FISS MRI Radial Pulse Sequence for Flow Artifact Suppression
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Solution Overview
Problem
Current magnetic resonance angiography (MRA) techniques, such as balanced steady-state free-precession (bSSFP) and fast low angle shot (FLASH) pulse sequences, face challenges like sensitivity to flow artifacts, inferior signal-to-noise ratio, and difficulties in fat suppression, especially at high magnetic fields, limiting their diagnostic utility.
Innovation Solution
The radial fast interrupted steady-state (FISS) technique involves a gradient echo pulse sequence with a high repetition rate, using a radial k-space trajectory and specific RF pulse modules to reduce flow and off-resonance artifacts, while maintaining high signal-to-noise ratio and image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If balanced steady-state free-precession (bSSFP) pulse sequence is used, then high signal from flowing blood is achieved, but sensitivity to flow artifacts and off-resonance artifacts increases
Solution Approach 1:
The patent applies periodic interruption of the steady-state free precession sequence at predetermined intervals. This periodic action allows the system to maintain high signal intensity from flowing blood while periodically resetting the magnetization to suppress accumulated flow artifacts and off-resonance artifacts, thereby resolving the contradiction between signal intensity and artifact sensitivity.
Solution Approach 2:
The patent changes the parameter of steady-state continuity by introducing controlled interruptions. By modifying the temporal parameter (continuous vs. interrupted steady-state) and adjusting the repetition rate, the system maintains high signal from blood while suppressing artifacts through parameter modulation, resolving the contradiction between signal quality and artifact suppression.
2Object-affected harmful factors
If fast low angle shot (FLASH) pulse sequence is used, then flow artifacts are reduced, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent employs periodic interruption of the steady-state sequence, which allows for suppression of flow artifacts through controlled resetting of magnetization. Simultaneously, by optimizing the repetition rate and interruption timing, the system maintains adequate signal accumulation to preserve signal-to-noise ratio, thus resolving the contradiction between artifact reduction and signal quality.
Solution Approach 2:
The patent modifies the FLASH sequence by implementing interrupted steady-state acquisition with optimized repetition rates. This parameter change enables the system to achieve both flow artifact suppression and maintained signal-to-noise ratio by balancing the interruption frequency with signal accumulation requirements.
3Object-affected harmful factors
If high repetition rate gradient echo pulse sequence is used, then flow artifacts are suppressed, but acquisition time increases
Solution Approach 1:
The patent implements periodic interruption at optimized intervals rather than continuous suppression. This periodic approach achieves flow artifact suppression while minimizing the time lost to interruptions, as the system maintains steady-state signal between interruptions. The optimization of interruption timing ensures that artifact suppression is achieved without excessive acquisition time penalty.
Solution Approach 2:
The patent optimizes the repetition rate parameter to balance artifact suppression with acquisition efficiency. By carefully selecting the repetition rate and interruption frequency, the system achieves effective flow artifact suppression while minimizing the impact on total acquisition time, resolving the contradiction between artifact reduction and time efficiency.
4Measurement precision
If gadolinium-based contrast agents are administered, then diagnostic capability of MRA is enhanced, but risk of nephrogenic systemic fibrosis increases
Solution Approach 1:
The patent extracts the dependency on gadolinium-based contrast agents by developing a non-contrast MRA method using interrupted steady-state gradient echo sequences. This extraction eliminates the harmful association with nephrogenic systemic fibrosis while maintaining diagnostic capability through optimized pulse sequence design that enhances flow signal without contrast agents.
Solution Approach 2:
The patent replaces expensive and potentially harmful contrast agents with a safe, endogenous signal-based approach using blood flow itself as the contrast mechanism. The interrupted steady-state sequence exploits the natural T2* effects and flow-related enhancement, eliminating the need for external contrast substances and their associated risks.
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
FISS effectively suppresses flow and off-resonance artifacts, providing improved image quality and contrast compared to existing methods, particularly at high magnetic fields, and reduces saturation artifacts, enhancing diagnostic capabilities in MRA without the need for contrast agents.
Implementation Method 1
the individual magnetic moments of the nuclei in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency
Implementation Method 2
magnetic field gradients Gx, Gy, and Gz are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used
Implementation Method 3
If the substance, or tissue, is subjected to a magnetic field (excitation field B1) that is in the x-y plane and that is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped', into the x-y plane to produce a net transverse magnetic moment Mxy
Implementation Method 4
balanced steady-state free-precession ('bSSFP'), also called trueFISP. The bSSFP pulse sequence is a highly efficient imaging technique that can be used to produce high signal from flowing blood
Data Source
AI summary
A system and method for controlling a magnetic resonance imaging (MRI) system to create magnetic resonance (MR) angiograms of a subject. The method includes controlling the MRI system to acquire MR data by performing a pulse sequence that includes at least one set of modules formed by a first α/2 module, a (readout, α)n module, a second α/2 module. In this case, α denotes a radiofrequency (RF) flip angle and n denotes a number of times that the set of modules is repeated. The method also includes reconstructing an MR angiogram of the subject from the MR data.