MRI Inversion RF Pulse Phase Control for FID Artifact Suppression
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Solution Overview
Problem
Conventional techniques fail to effectively eliminate FID artifacts in MRI images when parallel imaging is applied to spin-echo type pulse sequences, leading to artifacts overlapping with the subject image, especially at higher acceleration rates, which hinders the reduction of measurement time.
Innovation Solution
The MRI apparatus controls the phase of the inversion RF pulse as a quadratic function of the phase encode, making the absolute value of the FID signal constant and eliminating zipper-like artifacts by adjusting the phase encoding according to the reduction factor, rather than simply shifting them to the image edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the phase of the inversion RF pulse is inverted every repetition to eliminate FID artifacts, then FID artifacts are moved to both sides of the image, but when parallel imaging is applied, the FID artifacts appear overlapping with the subject image instead of at the edges
Solution Approach 1:
The patent changes the phase parameter of the inversion RF pulse from a simple inverted pattern (0 or 180 degrees) to a quadratic function of the phase encode step. This parameter change transforms the FID signal distribution from concentrated at image edges to uniformly distributed across the image, eliminating visible artifacts while maintaining image quality.
Solution Approach 2:
The patent introduces dynamic phase modulation where the phase of the inversion RF pulse varies according to the phase encode step number. This dynamic adjustment adapts the phase pattern to work effectively with parallel imaging techniques, resolving the contradiction between artifact suppression and image quality.
2Productivity
If the acceleration rate is increased to reduce measurement time, then productivity improves, but FID artifacts become more prominent and overlap with the subject image
Solution Approach 1:
By modifying the phase parameter of the inversion RF pulse to follow a quadratic function, the patent suppresses FID artifact visibility even at high acceleration rates. This enables the system to achieve faster measurement times without suffering from increased artifact prominence.
3Object-affected harmful factors
If conventional phase inversion is used to suppress FID signals, then FID artifacts are shifted to image edges, but this approach does not function when parallel imaging is applied
Solution Approach 1:
The patent transforms the static phase inversion approach into a dynamic phase modulation scheme where the phase varies quadratically with the phase encode step. This dynamic approach maintains FID suppression effectiveness while being fully compatible with parallel imaging techniques.
Solution Approach 2:
The patent changes the phase parameter from a binary inverted pattern to a continuous quadratic function, enabling the system to maintain adaptability with parallel imaging while effectively suppressing FID artifacts.
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 allows for the production of images without FID artifacts, enabling higher acceleration rates and shorter measurement times by ensuring the FID signal is uniformly distributed, thus improving image quality and reducing artifacts in spin-echo type pulse sequences, particularly under parallel imaging conditions.
Implementation Method 1
a static magnetic field generating magnet for generating a static magnetic field
Implementation Method 2
a high-frequency transmission unit for irradiating a high-frequency magnetic field pulse to the subject placed in a static magnetic field space
Implementation Method 3
receiving an echo signal generated from the subject
Implementation Method 4
a gradient magnetic field generating unit for generating a gradient magnetic field that encodes an echo signal
Data Source
AI summary
Generation of artifacts caused by the FID signal is suppressed even when the parallel imaging is applied to the imaging using a spin echo type pulse sequence. In performing a pulse sequence of a spin echo type using an excitation RF pulse for exciting nuclear spin and an inversion RF pulse for inverting excited nuclear spin as a high-frequency magnetic field pulse, a high-frequency transmitter of a MRI apparatus changes the phase of the inversion RF pulse according to the phase encoding and the phase encoding number imparted for each echo signal. Specifically, the phase of the inversion RF pulse is controlled to be a quadratic function of the phase encode of the echo signal.