Inter- and intrareader agreement for categorization of background parenchymal enhancement at baseline and after training

Background parenchymal enhancement (BPE) refers to enhancing fibroglandular tissue on initial contrast-enhanced MR images. BPE appears to impact the rate of abnormal MRI interpretation and may correlate with breast cancer risk. There are now minimal data as to the uniformity of radiologists' BPE assessments and no data as to whether training improves agreement. Therefore, for this study, we sought to assess interreader agreement for BPE at baseline and after dedicated training. This study included 119 breast MRI examinations performed in 119 patients (mean age, 47 years; age range, 25-79 years) in 2008. One week before training, four fellowship-trained breast imagers with 2-12 years' experience independently recorded BPE on a 4-point scale as follows: 1 (minimal, ≤ 25%), 2 (mild, 26-50%), 3 (moderate, 51-75%), or 4 (marked, > 75%). The same 119 cases were reread in a new random order within 1 week and at least 3 weeks after training. Interreader agreement and intrareader agreement were assessed using kappa coefficients. With training, interreader agreement increased from fair (κ = 0.36) to moderate (κ = 0.48). Improvement was sustained at 3 weeks after training (κ = 0.45). Intrareader agreement between time points 2 and 3 (κ: mean, 0.79; range, 0.56-0.98) was greater than between time points 1 and 2 (κ: mean, 0.62; range, 0.45-0.84), indicating readers learned and retained. Initial interreader agreement for BPE was fair among breast radiologists but achieved sustained improvement with training, highlighting the importance of education and inclusion of standardized BPE categories in a reference atlas.