Variable Flip Angle Profiles for MRI SAR Reduction
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Solution Overview
Problem
Simultaneous multislice imaging in magnetic resonance techniques faces challenges with high Specific Absorption Rate (SAR) exposure and peak power limitations, particularly at higher magnetic field strengths, which affects image quality and patient comfort.
Innovation Solution
The method involves using different temporal flip angle profiles for refocusing pulses in TSE sequences to minimize peak power and SAR, allowing for simultaneous multislice imaging by avoiding coincident maxima in flip angle curves and optimizing echo times to reduce overlap of high-power refocusing pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If simultaneous multislice imaging is performed with conventional refocusing pulses, then imaging speed and slice coverage are improved, but SAR exposure and peak power increase significantly
Solution Approach 1:
The patent applies parameter changes by modifying the flip angle of refocusing pulses from the conventional constant 180° to variable angles according to a flip angle curve. This changes the temporal distribution of RF energy, reducing peak power while maintaining echo train functionality, thereby lowering SAR exposure during simultaneous multislice imaging
Solution Approach 2:
The patent implements periodic action through the use of flip angle curves that modulate refocusing pulse angles periodically throughout the echo train. This periodic variation in pulse strength distributes energy more evenly over time, preventing sustained high peak power while maintaining the necessary refocusing function across multiple echoes
2Quantity of substance
If simultaneous multislice imaging is performed with conventional refocusing pulses, then slice coverage is improved, but peak power increases significantly
Solution Approach 1:
The patent changes the parameter of refocusing pulse flip angle from constant 180° to variable angles defined by a flip angle curve. This parameter modification reduces the peak power requirement while maintaining the ability to refocus spins across multiple echoes, enabling simultaneous multislice imaging with reduced peak power demands
3Manufacturing precision
If longer repetition time is used for T2-weighted imaging, then image contrast is improved, but imaging efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the refocusing pulse angles dynamic and variable throughout the echo train rather than static. This dynamic approach allows optimization of both contrast and efficiency by adjusting pulse angles to maintain necessary T2 weighting while reducing overall imaging time through more efficient echo train utilization
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 exposure and peak power, enabling more efficient and comfortable imaging, particularly at higher field strengths, while maintaining image quality and allowing for increased slice coverage and multi-contrast imaging.
Implementation Method 1
Magnetic resonance imaging is now an established imaging modality, particularly in the medical field. By excitation of a patient's nuclear spins aligned in a basic magnetic field in a recording area
Implementation Method 2
Electromagnetic energy is introduced into the patient's body by the excitation pulses and other radio-frequency pulses used in the course of a magnetic resonance sequence
Data Source
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AI summary
Method for operating a magnetic resonance device (29) during the acquisition of magnetic resonance data of a patient with a magnetic resonance sequence which, after at least one excitation pulse (8, 11), comprises several refocusing pulses (9, 12) during a readout period, wherein the strength of the refocusing pulses (9, 12) follows a temporal flip angle profile (1, 2, 20, 21, 23, 24, 26, 27) which is determined to minimize the SAR for the patient, wherein a multi-slice imaging technique is used for the simultaneous excitation and readout of at least two slices of a slice group to be acquired and the flip angle profiles (1, 2, 20, 21, 23, 24, 26, 27) are selected differently to further reduce the SAR for the patient compared to identical flip angle profiles.