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Field-shift calculation without aliasing.

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Field-shift calculation without aliasing.

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22 Jun 2012 (Updated )

Efficient forward Fourier-based calculation of the susceptibility-induced field shift in MRI

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Description

An efficient implementation of the Fourier-based procedure to calculate the susceptibility-induced field-shift if an object with known susceptibility distribution is placed within a strong homogeneous magnetic field (B0).
The original procedure (k-space filtering by Salomir in 2003) needed zero-padding to prevent aliasing (circular wrap-around). In this implementation, however, aliasing is removed by estimating this artifact using an additional convolution in a lower resolution.
* Update jan 2014: no extra convolution is needed anymore *
The method is very efficient since the aliasing-prevention is decoupled from the convolution of the Region Of Interest. We refer to this procedure as 'virtual Zero-Padding (vZP)'.
The article describing the principle of low resolution aliasing subtraction:
Job G. Bouwman, Chris J.G. Bakker. "Alias subtraction more efficient than conventional zero-padding in the Fourier based calculation of the susceptibility induced perturbation of the magnetic field in MR (2012) in "Magnetic Resonance in Medicine" 68:621–630 (2012).
Please refer to this article when using this script.

Required Products MATLAB
MATLAB release MATLAB 7.9 (R2009b)
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Comments and Ratings (3)
23 Oct 2013 Jürgen Hennig  
23 Oct 2013 Jürgen Hennig  
23 Oct 2013 Jürgen Hennig

excellent and neat program, very flexible to adapt to various scenarios

Updates
06 Jul 2012

Added a script (FBFC_example.m) for demonstration of the functions FBFC_CC_vZP and FBFC_KF_vZP. This script makes use of the function (FBFC_CC_no_padding.m).

14 Jun 2013

This version can handle anisotropic voxel sizes.

27 Jan 2014

Again 30% faster than previous version. Instead of doing two convolutions, the aliasing calculation is done in the imaginary channel of the initial convolution.

27 Jan 2014

Screenshot was incorrect

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