MRI Multi-Slice RF Pulse Segmentation for SAR Reduction
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) technologies, particularly turbo spin echo (TSE) sequences, face challenges in reducing specific absorption rate (SAR) and maintaining signal-to-noise ratio (SNR) when attempting to simultaneously acquire and refocus multiple slices, which limits examination time and image quality, especially at higher field strengths like 7T.
Innovation Solution
A method that involves emitting a sequence of spatially selective RF slice excitation pulses to excite multiple slices, followed by a preparation block with RF refocusing pulses to produce temporally separated echo signals, allowing for simultaneous refocusing and reduced RF power usage, while maintaining compatibility with diffusion-weighted imaging and T2 contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If multiple slices are simultaneously excited and refocused using conventional TSE sequences, then examination time is reduced, but specific absorption rate (SAR) increases and signal-to-noise ratio (SNR) deteriorates
Solution Approach 1:
The patent segments the echo train into multiple groups, where each group is refocused by a dedicated RF refocusing pulse. This segmentation allows for more efficient RF power distribution across multiple slices, reducing the peak SAR while maintaining the ability to simultaneously acquire multiple slices. The echo train segmentation enables independent optimization of refocusing pulses for different slice groups.
Solution Approach 2:
The patent dynamically adjusts the timing and configuration of RF refocusing pulses based on the specific acquisition requirements. By making the pulse sequence flexible and adaptive, the system can optimize the balance between examination speed and SAR reduction for each specific imaging scenario, rather than using a fixed conventional TSE approach.
2Loss of time
If multiple slices are simultaneously excited and refocused using conventional TSE sequences, then examination time is reduced, but signal-to-noise ratio (SNR) deteriorates
Solution Approach 1:
By segmenting the echo train into multiple groups with dedicated refocusing pulses, the patent prevents signal degradation that occurs in conventional approaches. Each segment maintains optimal echo spacing and refocusing timing, preserving SNR while enabling simultaneous multi-slice acquisition. This segmentation avoids the cumulative phase errors and signal loss that plague conventional simultaneous multi-slice TSE.
Solution Approach 2:
The patent changes key parameters of the pulse sequence, including echo spacing, refocusing pulse timing, and gradient configurations, to optimize both speed and SNR. By adjusting these parameters within the segmented framework, the system achieves faster examination times without sacrificing the signal quality needed for diagnostic imaging.
3Measurement precision
If RF refocusing pulses are emitted at high power to maintain SNR, then image quality is maintained, but specific absorption rate (SAR) increases
Solution Approach 1:
The segmentation of the echo train allows RF power to be distributed across multiple smaller refocusing pulses rather than requiring one or few high-power pulses. Each segmented group receives appropriate refocusing power, maintaining overall SNR while reducing peak SAR levels through temporal and spatial distribution of RF energy.
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 by a factor of m, enabling faster MRI examinations with improved SNR and compatibility with various contrasts, including T2-weighted imaging, even when the Carr Purcell Meiboom Gill condition is infringed, and reduces examination time without increasing RF radiation.
Implementation Method 1
nuclei in the examination object align with a non-zero nuclear magnetic dipole moment, often also called spin, along the field... radio-frequency excitation signals (RF pulses) are emitted by to be appropriate antenna setups, which cause the nuclear spins of specific nuclei to be resonantly excited
Implementation Method 2
several RF refocusing pulses are emitted to produce, respectively, a number of temporally separate echo signals per RF refocusing pulse
Implementation Method 3
By means of a gradient system, it is possible to superimpose the basic field with a magnetic field gradient by means of which, among other things, the magnetic resonance frequency (Larmor frequency) is modified in the direction of the field gradient
Implementation Method 4
radio-frequency excitation signals (RF pulses) are emitted by to be appropriate antenna setups, which cause the nuclear spins of specific nuclei to be resonantly excited by this radio-frequency field (i.e., by the Larmor frequency available at the respective location) to be tilted by a defined flip angle
Data Source
AI summary
In a magnetic resonance imaging procedure, multiple slices are initially spatially selectively excited in a first time interval by respective RF pulses followed by at least one RF refocusing pulse that causes one echo signal from each slice, with a time interval of two consecutive echo signals equal to the first time interval. A second RF refocusing pulse is emitted at a second time interval from the last echo signal that causes, one further echo signal per slice, with the time interval of two consecutive echo signals equal to the first time interval. At least one further RF refocusing pulse is emitted in a third time interval following the preceding RF refocusing pulse producing multiple temporally separated echo signals per refocusing pulse. The third time interval is selected so that the number of echo signals per RF refocusing pulse is twice the number of excited slices.