title: Ratio of Tumor to Normal Prostate Tissue Apparent Diffusion Coefficient as a Method for Quantifying DWI of the Prostate.
abstract: OBJECTIVE
  The purpose of this study was to investigate the ability of the apparent diffusion coefficient (ADC) ratio of tumor to normal prostate tissue to overcome inherent variability based on choice of b values, with whole-mount histopathologic analysis as the reference standard for tumor identification.
  
  
  METHODS
  Thirty-nine patients with prostate cancer underwent 3-T MRI, including DWI with b values of 0, 150, 750, and 1000 s/mm(2). ADC maps were derived from four b value combinations. Histologically derived ROIs were defined for prostate tumor and benign prostate tissue to generate a ratio. The concordance correlation coefficient was used to evaluate agreement and reproducibility at different b values. Bland-Altman plots were used to evaluate the pattern of relative measurement difference between b value combinations. The relationship between ADC values and Gleason score was tested by Spearman rank correlation.
  
  
  RESULTS
  ADC values varied depending on the b value combination selected. The concordance correlation coefficient was higher for ADC ratios (0.883; 95% CI, 0.816-0.927) compared with absolute ADC values for normal tissue (0.873; 95% CI, 0.799-0.921) and tumor (0.792; 95% CI, 0.688-0.864). The ADC ratio concordance correlation coefficient for transition zone tumors was considerably higher than that for the peripheral zone in all cases. Bland-Altman analysis showed higher variation for ADC maps incorporating a b value of zero for both ratio and absolute values. There was a stronger inverse relationship to Gleason score for ADC ratios (rho, -0.354 to -0.456) compared with absolute ADC values (rho, -0.117 to -0.379).
  
  
  CONCLUSIONS
  The use of a simple ratio of prostate tumor ADC to normal tissue ADC improved the concordance between different b value combinations and could provide a more robust means of assessing restricted diffusion in the prostate.
authors.affiliation: 1 Department of Radiology, Addenbrooke's Hospital and the University of Cambridge, Hills Rd, Cambridge, CB2 0QQ, UK.
authors.forename: Tristan
authors.initials: T
authors.lastname: Barrett
authors.affiliation: 1 Department of Radiology, Addenbrooke's Hospital and the University of Cambridge, Hills Rd, Cambridge, CB2 0QQ, UK.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Priest
authors.affiliation: 1 Department of Radiology, Addenbrooke's Hospital and the University of Cambridge, Hills Rd, Cambridge, CB2 0QQ, UK.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Lawrence
authors.affiliation: 2 Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY.
authors.forename: Debra A
authors.initials: DA
authors.lastname: Goldman
authors.affiliation: 3 Department of Histopathology, Addenbrooke's Hospital and the University of Cambridge, Cambridge, United Kingdom.
authors.forename: Anne Y
authors.initials: AY
authors.lastname: Warren
authors.affiliation: 4 Department of Urology, Addenbrooke's Hospital, Cambridge, United Kingdom.|5 Department of Oncology, Translational Prostate Cancer Group, University of Cambridge, Hutchinson-MRC Research Centre, Cambridge, United Kingdom.
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Gnanapragasam
authors.affiliation: 1 Department of Radiology, Addenbrooke's Hospital and the University of Cambridge, Hills Rd, Cambridge, CB2 0QQ, UK.|6 Present address: Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY.
authors.forename: Evis
authors.initials: E
authors.lastname: Sala
authors.affiliation: 1 Department of Radiology, Addenbrooke's Hospital and the University of Cambridge, Hills Rd, Cambridge, CB2 0QQ, UK.
authors.forename: Ferdia A
authors.initials: FA
authors.lastname: Gallagher
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D011467:Prostate / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology*; D012189:Retrospective Studies
keywords: DWI; Gleason score; MRI; prostate cancer