Automated Whole Breast Ultrasound - An Overview

Introduction:

Automated whole breast ultrasound (ABUS) is a secondary screening tool to detect breast cancer in women with dense breasts. Breast cancer is the most common cancer found among women. Mammography is an initial screening tool for breast cancer that misses about one-half of cancer in patients with dense breasts. ABUS can detect breast cancer missed by mammography in dense breasts as the sound waves produced by ultrasonography can penetrate better through the dense tissues. In patients' mammography reports, when the breast density is mentioned as a density score of 3 (heterogeneously dense breast) or density score of 4 (extremely dense breast), they are the right candidate for automated whole breast ultrasound screening.

How Does the Automated Whole Breast Ultrasound (ABUS) Work?

Ultrasound is a diagnostic tool that captures images of soft tissues. During the ultrasound, a handheld probe called the transducer directs high-frequency sound waves which bounce off the organs and are received by the transducer. The transducer processes the reflected waves, which the computer converts into images of the organs. The sound waves travel at various speeds depending on the type of tissue. Therefore, the speed of the sound waves and the amount of the sound waves yielded to the transducer determine the tissue types.

How Does Breast Density Affect Image Quality?

Breasts are made of dense glandular and fibrous tissues and less dense fatty tissues. About half of the women have dense breasts. In that, ten percent of women have extremely dense breasts. According to the breast cancer surveillance consortium reports, the sensitivity of mammography in detecting breast cancer in non-dense breast tissue is about 85.7 to 88.8 percent. It is reduced in dense breast tissue to 62.2 to 68.1 percent. Breast density is a high-risk factor for breast cancer. Women with dense breasts are at intermediate risk for breast cancer. Women with breast density greater or equal to 75 percent have four to six times increased risk, and a density of about 50 to 74 percent has 2.9 times increased risk compared to breast density less or equal to ten percent.

How Is the Automated Whole Breast Ultrasound Procedure Performed?

• Automated whole breast ultrasound is performed using an ABUS screening device that contains an ultrasound scanner and a transducer with an average frequency of about 10 MHz (megahertz) (5 to 14 MHz) that moves automatically. This scan is usually taken in the transverse direction with a field of view 15 to 17 cm, and the focal zone is set as wide and fixed. During the procedure, patients are asked to lie in a supine position. Then a wedge is placed below the back of the patient on the side of the breast to be examined. Placing the wedge helps flatten the breast, which improves contact with the transducer.

• After that, the radiologist applies an adequate amount of lotion over the skin of the breast to be examined. Still, the nipple-areolar complex requires more lotion to eliminate artifacts. Then a small probe called a transducer is moved with mild compression over the breast area to get images of the dense breast. Usually, the images are taken in anteroposterior, medial, and lateral views; sometimes, superior and inferior views are also taken for large breasts.

• For an anteroposterior view, the nipple is marked as a center point. The transducer is angled from the axilla towards the sternum for the lateral view. The medial view is taken by placing the transducer angled from the sternum towards the axilla. This procedure usually takes about 10 to 15 minutes for both sides. This series of axial images are sent to the workstation to obtain three-dimensional (3D) images. The slice thickness is usually 0.5 mm (millimeters), and approximately 448 axial slices are taken. The reading time is around 9 minutes.

What Are the Interpretations of Automated Whole Breast Ultrasound (ABUS)?

• The entire breast can be visualized in the coronal view of automated whole-breast ultrasound. Cancer's presence, location, size, number, outline, and borders can be visualized in ABUS. In addition, the echogenicity and the echo pattern (homogeneous or heterogeneous) of the lesion help detect breast cancer.

• The retraction phenomenon on automated whole breast ultrasound is seen as the stellate pattern around the breast lesion that indicates the presence of a malignant tumor.

• The white wall sign in automated whole breast ultrasound is seen as an echogenic wall in coronal view. It indicates benign breast lesions such as fibroadenoma (a non-cancerous solid breast lump), papilloma (a non-cancerous tumor), and simple cysts (fluid-filled cavity).

• In coronal view, automated whole breast ultrasound can differentiate the non-mass lesions from tumors such as ductal carcinoma in situ and papillary neoplasm.

What Are the Factors That Affect the Quality of the Automated Whole Breast Ultrasound Images?

• Poor contact between the skin of the breast and the transducer.

• Nipple shadow.

• Shadows of fibrotic tissues in the breast.

• Reverberation artifacts.

• Lack of training and less experienced radiologists.

Conclusion:

Standard mammography is less reliable in diagnosing breast cancer in dense breasts. Automated whole breast ultrasound is done as an additional imaging technique to mammography, not as an alternative. The final images of automated whole breast ultrasound should be compared with mammography images. ABUS is 80 to 89 percent sensitive and 96 to 100 percent specific in detecting breast cancer. When the breast tumor is small and in an early stage, it can be easily treated and thus save the patient's life. Breast cancer treatment at an early stage is less invasive and more economical.