B1 Map Correction for MR Image Intensity Uniformity
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Solution Overview
Problem
Magnetic resonance imaging algorithms assume perfect homogeneity of magnetic fields, ignoring inhomogeneities that lead to imperfections in image quality, particularly in the intensity of the B1 magnetic field, resulting in suboptimal image clarity and uniformity.
Innovation Solution
A method that maps B1 transmit intensity from an RF coil to a target volume, calculates a B1 transmit shading correction based on this map and pulse sequence parameters, and applies it to the MR image to correct for non-uniformities caused by B1 inhomogeneities, enhancing image clarity and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MR imaging algorithms assuming perfect magnetic field homogeneity are used, then the imaging process is simple and fast, but the image intensity uniformity and clarity deteriorate due to B1 field inhomogeneities
Solution Approach 1:
A B1 map is acquired before the actual MR imaging to characterize the transmit field inhomogeneities. This preliminary measurement allows the system to pre-calculate correction factors that are then applied during image reconstruction, eliminating the need to assume perfect field homogeneity while maintaining imaging efficiency
Solution Approach 2:
The imaging algorithm transitions from assuming constant B1 field parameters to using spatially varying B1 parameters derived from the B1 map. By incorporating the measured B1 distribution into the reconstruction model, the system corrects intensity non-uniformities while preserving the efficiency of conventional imaging sequences
2Manufacturing precision
If B1 map-based correction methods are applied, then image intensity uniformity and clarity improve, but the imaging process complexity and time increase
Solution Approach 1:
A B1 map serves as an intermediary data structure that bridges the gap between the physical B1 field inhomogeneities and the image correction process. The map is acquired through a dedicated calibration sequence and then used to generate correction factors that are applied during standard image reconstruction, modularizing the complexity
Solution Approach 2:
The system uses the acquired B1 map to generate feedback correction factors that are applied to the imaging algorithm. This feedback loop allows the system to automatically compensate for B1 inhomogeneities without requiring manual intervention or complex real-time adjustments during scanning
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
The solution produces MR images with improved clarity and uniformity by accounting for B1 transmit and receive sensitivity inhomogeneities, resulting in more accurate and detailed imaging compared to conventional methods.
Implementation Method 1
algorithms that presume perfect homogeneity of a constant magnetic field B0 that used to align spins of atoms within a target volume
Implementation Method 2
Homogeneity of a radio frequency magnetic field B1, the field used to perturb the spins of selected atoms within the target volume
Data Source
AI summary
A controller that is operatively connected with a magnet assembly, which defines a target volume; and an image processor, which is configured to obtain calibration data from the controller; map B1 transmit intensity from the magnet assembly to the target volume, based on the calibration data; calculate a B1 transmit shading correction based at least on the map of B1 transmit intensity and on pulse sequence parameters; obtain k-space data of an imaging subject within the target volume from the controller operating the magnet assembly based on the pulse sequence parameters; develop an MR image from the k-space data; and apply the B1 transmit shading correction to the MR image.