MRI Flip Angle Determination for SAR and Contrast Control
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Solution Overview
Problem
In MRI imaging, variable refocus flip angle sequences can lead to artifacts due to signal intensity differences when shifting echoes, and methods like half scanning degrade image resolution to avoid these issues.
Innovation Solution
The technique determines optimal flip angles for refocus high-frequency magnetic field pulses to achieve desired contrast while minimizing specific absorption rate (SAR) without degrading image quality by searching for flip angles that adjust signal decay patterns to match specified contrast information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable refocus flip angle sequence is used to reduce SAR, then specific absorption rate is reduced, but image contrast control becomes difficult and artifacts may occur
Solution Approach 1:
The patent adjusts the flip angle parameter of refocus RF pulses dynamically within the echo train. By varying the flip angle according to a predetermined pattern rather than using a fixed angle, the system achieves both SAR reduction and maintained contrast control. The flip angle is modified based on calculations involving T1 and T2 relaxation times to preserve desired contrast characteristics.
Solution Approach 2:
The patent transitions from a static flip angle approach to a dynamic one where the flip angle changes throughout the echo train. This dynamic adjustment allows the system to optimize both SAR reduction and image contrast by adapting the flip angle to the specific requirements of each echo position and the tissue relaxation characteristics.
2Manufacturing precision
If echo shifting is performed to adjust contrast equivalent TE, then desired image contrast is achieved, but signal intensity differences cause artifacts
Solution Approach 1:
Instead of physically shifting echoes in k-space, the patent changes the flip angle parameter to adjust the contrast equivalent TE. This parameter-based approach achieves the desired contrast adjustment without the signal intensity discontinuities that occur when echoes are shifted, thereby avoiding artifacts.
3Reliability
If half scanning is used to avoid signal intensity differences, then artifacts are reduced, but image resolution is degraded
Solution Approach 1:
The patent uses flip angle modulation to directly control signal intensity and contrast equivalent TE, eliminating the need for half-scanning techniques. By adjusting the flip angle parameter, the system achieves artifact-free images while maintaining full k-space acquisition and preserving image resolution.
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 creation of images with desired contrast while suppressing SAR and maintaining image quality, preventing artifacts and resolution loss.
Implementation Method 1
measures an NMR signal (echo signal) generated by an object, especially, the nuclear spins that form human tissue
Implementation Method 2
different phase encoding and different frequency encoding are given to NMR signals according to the gradient magnetic field
Data Source
AI summary
The purpose of the present invention is to obtain an image with a desired contrast while minimizing specific absorption rate and without deteriorating image quality in a variable refocus flip angle sequence. To this end, Teequiv specified by a signal decay pattern SSP obtained by a flip angle changing pattern FAP is compared with a designated Teequiv, and the flip angle changing pattern FAP is changed according to the comparison result to search for the flip angle changing pattern FAP which gives a desired contrast. Then, the flip angle changing pattern FAP which is capable of realizing the designated Teequiv is determined. Then, imaging is performed using each flip angle constitutes the determined flip angle changing pattern FAP.