title: FTRAC--a robust fluoroscope tracking fiducial.
abstract: C-arm fluoroscopy is ubiquitous in contemporary surgery, but it lacks the ability to accurately reconstruct three-dimensional (3D) information. A major obstacle in fluoroscopic reconstruction is discerning the pose of the x-ray image, in 3D space. Optical/magnetic trackers tend to be prohibitively expensive, intrusive and cumbersome in many applications. We present single-image-based fluoroscope tracking (FTRAC) with the use of an external radiographic fiducial consisting of a mathematically optimized set of ellipses, lines, and points. This is an improvement over contemporary fiducials, which use only points. The fiducial encodes six degrees of freedom in a single image by creating a unique view from any direction. A nonlinear optimizer can rapidly compute the pose of the fiducial using this image. The current embodiment has salient attributes: small dimensions (3 x 3 x 5 cm); need not be close to the anatomy of interest; and accurately segmentable. We tested the fiducial and the pose recovery method on synthetic data and also experimentally on a precisely machined mechanical phantom. Pose recovery in phantom experiments had an accuracy of 0.56 mm in translation and 0.33 degrees in orientation. Object reconstruction had a mean error of 0.53 mm with 0.16 mm STD. The method offers accuracies similar to commercial tracking systems, and appears to be sufficiently robust for intraoperative quantitative C-arm fluoroscopy. Simulation experiments indicate that the size can be further reduced to 1 x 1 X 2 cm, with only a marginal drop in accuracy.
authors.affiliation: Department of Computer Science, Johns Hopkins University, Baltimore, Maryland 21218, USA. jain@cs.jhu.edu
authors.forename: Ameet Kumar
authors.initials: AK
authors.lastname: Jain
authors.forename: Tabish
authors.initials: T
authors.lastname: Mustafa
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.forename: Clif
authors.initials: C
authors.lastname: Burdette
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Chirikjian
authors.forename: Gabor
authors.initials: G
authors.lastname: Fichtinger
mesh_terms: D000465:Algorithms; D005471:Fluoroscopy / Q000295:instrumentation / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity