title: Clinical evaluation of TOF versus non-TOF on PET artifacts in simultaneous PET/MR: a dual centre experience.
abstract: OBJECTIVE
  Our objective was to determine clinically the value of time-of-flight (TOF) information in reducing PET artifacts and improving PET image quality and accuracy in simultaneous TOF PET/MR scanning.
  
  
  METHODS
  A total 65 patients who underwent a comparative scan in a simultaneous TOF PET/MR scanner were included. TOF and non-TOF PET images were reconstructed, clinically examined, compared and scored. PET imaging artifacts were categorized as large or small implant-related artifacts, as dental implant-related artifacts, and as implant-unrelated artifacts. Differences in image quality, especially those related to (implant) artifacts, were assessed using a scale ranging from 0 (no artifact) to 4 (severe artifact).
  
  
  RESULTS
  A total of 87 image artifacts were found and evaluated. Four patients had large and eight patients small implant-related artifacts, 27 patients had dental implants/fillings, and 48 patients had implant-unrelated artifacts. The average score was 1.14 ± 0.82 for non-TOF PET images and 0.53 ± 0.66 for TOF images (p < 0.01) indicating that artifacts were less noticeable when TOF information was included.
  
  
  CONCLUSIONS
  Our study indicates that PET image artifacts are significantly mitigated with integration of TOF information in simultaneous PET/MR. The impact is predominantly seen in patients with significant artifacts due to metal implants.
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zurich, Switzerland. Edwin.terVoert@usz.ch.|University of Zurich, Zurich, Switzerland. Edwin.terVoert@usz.ch.
authors.forename: Edwin E G W
authors.initials: EEGW
authors.lastname: Ter Voert
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zurich, Switzerland.|University of Zurich, Zurich, Switzerland.|Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Veit-Haibach
authors.affiliation: GE Global Research, Niskayuna, NY, USA.
authors.forename: Sangtae
authors.initials: S
authors.lastname: Ahn
authors.affiliation: GE Global Research, München, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Wiesinger
authors.affiliation: GE Healthcare, Waukesha, WI, USA.
authors.forename: M Mehdi
authors.initials: MM
authors.lastname: Khalighi
authors.affiliation: Department of Radiology, Molecular Imaging Program at Stanford, Stanford University, Stanford, CA, USA.
authors.forename: Craig S
authors.initials: CS
authors.lastname: Levin
authors.affiliation: Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Stanford University, Stanford, CA, USA.
authors.forename: Andrei H
authors.initials: AH
authors.lastname: Iagaru
authors.affiliation: Department of Radiology, Neuroradiology, Stanford University, Stanford, CA, USA.
authors.forename: Greg
authors.initials: G
authors.lastname: Zaharchuk
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zurich, Switzerland.|University of Zurich, Zurich, Switzerland.|Department of Neuroradiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Huellner
authors.affiliation: GE Healthcare, Waukesha, WI, USA.
authors.forename: Gaspar
authors.initials: G
authors.lastname: Delso
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D015921:Dental Implants; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D059629:Signal-To-Noise Ratio; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D015921:Dental Implants
keywords: Artifacts; Clinical research; Magnetic resonance imaging; Positron emission tomography; Time-of-flight