Echo-Spacing Shuffling for Variable-Density EPI
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Solution Overview
Problem
Current EPI magnetic resonance imaging methods are incompatible with variable-density undersampling schemes, leading to image artifacts and reduced acquisition speed, which is problematic for applications like functional MRI and diffusion-weighted imaging that require fast imaging without compromising image quality.
Innovation Solution
An EPI magnetic resonance imaging method that combines variable-density undersampling with a switched frequency-encoding readout gradient and intermittently blipped low-magnitude phase-encoding gradient, maintaining a predetermined ratio of echo spacing to phase encoding gradient integral, allowing for partial k-space undersampling without introducing excessive image artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If variable-density undersampling is applied in EPI, then acquisition speed is improved, but image artifacts increase and image quality deteriorates
Solution Approach 1:
The patent applies dynamics by making the echo spacing variable rather than fixed. The echo spacing is dynamically adjusted based on the k-space location and undersampling pattern, allowing the system to adapt to different regions of k-space. This dynamic adjustment enables variable-density undersampling while maintaining image quality by compensating for phase errors that would otherwise cause artifacts.
Solution Approach 2:
The patent changes the parameter of echo spacing from a fixed value to a variable parameter that depends on the k-space position and undersampling scheme. By modifying this critical parameter, the system can implement aggressive undersampling in certain regions while maintaining adequate sampling in others, thus improving acquisition speed without sacrificing image quality.
2Productivity
If longer echo trains are used to reduce scan time, then productivity is improved, but image quality deteriorates due to increased artifacts
Solution Approach 1:
The patent uses dynamic echo spacing adjustment within the echo train to accommodate longer echo sequences. By varying the spacing between echoes based on their position in the train and the corresponding k-space location, the system can extend the echo train duration to reduce scan time while compensating for the accumulated phase errors that would normally degrade image quality.
3Manufacturing precision
If regular sampling is used in EPI, then image quality is maintained, but acquisition speed is reduced
Solution Approach 1:
The patent applies asymmetry by implementing non-uniform, variable-density sampling patterns instead of regular uniform sampling. The sampling density is asymmetrically distributed across k-space, with higher density in central regions and lower density in peripheral regions. This asymmetric sampling strategy, combined with dynamic echo spacing, maintains image quality while significantly improving acquisition speed.
Solution Approach 2:
The patent implements partial sampling by selectively acquiring only the most critical k-space lines needed for image reconstruction. By using variable-density undersampling with dynamic echo spacing, the system acquires sufficient data for high-quality image reconstruction without the need for complete k-space sampling, thus improving acquisition speed.
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 combination enables accelerated MR imaging with maintained image quality, allowing for longer echo trains and reduced scan time while preserving image quality, making it suitable for time-critical applications.
Implementation Method 1
Magnetic resonance imaging is based on the controlled manipulation of nuclear spins inside a patient's body and subsequent detection of the nuclear spin response
Implementation Method 2
In addition to the basic field, a gradient system is used to apply a magnetic field gradient by means of which the magnetic resonance frequency (Larmor frequency) is determined at the respective location
Implementation Method 3
the k-space is traversed over time along a 'gradient trajectory' (also called 'k-space trajectory') defined by the switching of the gradient pulses
Data Source
AI summary
The disclosure is directed to an Echo-Planar-Imaging (EPI) magnetic resonance imaging techniques combined with a variable-density undersampling scheme. The technique comprises generating an RF pulse, applying a switched frequency-encoding read out gradient in a variable time interval, and applying simultaneously an intermittently blipped low-magnitude phase-encoding gradient with a variable value of an integral of the phase-encoding gradient. The aforementioned steps are carried out such that the k-space is at least partially undersampled and the time interval of one read out gradient is varied depending on the integral of the phase encoding gradient, such that a ratio between the variable time interval of the read out gradient and the integral of the corresponding phase encoding gradient is kept above or at a predetermined constant value, which is related to a predetermined criteria of image quality.