title: Measuring femoral lesions despite CT metal artefacts: a cadaveric study.
abstract: OBJECTIVE
  Computed tomography is the modality of choice for measuring osteolysis but suffers from metal-induced artefacts obscuring periprosthetic tissues. Previous papers on metal artefact reduction (MAR) show qualitative improvements, but their algorithms have not found acceptance for clinical applications. We investigated to what extent metal artefacts interfere with the segmentation of lesions adjacent to a metal femoral implant and whether metal artefact reduction improves the manual segmentation of such lesions.
  
  
  METHODS
  We manually created 27 periprosthetic lesions in 10 human cadaver femora. We filled the lesions with a fibrotic interface tissue substitute. Each femur was fitted with a polished tapered cobalt-chrome prosthesis and imaged twice--once with the metal, and once with a substitute resin prosthesis inserted. Metal-affected CTs were processed using standard back-projection as well as projection interpolation (PI) MAR. Two experienced users segmented all lesions and compared segmentation accuracy.
  
  
  RESULTS
  We achieved accurate delineation of periprosthetic lesions in the metal-free images. The presence of a metal implant led us to underestimate lesion volume and introduced geometrical errors in segmentation boundaries. Although PI MAR reduced streak artefacts, it led to greater underestimation of lesion volume and greater geometrical errors than without its application.
  
  
  CONCLUSIONS
  CT metal artefacts impair image segmentation. PI MAR can improve subjective image appearance but causes loss of detail and lower image contrast adjacent to prostheses. Our experiments showed that PI MAR is counterproductive for manual segmentation of periprosthetic lesions and should be used with care.
authors: Department of Orthopaedics, Leiden University Medical Center, J11-R Albinusdreef 2, 2333ZA Leiden, The Netherlands. fmalan@medvis.org
authors: Daniel F
authors: DF
authors: Malan
authors: Charl P
authors: CP
authors: Botha
authors: Gert
authors: G
authors: Kraaij
authors: Raoul M S
authors: RM
authors: Joemai
authors: Huub J L
authors: HJ
authors: van der Heide
authors: Rob G H H
authors: RG
authors: Nelissen
authors: Edward R
authors: ER
authors: Valstar
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D016477:Artifacts; D002102:Cadaver; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008670:Metals; D010014:Osteolysis / Q000000981:diagnostic imaging* / Q000209:etiology; D019047:Phantoms, Imaging; D019736:Prostheses and Implants; D011475:Prosthesis Failure / Q000009:adverse effects; D011856:Radiographic Image Enhancement / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D008670:Metals