Evaluation of apparent diffusion coefficient (ADC) with regards to reproducibility and diagnostic accuracy as well as possible significance of pre - and post - contrast acquisition and employment of different b values.

Purpose: Ongoing efforts are focusing on optimizing diffusion-weighted imaging (DWI) as an essential part of breast MRI protocol. Our study aimed to evaluate the effect of contrast media (CM) on the apparent diffusion coefficients (ADC) acquired following current recommendations.

Patient And Methods: Patients who underwent 3 T breast MRI with a histologically verified suspicious lesion were included in this IRB-approved, single-center, cross-sectional retrospective study. Breast MRI protocol included a DWI sequence with multiple b-values, which was acquired before and after CM administration. ADC maps were calculated by in-line monoexponential fitting with b-values 0 /800 and 50/800. Two independent readers (R1, R2) reviewed the images in separate sessions for b values 0/800 and 50/800, pre- and post-CM. Bland Altmann plots as well as intraclass correlation coefficients (ICCs) for inter-reader agreement, different b-values, and pre- and post-CM were calculated. Diagnostic accuracy was evaluated and compared by calculating the area under the receiver operating characteristics curve (AUC).

Results: 91 lesions in 89 patients were examined (mean age 50.7 years, standard deviation 13.9). ADC values were significantly (P<0.05) lower post-CM (mean ranging from 1.28 x10 mm/s to 1.30 x10 mm/s) compared to pre-CM (mean ranging from 1.32 x10 mm/s to 1.37 x10 mm/s) for both b-values combinations (0/800 and 50/800 s/mm). We found an almost perfect inter-reader agreement pre-/post-CM with b values 0/800 and 50/800 (ICC ranging from 0.853 to 0.939). Bland Altman plot demonstrated no systematic difference between readers. ROC analysis revealed good diagnostic performance without significant differences (P>0.05) between b values 0/800 and 50/800 s/mm2 as well as pre- and post-CM with areas under the ROC curve between 0.834 and 0.877.

Conclusion: ADC values are slightly lower when acquiring b values 0/800 and post-CM. This effect does not reduce the diagnostic performance but may be relevant in case of definite cut-offs in medical decision making.