title: Biexponential analysis of diffusion-weighted imaging: comparison of three different calculation methods in transplanted kidneys.
abstract: BACKGROUND
  Biexponential analysis has been used increasingly to obtain contributions of both diffusion and microperfusion to the signal decay in diffusion-weighted imaging DWI of different parts of the body.
  
  
  OBJECTIVE
  To compare biexponential diffusion parameters of transplanted kidneys obtained with three different calculation methods.
  
  
  METHODS
  DWI was acquired in 15 renal allograft recipients (eight men, seven women; mean age, 52.4 ± 14.3 years) using a paracoronal EPI sequence with 16 b-values (b = 0-750 s/mm(2)) and six averages at 1.5T. No respiratory gating was used. Three different calculation methods were used for the calculation of biexponential diffusion parameters: Fp, ADCP, and ADCD were calculated without fixing any parameter a priori (calculation method 1); ADCP was fixed to 12.0 µm(2)/ms, whereas Fp and ADCD were calculated using the biexponential model (calculation method 2); multistep approach with monoexponential fitting of the high b-value portion (b ≥ 250 s/mm(2)) for determination of ADCD and assessment of the low b intercept for determination of Fp (calculation method 3). For quantitative analysis, ROI measurements were performed on the according parameter maps.
  
  
  RESULTS
  Mean ADCD values of the renal cortex using calculation method 1 were significantly lower than using calculation methods 2 and 3 (P < 0.001). There was a significant correlation between calculation methods 1 and 2 (r = 0.69 (P < 0.005) and calculation methods 1 and 3 (r = 0.59; P < 0.05) as well as calculation methods 2 and 3 (r = 0.98; P < 0.001). Mean Fp values of the renal cortex were higher with calculation method 1 than with calculation methods 2 and 3 (P < 0.001). For Fp, only the correlation between calculation methods 2 and 3 was significant (r = 0.98; P < 0.001).
  
  
  CONCLUSIONS
  Biexponential diffusion parameters differ significantly depending on the calculation methods used for their calculation.
authors.affiliation: University of Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Düsseldorf, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Heusch
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Wittsack
authors.forename: Gael
authors.initials: G
authors.lastname: Pentang
authors.forename: Christian
authors.initials: C
authors.lastname: Buchbender
authors.forename: Falk
authors.initials: F
authors.lastname: Miese
authors.forename: Julia
authors.initials: J
authors.lastname: Schek
authors.forename: Patric
authors.initials: P
authors.lastname: Kröpil
authors.forename: Gerald
authors.initials: G
authors.lastname: Antoch
authors.forename: Rotem S
authors.initials: RS
authors.lastname: Lanzman
mesh_terms: D064591:Allografts; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged
keywords: DWI; biexponential analysis; transplanted kidney