Spiral MR Imaging With Offset Trajectories for B0 Blur Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional spiral MR imaging is vulnerable to magnetic field inhomogeneities, leading to blurring artefacts that cannot be effectively resolved by existing de-blurring methods, especially in situations of strong B0 inhomogeneity, and reducing readout time to mitigate these artefacts significantly compromises method efficiency.
Innovation Solution
The method employs multiple planar spiral k-space trajectories with constant radial speed, offset in-plane from each other, to maintain sufficient k-space density and reduce artefacts without reducing efficiency, using threshold values to ensure radial k-space sampling density remains within gradient system capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-shot spiral imaging is used with full k-space coverage, then k-space coverage is complete, but blurring artefacts occur due to magnetic field inhomogeneities
Solution Approach 1:
The k-space sampling is divided into multiple interleaved spiral trajectories instead of a single continuous spiral. Each trajectory samples a subset of k-space points, and the combined data from multiple trajectories provides complete coverage while reducing the duration each trajectory spends in regions affected by B0 inhomogeneities, thereby reducing blurring artefacts
Solution Approach 2:
The imaging method dynamically adjusts the spiral trajectory parameters including variable radial velocity and interleaved sampling patterns. The radial velocity is modulated during the acquisition to optimize sampling density and reduce artefacts in different k-space regions, adapting to the local field inhomogeneity conditions
2Object-affected harmful factors
If readout time is shortened to reduce blurring artefacts, then artefact level decreases, but imaging efficiency is significantly reduced
Solution Approach 1:
By segmenting the k-space sampling into multiple interleaved trajectories, the method achieves complete k-space coverage without requiring excessively long readout times. The interleaved structure allows efficient packing of sampling points, maintaining high imaging efficiency while limiting the artefact-causing duration in each individual trajectory
Solution Approach 2:
The multiple spiral trajectories are designed to continuously and efficiently cover the entire k-space region without gaps or redundant sampling. This continuous coverage maintains high imaging efficiency and productivity while the optimized trajectory design ensures that no single trajectory spends excessive time in artefact-prone regions
3Measurement precision
If conventional spiral trajectories are used, then k-space coverage is achieved, but sampling density becomes insufficient in certain regions
Solution Approach 1:
The spiral trajectories employ variable radial velocity rather than constant velocity, dynamically adjusting the sampling rate according to the local requirements in different k-space regions. This dynamic approach optimizes sampling density where needed while maintaining manageable trajectory complexity through systematic velocity modulation functions
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 effectively reduces blurring artefacts caused by B0 inhomogeneities while maintaining scanning efficiency, allowing for high-quality MR imaging even in challenging magnetic environments.
Implementation Method 1
The magnetic field produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency)
Implementation Method 2
the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle
Implementation Method 3
the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 4
the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 5
magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field, leading to a linear spatial dependency of the spin resonance frequency
Data Source
AI summary
The invention relates to a method of MR imaging of an object (10) positioned in an examination volume of a MR device (1). It is an object of the invention to enable efficient spiral MR imaging without blurring artefacts, even in situations of strong B0 inhomogeneity. The method of the invention comprises the following steps: —subjecting the object (10) to an imaging sequence comprising at least one RF excitation pulse and modulated magnetic field gradients, —acquiring MR signals along two or more planar spiral k-space trajectories (31, 32, 33), wherein the radial k-space speed, i.e. the rate of variation of the radial distance from the spiral origin is essentially constant along each planar spiral k-space trajectory, and wherein the two or more k-space trajectories (31, 32, 33) are offset in-plane from each other, and—reconstructing an MR image from the acquired MR signals. Moreover, the invention relates to a MR device (1) and to a computer program for a MR device (1).