title: A transcutaneous bone digitizer for minimally invasive registration in orthopedics: a real-time focused ultrasound beam approach.
abstract: Computer-guided navigation of surgical tool position in computer-assisted orthopedic systems requires the registration of computer tomographic (CT) images with underlying bone. This process is presently performed by manually digitizing points on bone with a pointer and aligning them to a preoperative CT scan. We propose the use of ultrasound to obtain points on bone transcutaneously. A custom-made A-mode probe features a modular lens focusing system and a one-step calibration method. A stable and precise echo detection algorithm is also implemented. The accuracies of three signal detection algorithms--standard deviation, cross-correlation (XCORR) and short-time Fourier transform--were compared using a known reflected signal. XCORR showed the most accurate and stable operation. To test our method of obtaining bone surface points, a plastic model of the fourth human lumbar vertebra was CT scanned and then immersed in a water bath. Six surface registrations of the vertebra using an accurate pointing device were compared to ten registrations obtained using the US probe (using the XCORR algorithm). Student's T-test showed no significant difference in error between the two methods, proving that ultrasound registration, using our method, is equivalent to the more conventional pointer method.
authors.affiliation: Department of Electrical and Computer Engineering, The George Washington University, Washington, DC, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Moulder
authors.forename: Marwan
authors.initials: M
authors.lastname: Sati
authors.forename: Michael V
authors.initials: MV
authors.lastname: Wentkowski
authors.forename: Lutz-Peter
authors.initials: LP
authors.lastname: Nolte
mesh_terms: D000465:Algorithms; D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D019637:Orthopedic Procedures / Q000295:instrumentation*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional / Q000295:instrumentation*; D014584:User-Computer Interface