title: Prospective registration of human head magnetic resonance images for reproducible slice positioning using localizer images.
abstract: OBJECTIVE
  To facilitate assessing brain tumor growth and progression of stroke lesions by reproducible slice positioning in human head magnetic resonance (MR) images, a method for prospective registration is proposed that adjusts the image slice position without moving the patient and with no additional scans.
  
  
  METHODS
  The gradient reference frame of follow-up examinations was adjusted to achieve the same image slice positioning relative to the patient as in the previous examination. The three-dimensional geometrical transformation parameters for the gradients were determined using two-dimensional image registration of three orthogonal localizer images. The method was developed and evaluated using a phantom with arbitrarily adjustable position. Feasibility for in vivo applications was demonstrated with brain MR imaging (MRI) of healthy volunteers.
  
  
  RESULTS
  Standard retrospective registration was used for assessing the quality of the method. The accuracy of the realignment was 0.0 mm +/- 1.2 mm and -0.2 degrees +/- 0.9 degrees (mean +/- SD) in phantom experiments. In 10 examinations of volunteers, misalignments up to 49.2 mm and 21 degrees were corrected. The accuracy of the realignment after prospective registration was 0.1 mm +/- 1.5 mm and 0.2 degrees +/- 1.5 degrees.
  
  
  CONCLUSIONS
  Image-based prospective registration using localizer images of the pre- and postexaminations is a robust method for reproducible slice positioning.
authors.affiliation: Institutes for Medical Informatics, Charité University Medicine Berlin, Germany. egbert.gedat@charite.de
authors.forename: Egbert
authors.initials: E
authors.lastname: Gedat
authors.forename: Juergen
authors.initials: J
authors.lastname: Braun
authors.forename: Ingolf
authors.initials: I
authors.lastname: Sack
authors.forename: Johannes
authors.initials: J
authors.lastname: Bernarding
mesh_terms: D001921:Brain / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D015203:Reproducibility of Results