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Forward field-shift calculation for MRI

5.0 | 3 ratings Rate this file 15 Downloads (last 30 days) File Size: 11 KB File ID: #37278 Version: 1.14
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Forward field-shift calculation for MRI


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22 Jun 2012 (Updated )

Superfast MRI field shift calculation based on a known susceptibility distribution.

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Efficient implementation of Salomir's method from 2003: we use a multi-resolution trick to deal with aliasing.
* more than 6x faster (version of october 2014)
* allows to do simulations in a 2x higher resolution, without memory problems.
Explanation and references:
The presented algorithm is 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).
This method is based on the publication of: Salomir et al, "A fast calculation method for magnetic field inhomogeneity due to an arbitrary distribution of bulk susceptibility" Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, Volume 19B, Issue 1, pages 26–34, 2003.
A drawback of this method, is that it depends on (inefficient) zero-padding, to prevent the aliasing artefact (periodic wrap-around). See also: Cheng YCN, Neelavalli J, Haacke EM. "Limitations of calculating field distributions and magnetic susceptibilities in MRI using a Fourier based method". Phys Med Biol 2009;54:1169–1189.
In the here presented algorithm, aliasing is removed by calculating this artifact using an additional convolution in a lower resolution, which is does not lead to accuracy loss, due to the smooth decay of the dipole function. For further details the reader is referred to the article: 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, Magnetic Resonance in Medicine 68:621630 (2012). Please refer to this article when using this script.


This file inspired Mri Simulation Using Forecast: Fourier Based Off R Esonan Ce Artifact Simulation In The S Teady State.

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

06 Jul 2012 1.7

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 1.10

This version can handle anisotropic voxel sizes.

27 Jan 2014 1.12

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 1.13

Screenshot was incorrect

20 Oct 2014 1.14

1) Sub-functions are converted into nested functions. This enables / speeds up the convolution of very large susceptibility distributions.
2) Further optimization of the nested functions, yields an additional ~12% speed improvement.

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