Published in:
Open Access 01-03-2017 | Magnetic Resonance
Impact of post-processing methods on apparent diffusion coefficient values
Published in: European Radiology | Issue 3/2017
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Objective
The apparent diffusion coefficient (ADC) is increasingly used as a quantitative biomarker in oncological imaging. ADC calculation is based on raw diffusion-weighted imaging (DWI) data, and multiple post-processing methods (PPMs) have been proposed for this purpose. We investigated whether PPM has an impact on final ADC values.
Methods
Sixty-five lesions scanned with a standardized whole-body DWI-protocol at 3 T served as input data (EPI-DWI, b-values: 50, 400 and 800 s/mm2). Using exactly the same ROI coordinates, four different PPM (ADC_1–ADC_4) were executed to calculate corresponding ADC values, given as [10-3 mm2/s] of each lesion. Statistical analysis was performed to intra-individually compare ADC values stratified by PPM (Wilcoxon signed-rank tests: α = 1 %; descriptive statistics; relative difference/∆; coefficient of variation/CV).
Results
Stratified by PPM, mean ADCs ranged from 1.136–1.206 *10-3 mm2/s (∆ = 7.0 %). Variances between PPM were pronounced in the upper range of ADC values (maximum: 2.540–2.763 10-3 mm2/s, ∆ = 8 %). Pairwise comparisons identified significant differences between all PPM (P ≤ 0.003; mean CV = 7.2 %) and reached 0.137 *10-3 mm2/s within the 25th–75th percentile.
Conclusion
Altering the PPM had a significant impact on the ADC value. This should be considered if ADC values from different post-processing methods are compared in patient studies.
Key Points
• Post-processing methods significantly influenced ADC values.
• The mean coefficient of ADC variation due to PPM was 7.2 %.
• To achieve reproducible ADC values, standardization of post-processing is recommended.