MRI Fat Suppression Using Segmented CHESS Pulses
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Solution Overview
Problem
The CHESS method for fat suppression in MRI is ineffective when the irradiation magnetic field has spatial non-uniformity, leading to inconsistent fat suppression due to varying proton excitation states.
Innovation Solution
Optimizing the flip angles and application intervals of multiple CHESS pulses to ensure uniform suppression of fat signals, using a combination of first, second, and third CHESS pulses with specific flip angles and spoiler gradient magnetic fields to control longitudinal magnetization and minimize non-uniformity effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single CHESS pulse is applied for fat suppression, then the suppression process is simple and fast, but the suppression is insufficient in areas with non-uniform magnetic field irradiation
Solution Approach 1:
The patent divides a single CHESS pulse into multiple segmented pulses (first CHESS pulse, second CHESS pulse, third CHESS pulse) with different flip angles. This segmentation allows each pulse to target specific ranges of non-uniformity, collectively achieving uniform fat suppression across the entire imaging area while maintaining a structured and manageable pulse sequence.
Solution Approach 2:
The patent applies different flip angles to different CHESS pulses to address local variations in magnetic field uniformity. The first CHESS pulse with a larger flip angle targets regions with certain non-uniformity characteristics, while subsequent pulses with smaller flip angles address other regions, ensuring that each area receives optimized suppression tailored to its local field conditions.
2Reliability
If multiple CHESS pulses with different flip angles are applied to reduce non-uniformity effects, then fat suppression uniformity improves, but the determination of optimal flip angles and application intervals becomes complex
Solution Approach 1:
The patent systematically varies the flip angle parameter across multiple CHESS pulses (first pulse with larger angle, second and third pulses with smaller angles) to optimize fat suppression. By changing this key parameter in a structured sequence, the patent achieves uniform suppression across non-uniform fields while providing a clear framework for determining optimal parameters based on field characteristics.
Solution Approach 2:
The patent employs periodic application of CHESS pulses with specific intervals between them. This periodic action with defined timing allows the system to systematically address different regions of non-uniformity while maintaining a predictable and manageable optimization process, reducing the complexity of determining when to apply each pulse.
3Reliability
If conventional fat suppression techniques are used, then the imaging process is straightforward, but artifacts occur due to non-uniform magnetic field effects
Solution Approach 1:
The patent segments the fat suppression process into multiple pulses with different flip angles, which collectively eliminate artifacts caused by non-uniform magnetic fields. This segmented approach maintains image quality by ensuring uniform suppression across all regions while preserving imaging efficiency through a streamlined multi-pulse sequence that can be integrated into standard imaging protocols.
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
Achieves consistent and effective fat suppression across all spatial areas, reducing imaging time and minimizing artifacts caused by non-uniform magnetic fields, while maintaining high suppression efficiency and reducing SAR.
Implementation Method 1
protons of a fat tissue are selectively excited by high-frequency magnetic field pulses of 90° having the resonance frequency of the protons of the fat tissue
Implementation Method 2
a spoil pulse is applied so that transverse magnetization of the excited protons of the fat tissue is subjected to phase dispersion
Data Source
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Figure 3(a)~3(c)
AI summary
A magnetic resonance imaging device includes magnetic field generating means and control means for controlling receiving means according to a predetermined pulse sequence, the predetermined pulse sequence including an unnecessary material suppressing sequence unit for canceling a signal from an unnecessary material which is not a measurement target and a main imaging sequence unit for measuring a nuclear magnetic resonance signal used to create an image of an examinee. The unnecessary material suppressing sequence unit generates at least two or more high frequency magnetic field pulses so that the longitudinal magnetization of the unnecessary material is made spatially uniform in the imaging space under application of a first high frequency magnetic field pulse in the main imaging sequence unit. The magnetic resonance imaging device further includes adjusting means for adjusting the flip angles of the two or more high frequency magnetic field pulses, and the control means applies the two or more high frequency magnetic field pulses at the flip angles adjusted by the adjusting means.