Virtual Frequency Selective Inversion MRI Fat Suppression
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Solution Overview
Problem
Current MRI techniques face limitations in fat suppression, particularly with methods like STIR and SPIR, which require specific timing and contrast agents, and are sensitive to magnetic field inhomogeneities, leading to suboptimal image quality and increased data acquisition time.
Innovation Solution
The implementation of virtual frequency selective inversion (VFSI) method, which uses interleaved acquisitions with different echo times and phase-sensitive reconstruction to separate and invert MR signals without applying inversion RF pulses, reducing noise and power deposition while improving image contrast and robustness to magnetic field inhomogeneities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency selective saturation pulses (CHESS) are used for fat suppression, then fat signal suppression is achieved, but data acquisition time becomes excessively long (100-300 ms) causing fat magnetization recovery and poor suppression capability
Solution Approach 1:
The patent applies preliminary fat suppression by timing the frequency selective saturation pulse to occur before the TSE readout begins, specifically targeting the center of k-space acquisition. The pulse is applied at a predetermined time relative to the readout start, ensuring fat magnetization is suppressed before it can significantly recover during the lengthy acquisition window.
Solution Approach 2:
The patent changes the timing parameter of the saturation pulse relative to the TSE readout, positioning it to occur just before the readout begins rather than continuously or at other intervals. This temporal parameter adjustment optimizes the balance between achieving sufficient fat suppression and maintaining clinically acceptable acquisition times.
2Measurement precision
If non-frequency selective IR pulse is used for STIR, then fat signal is well suppressed, but additional IR pulse cannot be applied to impart T1-contrast as it unfavorably alters image luminance contrast and prevents fat signal suppression
Solution Approach 1:
The patent segments the fat suppression function from the T1-weighting function by using a frequency selective saturation pulse applied only to fat resonance frequencies, while keeping the TSE readout parameters optimized for both T1 contrast and fat suppression. This allows independent optimization of each function without mutual interference.
Solution Approach 2:
The patent applies frequency selective saturation specifically to the fat resonance frequency range while leaving other frequency ranges (water, other tissues) unaffected. This localized application of saturation enables fat suppression without altering the T1 contrast properties of other tissues, maintaining image luminance contrast integrity.
3Measurement precision
If STIR sequence is used with TSE readout, then fat suppression works well, but dark blood preparation is required and contrast agent cannot be used due to timing limitations
Solution Approach 1:
The patent employs dynamic adjustment of the saturation pulse timing and duration based on the specific TSE readout parameters and desired contrast enhancement timing. This dynamic optimization allows the sequence to accommodate contrast agent administration while maintaining effective fat suppression, removing the rigid timing constraints of traditional STIR.
4Measurement precision
If multiple reference datasets with different echo times are acquired for VFSI, then frequency separation and fat suppression are improved, but data acquisition complexity increases
Solution Approach 1:
The patent segments the frequency spectrum into distinct ranges (fat, water, other tissues) and acquires data at multiple echo times optimized for separating these frequency components. Each echo time is specifically chosen to maximize the phase difference between fat and water signals, enabling clean spectral separation.
Solution Approach 2:
The patent uses periodic modulation of the readout timing to systematically vary the echo times across multiple acquisitions. This periodic variation in acquisition timing creates the necessary phase evolution differences that enable frequency selective inversion while following a regular, reproducible pattern that simplifies reconstruction.
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
VFSI enhances image quality by reducing noise and power requirements, providing improved fat suppression and tissue contrast, and is less sensitive to magnetic field inhomogeneities, thus enabling more efficient and effective MRI data acquisition.
Implementation Method 1
separates components representing anatomical material having different ranges of resonance frequencies associated with different ranges of phases between an anatomical MR image representative dataset and an associated reference image dataset
Data Source
AI summary
A virtual frequency selective inversion (VFSI) method receives at least one MR image representative dataset and an associated phase reference dataset, and classifies anatomical material into a first component representing anatomical material having a first range of resonance frequencies associated with a first range of phase differences between the MR image representative dataset and the associated phase reference image dataset, and a second component representing anatomical material having a second range of resonance frequencies associated with a second range of phase differences between the MR image representative dataset and the associated phase reference image dataset. The method assigns different visual attributes to first and second components derived using phase differences between the MR image representative dataset and the reference image dataset and displays an image.