Non-Cartesian MRI Sampling With Adaptive Water-Fat Shift Alignment
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Solution Overview
Problem
Non-Cartesian k-space sampling patterns in magnetic resonance imaging result in varying readout directions, leading to spatial fat-water shifts that cause image blurring and unexpected appearances, making it difficult for radiologists accustomed to Cartesian patterns.
Innovation Solution
The method involves controlling a magnetic resonance imaging system to acquire k-space data using rotated Cartesian patterns within non-Cartesian sampling, aligning the effective water-fat shift direction with the chosen direction to mimic Cartesian acquisitions, and applying modifications such as varying readout gradients and view angle tilting to minimize spatial shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-Cartesian k-space sampling patterns are used, then imaging speed and coverage are improved, but spatial fat-water shifts occur in various directions causing image blurring
Solution Approach 1:
The patent applies local quality by making the readout gradient strength variable depending on the blade rotation angle. Specifically, the gradient strength is reduced for blades that would otherwise produce large fat-water shifts, while maintaining standard gradient strength for blades where shifts are minimal. This localized adjustment of gradient parameters eliminates the need for post-processing correction while preserving imaging speed benefits.
Solution Approach 2:
The patent changes the readout gradient strength parameter dynamically based on the blade rotation angle in non-Cartesian sampling patterns. By adjusting this parameter during acquisition, the method controls the magnitude of fat-water shifts in different directions, thereby improving image quality without sacrificing the productivity gains from non-Cartesian sampling.
2Manufacturing precision
If readout gradient strength is increased to reduce fat-water shift, then spatial distortion is reduced, but imaging time increases
Solution Approach 1:
Instead of uniformly increasing readout gradient strength across all directions, the patent applies gradient strength enhancement only selectively to those blades where fat-water shifts are problematic. This localized approach reduces spatial distortion where needed while maintaining efficient imaging timing overall, avoiding the penalty of extended scan time.
Solution Approach 2:
The patent implements partial action by applying readout gradient modulation only to specific blades in the non-Cartesian sampling pattern rather than all blades. This selective application achieves sufficient correction of fat-water shifts in critical directions without the excessive imaging time that would result from uniform gradient strengthening across the entire acquisition.
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 reduces image blurring and aligns the appearance of non-Cartesian images with Cartesian standards, enhancing readability and quality, particularly for radiologists.
Implementation Method 1
Due to a chemical shift in the NMR signal, fat and water tissue have slightly different resonant frequencies in the readout direction
Implementation Method 2
This excited region is then spatially encoded using magnetic field gradient encoding and phase encoding
Data Source
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AI summary
Disclosed herein is a medical system (100, 300) comprising a memory (110) storing machine executable instructions (120). The medical system further comprises a computational system (104). Execution of the machine executable instructions causes the computational system to: receive (200) initial pulse sequence commands (122), wherein the initial pulse sequence commands are configured for controlling a magnetic resonance imaging system (302) to acquire k-space data (332) following a non-Cartesian k-space sampling pattern (604, 604'), wherein the initial pulse sequence commands are configured for controlling the magnetic resonance imaging system to sample the non-Cartesian k-space sampling pattern by repeatedly sampling a Cartesian k-space sampling pattern (126) that is rotated for each acquisition, wherein the non-Cartesian k-space sampling pattern has an effective water-fat shift direction (606, 606'); receive (202) a chosen water-fat shift direction (124); and construct (204) modified pulse sequence commands by rotating the non-Cartesian k-space sampling pattern such that the effective water-fat shift direction is aligned with the water-fat shift direction.