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Forward field-shift calculation for MRI

version 1.14 (11 KB) by

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.

Comments and Ratings (3)

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

Updates

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.

1.13

Screenshot was incorrect

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.

1.10

This version can handle anisotropic voxel sizes.

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).

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