Magnetic Resonance Scanner Noise Reduction via Radial K-Space Spoke Acquisition
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Solution Overview
Problem
Magnetic resonance scanners generate loud vibrations due to rapid changes in magnetic field gradients, causing noise that can be distressing for patients during MR data acquisition.
Innovation Solution
The method involves acquiring MR data along radial k-space spokes with an RF excitation pulse, using an echo time greater than 1 ms to keep the slew rate of gradients low, eliminating the need for dephasing gradients, and employing half pulses or ramp sampling to minimize slice rephasing moments, allowing for reduced noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic field gradients are switched rapidly to acquire MR data, then data acquisition speed is improved, but loudness increases
Solution Approach 1:
The patent changes the temporal parameter of gradient switching by using a longer echo time (>1 ms), which allows gradients to be switched at a lower rate of rise (slew rate). This parameter change directly reduces the loudness generated during MR data acquisition while still enabling complete k-space sampling through radial spoke trajectories.
2Object-affected harmful factors
If echo time is extended to reduce slew rate, then loudness is reduced, but data acquisition time increases
Solution Approach 1:
The patent segments the k-space sampling into multiple radial spokes that are acquired sequentially from the same RF excitation pulse. This segmentation allows the use of longer echo times for each spoke while still completing the full data acquisition in a reasonable total time, effectively distributing the time penalty across multiple smaller sampling units.
Solution Approach 2:
The patent employs periodic radial spoke sampling through k-space center, where multiple spokes are acquired in a repeating sequence. This periodic action pattern allows optimization of individual spoke acquisition parameters (including echo time) while maintaining overall efficient data collection through the systematic repetition of the sampling pattern.
3Reliability
If dephasing gradients are used in conventional sequences, then signal refocusing is achieved, but additional gradient switching increases loudness
Solution Approach 1:
The patent extracts and eliminates the dephasing gradient component from the pulse sequence by using radial spoke sampling through k-space center. This sampling approach inherently provides the necessary signal refocusing without requiring additional dephasing gradients, thereby removing the source of extra loudness while maintaining signal quality.
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 the loudness of the magnetic resonance scanner to below 75 dB, even with short echo times and small slice thicknesses, while maintaining effective MR data acquisition.
Implementation Method 1
application of an RF excitation pulse; magnetic resonance system for acquiring MR data
Implementation Method 2
magnetic field gradients are switched; gradient coils generate the magnetic field gradients; this causes a Lorentz force to be generated that leads to a mechanical excitation of the gradient coil system
Data Source
AI summary
In a method and a magnetic resonance system for acquiring MR data in a predetermined volume segment of an examination subject, an RF excitation pulse is radiated and MR data are acquired along trajectories extending radially through the center of k-space. The MR data of one k-space spoke, which corresponds to one half of a trajectory, are acquired while gradients are switched. Starting from the same RF excitation pulse, only MR data of one k-space spoke are acquired by starting in the k-space center, acquiring the MR data continuously up to the k-space periphery. The echo time is greater than 1 ms.