Balanced SSFP Fat Suppression via Alternating TR
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Solution Overview
Problem
Current MRI techniques using steady-state free precession (SSFP) face challenges in fat suppression due to limitations in signal-to-noise ratio, partial volume effects, and stringent repetition time constraints, leading to incomplete fat signal cancellation and artifacts.
Innovation Solution
The method employs alternating TR RF excitation with two separate repetition times (TR1 and TR2) and balanced magnetic gradients to acquire in-phase and out-of-phase SSFP images, which are then combined using discrete Fourier transforms and complex weighting to achieve selective spectral suppression, resulting in a wide stop-band for effective fat suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If periodic spectral saturation is used to suppress fat signal, then fat signal is reduced, but transient signal oscillations occur due to steady-state disruption
Solution Approach 1:
The patent applies periodic flip angle variations at specific frequencies to create spectral nulls that suppress fat signal while maintaining steady-state conditions. The periodic modulation of the flip angle creates frequency-selective suppression without disrupting the overall steady-state, thereby avoiding transient oscillations while achieving fat signal reduction.
2Object-generated harmful factors
If multiple phase-cycled acquisitions are used for fat suppression, then spectral stop-band is created, but scan time increases
Solution Approach 1:
The patent combines spectral suppression and fat-water separation into a single integrated SSFP sequence. By incorporating frequency-selective flip angle modulation directly into the steady-state free precession sequence, the method achieves both fat signal suppression and water-fat separation simultaneously, eliminating the need for separate multiple acquisitions and thereby reducing scan time.
3Object-generated harmful factors
If binomial excitation patterns are used for fat suppression, then fat signal is reduced, but high RF linearity is required
Solution Approach 1:
The patent employs dynamic flip angle modulation where the flip angle is varied periodically during the steady-state sequence. This dynamic adjustment creates frequency-selective suppression through spectral nulls at specific modulation frequencies, achieving fat suppression without requiring complex binomial excitation patterns or high RF linearity, thereby simplifying the RF pulse requirements.
4Illumination intensity
If conventional SSFP is used for imaging, then high signal-to-noise ratio is achieved, but fat tissue appears bright causing poor tissue depiction
Solution Approach 1:
The patent applies frequency-selective suppression that targets specific frequency ranges corresponding to fat resonance while preserving the overall high signal-to-noise ratio of SSFP. By creating spectral nulls at fat-specific frequencies through periodic flip angle modulation, the method selectively suppresses fat signal in specific frequency bands while maintaining strong signal intensity for water and other tissues, thereby improving tissue depiction without sacrificing overall SNR.
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 provides robust and flexible fat suppression with minimal remnant signal, even in high field inhomogeneities, and allows for a wider range of repetition times, improving the depiction of structures by reducing fat signal interference.
Implementation Method 1
nuclear magnetic moments are excited at specific spin precession frequencies which are proportional to the local magnetic field. The radio-frequency signals resulting from the precession of these spins are received using pickup coils.
Implementation Method 2
The phase difference due to the chemical-shift between fat and water can be used to separate the two components.
Implementation Method 3
By manipulating the magnetic fields, an array of signals is provided representing different regions of the volume.
Data Source
AI summary
A method of providing selective spectral suppression in balanced steady-state free procession (SSFP) magnetic resonance imaging for a first species and a second species is provided. A plurality of balanced SSFP images are acquired, wherein each acquisition of a balanced SSFP image comprises applying an alternating TR RF excitation, wherein the alternating TR RF excitation has a first TR and a second TR, wherein a period of the first TR (TR1) is greater than a period of the second TR (TR2), applying balanced magnetic gradients, acquiring an in-phase acquisition of the first and second species, acquiring an out-of-phase acquisition of the first and second species, and combining the in-phase acquisition and the out-of-phase acquisition to produce a combined image.