MRI B1+ and B1− Field Mapping for Ultra-High-Field Correction
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Solution Overview
Problem
Existing methods for B1 field inhomogeneity correction in magnetic resonance imaging (MRI) are inadequate for ultra-high field conditions, leading to significant challenges in achieving uniform signal intensity and contrast, which are crucial for accurate diagnosis.
Innovation Solution
A method involving obtaining a B1+ field map and a B1− field map based on a first MR image, using a low-flip-angle gradient recalled echo pulse sequence, and applying a three-dimensional spline fitting algorithm to correct B1 field inhomogeneity in MR images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If B1 shimming technology is used for MRI less than or equal to 3 T, then B1+ field homogeneity is improved, but it cannot meet the correction requirements under ultra-high field conditions
Solution Approach 1:
The patent changes the correction parameters by introducing B1+ field map and B1− field map as correction factors, and develops a new correction formula that adapts to ultra-high field conditions where traditional B1 shimming parameters are no longer sufficient
Solution Approach 2:
The patent introduces field maps (B1+ field map and B1− field map) as intermediary elements that quantify the inhomogeneity and serve as the basis for correction, enabling the system to adapt to different field strengths including ultra-high fields
2Measurement precision
If coil arrays are used for image acquisition, then receive sensitivity is improved, but B1− field inhomogeneity increases at the periphery of imaging target
Solution Approach 1:
The patent incorporates B1− field map as a correction parameter to compensate for the non-uniform receive sensitivity of coil arrays, allowing the system to maintain both high sensitivity and uniform signal intensity across the imaging target
Solution Approach 2:
The patent uses the B1− field map (obtained through set calculation methods) as feedback information to correct the signal intensity non-uniformity, creating a closed-loop correction process that compensates for coil array inhomogeneity
3Stability of the object's composition
If parallel transmission is used to excite homogeneous flip angle, then B1+ field inhomogeneity is improved, but device complexity increases due to parallel transmission system installation
Solution Approach 1:
The patent replaces the complex hardware-based parallel transmission system with a software-based post-processing correction method using field maps and correction formulas, achieving similar homogeneity improvement without the mechanical complexity
4Stability of the object's composition
If N3 or N4ITK post-processing methods are used for B1 field correction, then B1 field inhomogeneity is improved, but accuracy decreases when bias field strengths are highly different
Solution Approach 1:
The patent changes the correction parameters by using actual measured field maps (B1+ and B1−) instead of assuming a Gaussian convolution model, and develops a new correction formula that maintains accuracy across highly varying bias field strengths
Solution Approach 2:
The patent inverts the traditional approach by using measured field maps to directly calculate correction factors, rather than using model-based methods that assume a specific mathematical form for the bias field
Data Source
AI summary
A method and device for radio-frequency field inhomogeneity correction in magnetic resonance imaging. The method includes: obtaining a first MR image by scanning a target tissue using a first pulse sequence; obtaining a B1+ field map of the target tissue; obtaining a B1−: field map of the target tissue based on the first MR image and the B1+ field map; and performing B1 field inhomogeneity correction on a second MR image of the target tissue based on the B1+ field map and the B1− field map, where the second MR image is an MR image obtained after scanning of the target tissue using any imaging protocol and any pulse sequence.