title: Depth-resolved registration of transesophageal echo to x-ray fluoroscopy using an inverse geometry fluoroscopy system.
abstract: OBJECTIVE
  Image registration between standard x-ray fluoroscopy and transesophageal echocardiography (TEE) has recently been proposed. Scanning-beam digital x-ray (SBDX) is an inverse geometry fluoroscopy system designed for cardiac procedures. This study presents a method for 3D registration of SBDX and TEE images based on the tomosynthesis and 3D tracking capabilities of SBDX.
  
  
  METHODS
  The registration algorithm utilizes the stack of tomosynthetic planes produced by the SBDX system to estimate the physical 3D coordinates of salient key-points on the TEE probe. The key-points are used to arrive at an initial estimate of the probe pose, which is then refined using a 2D/3D registration method adapted for inverse geometry fluoroscopy. A phantom study was conducted to evaluate probe pose estimation accuracy relative to the ground truth, as defined by a set of coregistered fiducial markers. This experiment was conducted with varying probe poses and levels of signal difference-to-noise ratio (SDNR). Additional phantom and in vivo studies were performed to evaluate the correspondence of catheter tip positions in TEE and x-ray images following registration of the two modalities.
  
  
  RESULTS
  Target registration error (TRE) was used to characterize both pose estimation and registration accuracy. In the study of pose estimation accuracy, successful pose estimates (3D TRE < 5.0 mm) were obtained in 97% of cases when the SDNR was 5.9 or higher in seven out of eight poses. Under these conditions, 3D TRE was 2.32 ± 1.88 mm, and 2D (projection) TRE was 1.61 ± 1.36 mm. Probe localization error along the source-detector axis was 0.87 ± 1.31 mm. For the in vivo experiments, mean 3D TRE ranged from 2.6 to 4.6 mm and mean 2D TRE ranged from 1.1 to 1.6 mm. Anatomy extracted from the echo images appeared well aligned when projected onto the SBDX images.
  
  
  CONCLUSIONS
  Full 6 DOF image registration between SBDX and TEE is feasible and accurate to within 5 mm. Future studies will focus on real-time implementation and application-specific analysis.
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Hatt
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Tomkowiak
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: David A P
authors.initials: DA
authors.lastname: Dunkerley
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Jordan M
authors.initials: JM
authors.lastname: Slagowski
authors.affiliation: Triple Ring Technologies, Inc., Newark, California 94560.
authors.forename: Tobias
authors.initials: T
authors.lastname: Funk
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53792.
authors.forename: Amish N
authors.initials: AN
authors.lastname: Raval
authors.affiliation: Departments of Medical Physics and Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Speidel
mesh_terms: D000465:Algorithms; D000818:Animals; D002138:Calibration; D057785:Catheters; D017548:Echocardiography, Transesophageal / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D005471:Fluoroscopy / Q000295:instrumentation* / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods*; D019047:Phantoms, Imaging; D013552:Swine; D014867:Water
chemical_list: D014867:Water