Multi-Slice STEAM Pulse Sequence for MRI Fat Suppression
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Solution Overview
Problem
Current diffusion-weighted STEAM sequences in magnetic resonance imaging are inefficient and time-consuming, particularly due to long 'mixing times' which extend examination times by several minutes, making them clinically unacceptable.
Innovation Solution
A multi-slice STEAM pulse sequence is developed that accelerates the imaging process by switching between excitation and readout modules for different slices during the mixing time, allowing for simultaneous or sequential execution of sub-sequences, thereby reducing the repetition time (TR) and making the acquisition time independent of the mixing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional STEAM sequence is used with long mixing time to suppress olefinic fat signals, then the fat suppression is achieved, but the examination time is extended by several minutes making it clinically unacceptable
Solution Approach 1:
The patent segments the examination into multiple slices, where each slice is excited and read out separately. By distributing the excitation and readout operations across multiple slices in a time-interleaved manner, the system can utilize the mixing time period more efficiently and reduce the overall repetition time while still achieving adequate fat suppression through the extended effective mixing time across all slices.
Solution Approach 2:
The patent applies preliminary fat suppression preparation by setting the mixing time to match the T1 relaxation time of olefinic fat before the actual readout. This preliminary action allows the fat signal to be suppressed in advance, and then the accelerated multi-slice sequence rapidly acquires all necessary slice data without requiring prolonged examination time.
2Object-affected harmful factors
If the mixing time is extended to suppress olefinic fat, then the fat suppression effectiveness is improved, but the repetition time and acquisition time increase significantly
Solution Approach 1:
The patent divides the imaging task into multiple slice segments that can be excited and read out in an interleaved fashion. This segmentation allows the system to maintain a long effective mixing time for fat suppression while reducing the repetition time by overlapping excitation and readout operations across different slices, thereby resolving the contradiction between fat suppression effectiveness and repetition time.
3Productivity
If a multi-slice STEAM sequence is implemented to accelerate imaging, then the examination time is reduced, but the sequence complexity and timing coordination requirements increase
Solution Approach 1:
The patent segments the multi-slice acquisition into modular excitation and readout blocks that can be systematically coordinated. Each slice has its own excitation module and readout module that are time-interleaved in a predictable pattern, reducing the overall sequence complexity while maintaining high imaging speed. This modular segmentation makes the timing coordination more manageable compared to non-modular approaches.
Solution Approach 2:
The patent employs periodic excitation and readout cycles for different slices in a time-interleaved manner. This periodic action creates a regular, predictable timing pattern that simplifies the coordination of multiple slices while achieving accelerated imaging. The systematic alternation between slice excitations and readouts reduces sequence complexity compared to irregular timing schemes.
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 the examination time by a factor of up to 10 without compromising signal-to-noise ratio (SNR), enabling clinically acceptable diffusion-weighted STEAM imaging by allowing for the suppression of olefinic fat signals that cannot be suppressed using conventional methods.
Implementation Method 1
High-frequency excitation signals (RF signals) are then emitted via a radiofrequency transmit system by means of suitable antenna devices, causing the nuclear spins of certain atoms, which have been excited to resonance by this radiofrequency field, to be tipped through a defined flip angle with respect to the magnetic field lines of the main magnetic field.
Implementation Method 2
For a magnetic field of 3 T, olefinic fat has a T1 time of about 521 ms, which is relatively short compared with other tissue components. If the TM time, i.e. the time between a second RF pulse and a third RF pulse, in a diffusion-weighted STEAM sequence is chosen to be in the region of the T1 relaxation time or longer, then it is possible to significantly reduce the signal contributed by olefinic fat.
Data Source
AI summary
The present disclosure is directed to controlling a magnetic resonance imaging system for generating magnetic resonance image data from an object under examination, in which magnetic resonance raw data is captured, and at least one multi-slice STEAM pulse sequence is generated. The multi-slice STEAM pulse sequence comprises one excitation module for each slice, in each of which are generated a first slice-selective RF excitation pulse and a second slice-selective RF pulse, and one readout module for each slice for acquiring magnetic resonance raw data, which readout module comprises a third slice-selective RF pulse and further sequence elements for spatial encoding and for receiving RF signals. Between the excitation module and the readout module of a first slice is implemented at least one excitation module or one readout module for another slice.