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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. PURPOSE: To compare biexponential diffusion parameters of transplanted kidneys obtained with three different calculation methods. MATERIAL AND 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). CONCLUSION: Biexponential diffusion parameters differ significantly depending on the calculation methods used for their calculation.
Heusch et al. (2013) studied this question.