Deciphering ADC disparities in breast MRI: Implications for left-right asymmetry and standardization.

PURPOSE: To systematically evaluate the impact of MRI software updates on apparent diffusion coefficient (ADC) values, assess potential left-right asymmetry in bilateral breast ADC values, and explore standardization techniques to enhance diagnostic reliability in lesion classification. METHODS: A total of 420 patients (mean age, 54.2 ± 14.2 years) who underwent 3 T breast MRI between 2021 and 2025 were retrospectively analyzed. The ADC values in fibroglandular tissue (FGT) and pectoralis major muscle (PMM) were compared before and after a software update using an unpaired t-test. Left-right asymmetries were assessed using paired and unpaired t-tests. Differences in lesion ADC values between malignancies were analyzed. The diagnostic performance of three region of interest (ROI) methods-whole-lesion mean (WL-mean), small-ROI mean (SR-mean), and small-ROI minimum (SR-min)-was evaluated using receiver operating characteristic analysis. The effect of standardization using ratios or differences relative to FGT and PMM on diagnostic accuracy was also examined. RESULTS: The ADC values were affected by the software update, and notable left-right asymmetries were observed in both FGT and PMM. Malignancies had significantly lower ADC values than benign lesions. Among the ROI methods, SR-min yielded the highest diagnostic accuracy, although diagnostic performance was lower in non-mass lesions than in mass lesions across the ROI methods. Standardization using ratios or differences relative to FGT and PMM did not improve diagnostic performance. CONCLUSIONS: ADC measurements are sensitive to technical variables and exhibit unexpected laterality effects, thereby complicating standardization. While general thresholds may guide interpretation, establishing universally standardized ADC values remains challenging.