title: High-density materials do not always induce artifacts on PET/CT: what is responsible for the difference?
abstract: OBJECTIVE
  PET/CT often show increased uptake at sites of high-density materials. However, some materials seldom demonstrate increased uptake on PET/CT, such as the materials used in hip prostheses. We hypothesized that the motion of materials may be crucial for such artifacts. Here, we present representative cases, and validate our hypothesis based on the results of phantom studies.
  
  
  METHODS
  A standard cylinder, 20 cm in diameter, was filled with approximately 37 MBq of 18F-based activity, and a pacemaker was attached to the side of the cylinder. This phantom was placed on the bed with the pacemaker side facing the scanner. PET scans were performed using a Biograph LSO DUO. CT scans were performed first for transmission scans, followed by acquisition of emission scans. The phantom was first scanned (protocol 1). The phantom was then moved about 2 cm closer to the distal edge of the bed just after transmission CT scan, and the emission scan was performed (protocol 2).
  
  
  RESULTS
  Homogenous uptake was seen in the cylinder in protocol 1, and there was no visible uptake at the site of the pacemaker. In contrast, a clear hotspot was seen at the site of the pacemaker in protocol 2. The uptake in the cylinder was inhomogeneous; that on the pacemaker side of the cylinder was low, while that on the opposite side was high.
  
  
  CONCLUSIONS
  High-density materials do not show false increased uptake without motion on PET/CT. Motion of these materials surrounded by radioactive organs may play an important role in inducing false increased uptake on PET/CT.
authors: Department of Diagnostic Radiology, Graduate School of Medicine, Tohoku University, Sendai, Japan. kaneta@rad.med.tohoku.ac.jp
authors: Tomohiro
authors: T
authors: Kaneta
authors: Kentaro
authors: K
authors: Takanami
authors: Yuji
authors: Y
authors: Wakayama
authors: Akihiro
authors: A
authors: Sato
authors: Shuichi
authors: S
authors: Higano
authors: Hiroshi
authors: H
authors: Fukuda
authors: Shogo
authors: S
authors: Yamada
authors: Shoki
authors: S
authors: Takahashi
mesh_terms: D000818:Animals; D016477:Artifacts; D006801:Humans; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*