title: [Comparison of susceptibility artifacts generated by microchips with different geometry at 1.5 Tesla magnet resonance imaging. A phantom pilot study referring to the ASTM standard test method F2119-07].
abstract: OBJECTIVE
  Ferromagnetic material in microchips, used for animal identification, causes local signal increase, signal void or distortion (susceptibility artifact) on MR images. To measure the impact of microchip geometry on the artifact's size, an MRI phantom study was performed.
  
  
  METHODS
  Microchips of the labels Datamars®, Euro-I.D.® and Planet-ID® (n  =  15) were placed consecutively in a phantom and examined with respect to the ASTM Standard Test Method F2119-07 using spin echo (TR 500 ms, TE 20 ms), gradient echo (TR 300 ms, TE 15 ms, flip angel 30°) and otherwise constant imaging parameters (slice thickness 3 mm, field of view 250 x 250 mm, acquisition matrix 256 x 256 pixel, bandwidth 32 kHz) at 1.5 Tesla. Image acquisition was undertaken with a microchip positioned in the x- and z-direction and in each case with a phase-encoding direction in the y- and z-direction. The artifact size was determined with a) a measurement according to the test method F2119-07 using a homogeneous point operation, b) signal intensity measurement according to Matsuura et al. and c) pixel counts in the artifact according to Port and Pomper.
  
  
  RESULTS
  There was a significant difference in artifact size between the three microchips tested (Wilcoxon p = 0.032). A two- to three-fold increase in microchip volume generated an up to 76% larger artifact, depending on the sequence type, phase-encoding direction and chip position to B0.
  
  
  CONCLUSIONS
  The smaller the microchip geometry, the less is the susceptibility artifact. Spin echoes (SE) generated smaller artifacts than gradient echoes (GE). In relation to the spatial measurement of the artifact, the switch in phase-encoding direction had less influence on the artifact size in GE- than in SE-sequences. However, the artifact shape and direction of SE-sequences can be changed by altering the phase. The artifact size, caused by the microchip, plays a major clinical role in the evaluation of MRI from the head, shoulder and neck regions.
authors.affiliation: Sabine Dengg, Klinische Abteilung für Bildgebende Diagnostik, Veterinärmedizinische Universität Wien, Veterinärplatz 1, A-1210 Wien, E-Mail: sabine.dengg@vetmeduni.ac.at.
authors.forename: S
authors.initials: S
authors.lastname: Dengg
authors.forename: S
authors.initials: S
authors.lastname: Kneissl
mesh_terms: D000823:Animal Identification Systems / Q000295:instrumentation* / Q000592:standards*; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000662:veterinary*; D059346:Magnets / Q000737:chemistry*; D046228:Microarray Analysis / Q000662:veterinary; D019047:Phantoms, Imaging; D010865:Pilot Projects
keywords: Highfield magnetic resonace Imaging (MRI); RFID-system; ferromagnetic material; image artifact