title: Analysis of eddy currents induced by transverse and longitudinal gradient coils in different tungsten collimators geometries for SPECT/MRI integration.
abstract: OBJECTIVE
  We investigated the temporal variation of the induced magnetic field due to the transverse and the longitudinal gradient coils in tungsten collimators arranged in hexagonal and pentagonal geometries with and without gaps between the collimators.
  
  
  METHODS
  We modeled x-, y-, and z-gradient coils and different arrangements of single-photon emission computed tomography (SPECT) collimators using FEKO, a three-dimensional 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.
  
  
  RESULTS
  Simulations showed an induced magnetic field representing 4.66% and 0.87% of the applied gradient field (gradient strength = 500 mT/m) for longitudinal and transverse gradient coils, respectively. These values can be reduced by 75% by adding gaps between the collimators for the pentagonal arrangement, bringing the maximum induced magnetic field to less than 2% of the applied gradient for all of the gradient coils.
  
  
  CONCLUSIONS
  Characterization of the maximum induced magnetic field shows that by adding gaps between the collimators for an integrated SPECT/MRI system, eddy currents can be corrected by the MRI system to avoid artifact. The numerical model was validated and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.
authors.affiliation: Department of Information Technology (INTEC), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Amine M
authors.initials: AM
authors.lastname: Samoudi
authors.affiliation: Electronics and Information Systems (ELIS), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Karen
authors.initials: K
authors.lastname: Van Audenhaege
authors.affiliation: Department of Information Technology (INTEC), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Günter
authors.initials: G
authors.lastname: Vermeeren
authors.affiliation: Institute of Neuroscience and Medicine, Jülich, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Poole
authors.affiliation: Department of Information Technology (INTEC), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Emmeric
authors.initials: E
authors.lastname: Tanghe
authors.affiliation: Department of Information Technology (INTEC), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Martens
authors.affiliation: Electronics and Information Systems (ELIS), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Roel
authors.initials: R
authors.lastname: Van Holen
authors.affiliation: Department of Information Technology (INTEC), Ghent University/iMinds, Ghent, Belgium.
authors.forename: Wout
authors.initials: W
authors.lastname: Joseph
mesh_terms: D016477:Artifacts; D004574:Electromagnetic Fields; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D064847:Multimodal Imaging / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D018511:Systems Integration; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation*; D014414:Tungsten / Q000737:chemistry*
chemical_list: D014414:Tungsten
keywords: MRI; SPECT; collimator; eddy currents; electromagnetic simulation; gradient coils