Dynamic contrast-enhanced MRI of the breast: quantitative method for kinetic curve type assessment

Abstract

Objective: The type of contrast enhancement kinetic curve (i.e., persistently enhancing, plateau, or washout) seen on dynamic contrast-enhanced MRI (DCE-MRI) of the breast is predictive of malignancy. Qualitative estimates of the type of curve are most commonly used for interpretation of DCE-MRI. The purpose of this study was to compare qualitative and quantitative methods for determining the type of contrast enhancement kinetic curve on DCE-MRI.

Materials and methods: Ninety-six patients underwent breast DCE-MRI. The type of DCE-MRI kinetic curve was assessed qualitatively by three radiologists on two occasions. For quantitative assessment, the slope of the washout curve was calculated. Kappa statistics were used to determine inter- and intraobserver agreement for the qualitative method. Matched sample tables, the McNemar test, and receiver operating characteristic (ROC) curve statistics were used to compare quantitative versus qualitative methods for establishing or excluding malignancy.

Results: Seventy-eight lesions (77.2%) were malignant and 23 (22.8%) were benign. For the qualitative assessment, the intra- and interobserver agreement was good (kappa = 0.76-0.88), with an area under the ROC curve (AUC) of 0.73-0.77. For the quantitative method, the highest AUC was 0.87, reflecting significantly higher diagnostic accuracies compared with qualitative assessment (p < 0.01 for the difference between the two methods).

Conclusion: Quantitative assessment of the type of contrast enhancement kinetic curve on breast DCE-MRI resulted in significantly higher diagnostic performance for establishing or excluding malignancy compared with assessment based on the standard qualitative method.

Fig. 1

Illustration of quantitative method for kinetic curve type assessment by categorizing washout parameters (percentage-enhancement difference in this figure). Any change from −5% to 5% was considered plateau (gray), more than 5% change was considered persistent, and less than −5% was considered washout.

Fig. 2

Comparison between receiver operating characteristic (ROC) curves of quantitative method using 0.03%/s average washout slope as cutoff point and qualitative method assessed by each of three radiologists separately. Area under ROC curve (AUC) of quantitative method was significantly higher than that of qualitative method (p < 0.01).

Fig. 3

Case examples of disagreement between qualitative method versus quantitative method in 39-year-old woman after lumpectomy undergoing breast MRI for 6-month follow-up (A–C) and 41-year-old woman undergoing breast MRI for assessment of recently diagnosed right breast cancer (D–F). A and B, Axial (A) and sagittal (B) high-spatial-resolution T1-weighted images of right breast show irregular mildly enhancing lesion at upper outer quadrant (arrow, B). C, Kinetic curve was categorized as persistent enhancement by three of three readers, whereas quantitative method categorized curve as plateau (i.e., suggestive of malignancy). Biopsy result showed mass to be in situ ductal carcinoma and infiltrating ductal carcinoma. D and E, Axial (D) and sagittal (E) high-spatial-resolution T1-weighted images of right breast show retroareolar lobulated mass (arrowhead, D). F, Kinetic curve was interpreted by three of three readers as persistently enhancing curve, whereas quantitative method categorized kinetic curve as plateau (i.e., suggestive of malignancy). Infiltrating ductal carcinoma was revealed by biopsy.