title: Effective methods to correct contrast agent-induced errors in PET quantification in cardiac PET/CT.
abstract: In combined PET/CT studies, x-ray attenuation information from the CT scan is generally used for PET attenuation correction. Iodine-containing contrast agents may induce artifacts in the CT-generated attenuation map and lead to an erroneous radioactivity distribution on the corrected PET images. This study evaluated 2 methods of thresholding the CT data to correct these contrast agent-related artifacts.
  
  
  METHODS
  PET emission and attenuation data (acquired with and without a contrast agent) were simulated using a cardiac torso software phantom and were obtained from patients. Seven patients with known coronary artery disease underwent 2 electrocardiography-gated CT scans of the heart, the first without a contrast agent and the second with intravenous injection of an iodine-containing contrast agent. A 20-min PET scan (single bed position) covering the same axial range as the CT scans was then obtained 1 h after intravenous injection of (18)F-FDG. For both the simulated data and the patient data, the unenhanced and contrast-enhanced attenuation datasets were used for attenuation correction of the PET data. Additionally, 2 threshold methods (one requiring user interaction) aimed at compensating for the effect of the contrast agent were applied to the contrast-enhanced attenuation data before PET attenuation correction. All PET images were compared by quantitative analysis.
  
  
  RESULTS
  Regional radioactivity values in the heart were overestimated when the contrast-enhanced data were used for attenuation correction. For patients, the mean decrease in the left ventricular wall was 23%. Use of either of the proposed compensation methods reduced the quantification error to less than 5%. The required time for postprocessing was minimal for the user-independent method.
  
  
  CONCLUSIONS
  The use of contrast-enhanced CT images for attenuation correction in cardiac PET/CT significantly impairs PET quantification of tracer uptake. The proposed CT correction methods markedly reduced these artifacts; additionally, the user-independent method was time-efficient.
authors.affiliation: Department of Nuclear Medicine, University of Münster, Münster, Germany. butherf@uni-muenster.de
authors.forename: Florian
authors.initials: F
authors.lastname: Büther
authors.forename: Lars
authors.initials: L
authors.lastname: Stegger
authors.forename: Mohammad
authors.initials: M
authors.lastname: Dawood
authors.forename: Felix
authors.initials: F
authors.lastname: Range
authors.forename: Michael
authors.initials: M
authors.lastname: Schäfers
authors.forename: Roman
authors.initials: R
authors.lastname: Fischbach
authors.forename: Thomas
authors.initials: T
authors.lastname: Wichter
authors.forename: Otmar
authors.initials: O
authors.lastname: Schober
authors.forename: Klaus P
authors.initials: KP
authors.lastname: Schäfers
mesh_terms: D016477:Artifacts; D003287:Contrast Media; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D019788:Fluorodeoxyglucose F18; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007472:Iohexol / Q000031:analogs & derivatives; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D007472:Iohexol; C038192:iopromide