title: A head-mounted operating binocular for augmented reality visualization in medicine--design and initial evaluation.
abstract: Computer-aided surgery (CAS), the intraoperative application of biomedical visualization techniques, appears to be one of the most promising fields of application for augmented reality (AR), the display of additional computer-generated graphics over a real-world scene. Typically a device such as a head-mounted display (HMD) is used for AR. However, considerable technical problems connected with AR have limited the intraoperative application of HMDs up to now. One of the difficulties in using HMDs is the requirement for a common optical focal plane for both the realworld scene and the computer-generated image, and acceptance of the HMD by the user in a surgical environment. In order to increase the clinical acceptance of AR, we have adapted the Varioscope (Life Optics, Vienna), a miniature, cost-effective head-mounted operating binocular, for AR. In this paper, we present the basic design of the modified HMD, and the method and results of an extensive laboratory study for photogrammetric calibration of the Varioscope's computer displays to a real-world scene. In a series of 16 calibrations with varying zoom factors and object distances, mean calibration error was found to be 1.24 +/- 0.38 pixels or 0.12 +/- 0.05 mm for a 640 x 480 display. Maximum error accounted for 3.33 +/- 1.04 pixels or 0.33 +/- 0.12 mm. The location of a position measurement probe of an optical tracking system was transformed to the display with an error of less than 1 mm in the real world in 56% of all cases. For the remaining cases, error was below 2 mm. We conclude that the accuracy achieved in our experiments is sufficient for a wide range of CAS applications.
authors.affiliation: CARCAS-Group at the Kantonsspital Basel, Switzerland. wbirk-fellner@uhbs.ch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Birkfellner
authors.forename: Michael
authors.initials: M
authors.lastname: Figl
authors.forename: Klaus
authors.initials: K
authors.lastname: Huber
authors.forename: Franz
authors.initials: F
authors.lastname: Watzinger
authors.forename: Felix
authors.initials: F
authors.lastname: Wanschitz
authors.forename: Johann
authors.initials: J
authors.lastname: Hummel
authors.forename: Rudolf
authors.initials: R
authors.lastname: Hanel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Greimel
authors.forename: Peter
authors.initials: P
authors.lastname: Homolka
authors.forename: Rolf
authors.initials: R
authors.lastname: Ewers
authors.forename: Helmar
authors.initials: H
authors.lastname: Bergmann
mesh_terms: D002138:Calibration; D003196:Computer Graphics; D003867:Depth Perception; D004867:Equipment Design; D019544:Equipment Failure Analysis; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D018715:Microscopy, Video / Q000295:instrumentation*; D008866:Microsurgery / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013523:Surgical Equipment; D014584:User-Computer Interface; D014741:Video Recording / Q000295:instrumentation / Q000379:methods