Skip to main content

Advertisement

Temporal analysis of Z-Gradient coil eddy currents in tungsten collimator with different resistivities for SPECT/MRI

Article metrics

Combining Single Photon Emission Computed Tomography (SPECT) with Magnetic Resonance Imaging (MRI) results in an interaction of the time-varying magnetic field gradients with the highly conducting tungsten collimator, which generates a secondary magnetic field causing spatial distortions in reconstructed MR images. Accurate simulations are important for the characterization of these eddy currents and to further optimize the gradient coils and the collimator design.

This study investigated the temporal variations of eddy currents in a tungsten collimator for pre-clinical SPECT/MRI due to only the z-gradient coil for different resistivities of tungsten, which can be obtained through additive manufacturing.

We modeled a z-gradient coil and a collimator using FEKO, a 3D electromagnetic simulation tool. A time analysis approach was used to generate the pulsed magnetic field gradient. The approach was validated with measurements using a 7T MRI scanner.

Simulations show that when tungsten with high resistivity (ρ=370 nΩ.m) is used, eddy currents generate an added magnetic field representing 1.72 % of the nominal gradient field in a Field Of View (FOV) of 3 cm. This percentage increases rapidly for tungsten with lower resistivities, which was expected since a higher resistivity implies lower current densities. A higher density of tungsten is preferred leading to low resistivity but results in stronger induced eddy currents. A compromise needs to be made between the eddy currents strength and the design of the collimator. Using the insights gained from these simulations, the next step is to optimize the design of the gradient coils and the collimator to further reduce the eddy current effects.

Author information

Correspondence to Amine Samoudi.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0), which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Samoudi, A., Van Audenhaege, K., Vermeeren, G. et al. Temporal analysis of Z-Gradient coil eddy currents in tungsten collimator with different resistivities for SPECT/MRI. EJNMMI Phys 1, A22 (2014) doi:10.1186/2197-7364-1-S1-A22

Download citation

Keywords

  • Single Photon Emission Compute Tomography
  • Additive Manufacturing
  • Eddy Current
  • Magnetic Field Gradient
  • Gradient Coil