In vivo assessment of optimal b-value range for perfusion-insensitive apparent diffusion coefficient imaging

Purpose: To assess the optimal b-values range for perfusion-insensitive apparent diffusion coefficient (ADC) imaging of abdominal organs using short-duration DW-MRI acquisitions with currently available ADC estimation methods. Methods: DW-MRI data of 15 subjects were acquired with eight b-values in the range of 5-800 smm². The reference-standard, a perfusion insensitive, ADC value (ADC_IVIM), was computed using an intravoxel incoherent motion (IVIM) model with all acquired diffusion-weighted images. Simulated DW-MRI data was generated using an IVIM model with b-values in the range of 0-1200 smm². Monoexponential ADC estimates were calculated using: (1) Two-point estimator (ADC₂); (2) least squares three-point (ADC₃) estimator and; (3) Rician noise model estimator (ADC _R). The authors found the optimal b-values for perfusion-insensitive ADC calculations by minimizing the relative root mean square error (RRMS) between the ADC_IVIM and the monoexponential ADC values for each estimation method and organ. Results: Low b-value 300 smm² and high b-value 1200 smm² minimized the RRMS between the estimated ADC and the reference-standard ADC_IVIM to less than 5 using the ADC ₃ estimator. By considering only the in vivo DW-MRI data, the combination of low b-value 270 smm² and high b-value of 800 smm ² minimized the RRMS between the estimated ADC and the reference-standard ADC_IVIM to < 7 using the ADC₃ estimator. For all estimators, the RRMS between the estimated ADC and the reference standard ADC correlated strongly with the perfusion-fraction parameter of the IVIM model (r 0.78-0.83, p ≤ 0.003). Conclusions: The perfusion compartment in DW-MRI signal decay correlates strongly with the RRMS in ADC estimates from short-duration DW-MRI. The impact of the perfusion compartment on ADC estimations depends, however, on the choice of b-values and estimation method utilized. Likewise, perfusion-related errors can be reduced to < 7 by carefully selecting the b-values used for ADC calculations and method of estimation.