MRI Actuation Sequence for Simultaneous Multi-Slice Imaging
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Solution Overview
Problem
Magnetic resonance imaging (MRI) is a slow process due to long relaxation times of spins, leading to prolonged imaging times, discomfort for patients, and the inability to move or change position during scanning, with existing acceleration methods like simultaneous multi-slice (SMS) imaging facing challenges in SAR stress and RF peak power limitations, especially in high-field applications, and requiring complex post-editing for images with different contrasts.
Innovation Solution
A method for MRI that allows simultaneous excitation and imaging of multiple slices with different transverse magnetizations using a customized actuation sequence with slice selection gradient pulses, RF excitation pulses, and varying imaging parameters like flip angles and sequence types, reducing SAR stress and enabling simultaneous recording of images with different contrasts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sequential slice-by-slice imaging is used, then imaging accuracy and reliability are maintained, but imaging time becomes excessively long and patient comfort deteriorates
Solution Approach 1:
The imaging volume is segmented into multiple slices that are excited and imaged simultaneously using distinct RF frequency bands. Each slice receives a tailored pulse sequence with specific imaging parameters (flip angle, echo time, repetition time) optimized for its contrast requirements, enabling parallel acquisition while maintaining individual slice quality
Solution Approach 2:
The patent extends the imaging approach from temporal sequencing (one slice at a time) to spatial-frequency domain parallelism by assigning different frequency bands to different slices. This dimensional transition allows simultaneous multi-slice excitation and imaging, dramatically reducing total acquisition time while preserving diagnostic reliability
2Productivity
If simultaneous multi-slice imaging with identical imaging parameters is used, then imaging speed increases, but SAR stress and RF peak power increase excessively
Solution Approach 1:
Each slice is assigned local imaging parameters (flip angle, echo time, repetition time, pulse sequence type) optimized for its specific contrast requirements and tissue characteristics. This localized parameter optimization allows simultaneous excitation of multiple slices with different RF power demands, reducing peak SAR stress compared to uniform high-power excitation of all slices
Solution Approach 2:
The patent varies multiple imaging parameters across different slices including flip angle, echo time, repetition time, and pulse sequence type. By changing these parameters, the RF pulse characteristics and timing are optimized for each slice, distributing the SAR load more evenly and reducing peak power requirements while maintaining imaging speed
3Productivity
If simultaneous multi-slice imaging with different imaging parameters is used, then imaging speed increases and SAR stress reduces, but system complexity and post-editing requirements increase
Solution Approach 1:
The system performs preliminary assignment of distinct RF frequency bands to each slice before the imaging sequence begins. This pre-configuration of frequency-to-slice mapping and parameter assignment simplifies the simultaneous multi-parameter control during acquisition, as the system already knows which frequency band corresponds to which slice and its optimal parameters
Solution Approach 2:
The patent introduces an intermediary processing layer that manages the complex coordination of multiple pulse sequences, gradient fields, and RF pulses across different slices. This intermediary system handles the synchronization and parameter management, shielding the user from the underlying complexity while enabling simultaneous multi-slice imaging with different parameters
4Ease of operation
If patients are allowed to move during sequential imaging, then patient comfort improves, but imaging reliability and data quality deteriorate
Solution Approach 1:
The patent implements continuous simultaneous imaging of multiple slices throughout the entire acquisition period, eliminating the temporal gaps between slice acquisitions. This continuous parallel acquisition maintains consistent spatial relationships and reduces motion artifacts, improving reliability while allowing patients more freedom to adjust their position comfortably
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 SAR stress and RF peak power, allows for faster imaging with consistent spatial information, and minimizes post-editing work by acquiring images with different contrasts simultaneously, while maintaining high image quality and flexibility.
Implementation Method 1
at least one slice selection gradient pulse in the slice selection direction
Implementation Method 2
at least one RF excitation pulse to influence N partial volumes to be depicted simultaneously such that the magnetization state of at least a part of the plurality of N partial volumes to be depicted simultaneously and influenced by a further imaging parameter
Data Source
AI summary
In a method and a magnetic resonance imaging system to generate magnetic resonance image data of an object, during the acquisition of magnetic resonance raw data, different transverse magnetizations are excited in multiple sub-volumes to be depicted and used for imaging. These different transverse magnetizations are simultaneously present in at least one time interval of the measurement. Image data are reconstructed from the acquired raw data.