title: Effects of ROI definition and reconstruction method on quantitative outcome and applicability in a response monitoring trial.
abstract: OBJECTIVE
  Quantitative measurement of tracer uptake in a tumour can be influenced by a number of factors, including the method of defining regions of interest (ROIs) and the reconstruction parameters used. The main purpose of this study was to determine the effects of different ROI methods on quantitative outcome, using two reconstruction methods and the standard uptake value (SUV) as a simple quantitative measure of FDG uptake.
  
  
  METHODS
  Four commonly used methods of ROI definition (manual placement, fixed dimensions, threshold based and maximum pixel value) were used to calculate SUV (SUV([MAN]), SUV15 mm, SUV50, SUV75 and SUVmax, respectively) and to generate "metabolic" tumour volumes. Test-retest reproducibility of SUVs and of "metabolic" tumour volumes and the applicability of ROI methods during chemotherapy were assessed. In addition, SUVs calculated on ordered subsets expectation maximisation (OSEM) and filtered back-projection (FBP) images were compared.
  
  
  RESULTS
  ROI definition had a direct effect on quantitative outcome. On average, SUV[MAN), SUV15 mm, SUV50 and SUV75, were respectively 48%, 27%, 34% and 15% lower than SUVmax when calculated on OSEM images. No statistically significant differences were found between SUVs calculated on OSEM and FBP reconstructed images. Highest reproducibility was found for SUV15 mm and SUV[MAN] (ICC 0.95 and 0.94, respectively) and for "metabolic" volumes measured with the manual and 50% threshold ROIs (ICC 0.99 for both). Manual, 75% threshold and maximum pixel ROIs could be used throughout therapy, regardless of changes in tumour uptake or geometry. SUVs showed the same trend in relative change in FDG uptake after chemotherapy, irrespective of the ROI method used.
  
  
  CONCLUSIONS
  The method of ROI definition has a direct influence on quantitative outcome. In terms of simplicity, user-independence, reproducibility and general applicability the threshold-based and fixed dimension methods are the best ROI methods. Threshold methods are in addition relatively independent of changes in size and geometry, however, and may therefore be more suitable for response monitoring purposes.
authors.affiliation: Clinical PET Centre, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Nanda C
authors.initials: NC
authors.lastname: Krak
authors.forename: R
authors.initials: R
authors.lastname: Boellaard
authors.forename: Otto S
authors.initials: OS
authors.lastname: Hoekstra
authors.forename: Jos W R
authors.initials: JW
authors.lastname: Twisk
authors.forename: Corneline J
authors.initials: CJ
authors.lastname: Hoekstra
authors.forename: Adriaan A
authors.initials: AA
authors.lastname: Lammertsma
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging*; D002986:Clinical Trials as Topic / Q000379:methods; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011379:Prognosis; D012372:ROC Curve; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18