title: Virtual tape measure for the operating microscope: system specifications and performance evaluation.
abstract: OBJECTIVE
  The Virtual Tape Measure for the Operating Microscope (VTMOM) was created to assist surgeons in making accurate 3D measurements of anatomical structures seen in the surgical field under the operating microscope. The VTMOM employs augmented reality techniques by combining stereoscopic video images with stereoscopic computer graphics, and functions by relying on an operator's ability to align a 3D graphic pointer, which serves as the end-point of the virtual tape measure, with designated locations on the anatomical structure being measured. The VTMOM was evaluated for its baseline and application performances as well as its application efficacy.
  
  
  METHODS
  Baseline performance was determined by measuring the mean error (bias) and standard deviation of error (imprecision) in measurements of non-anatomical objects. Application performance was determined by comparing the error in measuring the dimensions of aneurysm models with and without the VTMOM. Application efficacy was determined by comparing the error in selecting the appropriate aneurysm clip size with and without the VTMOM.
  
  
  RESULTS
  Baseline performance indicated a bias of 0.3 mm and an imprecision of 0.6 mm. Application bias was 3.8 mm and imprecision was 2.8 mm for aneurysm diameter. The VTMOM did not improve aneurysm clip size selection accuracy.
  
  
  CONCLUSIONS
  The VTMOM is a potentially accurate tool for use under the operating microscope. However, its performance when measuring anatomical objects is highly dependent on complex visual features of the object surfaces.
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, Department of Surgery, Division of Neurosurgery, University of Toronto, Ontario, Canada.
authors.forename: M Y
authors.initials: MY
authors.lastname: Kim
authors.forename: J M
authors.initials: JM
authors.lastname: Drake
authors.forename: P
authors.initials: P
authors.lastname: Milgram
mesh_terms: D000783:Aneurysm / Q000473:pathology; D015982:Bias; D002138:Calibration; D003196:Computer Graphics; D003626:Data Display; D005069:Evaluation Studies as Topic; D006801:Humans; D008853:Microscopy / Q000295:instrumentation*; D008953:Models, Anatomic; D012984:Software; D013514:Surgical Procedures, Operative; D013813:Therapy, Computer-Assisted / Q000295:instrumentation; D014584:User-Computer Interface; D014741:Video Recording / Q000295:instrumentation