conventional cine MR scan requires multiple breath-holds for whole heart scan, then the acquisition sequence remains simple, but patient comfort and reliability deteriorate
Solution Approach 1:
The patent segments the total number of slices into multiple groups that can be acquired in fewer breath-holds. For example, 12-16 heart slices are divided into 3-4 groups, allowing the entire heart to be scanned in 3-4 breath-holds instead of 6-12, significantly reducing the burden on patients with breathing difficulties while maintaining clinical diagnostic quality
Solution Approach 2:
The patent changes the acquisition parameter from sequential slice-by-slice scanning to simultaneous multi-slice scanning with parallel imaging acceleration. This parameter change reduces the number of required breath-holds from proportional to the total slice count to a fixed small number, improving patient comfort without extending scan time
3Productivity
If SMS imaging technique excites multiple slice locations simultaneously, then scanning efficiency improves, but image reconstruction complexity increases
Solution Approach 1:
The patent introduces an intermediary acceleration factor that quantifies the relationship between simultaneous slice excitation and reconstruction complexity. By using compressed sensing with sparsity constraints and parallel imaging with calibration scans, the system mediates between the high productivity of multi-slice excitation and the complexity of reconstruction, achieving acceptable reconstruction complexity through iterative algorithms that exploit signal sparsity and coil sensitivity information
Solution Approach 2:
The patent implements feedback mechanisms through calibration scans that acquire reference data from a subset of slices. This feedback information about coil sensitivity profiles and slice cross-talk is used to adjust and optimize the reconstruction algorithm, enabling accurate image recovery from simultaneously acquired multi-slice data while controlling reconstruction complexity through adaptive parameter selection
4Measurement precision
If additional reference scans are performed for slice separation, then image reconstruction accuracy improves, but scan time increases
Solution Approach 1:
The patent performs preliminary calibration scans before the actual multi-slice acquisition to obtain reference data about coil sensitivities and slice characteristics. This preliminary action captures the necessary information for slice separation in advance, allowing the main imaging sequence to proceed without additional reference scans interspersed throughout, thereby maintaining reconstruction accuracy while minimizing total scan time
Solution Approach 2:
The patent discards the need for repeated reference scans during the imaging sequence by recovering and reusing the calibration information obtained in the preliminary scan. The stored coil sensitivity profiles and slice separation parameters are applied throughout the acquisition, eliminating redundant reference scans and reducing scan time while preserving slice separation accuracy through the recovered calibration data
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, improves patient comfort by eliminating the need for repeated breath-holds, and enhances imaging efficiency by allowing simultaneous imaging of multiple slices with higher acceleration factors, such as achieving 16-fold acceleration for a whole heart cine in under 12 seconds.
Implementation Method 1
a plurality of phase-encoding (PE) steps to each of a plurality of slice locations of a subject to acquire a set of echo signals
Implementation Method 2
A phase modulation magnetic field gradient may be applied during each of at least some of the plurality of PE steps in the frame
Data Source
AI summary
A system for MRI is provided. The system may obtain a plurality of sets of under-sampled k-space data corresponding to a plurality of frames. Each set of under-sampled k-space data may be acquired simultaneously from a plurality of slice locations of a subject in one of the frames using an MRI scanner. The system may reconstruct a plurality of reference slice images based on the sets of under-sampled k-space data of the plurality of frames. Each of the reference slice images may be representative of one of the slice locations in more than one frame of the frames. The system may further reconstruct a plurality of image series based on the sets of under-sampled k-space data and the reference slice images. Each image series may correspond to one of the slice locations and include a plurality of slice images of the corresponding slice location in the plurality of frames.