title: PET/CT: artifacts caused by bowel motion.
abstract: OBJECTIVE
  In a combined positron emission tomography (PET) and computed tomography (CT) system, the CT images can be used for attenuation correction as well as for image fusion. However, quantitative and qualitative differences have been reported between CT based attenuation corrected PET and conventional transmission scan corrected PET images. The purpose of this study was to investigate potential differences in PET/CT caused by attenuation differences in bowel due to motion.
  
  
  METHODS
  Twelve patients had PET/CT scans performed using 68Ge transmission and CT attenuation correction methods. Three emission imaging datasets were generated including CT corrected PET, Ge corrected PET, and the difference images (CT corrected PET minus Ge corrected PET). PET difference images were used to identify regions of mismatch and to quantify possible discordance between images by using standardized uptake values (SUVs). Using the Ge corrected PET as the standard, differences in emission images were classified as an overestimation (pattern A) or an underestimation (pattern B) in these difference images.
  
  
  RESULTS
  One hundred and twenty-three mismatched areas were identified. Among them, overestimated areas in CT corrected image were detected in 36 regions (pattern A), while underestimated areas were evaluated in the remaining 87 regions (pattern B). The mean value of the difference in pattern A (mean +/- standard deviation = 0.84 +/- 0.44) was slightly higher than that in pattern B (0.60 +/- 0.23), and statistically significant. Six of 36 regions in pattern A had an SUV of greater than 2.5 in CT corrected PET but less than 2.5 in Ge corrected PET; two of 87 regions with pattern B demonstrated an SUV greater than 2.5 in Ge corrected PET and less than 2.5 in CT corrected PET.
  
  
  CONCLUSIONS
  Physiological bowel motion may result in attenuation differences and subsequent differences in SUVs. Overestimation of fluorodeoxyglucose uptake should not be misinterpreted as disease.
authors.affiliation: Division of Nuclear Medicine, Johns Hopkins School of Medicine, Baltimore 21287-0817, USA.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nakamoto
authors.forename: Bennett B
authors.initials: BB
authors.lastname: Chin
authors.forename: Christian
authors.initials: C
authors.lastname: Cohade
authors.forename: Medhat
authors.initials: M
authors.lastname: Osman
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Tatsumi
authors.forename: Richard L
authors.initials: RL
authors.lastname: Wahl
mesh_terms: D000008:Abdominal Neoplasms / Q000175:diagnosis / Q000378:metabolism; D016477:Artifacts; D003951:Diagnostic Errors; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009068:Movement; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014055:Tomography, Emission-Computed / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18