Pulse Gap Cycling for SWIFT MRI Bullseye Artifacts
Solution Overview
Problem
Magnetic resonance imaging systems using Sweep Imaging with Fourier Transform (SWIFT) often produce undesirable bullseye artifacts due to gated transmit and receive signals, which current systems are inadequate in mitigating.
Innovation Solution
Implementing pulse gap cycling by shifting the gap positions among discrete locations in the transmitter and receiver sequences, combined with oversampled digitization and digital filtering, to reduce image artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gated transmit and receive signals are used in SWIFT, then image acquisition is enabled, but bullseye artifacts with concentric rings appear in the image
Solution Approach 1:
The pulse sequence is divided into multiple segments with different gap positions. Instead of using a single fixed gap position, the method segments the acquisition into multiple shots where each shot uses a different gap position among N discrete positions. This segmentation allows the artifact to be distributed and then averaged out, resolving the contradiction between enabling image acquisition and eliminating bullseye artifacts.
Solution Approach 2:
The gap position is cycled periodically through N discrete positions across multiple pulse sequences. This periodic variation in gap positioning causes the artifact to manifest at different locations in each cycle, and when the data from all cycles are combined, the artifacts average out. This periodic action maintains productivity while eliminating the harmful bullseye artifact.
2Manufacturing precision
If gap cycling is implemented to reduce artifacts, then image quality improves, but the complexity of the pulse sequence increases
Solution Approach 1:
The method changes the temporal parameter of the pulse sequence by varying the gap position among N discrete positions. This parameter change is systematic and controlled, allowing artifact reduction while maintaining a relatively simple implementation. The complexity is managed by using a regular cycling pattern rather than complex variable parameters.
Solution Approach 2:
The pulse sequence is made dynamic by allowing the gap position to change across different shots rather than remaining fixed. This dynamic adjustment of the gap position enables artifact reduction while keeping the overall sequence structure simple and manageable, resolving the contradiction between image quality and sequence complexity.
Data Source
AI summary
A magnetic resonance image is produced by shifting a gap during acquisition of spin data for a specimen. The spin data is generated by a gapped excitation sequence.