title: Analyzing 3-tesla magnetic resonance imaging units for implementation in radiosurgery.
abstract: OBJECTIVE
  The limiting factor affecting accuracy during gamma knife surgery is image quality. The new generation of magnetic resonance (MR) imaging units with field strength up to 3 teslas promise superior image quality for anatomical resolution and contrast. There are, however, questions about chemical shifts or susceptibility effects, which are the subject of this paper.
  
  
  METHODS
  The 3-tesla MR imaging unit (Siemens Trio) was analyzed and compared with a 1-tesla unit (Siemens Magnetom Expert) and to a 1.5-tesla unit (Philips Gyroscan). Evaluation of the magnitude of error was performed within transverse slices in two orientations (axial/coronal) by using a cylindrical phantom with an embedded grid. Deviations were determined for 21 targets in a slab phantom with known geometrical positions within the stereotactic frame. Distortions caused by chemical shift and/or susceptibility effects were analyzed in a head phantom. Inhouse software was used for data analyses. The mean deviation was less than 0.3 mm in axial and less than 0.4 mm in coronal orientations. For the known targets the maximum deviation was 1.16 mm. By optimizing these parameters in the protocol these inaccuracies could be reduced to less than 1.1 mm. Due to inhomogeneities a shift in the z direction of up to 1.5 mm was observed for a dataset, which was shown to be compressed by 1.2 mm.
  
  
  CONCLUSIONS
  The 3-tesla imaging unit showed superior anatomical contrast and resolution in comparison with the established 1-tesla and 1.5-tesla units; however, due to the high field strength the field within the head coil is very sensitive to inhomogeneities and therefore 3-tesla imaging data will have be handled with care.
authors.affiliation: Gamma Knife Centre, Frankfurt, Germany. a.mack@gkfrankfurt.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Mack
authors.forename: Robert
authors.initials: R
authors.lastname: Wolff
authors.forename: Stefan
authors.initials: S
authors.lastname: Scheib
authors.forename: Marcus
authors.initials: M
authors.lastname: Rieker
authors.forename: Dirk
authors.initials: D
authors.lastname: Weltz
authors.forename: G
authors.initials: G
authors.lastname: Mack
authors.forename: Hans-Jürg
authors.initials: HJ
authors.lastname: Kreiner
authors.forename: Ulrich
authors.initials: U
authors.lastname: Pilatus
authors.forename: Friedhelm E
authors.initials: FE
authors.lastname: Zanella
authors.forename: Heinz D
authors.initials: HD
authors.lastname: Böttcher
authors.forename: Volker
authors.initials: V
authors.lastname: Seifert
mesh_terms: D004867:Equipment Design; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000295:instrumentation*