Mammography is the gold standard for screening in the detection of early breast cancer, since it has proven to reduce mortality by 44%. The efficacy of mammography depends on the technical quality of the mammogram, the expertise of the interpreting radiologist, and proper implementation of a screening program. Mammography relies on the relative densities of breast tissues to differentiate normal from abnormal tissue. Breast density is the most significant independent predictor of mammographic sensitivity at any age; in the fatty breast, sensitivity is 98%; in the very dense breast, sensitivity is 48%. The overall mammographic sensitivity is 85% but this decreases to 45% in women with dense breast tissue or breast implants, or in the postsurgical breast. In general, sensitivity is lower in women under 49 years of age.

Compared to screen film mammography, digital mammography exposes patients to slightly lower doses of radiation, while optimizing the image contrast. Digital mammography improves the sensitivity of breast cancer detection from 55% to 70% in women younger than 50 years (pre- or perimeopausal) with dense breasts. However, digital mammography is significantly more expensive than film screen mammography. The equipment costs approximately $400,000 vs $100,000 plus is associated with higher expenses for maintenance, storage, and retrieval.

Studies have shown that a second mammography reader can increase the number of cancers detected by 4% to 14% without changing the false-positive rates. However, this added cost is not reimbursed and therefore is impractical in most practices. Computed-aided detection (CAD) achieves the same detection rate as two readers and increases the sensitivity (especially for microcalcifications), but it is not as effective for masses. However the improved sensitivity with CAD is offset by both an increase in false positives and biopsy rates.

Ultrasound of the breast is the most common adjunct modality used for breast evaluation. It employs no ionizing radiation, does not require intravenous contrast material, and is well tolerated and widely available. The breast is an ideal subject for ultrasound imaging because it is superficially located and easily accessible (without overlying structures) for interventional procedures. In addition, the sensitivity of ultrasound is not affected by the type of breast tissue. Optimal results depend on having adequate equipment with high frequency transducers and are highly operator-dependent. Reliability varies according to the operator’s expertise which determines the reproducibility of images and rates of false-negative and false-positive results.

The indications for breast ultrasound include:

(1) evaluation of a palpable or mammographically visualized mass;
(2) guidance for interventional procedures, for radiation planning, the initial imaging technique for the young (under 30 years of age), in pregnant, or lactating women;
(3) for the evaluation of implants, especially silicone.

Additionally, ultrasound has been very useful for the second-look targeted ultrasound after a suspicious lesion is seen on the MRI or breast-specific gamma imaging for guidance of the biopsy. Screening is not an indication for breast ultrasound, however, various studies have shown that the addition of ultrasound to mammography in high-risk women with dense breast tissue will increase detection of breast cancer. The ACRIN 6666 study found that in this group of women, the addition of ultrasound to mammography yielded an additional 7.2 cancers per 1,000 women. The sensitivity of combined mammography and ultrasound was 77.5% compared to 49% with mammography alone. In this multicentered study, 29% of the cancers were only visualized by ultrasound. However, it is important to realize that the positive predictive value of screening ultrasound is low, that is to say that only 8.6% of the biopsies performed are positive for breast cancer compared to 14.7% with mammography. The increased number of false positives resulted in additional biopsies and cost, and created unnecessary anxiety in patients.


In contrast to mammography and ultrasound which use anatomic approaches, molecular or functional imaging characterizes and measures the metabolic activity at the cellular level. Molecular imaging includes contrast-enhanced MRI, MR spectroscopy (MRS), and nuclear medicine imaging such as breast-specific gamma imaging (BSGI) and positron emission mammography (PEM). Functional positron emission tomography (PET) with fluorodeoxyglucose (FDG) combined with computed tomography (PET-CT) can be used for diagnosis, staging, and monitoring therapy for breast cancer. However, whole-body PET or PET-CT is of minimal value in patients with early-stage disease.

Breast MRI has become an important tool for the detection and characterization of breast cancer. It has been reported to have diagnostic sensitivities of 94% to 99% for invasive breast malignancies and 58% to 89% for DCIS. Applications of breast MRI include: evaluation of the extent of ipsilateral malignancy, screening of the contralateral breast in patients with newly diagnosed breast cancer, screening women who are at high risk, for the evaluation of patients with metastatic axillary adenocarcinoma and an unknown primary cancer site, and for the assessment of silicone implant integrity.  However, MRI costs approximately 10 times more than mammography, is not widely available, and cannot be used in women with implanted medical devices or who suffer from claustrophobia.

In addition, the overlap in the MRI features of certain benign and malignant lesions decrease the specificity and positive predictive value, which results in an increase in the biopsy rate. If a suspicious lesion is clinically and mammographically occult and cannot be found on a targeted ultrasound (which can detect 46% of these lesions), the biopsy or needle localization needs to be done with MRI guidance. MRI-guided procedures are time consuming and costly.

Breast-specific gamma imaging or BSGI (Dilon) complements mammography and ultrasound. After intravenous injection of 99m technetium sestamibi, images of both breasts are obtained using a gamma camera with a small field of view device which is able to detect cancers greater than 3 mm. Positron emission mammography or PEM (Naviscan) involves intravenously injecting a glucose-containing radiopharmaceutical fluordexoyglucose (FDG) and imaging with a high-resolution, organ-specific PET scanner. Since both sestamibi and glucose uptake is greater in cancerous cells, BSGI and PEM demonstrate many of the same advantages as MRI including for presurgical planning and in differentiating a scar from a recurrent cancer. Image acquisition is made with the patient in a seated position so that claustrophobia is not an issue and being able to obtain the standard mammographic views makes it easy to compare modalities.

Interpretation of the BSGI and PEM is much faster than with MRI since the number of images obtained is significantly less. Both modalities achieve high sensitivity for the detection of breast cancer and higher specificity than mammography with no difference noted between the detection of cancer in the fatty and dense breast. False positives such as fibroadenomas, fibrocystic changes, and fat necrosis are seen on BSGI and PEM but less frequently than with MRI. PEM can be followed with whole-body PET imaging to evaluate for metastatic disease. It should be noted that, the radiotracer and procedure cost is higher for PEM than BSGI. PEM also requires patient to fast for imaging to begin one hour after the injection, and with the patient needing to maintain a distance from others for 45 minutes after the procedure. In addition, PEM studies are only reimbursed in those patients with known cancer, whereas with BSGI reimbursement is for both pre- and post-diagnosis of breast cancer. Similar to MRI, these techniques require image-specific biopsy capabilities, so that when a suspicious lesion is visualized it can be sampled using that modality. The BSGI guided biopsy device is currently not FDA approved.