title: Application of intravenous contrast in PET/CT: does it really introduce significant attenuation correction error?
abstract: The current perception of using contrast-enhanced CT (CECT) for attenuation correction (AC) is that of caution, as it might lead to erroneously elevated (18)F-FDG uptake on the PET scan. This study evaluates in vivo whether an intravenous iodinated contrast agent produces a significant AC artifact in the level of standardized uptake value (SUV) changes in PET/CT.
  
  
  METHODS
  Fifty-four patients referred for whole-body (WB) PET/CT scans were enrolled and subdivided into 2 groups. In part I, 26 patients had a single WB PET scan that was corrected for attenuation using noncontrast and intravenous CECT obtained before and after the emission data, respectively. The final PET images were compared for any visual and SUV maximum (SUV(max)) measurement difference. This allowed analysis of the compatibility of the scaling processes between the 2 different CTs and the PET. The SUV(max) values were obtained from ascending aorta, upper lung, femoral head, iliopsoas muscle, spleen, liver, and the site of pathology (total, 193 regions). Part II addressed whether intravenous contrast also influenced the PET emission data. For that purpose, the remaining 28 patients underwent a limited plain CT scan from lung base to lower liver edge, followed by a 1-bed PET scan of the same region and then a WB intravenous contrast CT scan in tandem with a WB PET scan. SUV(max) values were obtained at the lung base, liver, spleen, T11 or T12 vertebra, and paraspinal muscle (total, 135 regions). The data obtained from pre- and post-intravenous contrast PET scans were analyzed as in part I.
  
  
  RESULTS
  There was no statistically significant elevation of the SUV level in the measured anatomic sites as a whole (part I: mean SUV(max) difference = 0.06, P > 0.05; Part II: mean SUV(max) difference = -0.02, P > 0.05). However, statistically significant results as a group (mean SUV(max) difference = 0.26, P < 0.05)--albeit considered to be clinically insignificant--were observed for areas of pathology in the part I study. No abnormal focal increased (18)F-FDG activity was detected as a result of the intravenous contrast in both parts of this examination.
  
  
  CONCLUSIONS
  No statistically or clinically significant spuriously elevated SUV level that might potentially interfere with the diagnostic value of PET/CT was identified as a result of the application of intravenous iodinated contrast.
authors.affiliation: Department of Nuclear Medicine and PET-CT, AmMed Cancer Center, Adventist Hospital, Hong Kong, China. yyyau@hkah.org.hk
authors.forename: Yat-Yin
authors.initials: YY
authors.lastname: Yau
authors.forename: Wing-Sze
authors.initials: WS
authors.lastname: Chan
authors.forename: Yat-Man
authors.initials: YM
authors.lastname: Tam
authors.forename: Phil
authors.initials: P
authors.lastname: Vernon
authors.forename: So
authors.initials: S
authors.lastname: Wong
authors.forename: Marc
authors.initials: M
authors.lastname: Coel
authors.forename: Simon Kwok-Fai
authors.initials: SK
authors.lastname: Chu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D003287:Contrast Media; D003951:Diagnostic Errors / Q000517:prevention & control; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007275:Injections, Intravenous; D007479:Iopamidol / Q000008:administration & dosage; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D007479:Iopamidol