Error analysis for a free-hand three-dimensional ultrasound system for neuronavigation

Abstract

Image-guided neurosurgery that is directed by a preoperative imaging study, such as magnetic resonance (MR) imaging or computerized tomography (CT) scanning, can be very accurate provided no significant changes occur during surgery. A variety of factors known to affect brain tissue movement are not reflected in the preoperative images used for guidance. To update the information on which neuronavigation is based, the authors propose the use of three-dimensional (3-D) ultrasound images in conjunction with a finite-element computational model of the deformation of the brain. The 3-D ultrasound system will provide real-time information on the displacement of deep structures to guide the mathematical model. This paper has two goals: first, to present an outline of steps necessary to compute the location of a feature appearing in an ultrasound image in an arbitrary coordinate system; and second, to present an extensive evaluation of this system's accuracy. The authors have found that by using a stylus rigidly coupled to the 3-D tracker's sensor, they were able to locate a point with an overall error of 1.36 ± 1.67 mm (based on 39 points). When coupling the tracker to an ultrasound scanhead, they found that they could locate features appearing on ultrasound images with an error of 2.96 ± 1.85 mm (total 58 features). They also found that when registering a skull phantom to coordinates that were defined by MR imaging or CT scanning, they could do so with an error of 0.86 ± 0.61 mm (based on 20 coordinates). Based on their previous finding of brain shifts on the order of 1 cm during surgery, the accuracy of their system warrants its use in updating neuronavigation imaging data.