MR Pulse Sequence Noise Reduction via Gradient Polarity Inversion
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Solution Overview
Problem
Current magnetic resonance (MR) examinations produce high noise levels due to rapid gradient switching during selective RF excitation, leading to patient discomfort and potential hearing damage, as the polarity reversal of selection gradients generates significant noise.
Innovation Solution
A method and apparatus for creating and optimizing pulse sequences in MR systems that include an excitation event block with an RF excitation pulse and a selection gradient, ensuring only spins within a predetermined volume section are excited with the same phase position at the end of the block, without polarity reversal of the selection gradient, thereby reducing noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarity reversal of selection gradient is used for rephasing, then gradient moment compensation is achieved, but noise generation increases significantly
Solution Approach 1:
The patent applies inversion by reversing the conventional approach: instead of using polarity reversal for rephasing, the invention uses a gradient without polarity reversal. The RF pulse is designed with specific phase modulation (e.g., chirp modulation) to achieve rephasing without the harmful polarity switch, thereby eliminating noise while maintaining gradient moment compensation.
Solution Approach 2:
The patent changes the parameters of the RF pulse and gradient combination. By modifying the RF pulse phase profile (using quadratic or higher-order phase modulation) and adjusting the gradient waveform parameters, the system achieves the same rephasing effect without polarity reversal, thus reducing noise generation while maintaining excitation precision.
2Productivity
If high slew rates and gradient amplitudes are used for rephasing, then rephasing efficiency is improved, but noise levels increase
Solution Approach 1:
The patent changes the operational parameters by using modified RF pulse sequences (such as chirp pulses with quadratic phase modulation) that allow effective rephasing with lower gradient amplitudes and slew rates. This parameter optimization maintains rephasing efficiency while significantly reducing the noise-generating gradient switching requirements.
3Loss of time
If pulse sequence timing is shortened, then examination efficiency is improved, but noise generation increases due to higher gradient moments required
Solution Approach 1:
The patent optimizes the pulse sequence parameters by using advanced RF pulse designs (e.g., compressed sensing sequences, parallel transmission techniques) that achieve the required excitation and rephasing in shorter time with reduced gradient moments. This allows maintaining examination efficiency while lowering noise generation through improved parameter selection.
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
Significantly reduces noise emission during MR examinations, improves MR data quality by accounting for magnetic field inhomogeneities, and allows for simultaneous use of multiple antennas, enhancing flexibility and reducing radiation exposure.
Implementation Method 1
The excitation event block includes an RF excitation pulse and at least one selection gradient. The pulse sequence is created such that only spins in the predetermined volume section are excited in the predetermined manner
Implementation Method 2
A predetermined volume section is specified in which nuclear spins are to be excited with the magnetic resonance system in a predetermined manner (for example defined by the flip angle)
Data Source
AI summary
In a method and magnetic resonance apparatus for creating an optimizing pulse sequence for selective RF excitation in the magnetic resonance apparatus, the pulse sequence has an excitation event block, which has an RF pulse and a selection gradient. Nuclear spins are excited in a predefined volume section in a predetermined manner by this excitation event block, which is designed to so that the spins inside the volume section have the same phase position after the excitation event block of the pulse sequence. The selection gradient does not have a polarity reversal.