Frequency-Modulated bSSFP Sequence for Water-Fat Separation
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Solution Overview
Problem
Magnetic resonance imaging (MRI) using balanced steady-state free precession (bSSFP) sequences is prone to banding artifacts, which degrade image quality and make it difficult to separate water and fat pixels, especially in high-field inhomogeneities.
Innovation Solution
A frequency-modulated bSSFP acquisition sequence with regional phase correction is used to separate water and fat pixels, allowing for robust separation without banding artifacts and tissue swaps, even in high-field conditions, by exploiting the phase-sensitive differences between water and fat signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard bSSFP sequence is used for imaging, then scan time is short and SNR is high, but banding artifacts occur that reduce image quality
Solution Approach 1:
The patent applies frequency modulation to the bSSFP sequence, dynamically varying the frequency during the acquisition to sweep through different resonance conditions. This dynamic frequency adjustment allows the system to avoid the static banding artifacts that plague conventional bSSFP while maintaining the sequence's inherent speed and signal strength advantages.
Solution Approach 2:
The invention changes the frequency parameter dynamically during the imaging sequence. By modulating the frequency across a range of values rather than maintaining a fixed frequency, the system can navigate around the banding artifact problem zones while still acquiring the necessary data for high-quality water-fat separation imaging.
2Object-affected harmful factors
If multiple acquisitions are performed to remove banding artifacts, then image quality improves, but measurement time increases
Solution Approach 1:
Instead of performing multiple static acquisitions and combining them, the patent uses a single dynamic frequency-modulated acquisition that continuously sweeps through the frequency range. This eliminates the need for multiple separate scans while achieving the same banding artifact removal effect, thereby reducing total measurement time.
Solution Approach 2:
The frequency modulation creates a continuous sweep through different frequency conditions within a single acquisition. This continuous variation allows the system to gather all necessary information in one go, maintaining useful action throughout the scan rather than requiring discrete multiple acquisitions to be combined.
3Measurement precision
If frequency modulation is applied to bSSFP, then water-fat separation improves and banding artifacts are reduced, but sequence complexity increases
Solution Approach 1:
The patent implements frequency modulation by systematically varying the frequency parameter according to a predefined modulation scheme. While this adds complexity to the sequence design, the use of standard frequency modulation techniques and post-processing methods keeps the implementation manageable while achieving superior water-fat separation and artifact reduction.
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 enables robust water-fat separation in a single acquisition, reducing measurement time and improving robustness against off-resonance effects, compared to standard bSSFP and multiple acquisition methods, while maintaining high image quality.
Implementation Method 1
Water and fat are then separated in the resulting image, based on the sign of the real part of the signal of each pixel
Implementation Method 2
Typically, this requires several excitations of nuclear spins in the region of interest in the subject, and readout of the resulting MR signals along different trajectories in k-space
Implementation Method 3
Balanced steady-state free precession (bSSFP) sequences are known and often used in MR imaging due to their short scan times, high SNR and excellent contrast
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for data acquisition with fat-water separation in a resulting MR image, an MR data acquisition sequence is operated to acquire MR signals from a subject. Said MR signals comprise fat signals originating from fat in the subject and water signals originating from water in the subject, are acquired by executing a frequency-modulated balanced steady-state free-precession (bSSFP) sequence. The MR signals are entered as numerical values into a memory organized as k-space, the memory thereby containing k-space data. An image is reconstructed from the k-data and subjected to regional phase correction. The corrected image being composed of respective pixels having an intensity produced by the fat signals and an intensity produced by the water signals, with the respective pixels being readily distinguishable from each other in the image due to use of the frequency-modulated bSSFP sequence and the block regional correction.