title: Reproducibility of geometric distortion in magnetic resonance imaging based on phantom studies.
abstract: OBJECTIVE
  Image distortion is one of the major drawbacks of magnetic resonance (MR) imaging for use in radiotherapy treatment planning (RTTP). In this study, the reproducibility of MR imaging distortion was evaluated by repeated phantom measurements.
  
  
  METHODS
  A grid-pattern acrylic phantom was scanned with a 0.2-Tesla permanent magnetic unit. We repeated a series of scans three times to evaluate the reproducibility of the distortion. In each series, co-ordinates at 432 intersections of the grid were measured for both T1- and T2-weighted spin-echo (SE) pulse sequences. Positional displacements and their variations at the intersections were calculated.
  
  
  RESULTS
  Averages of the displacements were distributed between 1.58 and 1.74 mm, and maximum values (MAX) between 12.6 and 15.0 mm. Within 120 mm of the image center, the average values ranged from 0.73 to 0.80 mm, and from 3.4 to 5.0 mm for MAX. The absolute values of the positional variations among three series were distributed between 0.41 and 0.88 mm for average values, and between 1.4 and 4.5 mm for MAX.
  
  
  CONCLUSIONS
  The positional variations were mostly within 3 pixels, and most of the positional displacements within the radius of 120 mm of the image center were 2 mm or less. Therefore, it will be possible to use this MR system in RTTP under limited situations, although careful applications are required for RTTP of the body. The development of a computer program to correct image distortion is expected.
authors.affiliation: Department of Radiology, Faculty of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Mizowaki
authors.forename: Y
authors.initials: Y
authors.lastname: Nagata
authors.forename: K
authors.initials: K
authors.lastname: Okajima
authors.forename: M
authors.initials: M
authors.lastname: Kokubo
authors.forename: Y
authors.initials: Y
authors.lastname: Negoro
authors.forename: N
authors.initials: N
authors.lastname: Araki
authors.forename: M
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D016477:Artifacts; D004867:Equipment Design; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity