Scintimammography (nuclear medicine breast imaging) is a supplemental breast exam that may be used in some patients to investigate a breast abnormality. A nuclear medicine test is not a primary investigative tool for breast cancer but can be helpful in selected cases after diagnostic mammography has been performed. Nuclear medicine breast imaging involves injecting a radioactive tracer (dye) into the patient. Since the dye accumulates differently in cancerous and non-cancerous tissues, scintimammography can help physicians determine whether cancer is present.
Scintimammography is especially useful for women with dense breasts, which are typically found in younger women before menopause. As dense breast tissue is hard to interpret with conventional mammography, scintimammography is an imaging technique that can reduce the occurrence of false positives that lead to unnecessary biopsies. Compared to a standard mammogram, some studies have shown that a scintimammography test has an accuracy rate of as high as 90%. However, this technique is not meant as a substitute to a mammogram or other tests but used in conjunction with them.
A very small amount of radioactive isotope (tracer) is injected into a vein in the arm or foot, much like taking a blood sample. Once injected, the tracer then travels throughout the body via the bloodstream and can be seen by a group of special detectors, called gamma cameras, “marking” certain biological processes to locate a tumour. No special preparation is required before the test and it takes about 30 minutes to complete.
Who is a suitable candidate for scintimammography?
As this imaging technique is not a screening tool for breast cancer, it is appropriate for certain patients after a physical breast exam, mammography, and ultrasound are performed. It can help determine a suspicious breast abnormality that would otherwise require a biopsy to confirm.
These patients include those with:
- Dense breast tissue
- Large, palpable (able to be felt) abnormalities that cannot be imaged well with mammography or ultrasound
- Breast implants
- When multiple tumours are suspected (see below)
- A lump at the surgical site after mastectomy (breast removal) since scar tissue may be difficult to distinguish from other tumours with other breast imaging exams
- To check the axillary (underarm) lymph nodes to determine whether they contain cancer cells (sentinel lymph node biopsy)
How useful is scintimammography in the diagnosis of breast cancer?
As magnetic resonance imaging (MRI) of the breast, scintimammography may also be helpful to determine if multiple breast tumours are present. For instance, a mammogram or ultrasound (sonogram) of the breast may reveal breast cancer in one area. However, a nuclear medicine breast imaging test may show that the cancer is in fact multi-focal; tumours are present in several areas of the breast.
Determining the extent of breast cancer with nuclear medicine can help indicate treatment: breast conserving surgery (lumpectomy) or breast removal (mastectomy). Mastectomy is indicated if there are multiple tumours.
Studies show that scintimammography is only 40% to 60% accurate in imaging small breast abnormalities but more than 90% accurate in detecting abnormalities over one centimetre. However, mammography and physical exams are often very useful for detecting large abnormalities. It is the small abnormalities that tend to need additional imaging. Therefore, in this respect, scintimammography is often of limited value.