Computer Assisted 3D Measurements for Micro-Surgery

Abstract

A unique measuring tool, the Virtual Tape Measure (VTM), was developed in prototype form to minimize the inaccuracy surgeons encounter when trying to estimate the measurement of structures seen under the operating microscope. Superimposed on a stereo-video image of the surgical field taken through an operating microscope, the VTM is a three-dimensional measuring tool comprising a stereo-computer graphic pointer and a tethering line. The human operator simply places the VTM pointer adjacent two points he wishes to measure on the stereo-video image by controlling a three degrees of freedom (x, y, z-axes) input device. Active liquid shutter glasses must be worn to visualize the pointer and video images in stereo. To test the accuracy of the system, seven subjects used the VTM to measure distances between two dot models placed under the operating microscope. The absolute distance between the two dots ranged from 4 mm to 27 mm in a field of view measuring 20 mm × 30 mm. The distance in depth between the two dots ranged from 0 mm to 19 mm. Overall bias was an overestimation of 0.3 mm with a 95% confidence interval of 0.1 mm to 0.5 mm. The overall precision, as defined by variance of the error was 0.4 mm with a 95% confidence interval of 0.3 to 0.6 mm. Testing shows the VTM prototype system to be an accurate and reliable tool for measuring small objects with size scales typically encountered under the operating microscope during surgical procedures.