MR Pulse Sequence Spoiler Gradients for Artifact Reduction
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Solution Overview
Problem
Conventional magnetic resonance imaging techniques face challenges in eliminating flow artifacts and free induction decay (FID) artifacts, particularly in spinal imaging due to cerebral spinal fluid movement and non-slice-selective refocusing pulses.
Innovation Solution
A method involving the application of RF excitation and refocusing pulses with spoiler gradients in the readout direction to prevent artifacts, where the spoiler gradients are switched during the wait phase to minimize measurement time and eliminate FID and flow-related artifacts without increasing the acquisition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional refocusing pulses are applied without spoiler gradients, then the measurement time is reduced, but FID and flow artifacts occur in the MR images
Solution Approach 1:
Spoiler gradients are applied in the wait phase before the acquisition phase to pre-eliminate FID and flow artifacts. This preliminary action prevents artifacts from forming during the measurement, allowing artifact-free imaging without extending the total acquisition time.
Solution Approach 2:
The harmful FID and flow signal components are selectively removed using spoiler gradients applied in the readout direction. By extracting these unwanted signal components during the wait phase, the method prevents them from contaminating the useful MR signal during acquisition.
2Object-affected harmful factors
If spoiler gradients are applied in the readout direction during the wait phase, then FID and flow artifacts are eliminated, but the sequence complexity increases
Solution Approach 1:
The spoiler gradient application is merged into the existing wait phase of the pulse sequence, combining artifact elimination with the standard pulse sequence structure. This integration adds minimal complexity while effectively eliminating FID and flow artifacts.
Solution Approach 2:
Spoiler gradients are applied specifically in the readout direction during the wait phase, targeting only the specific artifact sources (FID and flow) without affecting other parts of the pulse sequence. This localized approach minimizes overall sequence complexity while achieving artifact elimination.
3Object-affected harmful factors
If the wait phase is extended to apply spoiler gradients, then artifact elimination is improved, but the total acquisition time increases
Solution Approach 1:
The spoiler gradients are applied periodically during the wait phase between excitation and acquisition, utilizing the existing temporal structure of the pulse sequence. This periodic application eliminates artifacts without requiring additional time beyond the standard wait phase duration.
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
The method effectively reduces FID and flow artifacts in magnetic resonance data acquisition, enhancing image quality by preventing unwanted signal overlap and motion-related distortions without extending the measurement time.
Implementation Method 1
To trigger nuclear spin resonances that can be measured as signals, radiofrequency excitation pulses (RF pulses) are applied to the object under examination
Implementation Method 2
For spatial encoding of the measurement data, rapidly switched magnetic gradient fields, called gradients for short, are superimposed on the main magnetic field
Implementation Method 3
In the wait phase at least two spoiler gradients are switched in the readout direction
Data Source
AI summary
A method a for acquiring magnetic resonance data of an object under examination by means of a magnetic resonance system comprises: in an excitation phase, applying an RF excitation pulse; in a wait phase following the excitation phase, applying at least one first RF refocusing pulse after the applied RF excitation pulse according to a first echo spacing; in an acquisition phase following the wait phase, applying at least two further RF refocusing pulses to generate echo signals according to a second echo spacing, wherein the second echo spacing is smaller than the first echo spacing; and reading out the echo signals generated in the acquisition phase as magnetic resonance data from which image data can be reconstructed, wherein in the wait phase at least two spoiler gradients are switched in the readout direction.