MultiPINS RF Pulse Waveform for MRI Slice Excitation
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Solution Overview
Problem
Current MRI technologies face limitations in simultaneous multi-slice excitation due to high energy deposition and peak power requirements, especially at high field strengths, which restrict the usability of multi-band pulses and introduce off-resonance effects, while periodic slice excitation methods like PINS pulses suffer from slow k-space traversal and sensitivity to off-resonance.
Innovation Solution
A novel RF pulse waveform is developed by combining multiband and power-independent-of-number-of-slices (PINS) pulses, transforming the multiband pulse to match the k-space trajectory of PINS, and optimizing the mixing ratio to reduce energy deposition and off-resonance effects, resulting in a 'MultiPINS' pulse that balances energy transmission and pulse duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional multi-band RF pulses are used for simultaneous multi-slice excitation, then multiple slices can be excited at the same time, but the transmitted energy and peak power increase linearly with the number of slices
Solution Approach 1:
The patent combines two different RF pulse types (multi-band pulse and PINS pulse) into a hybrid pulse sequence. The multi-band component provides simultaneous excitation of multiple slices, while the PINS component reduces the overall energy transmission. This merging allows the system to achieve both high productivity (simultaneous multi-slice excitation) and low energy consumption (reduced SAR), resolving the technical contradiction between these two parameters.
2Use of energy by moving object
If VERSE algorithm is used to reduce RF energy, then both peak RF and total energy transmission are reduced, but pulse duration constraints and susceptibility gradients distort and shift slice profiles
Solution Approach 1:
The patent segments the RF pulse into multiple discrete sub-pulses separated by gradient blips, rather than using a continuous VERSE-modified pulse. This segmentation allows the system to reduce RF energy transmission while maintaining slice profile accuracy, because each sub-pulse can be precisely controlled and the gradient blips provide accurate spatial encoding without the distortion issues that affect continuous VERSE pulses.
3Use of energy by moving object
If PINS pulses are used for periodic slice excitation, then RF energy transmission is reduced and is independent of the number of slices, but k-space traversal is slow and the method is sensitive to off-resonance effects
Solution Approach 1:
The patent merges the multi-band pulse component (which enables faster k-space traversal through continuous RF excitation) with the PINS pulse component (which reduces energy transmission). The resulting hybrid pulse achieves both low RF energy transmission and improved k-space traversal speed, while the gradient blips provide robust encoding that reduces sensitivity to off-resonance effects compared to pure PINS sequences.
4Productivity
If the number of simultaneously excited slices is increased, then temporal efficiency of imaging is improved, but specific absorption rate (SAR) constraints limit the capability
Solution Approach 1:
The patent combines multi-band and PINS pulse characteristics to create a hybrid sequence that can simultaneously excite multiple slices (improving temporal efficiency) while maintaining low RF energy transmission (reducing SAR). This merging allows the system to increase the number of simultaneously excited slices without proportionally increasing SAR, thereby resolving the contradiction between productivity and harmful thermal effects.
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
The MultiPINS pulse waveform effectively minimizes energy transmission and peak power, reducing off-resonance effects and allowing for faster k-space traversal without exceeding specific absorption rate (SAR) limits, enhancing the efficiency and accuracy of simultaneous multi-slice MRI acquisitions.
Implementation Method 1
A multiband (MB) RF pulse waveform that is associated with excitation of multiple different slice locations is selected. An RF pulse waveform that includes a plurality of sub-pulses spaced apart in time is also selected.
Implementation Method 2
A gradient waveform that defines a plurality of gradient blips to be played out between the plurality of sub-pulses in the PINS RF pulse waveform is selected.
Data Source
AI summary
Systems and methods for controlling a magnetic resonance imaging (MRI) system to simultaneously excite multiple different slice locations. A multiband (MB) radio frequency (RF) pulse waveform is combined with an RF pulse waveform that results in periodic excitation of the slice locations, such as a power independent of a number of slices (PINS) RF pulse waveform. Before combination, the MB RF pulse waveform is preferably transformed to traverse the excitation k-space trajectory defined by a plurality of slice-encoding gradient blips. The combined RF pulse waveform is used to generate an RF excitation field generated while the plurality of slice-encoding gradient blips are played out. The portions of the combined RF pulse associated with the MB RF pulse are played out during the gradient blips, and the portions associated with the PINS RF pulse are played out between the gradient blips.