Spiral MRI Trajectory Segmentation for Artifact Reduction
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Solution Overview
Problem
Spiral-shaped magnetic resonance imaging (MRI) trajectories face challenges in achieving high spatial resolution due to fast gradient modulations, which can stimulate peripheral nerves and result in image artifacts from field inhomogeneities and off-resonance effects, limiting the usability of spiral imaging for MR imaging.
Innovation Solution
The method involves switching gradient fields to traverse spiral segments in opposite directions during acquisition intervals, with the post-trajectory point positioned outside the k-space center, especially at times defined by RF pulses, to reduce interference artifacts and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spiral-shaped k-space trajectories are used for high efficiency data acquisition, then productivity is improved, but object-affected harmful factors worsen due to peripheral nerve stimulation from fast gradient modulations
Solution Approach 1:
The continuous spiral trajectory is divided into multiple spiral segments, each acquired during separate acquisition intervals. This segmentation allows the use of RF refocusing pulses between segments to manage gradient modulation effects and reduce peripheral nerve stimulation while maintaining overall acquisition efficiency.
Solution Approach 2:
The method employs periodic RF refocusing pulses at defined times between spiral segment acquisitions. This periodic action resets the magnetization and manages the effects of fast gradient modulations, reducing harmful peripheral nerve stimulation while preserving the efficiency benefits of spiral imaging.
2Manufacturing precision
If spiral-shaped trajectories are used for high-resolution imaging, then manufacturing precision is improved, but object-affected harmful factors worsen due to image artifacts from field inhomogeneities and off-resonance effects
Solution Approach 1:
RF refocusing pulses are applied at predetermined times between spiral segment acquisitions to preemptively correct for field inhomogeneity effects and off-resonance dephasing. This preliminary action prevents the accumulation of phase errors that would otherwise manifest as image artifacts, thereby maintaining high spatial resolution.
Solution Approach 2:
The method uses the timing of RF refocusing pulses relative to the spiral segment acquisitions to actively manage and correct for field inhomogeneity effects. By placing refocusing pulses at specific times, the system feedback-corrects for dephasing effects, reducing artifacts and preserving image quality.
3Loss of time
If the entire spiral-shaped k-space trajectory is traversed during a single acquisition interval, then loss of time is reduced, but measurement precision worsens due to low spatial resolution
Solution Approach 1:
The spiral trajectory is segmented into multiple portions acquired during separate intervals, allowing high-resolution sampling while managing the total acquisition time. Each segment can be optimized for resolution, and the segmentation enables the use of RF refocusing to maintain signal quality across multiple acquisitions.
4Productivity
If gradient fields are switched rapidly for spiral trajectory traversal, then productivity is improved, but object-generated harmful factors worsen due to discontinuous signal changes at connection points
Solution Approach 1:
RF refocusing pulses are applied preliminarily between spiral segment acquisitions to reset the magnetization state and prevent the accumulation of phase discontinuities. This preliminary action ensures continuous signal evolution across segment boundaries, eliminating artifacts while maintaining fast gradient switching for efficient traversal.
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 enhances the image quality and usability of spiral imaging by minimizing signal interferences and discontinuous signal changes at connection points, effectively suppressing off-resonant free induction decay and reducing phase jumps, leading to improved spatial resolution and artifact reduction.
Implementation Method 1
gradient fields are switched in such a way for spatial encoding that spiral segments of a spiral-shaped scanning pattern formed in k-space are traversed during the acquisition intervals
Implementation Method 2
acquisition intervals during which a magnetic resonance signal is acquired
Data Source
AI summary
Improvements in MR spiral imaging are provided in that spiral segments (2 to 8) are reordered, in particular alternately traversed and/or permuted. Moreover, repeatedly approaching the same post-trajectory points (16) between the acquisitions of the spiral segments (2 to 8) is provided, in which the post-trajectory points (16) are located outside of the center (18) of k-space (9), preferably outside of a region (20) of the k-space (9) covered by the spiral segments (2 to 8).