Variability of renal apparent diffusion coefficients: limitations of the monoexponential model for diffusion...

Area of Science:

• Radiology
• Medical Imaging
• Renal Physiology

Background:

• Apparent diffusion coefficient (ADC) is a key MRI metric for assessing renal tissue.
• Significant variability exists in reported renal ADC values across studies.
• This variability may stem from differences in imaging parameters and data analysis methods.

Purpose of the Study:

• To determine if variations in diffusion weighting (b values) and monoexponential modeling explain the discrepancies in reported renal ADC values.
• To investigate the impact of these factors on the reliability of renal ADC quantification.

Main Methods:

• A meta-analysis of 19 published studies on normal kidney ADC values was performed.
• Reference diffusion decay curves from healthy volunteers were resampled at b values used in the literature.
• A monoexponential model was applied to resampled data to predict ADC values.
• Predicted ADC values were compared to published values using correlation plots.

Main Results:

• A significant correlation was observed between reported and predicted ADC values for the whole renal parenchyma (R(2) = 0.50), cortex (R(2) = 0.87), and medulla (R(2) = 0.61).
• These findings indicate that the choice of b values and the use of a monoexponential model are major contributors to the variability in reported renal ADC.
• The monoexponential model's limitations and differing b values significantly impact ADC quantification.

Conclusions:

• The use of a monoexponential function and variable b values substantially contributes to the variability in healthy kidney ADC measurements.
• Standardizing b values or employing a biexponential model is recommended for more reliable renal ADC quantification.
• This study highlights the importance of methodological consistency in diffusion-weighted MRI of the kidneys.