Clinical performance of a cone/annular array ultrasound breast scanner

Ultrasound is a useful adjunctive imaging modality to x-ray mammography for the detection and management of breast disease. A high resolution (0.3 mm at -6 dB) transducer consisting of co-axially aligned cone and annular array transducers has been incorporated into a prototype breast imaging system. The prototype scanner had an operating frequency of 4 MHz and scanning was performed in the prone position. We hypothesized that the increased resolution of this system would lead to improved detection of smaller, nonpalpable lesions and would thus contribute to the early detection of breast cancer. Results of a four year clinical study of the prototype involving 1743 patients are reported. The overall true positive (TP) fraction for the detection of malignancy was 52.5% compared with 86.6% for x-ray mammography. Improved performance of ultrasound approaching that of mammography is demonstrated for the youngest age group (less than 34 years) and for women whose breasts are predominantly dysplastic. However, the detection of nonpalpable tumours is disappointing with a TP fraction of only 22%. Causes for the failure of the prototype breast scanner to detect early breast lesions are presented and general conclusions on the use of large aperture transducers for automated breast imaging are discussed.