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Phantom-based field maps for gradient nonlinearity correction in diffusion imaging
Author(s): Baxter P. Rogers; Justin Blaber; Allen T. Newton; Colin B. Hansen; E. Brian Welch; Adam W. Anderson; Jeffrey J. Luci; Carlo Pierpaoli; Bennett A. Landman
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Paper Abstract

Gradient coils in magnetic resonance imaging do not produce perfectly linear gradient fields. For diffusion imaging, the field nonlinearities cause the amplitude and direction of the applied diffusion gradients to vary over the field of view. This leads to site- and scan-specific systematic errors in estimated diffusion parameters such as diffusivity and anisotropy, reducing reliability especially in studies that take place over multiple sites. These errors can be substantially reduced if the actual scanner-specific gradient coil magnetic fields are known. The nonlinearity of the coil fields is measured by scanner manufacturers and used internally for geometric corrections, but obtaining and using the information for a specific scanner may be impractical for many sites that operate without special-purpose local engineering and research support. We have implemented an empirical field-mapping procedure using a large phantom combined with a solid harmonic approximation to the coil fields that is simple to perform and apply. Here we describe the accuracy and precision of the approach in reproducing manufacturer gold standard field maps and in reducing spatially varying errors in quantitative diffusion imaging for a specific scanner. Before correction, median B value error ranged from 33 - 41 relative to manufacturer specification at 100 mm from isocenter; correction reduced this to 0 - 4. On-axis spatial variation in the estimated mean diffusivity of an isotropic phantom was 2.2% - 4.1% within 60 mm of isocenter before correction, 0.5% - 1.6% after. Expected fractional anisotropy in the phantom was 0; highest estimated fractional anisotropy within 60 mm of isocenter was reduced from 0.024 to 0.012 in the phase encoding direction (48% reduction) and from 0.020 to 0.006 in the frequency encoding direction (72% reduction).

Paper Details

Date Published: 9 March 2018
PDF: 5 pages
Proc. SPIE 10573, Medical Imaging 2018: Physics of Medical Imaging, 105733N (9 March 2018); doi: 10.1117/12.2293786
Show Author Affiliations
Baxter P. Rogers, Vanderbilt Univ. Institute of Imaging Science (United States)
Vanderbilt Univ. Medical Ctr. (United States)
Vanderbilt Univ. (United States)
Justin Blaber, Vanderbilt Univ. (United States)
Allen T. Newton, Vanderbilt Univ. Institute of Imaging Science (United States)
Vanderbilt Univ. Medical Ctr. (United States)
Colin B. Hansen, Vanderbilt Univ. (United States)
E. Brian Welch, Vanderbilt Univ. Institute of Imaging Science (United States)
Vanderbilt Univ. Medical Ctr. (United States)
Adam W. Anderson, Vanderbilt Univ. Medical Ctr. (United States)
Vanderbilt Univ. (United States)
Jeffrey J. Luci, The Univ. of Texas at Austin (United States)
Carlo Pierpaoli, National Institute of Biomedical Imaging and Bioengineering (United States)
Bennett A. Landman, Vanderbilt Univ. Institute of Imaging Science (United States)
Vanderbilt Univ. Medical Ctr. (United States)
Vanderbilt Univ. (United States)


Published in SPIE Proceedings Vol. 10573:
Medical Imaging 2018: Physics of Medical Imaging
Joseph Y. Lo; Taly Gilat Schmidt; Guang-Hong Chen, Editor(s)

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