Gradient Echo (GRE) background phase removal using 'projection onto dipole fields' method
Updated 25 Sep 2016
# Input & Output:
function [NPhase, J, R] = pdf_method(data,mask,N) | Outputs corrected phase image (NPhase), the estimated background field (J), and the conjugate gradient L2 norm residuals (R). Inputs of the raw phase data with artifact (data), mask of the image (mask) and number of iterations (N)
Example result in results_figure.pdf shows the raw phase image, the background field which was estimated and then removed, the conjugate gradient convergence pattern with N=20, and the corrected phase image. The data and mask files used in this example are in the file example_data.mat
# Motivation & Theory:
This algorithm was developed as part of my PhD project to remove large spatially varying background field artifacts in 2D gradient echo (GRE) phase images. The minimization formulated in Equation 4 of the cited paper is solved using a Conjugate Gradient on Normal Equations or CGNE technique.
This approach is first described in Liu et al. 2011. A novel background field removal method for MRI using projection onto dipole fields (PDF). NMR Biomedicine. "For optimal image quality in susceptibility-weighted imaging and accurate quantification of susceptibility, it is necessary to isolate the local field generated by local magnetic sources (such as iron) from the background field that arises from imperfect shimming and variations in magnetic susceptibility of surrounding tissues (including air). A nonparametric background field removal technique based on projection onto dipole fields (PDF). In this PDF technique, the background field inside an ROI is decomposed into a field originating from dipoles outside the ROI using the projection theorem in Hilbert space. This novel PDF background removal technique was validated on a numerical simulation and a phantom experiment and was applied in human brain imaging, demonstrating substantial improvement in background field removal compared with the commonly used high-pass filtering method."
Ti Xu (2021). Gradient Echo (GRE) background phase removal using 'projection onto dipole fields' method (https://github.com/BluesBlues213/projection-onto-dipole-fields), GitHub. Retrieved .
MATLAB Release Compatibility
Platform CompatibilityWindows macOS Linux
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!Start Hunting!