title: Metal artifact reduction from reformatted projections for hip prostheses in multislice helical computed tomography: techniques and initial clinical results.
abstract: OBJECTIVE
  Hip prosthesis is one of the most common types of metal implants and can cause significant artifacts in computed tomography (CT) examinations. The purpose of this work was to develop a projection-based method for reducing metal artifacts caused by hip prostheses in multislice helical CT.
  
  
  METHODS
  The proposed method is based on a novel concept, reformatted projection, which is formed by combining the projection data at the same view angle over the full longitudinal scan range. Detection and segmentation of the metal were performed on each reformatted projection image. Two dimensional interpolation based on Delaunay triangulation was used to fill voids left after removal of the metal in the reformatted projection. The corrected data were then reconstructed using a commercially available algorithm. The main advantage of this method is that both the detection of the metal objects and the interpolations are performed on complete reformatted projections with the entire metal region present, which is particularly useful for long hip prostheses. Twenty clinical abdominal/pelvis exams with hip prostheses were corrected and clinically evaluated.
  
  
  RESULTS
  The overall image quality and the conspicuity in some critical organs were significantly improved compared with the uncorrected images: overall quality (P = 0.0024); bladder base (P = 0.0027), and rectum (P = 0.0078). The average noise level in the bladder base was reduced from 86.7 HU to 36.2 HU. In 17 of 20 cases, the radiologists preferred either coronal (13) or axial (4) views of the corrected images.
  
  
  CONCLUSIONS
  A novel method for reducing metal artifact in multislice helical CT was developed. Initial clinical results showed that the proposed method can effectively reduce the artifacts caused by metal implants for the cases of unilateral and bilateral hip prothesis.
authors.affiliation: Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. yu.lifeng@mayo.edu
authors.forename: Lifeng
authors.initials: L
authors.lastname: Yu
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Jan
authors.initials: J
authors.lastname: Mueller
authors.forename: James M
authors.initials: JM
authors.lastname: Kofler
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Primak
authors.forename: Joel G
authors.initials: JG
authors.lastname: Fletcher
authors.forename: Luis S
authors.initials: LS
authors.lastname: Guimaraes
authors.forename: Thanila
authors.initials: T
authors.lastname: Macedo
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000465:Algorithms; D016477:Artifacts; D006622:Hip Prosthesis; D006801:Humans; D008670:Metals; D010865:Pilot Projects; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011860:Radiography, Abdominal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D008670:Metals