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Lesion Detection and Characterization in a Breast US Phantom: Results of the ACRIN 6666 Investigators¹

¹ From American College of Radiology Imaging Network, American Radiology Services, Johns Hopkins Green Spring, 10755 Falls Rd, Lutherville, MD 21093 (W.A.B.); Center for Statistical Sciences, Brown University, Providence, RI (J.D.B., J.B.C.); Department of Radiology, Northwestern University School of Medicine, Chicago, Ill (E.B.M.); and Department of Medical Physics, University of Wisconsin, Madison, Wis (E.L.M.). Received June 25, 2005; revision requested August 16; revision received September 1; final version accepted September 21. Supported by grants from the National Cancer Institute (CA89008) and the Avon Foundation. Address correspondence to W.A.B. (e-mail: wendieberg{at}hotmail.com).

View larger version (30K): [in a new window]   Figure 1: Sample map of phantom scanning results by investigator (red) and known locations of simulated masses (black). Numbers refer to the lesion recorded by the reader (red) or the actual lesion number (black, Table 1). Bold = hyperechoic lesion, = lesion with shadowing. Relative mean diameter of the lesions is drawn to scale, with the alphanumeric scale delimiting centimeter marks. In this example, lesions 14 and 17 were not identified, lesion 8 was identified twice (duplicate), and lesion 7 was underestimated in size by more than 1 mm.

View larger version (124K): [in a new window]   Figure 2: Transverse US scan without spatial compounding shows superficial 6-mm "cyst," lesion 17 (arrowhead), reported by only seven (11%) of 64 readers. Its location in a corner of the phantom, as well as the reverberation artifacts, may have hampered lesion detection.

View larger version (70K): [in a new window]   Figure 3: Sagittal panoramic spatially compounded US scan of phantom shows lesions 1, 11, 4, and 12. A 3-mm anechoic lesion (lesion 16) was not seen on this image, midway between lesions 11 and 4, but was identified by 59 (92%) of 64 readers. Lesion 1, a hyperechoic, round, 10-mm mass with posterior shadowing was identified by 62 readers (97%) and accurately characterized as hyperechoic by 58 (94%) and as showing posterior shadowing by 58 (94%). The 6-mm anechoic mass, lesion 11, was identified by 62 readers (97%) and characterized as anechoic by 42 (68%). Lesion 4, a 3-mm hyperechoic round mass, was reported by 50 readers (78%). Lesion 12, a hypoechoic mass with shadowing, was seen by 55 readers (86%) and accurately characterized as showing shadowing in 52 detections (95%).

View larger version (176K): [in a new window]   Figure 4: Transverse US scan without spatial compounding shows 3-mm irregular hypoechoic lesion (lesion 5, arrowhead), which was detected by only 23 (36%) of 64 readers.

View larger version (185K): [in a new window]   Figure 5: Distinction of an anechoic "cyst" from a hypoechoic mass was problematic at times. Transverse US scan without spatial compounding shows two adjacent anechoic 6-mm lesions. The lesion to the left (arrow, lesion 11) appears hypoechoic on this image, possibly due to its depth in the phantom, and was considered anechoic by 42 (66%) of 64 observers, complex cystic by two (3%), and hypoechoic by 18 (28%). The lesion to the right (arrowhead, lesion 13) was correctly classified as anechoic by 56 (92%) of 61 observers and considered complex cystic by two (3%) and hypoechoic by three (5%).

View larger version (175K): [in a new window]   Figure 6a: Transverse US scans demonstrate that posterior features are more difficult to depict with spatial compounding. (a) Scan without spatial compounding shows hyperechoic lesion (left, lesion 1) with posterior shadowing (arrow) and hypoechoic lesion (right, lesion 2) with posterior shadowing (arrowhead). (b) Scan with spatial compounding shows the same lesions. Posterior shadowing is still evident for lesion 1 (arrow) but is much less apparent for lesion 2 (arrowhead). Of 62 readers who identified lesion 1, 58 (94%) recognized posterior shadowing, whereas only 34 (55%) described lesion 2 as having shadowing. We did not control for use of spatial compounding, which decreases conspicuity of posterior features.

View larger version (147K): [in a new window]   Figure 6b: Transverse US scans demonstrate that posterior features are more difficult to depict with spatial compounding. (a) Scan without spatial compounding shows hyperechoic lesion (left, lesion 1) with posterior shadowing (arrow) and hypoechoic lesion (right, lesion 2) with posterior shadowing (arrowhead). (b) Scan with spatial compounding shows the same lesions. Posterior shadowing is still evident for lesion 1 (arrow) but is much less apparent for lesion 2 (arrowhead). Of 62 readers who identified lesion 1, 58 (94%) recognized posterior shadowing, whereas only 34 (55%) described lesion 2 as having shadowing. We did not control for use of spatial compounding, which decreases conspicuity of posterior features.