Asymmetric k-space Sampling for MRI Acquisition Time Reduction
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) techniques, such as Dixon imaging, require twice the measurement time due to the need for acquiring data at two distinct time points for in-phase and out-of-phase conditions, which limits acquisition efficiency.
Innovation Solution
The method involves asymmetric sampling of momentum space in the read-out direction to acquire out-of-phase echo signals, reducing the acquisition time by focusing on either positive or negative momenta, while maintaining symmetric sampling for in-phase signals, thereby reducing the overall measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Dixon imaging is performed by acquiring data at two distinct time points for in-phase and out-of-phase conditions, then fat and water signals can be separated to create two images, but the measurement time doubles compared to standard sequences
Solution Approach 1:
The patent applies asymmetric sampling in the readout direction for one of the two acquisitions (in-phase or out-of-phase). Instead of using symmetric echo trains for both time points, the method samples only a portion of k-space (e.g., only positive or only negative momenta) during one acquisition. This asymmetric approach reduces the number of echoes needed for one material type while maintaining sufficient sampling for fat-water separation, thereby cutting the measurement time approximately in half compared to conventional Dixon imaging that requires complete symmetric sampling at both time points.
2Loss of time
If asymmetric sampling is used to reduce acquisition time, then measurement time is reduced, but signal-to-noise ratio may be compromised
Solution Approach 1:
The patent changes the sampling parameters dynamically based on the field strength and the specific acquisition conditions. At lower field strengths where the in-phase/out-of-phase interval is larger, asymmetric sampling is applied more aggressively to reduce acquisition time. At higher field strengths where the interval is smaller, the sampling strategy is adjusted to maintain adequate signal-to-noise ratio. This parameter adaptation allows the system to optimize between acquisition speed and signal quality depending on the operating conditions.
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 allows for a significant reduction in acquisition time for MRI imaging while retaining signal-to-noise ratio, particularly beneficial for lower field strengths and enabling higher spatial resolution at intermediate or high field strengths.
Implementation Method 1
Different materials or molecules, in particular, water molecules and fat molecules, have slightly different nuclear spin resonance frequencies
Implementation Method 2
The time points of the different materials spins being in-phase or out-of-phase depend on the field strength of the MRI main magnetic field
Data Source
AI summary
In a method for MRI of an object, spins of a first material and spins of a second material are excited. An in-phase echo signal is acquired when the spins are in-phase and an out-of-phase echo signal is acquired, when the spins are out of phase. A first image for the first material and/or a second image for the second material is generated by a computing unit depending on the in-phase echo signal and the out-of-phase echo signal. For acquiring the out-of-phase echo signal, a momentum space is sampled asymmetrically in a read-out direction.