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Suspicious Breast Lesions: Assessment of 3D Doppler US Indexes for Classification in a Test Population and Fourfold Cross-Validation Scheme¹

¹ From the Departments of Radiology (G.L.L., M.A.R., J.B.F., J.F.K., K.A.H., C.P., N.J.T., K.D.E., P.L.C.), Biomedical Engineering (J.B.F., P.L.C.), and Biostatistics (T.D.J.), University of Michigan, 200 Zina Pitcher Pl, Room 3315, Ann Arbor, MI 48109-0553. Received May 22, 2006; revision requested August 21; revision received November 4, 2007; accepted December 18; final version accepted May 13, 2008. Supported in part by grant RO1CA55076 from the National Cancer Institute and by the U.S. Army Medical Research and Material Command under contract DAMD17-01-1-0327 and grants R01CA091713 and P01CA87634 from the National Cancer Institute. Address correspondence to G.L.L. (e-mail: gllec{at}umich.edu).

Purpose: To assess the diagnostic performance of various Doppler ultrasonographic (US) vascularity measures in conjunction with grayscale (GS) criteria in differentiating benign from malignant breast masses, by using histologic findings as the reference standard.

Materials and Methods: Institutional Review Board and HIPAA standards were followed. Seventy-eight women (average age, 49 years; range, 26–70 years) scheduled for breast biopsy were included. Thirty-eight patient scans were partially analyzed and published previously, and 40 additional scans were used as a test set to evaluate previously determined classification indexes. In each patient, a series of color Doppler images was acquired and reconstructed into a volume encompassing a suspicious mass, identified by a radiologist-defined ellipsoid, in which six Doppler vascularity measures were calculated. Radiologist GS ratings and patient age were also recorded. Multivariable discrimination indexes derived from the learning set were applied blindly to the test set. Overall performance was also confirmed by using a fourfold cross-validation scheme on the entire population.

Results: By using all cases (46 benign, 32 malignant), the area under the receiver operating characteristic curve (A_z) values confirmed results of previous analyses: Speed-weighted pixel density (SWPD) performed the best as a diagnostic index, although statistical significance (P = .01) was demonstrated only with respect to the normalized power-weighted pixel density. In both learning and test sets, the three-variable index (SWPD-age-GS) displayed significantly better diagnostic performance (A_z = 0.97) than did any single index or the one two-variable index (age-GS) that could be obtained without the data from the Doppler scan. Results of the cross validation confirmed the trends in the two data sets.

Conclusion: Quantitative Doppler US vascularity measurements considerably contribute to malignant breast tissue identification beyond subjective GS evaluation alone. The SWPD-age-GS index has high performance (A_z = 0.97), regardless of incidental performance variations in its single variable components.

© RSNA, 2008