title: A volumetric model-based 2D to 3D registration method for measuring kinematics of natural knees with single-plane fluoroscopy.
abstract: OBJECTIVE
  Accurate measurement of the three-dimensional (3D) rigid body and surface kinematics of the natural human knee is essential for many clinical applications. Existing techniques are limited either in their accuracy or lack more realistic experimental evaluation of the measurement errors. The purposes of the study were to develop a volumetric model-based 2D to 3D registration method, called the weighted edge-matching score (WEMS) method, for measuring natural knee kinematics with single-plane fluoroscopy to determine experimentally the measurement errors and to compare its performance with that of pattern intensity (PI) and gradient difference (GD) methods.
  
  
  METHODS
  The WEMS method gives higher priority to matching of longer edges of the digitally reconstructed radiograph and fluoroscopic images. The measurement errors of the methods were evaluated based on a human cadaveric knee at 11 flexion positions.
  
  
  RESULTS
  The accuracy of the WEMS method was determined experimentally to be less than 0.77 mm for the in-plane translations, 3.06 mm for out-of-plane translation, and 1.13 degrees for all rotations, which is better than that of the PI and GD methods.
  
  
  CONCLUSIONS
  A new volumetric model-based 2D to 3D registration method has been developed for measuring 3D in vivo kinematics of natural knee joints with single-plane fluoroscopy. With the equipment used in the current study, the accuracy of the WEMS method is considered acceptable for the measurement of the 3D kinematics of the natural knee in clinical applications.
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 10051, Taiwan, Republic of China.
authors.forename: Tsung-Yuan
authors.initials: TY
authors.lastname: Tsai
authors.forename: Tung-Wu
authors.initials: TW
authors.lastname: Lu
authors.forename: Chung-Ming
authors.initials: CM
authors.lastname: Chen
authors.forename: Mei-Ying
authors.initials: MY
authors.lastname: Kuo
authors.forename: Horng-Chaung
authors.initials: HC
authors.lastname: Hsu
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D005471:Fluoroscopy / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000502:physiology*; D008954:Models, Biological; D010363:Pattern Recognition, Automated / Q000379:methods; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*