title: A CT method for following patients with both prosthetic replacement and implanted tantalum beads: preliminary analysis with a pelvic model and in seven patients.
abstract: BACKGROUND
  Radiostereometric analysis (RSA) is often used for evaluating implanted devices over time. Following patients who have had tantalum beads implanted as markers in conjunction with joint replacements is important for longitudinal evaluation of these patients and for those with similar implants. As doing traditional RSA imaging is exacting and limited to specialized centers, it is important to consider alternative techniques for this ongoing evaluation. This paper studies the use of computed tomography (CT) to evaluate over time tantalum beads which have been implanted as markers.
  
  
  METHODS
  The project uses both a hip model implanted with tantalum beads, acquired in several orientations, at two different CT energy levels, and a cohort of seven patients. The model was evaluated twice by the same observer with a 1-week interval. All CT volumes were analyzed using a semi-automated 3D volume fusion (spatial registration) tool which provides landmark-based fusion of two volumes, registering a target volume with a reference volume using a rigid body 3D algorithm. The mean registration errors as well as the accuracy and repeatability of the method were evaluated.
  
  
  RESULTS
  The mean registration error, maximum value of repeatability, and accuracy for the relative movement in the model were 0.16 mm, 0.02° and 0.1 mm, and 0.36° and 0.13 mm for 120 kVp and 0.21 mm, 0.04° and 0.01 mm, and 0.39° and 0.12 mm for 100 kVp. For the patients, the mean registration errors per patient ranged from 0.08 to 0.35 mm. These results are comparable to those in typical clinical RSA trials. This technique successfully evaluated two patients who would have been lost from the cohort if only RSA were used.
  
  
  CONCLUSIONS
  The proposed technique can be used to evaluate patients with tantalum beads over time without the need for stereoradiographs. Further, the effective dose associated with CT is decreasing.
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-17176, Stockholm, Sweden. henrik.olivecrona@karolinska.se.
authors.forename: Henrik
authors.initials: H
authors.lastname: Olivecrona
authors.affiliation: School of Information and Communication Technology, KTH Royal Institute of Technology, Stockholm, Sweden. maguire@kth.se.
authors.forename: Gerald Q
authors.initials: GQ
authors.lastname: Maguire
authors.affiliation: Department of Radiology, New York University School of Medicine, 560 First Avenue, New York, NY, 10016, USA. marilyne.noz@gmail.com.
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Noz
authors.affiliation: School of Computing, College of Engineering, University of Utah, Salt Lake City, UT, USA. zeleznik@cs.utah.edu.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Zeleznik
authors.affiliation: Department of Orthopedics, Skåne University Hospital, Lund, Sweden. uldis.kesteris@med.lu.edu.
authors.forename: Uldis
authors.initials: U
authors.lastname: Kesteris
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-17176, Stockholm, Sweden. lars.weidenhielm@karolinska.se.
authors.forename: Lars
authors.initials: L
authors.lastname: Weidenhielm
mesh_terms: D000465:Algorithms; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D006622:Hip Prosthesis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008134:Long-Term Care / Q000379:methods; D008137:Longitudinal Studies; D008953:Models, Anatomic; D011475:Prosthesis Failure; D011829:Radiation Dosage; D059869:Radiostereometric Analysis; D015203:Reproducibility of Results; D013635:Tantalum; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D013635:Tantalum