title: Adjustment of overestimated CT-based attenuation correction on bone SPECT/CT after hip-resurfacing arthroplasty.
abstract: SPECT/CT has made it possible to perform attenuation correction easily. However, CT-based attenuation correction (CTAC) is overestimated when metal is inside the body. The aim of this investigation was to create and test a new attenuation correction formula for CTAC that decreases the overestimation caused by an artificial femoral head and hip joint.
  
  
  METHODS
  We tested the usefulness of the new formula in a phantom study. The phantom contained "bones" made from gypsum. The components were placed in the phantom, the point source was placed both near metal and away from metal, and the counts were compared to verify the usefulness of the new attenuation correction formula. The new formula included use of thresholds to prevent the overestimation caused by proximity to metal.
  
  
  RESULTS
  With the standard formula, the maximum overestimation was 18% for a 22-cm artificial hip joint placed in the acetabular roof. With the new formula, using 2 thresholds, the overestimation decreased to 4%.
  
  
  CONCLUSIONS
  The new attenuation correction formula helps provide more correct data in SPECT/CT examinations of patients with metallic implants.
authors.affiliation: Diagnostic Imaging Center, Japanese Red Cross Sendai Hospital, Miyagi, Japan. hokumeiryou@hotmail.co.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Suzuki
authors.forename: Kichiro
authors.initials: K
authors.lastname: Koshida
authors.forename: Kosuke
authors.initials: K
authors.lastname: Matsubara
mesh_terms: D019644:Arthroplasty, Replacement, Hip; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D007091:Image Processing, Computer-Assisted; D064847:Multimodal Imaging; D019047:Phantoms, Imaging; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*
keywords: CTAC; SPECT/CT; bone; metal