Quiet Echo-Planar Imaging Using Sinusoidal Gradient Sequences
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Solution Overview
Problem
Echo-planar imaging (EPI) methods suffer from high noise levels and artifacts due to rapid gradient switching, which affects image quality, especially in functional MRI, and existing noise reduction techniques like sinusoidal readout gradients require data correction and limit the use of Cartesian imaging methods.
Innovation Solution
A method using alternating readout and phase-encoding gradients with longer phase-encoding gradients activated for at least a quarter of the time interval between MR signal echoes, allowing continuous signal acquisition and non-Cartesian data acquisition, which reduces noise and artifacts by optimizing the trajectory in the raw-data space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rapid gradient switching is used for echo-planar imaging, then imaging speed is improved, but noise level increases
Solution Approach 1:
The patent applies periodic action by using sinusoidal readout gradients with specific frequencies that are separated from the acoustic resonance spectrum of the gradient system. The readout gradient oscillates sinusoidally rather than switching rapidly, and phase-encoding gradients are applied periodically at optimized intervals to achieve both fast imaging and noise reduction.
Solution Approach 2:
The patent changes the parameters of the gradient sequences by using sinusoidal waveforms instead of triangular pulses, optimizing the frequency of the readout gradient to avoid resonance, and adjusting the timing and amplitude of phase-encoding gradients to minimize noise while maintaining imaging speed.
2Object-generated harmful factors
If sinusoidal readout gradients are used to reduce noise, then noise level is reduced, but data acquisition efficiency decreases
Solution Approach 1:
The patent ensures continuous data acquisition during the entire duration of the readout gradient activation without interruption. The sinusoidal readout gradient continuously samples k-space throughout its oscillation cycle, and phase-encoding gradients are applied in a continuous sequence, eliminating dead times and maximizing data acquisition efficiency while maintaining noise reduction.
3Object-generated harmful factors
If phase-encoding gradients with long duration are used, then noise is reduced, but data acquisition time increases
Solution Approach 1:
The patent applies dynamics by using variable duration phase-encoding gradients that are activated for optimized time periods (at least a quarter of the time interval between two MR signal echoes). The gradient durations are dynamically adjusted based on the specific k-space location being sampled, allowing longer gradients for noise reduction while maintaining overall acquisition efficiency through optimized sequencing.
4Object-generated harmful factors
If non-Cartesian trajectory is used for data acquisition, then noise and artifacts are minimized, but reconstruction complexity increases
Solution Approach 1:
The patent uses a curved, non-Cartesian trajectory in k-space that follows the sinusoidal readout gradient pattern. This curved trajectory naturally avoids the high-frequency noise and artifacts associated with Cartesian sampling while the data is reconstructed using iterative non-Cartesian methods that are computationally intensive but produce superior image quality with minimized artifacts.
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 minimizes noise and artifacts, enabling quieter MR image acquisition with improved signal-to-noise ratio and image quality, even with incomplete data sampling, while allowing for accelerated imaging and use of iterative non-Cartesian reconstruction methods.
Implementation Method 1
An RF excitation pulse is radiated that produces transverse magnetization of nuclear spins
Implementation Method 2
a temporal sequence of a readout gradient is activated with alternating positive and negative values, as result of which MR signal echoes are generated
Implementation Method 3
multiple phase-encoding gradients are activated in a temporal sequence such that a value of each phase-encoding gradient is maximum when a value of the readout gradient is minimum
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for echo-planar acquisition of MR images using multiple reception coils, an RF excitation pulse is radiated to generate transverse magnetization, and a temporal sequence of a readout gradient is activated with alternating positive and negative values, thereby producing MR signal echoes. Multiple phase-encoding gradients are activated in a temporal sequence with a value of the phase-encoding gradients being maximum when a value of the readout gradients is minimum, and vice versa. A time period during which a single phase-encoding gradient is applied is at least a quarter of a time interval between two MR signal echoes. The MR signal echoes are read with the multiple reception coils in a trajectory in k-space, continuously without interruption during the readout gradient. The trajectory does not completely fill k-space with raw data in an edge region according to the Nyquist condition.