title: Impact of post-processing methods on apparent diffusion coefficient values.
abstract: OBJECTIVE
  The apparent diffusion coefficient (ADC) is increasingly used as a quantitative biomarker in oncological imaging. ADC calculation is based on raw diffusion-weighted imaging (DWI) data, and multiple post-processing methods (PPMs) have been proposed for this purpose. We investigated whether PPM has an impact on final ADC values.
  
  
  METHODS
  Sixty-five lesions scanned with a standardized whole-body DWI-protocol at 3 T served as input data (EPI-DWI, b-values: 50, 400 and 800 s/mm2). Using exactly the same ROI coordinates, four different PPM (ADC_1-ADC_4) were executed to calculate corresponding ADC values, given as [10-3mm2/s] of each lesion. Statistical analysis was performed to intra-individually compare ADC values stratified by PPM (Wilcoxon signed-rank tests: α = 1 %; descriptive statistics; relative difference/∆; coefficient of variation/CV).
  
  
  RESULTS
  Stratified by PPM, mean ADCs ranged from 1.136-1.206 *10-3mm2/s (∆ = 7.0 %). Variances between PPM were pronounced in the upper range of ADC values (maximum: 2.540-2.763 10-3mm2/s, ∆ = 8 %). Pairwise comparisons identified significant differences between all PPM (P ≤ 0.003; mean CV = 7.2 %) and reached 0.137 *10-3mm2/s within the 25th-75th percentile.
  
  
  CONCLUSIONS
  Altering the PPM had a significant impact on the ADC value. This should be considered if ADC values from different post-processing methods are compared in patient studies.
  
  
  CONCLUSIONS
  • Post-processing methods significantly influenced ADC values. • The mean coefficient of ADC variation due to PPM was 7.2 %. • To achieve reproducible ADC values, standardization of post-processing is recommended.
authors.affiliation: Institute of Diagnostic Radiology, University of Erlangen-Nuremberg, Maximiliansplatz 1, D-91054, Erlangen, Germany.
authors.forename: Martin Georg
authors.initials: MG
authors.lastname: Zeilinger
authors.affiliation: Institute of Diagnostic Radiology, University of Erlangen-Nuremberg, Maximiliansplatz 1, D-91054, Erlangen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Lell
authors.affiliation: Department of Radiology and Nuclear Medicine, Medical University Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. pascal.baltzer@meduniwien.ac.at.
authors.forename: Pascal Andreas Thomas
authors.initials: PA
authors.lastname: Baltzer
authors.affiliation: Department of Neuroradiology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054, Erlangen, Germany.
authors.forename: Arnd
authors.initials: A
authors.lastname: Dörfler
authors.affiliation: Institute of Diagnostic Radiology, University of Erlangen-Nuremberg, Maximiliansplatz 1, D-91054, Erlangen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Uder
authors.affiliation: Department of Neuroradiology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054, Erlangen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Dietzel
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D015203:Reproducibility of Results; D051598:Whole Body Imaging / Q000379:methods*
keywords: ADC; DWI; MRI; Reproducibility; Tumour