title: The rotate-plus-shift C-arm trajectory. Part I. Complete data with less than 180° rotation.
abstract: OBJECTIVE
  In the last decade, C-arm-based cone-beam CT became a widely used modality for intraoperative imaging. Typically a C-arm CT scan is performed using a circular or elliptical trajectory around a region of interest. Therefore, an angular range of at least 180° plus fan angle must be covered to ensure a completely sampled data set. However, mobile C-arms designed with a focus on classical 2D applications like fluoroscopy may be limited to a mechanical rotation range of less than 180° to improve handling and usability. The method proposed in this paper allows for the acquisition of a fully sampled data set with a system limited to a mechanical rotation range of at least 180° minus fan angle using a new trajectory design. This enables CT like 3D imaging with a wide range of C-arm devices which are mainly designed for 2D imaging.
  
  
  METHODS
  The proposed trajectory extends the mechanical rotation range of the C-arm system with two additional linear shifts. Due to the divergent character of the fan-beam geometry, these two shifts lead to an additional angular range of half of the fan angle. Combining one shift at the beginning of the scan followed by a rotation and a second shift, the resulting rotate-plus-shift trajectory enables the acquisition of a completely sampled data set using only 180° minus fan angle of rotation. The shifts can be performed using, e.g., the two orthogonal positioning axes of a fully motorized C-arm system. The trajectory was evaluated in phantom and cadaver examinations using two prototype C-arm systems.
  
  
  RESULTS
  The proposed trajectory leads to reconstructions without limited angle artifacts. Compared to the limited angle reconstructions of 180° minus fan angle, image quality increased dramatically. Details in the rotate-plus-shift reconstructions were clearly depicted, whereas they are dominated by artifacts in the limited angle scan.
  
  
  CONCLUSIONS
  The method proposed here employs 3D imaging using C-arms with less than 180° rotation range adding full 3D functionality to a C-arm device retaining both handling comfort and the usability of 2D imaging. This method has a clear potential for clinical use especially to meet the increasing demand for an intraoperative 3D imaging.
authors.affiliation: Ziehm Imaging GmbH, Donaustraße 31, Nürnberg 90451, Germany.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Ritschl
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Kuntz
authors.affiliation: Ziehm Imaging GmbH, Donaustraße 31, Nürnberg 90451, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Fleischmann
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Kachelrieß
mesh_terms: D016477:Artifacts; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods*; D008953:Models, Anatomic; D019637:Orthopedic Procedures; D019047:Phantoms, Imaging; D012399:Rotation; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods