Variable k-Space Sampling for MRI Acquisition Speed
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Solution Overview
Problem
Magnetic resonance imaging systems face limitations in acquiring image data quickly for moving subjects, such as the heart, due to the strict sampling requirements of the Nyquist-Shannon theorem, often resulting in low spatial resolution to meet minimum time constraints.
Innovation Solution
A method for controlling a magnetic resonance imaging system that uses sparse sampling of readout pairs in k-space with varying sampling intervals, allowing for accelerated data acquisition without significant quality loss, by arranging readout pairs with different sampling intervals along the readout axis, and applying different sampling rules based on distance from the k-space center, enabling efficient reconstruction of image data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strict Nyquist-Shannon sampling rate is used to ensure image quality, then spatial resolution is maintained, but acquisition time increases and productivity decreases
Solution Approach 1:
The patent changes the sampling parameters by using variable sampling intervals instead of uniform sampling. The sampling interval is adjusted based on the distance from the k-space center, with smaller intervals near the center (where most signal energy resides) and larger intervals in peripheral regions. This parameter change allows accelerated acquisition while maintaining image quality.
Solution Approach 2:
The patent applies different sampling densities to different regions of k-space. High-density sampling is applied to the central region where the majority of signal energy is concentrated, while low-density sampling is applied to peripheral regions. This local differentiation maintains image quality in critical areas while reducing overall sampling requirements to enable faster acquisition.
2Reliability
If uniform sampling according to Nyquist-Shannon theorem is used, then complete k-space coverage is achieved, but acquisition time is excessive for dynamic imaging
Solution Approach 1:
The patent modifies the sampling parameters by implementing variable sampling intervals that change based on position in k-space. The sampling interval increases with distance from the k-space center, allowing fewer samples to be taken in peripheral regions while maintaining adequate sampling density in the central region where most diagnostic information is contained.
Solution Approach 2:
The patent applies partial sampling by acquiring data from only a subset of k-space points rather than uniformly sampling all points. By strategically selecting which k-space points to sample (with higher density near the center and lower density at the periphery), the system achieves adequate image quality with reduced total sampling, thereby decreasing acquisition time.
3Productivity
If low spatial resolution is selected to meet minimum time constraints, then acquisition speed increases, but image quality deteriorates
Solution Approach 1:
The patent applies non-uniform sampling density across different k-space regions, with higher sampling density in the central region and lower density in peripheral regions. This local quality differentiation allows the system to maintain adequate spatial resolution in critical areas while reducing overall sampling requirements to enable faster acquisition.
Solution Approach 2:
The patent changes the sampling parameters by using variable sampling intervals instead of uniform sampling. The sampling interval is adjusted based on the distance from the k-space center, with smaller intervals near the center (where most signal energy resides) and larger intervals in peripheral regions. This parameter change allows accelerated acquisition while maintaining image quality.
4Loss of time
If fast sampling is implemented for dynamic imaging, then acquisition time decreases, but eddy current artifacts increase
Solution Approach 1:
The patent changes the sampling parameters by implementing variable sampling intervals that increase with distance from the k-space center. This parameter modification allows the system to use longer inter-sampling intervals in peripheral regions, reducing the rate of gradient switching and thereby minimizing eddy current generation while still achieving fast overall acquisition.
Solution Approach 2:
The patent applies different sampling strategies to different k-space regions. In peripheral regions where eddy currents are most problematic, the sampling interval is increased to reduce gradient switching frequency. In central regions where diagnostic information is most concentrated, adequate sampling density is maintained. This local differentiation reduces eddy current artifacts while preserving image 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 enables nearly real-time acquisition of high-quality magnetic resonance image data with increased speed and reduced eddy current artifacts, allowing for rapid image generation and presentation, particularly suitable for dynamic imaging like CINE acquisitions.
Implementation Method 1
the dephasing or relaxation time of the nuclear spins is determined after a deflection of their magnetization out of the initial alignment, such that different relaxation mechanisms or relaxation times, which are typical to the material, can be identified
Implementation Method 2
the spatial resolution is based on a chronologically established manipulation of the deflected magnetization with the use of the gradient field in a collection of pulses known as a measurement sequence
Implementation Method 3
The magnitude of the magnetization (in particular the transverse magnetization, defined in a plane transverse to the basic magnetic field) at a defined location of the examination subject can be determined from the data of the readout point, through a Fourier transformation that calculates the signal strength of the signal in the spatial domain from a signal strength (magnitude of the magnetization) that is associated with a defined frequency (the spatial frequency) or phase position
Data Source
AI summary
In a method to control a magnetic resonance imaging system to generate magnetic resonance image data of an examination subject, raw magnetic resonance data are acquired that include measurement values at multiple readout points in k-space. The readout points are arranged along a readout axis in k-space as readout pairs with a predetermined pair spacing relative to one another. Readout pairs that are adjacent in k-space along the readout axis have a sampling interval that is different than the pair spacing, which sampling interval varies along the readout axis. A control sequence determination system is designed to determine a control sequence for a magnetic resonance imaging system that is designed to control the magnetic resonance imaging system according to this method, and a magnetic resonance imaging system that has a control device designed to control the magnetic resonance imaging system according to such a method.