Mammography is a very common and widely accepted breast cancer-screening tool which was developed in the mid-1960s . Several large clinical trials demonstrated that the detection of small tumors using mammography devices at an early stage reduces or delays mortality . An X-ray image of the breast is called a mammogram. The mammogram exam is specifically designed for the identification of certain characteristic masses and/or microcalcifications that might develop to cancer. However, a mammogram can also help in identifying other forms of cysts, calcifications, and tumors within the breast. Mammograms are so far the most efficient screening method for the early detection of breast cancer. As a recommendation by the American Cancer Society, a woman should get her first standard mammogram between the age of 35 and 40. Two types of mammograms exist, namely; screening and diagnostic. Screening mammograms are done to check for breast cancer in women that present no symptoms whereas diagnostic mammograms are done in the presence of unusual signs or symptoms in the breast. Diagnostic mammogram of the breast gives detailed images using specialized techniques. .
For quite some time, screening mammogram has been regarded as a “gold standard” for breast cancer. It consists of two-dimensional X-ray images of each breast. Not only it can provide adequate visualization of soft tissue abnormalities, it can also depict subtle calcifications. The obtained image can either be captured on film (screening-film-mammography) or processed digitally (screening-digital-mammography). The former is very cost effective and relatively easy to perform. However, it has intrinsic limitations related with its sensitivity to substandard film processing conditions, constrained dynamic range, granularity and contrast attributes . Screening digital mammography gives the advantage of digital image communication, manipulation and archival. It uses multiple or single detector assembly to acquire an image the X-rays that pass through the breast which can later be displayed, stored, and communicated electronically . On the other hand, a diagnostic mammogram is a more detailed X-ray examination of the breast. Diagnostic mammograms are generally used to check for breast cancer after a lump or other symptoms of the disease have been observed. Screening mammography imaging lasts shorter than diagnostic mammography since diagnostic mammography needs more X-rays to obtain views of the breast from several different angles. Clinical investigations comparing screen-film mammography with digital mammography in a chosen population demonstrate similarity for cancer detection, , , , while digital mammography functions better for pre-menopausal women under the age of 50 years with dense breasts , .
2. Breast Magnetic Resonance Imaging (MRI)
Breast MRI scan uses strong magnets and radio frequency pulse to produce very detailed images of the breast. It is a non-invasive technique that produces 3d images without the use of ionizing radiation. In some selected investigations, it requires the use of an agent introduced via the vein to improve tissue contrast . The most useful breast MRI exam for breast imaging uses a contrast agent (gadolinium) that is injected into a vein in the arm through a catheter before or during the exam. This enhances the ability of the MRI to clearly image breast tissue details. Possible uses include :
Evaluation of a woman who has a palpable mass that isn’t visible with mammography.
Evaluation of a lesion in the breast of young women.
Evaluation of a woman who has breast cancer cells in an underarm lymph node.
Determining if a cancer is limited to one area of the breast, or if it is “multicentric” and involves more than one area.
Breast MRI can be limited to the below-listed situations :
• When screening for young women who are prone to breast cancer (gene mutation BRCA1 or BRCA2).
• Assessment of a woman diagnosed with a lump in an underarm lymph node however who has no indication of tumor on breast self-examination or mammogram.
• Assessment of a woman with lately diagnosed breast cancer and whose mammogram showed a highly dense breast.
Nuclear Medicine Approach
Scintimammography is an investigative technique that uses radioactive drugs to give images of an abnormal breast. It is mostly used in women prone to breast cancer yet cannot be screened with MRI. Scintimammography is now regarded as a modality of choice rather than just being contributory due to its non-invasiveness, simplicity, safety, availability and also ability to give the beneficial information required in the proper management of breast lesions . However, scintimammography may not detect very small tumors, such as those less than 1 cm in diameter. Additionally, the scan results may be affected by the activity of visceral organs like the heart or liver. A radioactive tracer known as technetium sestamibi was developed in the 1990s and used to study palpable breast tumors in 1994 . The outcome of the study was 32 episodes of breast cancer, of which 27 were identified by Tc-99m sestamibi, with a specificity of 100%, a sensitivity of 84%, and an accuracy of 87% . In the year 1993, Tl-201 was compared with Tc-99m and the report showed that Tc-99m had a superior sensitivity in detecting breast cancer . Another study which involved more than 2500 patients showed that the specificity and sensitivity of scintimammography in the detecting cancerous breast tumor was about 85% , . For this test, a small intravenous injection of the radiotracer (Tc-99m sestamibi) is injected into the patient’s vein. The patient is then positioned on a comfortable scanning bed. The radiotracer collects in the breast, where its then released as gamma rays. After gamma camera detects this energy, the radiotracer is then analyzed by a computer system which produces images containing both functional and structural information of the tissues and organs (Figure 2.1). Further analysis showed that for tumors whose size is less than 1cm, the sensitivity of scintimammography is only 48% .