title: Diffusion-weighted imaging of prostate cancer: effect of b-value distribution on repeatability and cancer characterization.
abstract: OBJECTIVE
  To evaluate the effect of b-value distribution on the repeatability and Gleason score (GS) prediction of prostate cancer (PCa).
  
  
  METHODS
  Fifty PCa patients underwent two repeated 3T diffusion-weighted imaging (DWI) examinations using 12 b values in the range from 0 to 2000s/mm(2) and diffusion time of 20.3ms. Mean signal intensities of regions of interest, placed in PCa using whole mount prostatectomy sections as the reference, were fitted using monoexponential, kurtosis, stretched exponential, and biexponential models. In total, 4083 different b-value combinations consisting of 2 to 12 b values were evaluated. Repeatability was assessed by intraclass correlation coefficient, ICC(3,1), and coefficient of repeatability (CoR). Areas under receiver operating characteristic curve (AUCs) for PCa characterization were estimated while the correlation of the fitted values with GS groups (3+3, 3+4, >3+4) was evaluated by using the Spearman correlation coefficient (ρ).
  
  
  RESULTS
  The parameters of monoexponential, kurtosis, and stretched exponential models estimated using only 4-5, 5-7, 5-7 b values, respectively, had similar ICC(3,1), CoR, AUC, and ρ values as the parameters estimated using all 12 b values. Optimized b-value distributions demonstrated improved ICC(3,1) and CoR values but failed to improve AUC and ρ values. The parameters of biexponential model demonstrated the worst repeatability and diagnostic performance.
  
  
  CONCLUSIONS
  B-value distribution influences mainly the repeatability of DWI-derived parameters rather than the diagnostic performance.
authors.affiliation: Department of Information Technology, University of Turku, Turku, Finland; Turku PET Centre, University of Turku, Turku, Finland.
authors.forename: Harri
authors.initials: H
authors.lastname: Merisaari
authors.affiliation: Department of Information Technology, University of Turku, Turku, Finland; Department of Diagnostic Radiology, University of Turku, Turku, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Toivonen
authors.affiliation: Department of Diagnostic Radiology, University of Turku, Turku, Finland.
authors.forename: Marko
authors.initials: M
authors.lastname: Pesola
authors.affiliation: Department of Pathology, University of Turku and Turku University Hospital, Turku, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Taimen
authors.affiliation: Department of Urology, Turku University Hospital, Turku, Finland.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Boström
authors.affiliation: Department of Information Technology, University of Turku, Turku, Finland.
authors.forename: Tapio
authors.initials: T
authors.lastname: Pahikkala
authors.affiliation: Department of Diagnostic Radiology, University of Turku, Turku, Finland; Medical Imaging Centre of Southwest Finland, Turku University Hospital, Turku, Finland.
authors.forename: Hannu J
authors.initials: HJ
authors.lastname: Aronen
authors.affiliation: Department of Diagnostic Radiology, University of Turku, Turku, Finland. Electronic address: ivjamb@utu.fi.
authors.forename: Ivan
authors.initials: I
authors.lastname: Jambor
mesh_terms: D019540:Area Under Curve; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D060787:Neoplasm Grading; D011467:Prostate / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology*; D012372:ROC Curve; D012680:Sensitivity and Specificity
keywords: Diffusion-weighted imaging; Gleason score; Intraclass correlation coefficient; Prostate cancer; Repeatability; b values