Breast Imaging

Description: To understand the imaging modalities available to detect occult breast disease and characterize clinically identified lesions.

Scope of the Problem: Imaging is paramount for the early detection and staging of breast cancer, as well as to inform management decisions and direct therapy for this and other breast conditions.

Objectives of Management: To appropriately use imaging modalities for evaluating breast disease and to improve the efficacy of screening.

Relevant Pathophysiology: In both ultrasonography and mammography, energy (ultrasonic or x-ray) is passed into the breast tissue, where it is reflected, scattered, and attenuated. In ultrasonography, sound waves are reflected from tissue interfaces where the characteristic acoustic impedance (ability to transmit sound) differ; the greater the differences in the tissues, the greater the reflection (and refraction) of the sound waves. Reflected sound wave are detected and used to create an image of the tissues in the path of the sound beam. In mammography, x-rays are attenuated, based upon the characteristics of the breast tissue, and are then absorbed on the recording device (x-ray film or digital screen). The resultant shadows allow the architecture of the tissues to be discerned. Ultrasonography tends to be used in a targeted manner, whereas x-ray mammography routinely uses two views (craniocaudal and mediolateral oblique) of each whole breast.

The ability of digitally mammographic images to be captured rapidly and manipulated by computer programs has led to the development of three-dimensional breast tomosynthesis. Breast tomosynthesis involves acquiring images of a stationary compressed breast at multiple angles during a short scan. These images are reconstructed into a series of thin (1 mm) high-resolution slices that can be displayed in various ways. Digital breast tomosynthesis still requires breast compression for optimal images. (Compression increases the image contrast and decreases the radiation dose.) Initial data indicated a doubling of the mean glandular radiation dose with tomosynthesis compared with standard digital mammography (0.7 mSv, equivalent to natural background radiation over 3 months). Subsequent data suggest that it 8% higher compared with digital mammogram. Clinical data suggest that tomosynthesis produces a better image, improved accuracy, and lower recall rates compared with digital mammography alone (especially for women younger than 50 and those with dense breasts), but higher false-positive rates and uncertain cost-effectiveness and impact on breast cancer survival means the technology’s role remains to be proved. Computed tomography is not a cost-effective screening tool but does have a place when evaluating the possibility of advanced disease.

Magnetic resonance imaging (MRI) uses strong magnetic fields, magnetic field gradients, and radio waves to form its images. Some atomic nuclei (most often hydrogen) can absorb radio frequency energy when in a strong external magnetic field. Pulses of radio waves excite the nuclear spin energy transition. The resultant evolving spin polarization can induce a radio frequency signal in a receiving coil and thereby be detected. Magnetic field gradients localize the polarization within the tissues, painting a three-dimensional image. Hydrogen atoms are abundant in the body’s water and fat, allowing tissues to be visualized. For most studies, a contrast material (gadolinium) is given IV before the images are taken. MRI breast cancer screening has a greater sensitivity but less specificity than mammography for detecting breast cancer in high-risk women.

Efforts have been made to apply other technologies to the problem of breast imaging. Positron emission tomography (PET) scan uses a radioactive tracer to identify breast cancer and its spread. Positron emission mammography (PEM) is a newer imaging test that combines some aspects of a PET scan and a mammogram. Contrast-enhanced spectral mammography (CESM) uses a contrast dye (containing iodine) that is injected into the blood a few minutes before two sets of mammograms (using different energy levels) are taken. The contrast helps the x-rays show any abnormalities. Other modalities such as thermal imaging (thermography), molecular breast imaging (scintimammography or breast-specific gamma imaging), shear-wave elastography (elastography), electrical impedance imaging (T-scan), and transillumination, are either experimental or have not proven to be effective.

Strategies: Breast imaging technologies may be used for either screening or diagnosis. The ideal screening technology must be cost-effective, safe, widely available and easy to administer, exquisitely sensitive (high probability of detecting disease), and extremely specific (high probability that those without the disease will screen negative). Based on current experience, mammography remains the best screening modality for breast cancer. When the patient is younger than 30 years, has particularly dense breasts, or is at a greater than 20% lifetime risk, mammography augmented by MRI is recommended. Although ultrasonography is less sensitive than MRI (detects fewer tumors), it has the advantage of costing less and being more widely available. Ultrasonography is useful in the evaluation of palpable masses that are mammographically occult, in the evaluation of clinically suspected breast lesions in women younger 30 years, and in the follow-up of abnormalities seen on mammography. When a clinically identified mass is present, ultrasonography is the most effective modality for differentiating solid from cystic elements or for guiding percutaneous biopsy techniques.

Patient Education:

American College of Obstetricians and Gynecologists Patient Education Pamphlet:

• Mammography and Other Screening Tests for Breast Problems, 2017