title: Optimization of b-value distribution for four mathematical models of prostate cancer diffusion-weighted imaging using b values up to 2000 s/mm(2): simulation and repeatability study.
abstract: OBJECTIVE
  To find optimal b-value distributions for monoexponential, stretched exponential, kurtosis, and biexponential models of prostate cancer (PCa) diffusion-weighted imaging (DWI) using simulations and repeated DWI examinations.
  
  
  METHODS
  Simulations aiming to minimize estimation accuracy error were performed. Ten PCa patients underwent in total four repeated 3-tesla DWI examinations using 12 equally spaced b values (0-2000 s/mm(2) ). Normalized mean signal intensities of regions-of-interest placed in normal tissue and PCa were fitted. In total, 210 different b-value combinations consisting of six b values, 0 and 100 s/mm(2) included in every b-value distribution, were evaluated in terms of accuracy and repeatability.
  
  
  RESULTS
  The simulations and in vivo DWI data suggest the optimal b-value distribution for the monoexponential model consists of four to five equally distributed b values in the range of 0 to 1200 s/mm(2) . The parameters of the stretched exponential and kurtosis models are best estimated using five to seven b values in the ranges of 300 to 700 and close to 2000 s/mm(2) , in addition to low b value. B-value distribution consisting of eight to 10 b values in the ranges of 0 to 100, 800 to 1200, and 1800 to 2000 s/mm(2) is the preferred method for estimation of the biexponential model parameters of PCa DWI.
  
  
  CONCLUSIONS
  The optimized b-value distributions demonstrated improved estimation accuracy and repeatability of DWI signal decay-derived parameters.
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.forename: Ivan
authors.initials: I
authors.lastname: Jambor
mesh_terms: D000465:Algorithms; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008432:Mathematical Computing; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011467:Prostate / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D012016:Reference Values; D051598:Whole Body Imaging / Q000295:instrumentation / Q000379:methods
keywords: b value; diffusion-weighted imaging; intraclass correlation coefficient; prostate cancer; repeatability