General awareness, along with self and clinical examination, would detect palpable abnormality. So far, mammography was the mainstay for treating the occult disease. Mammography, however, has well-recognised limitations and, thus other imaging modalities including ultrasound and magnetic resonance imaging (MRI) have been used as adjunctive tools, mainly for women who may be at increased risk for the development of breast cancer. In this article, we will briefly review different breast imaging modalities with their advantages and limitations.
Mammography
Mammography is the process of using low-energy X-rays to examine the human breast and is used as a diagnostic and screening tool. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses and/or micro-calcifications. A mammography unit is a rectangular box that houses the tube in which X-rays are produced. The unit is used exclusively for X-ray exams of the breast, with special accessories that allow only the breast to be exposed to the X-rays. Attached to the unit is a device that holds and compresses the breast and positions it so images can be obtained at different angles.
Mammography is possibly the most intensely scrutinised and debated medical procedure, but there is no other breast cancer screening tool that has a better combination of sensitivity and specificity.
Breast tomosynthesis or 3D mammography
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Dr Priya Chudgar
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Conventional 2D mammography produces a single, flattened image of the breast, making it difficult to detect small cancers. Tomosynthesis minimises the impact of overlapping breast tissue during imaging because the camera moves over the breast taking images from multiple angles. These images are combined to create a three dimensional rendering of the entire breast. Thus, it provides a clearer, more accurate view of the breast and allows radiologists to more effectively pinpoint the size, shape and location of any abnormalities. This can lead to better detection and increased accuracy.
Ultrasound
More than 40 per cent of women have dense breast tissue, which makes tumours harder to see with mammography alone. Ultrasound is better than mammography at identifying tumours within dense breast tissue. Studies have shown mammography combined with ultrasound can find more breast cancers than mammography alone in women with dense breasts. Ultrasound uses sound waves to make images of the breast. It is non-invasive and is often used as follow-up test after an abnormal finding on a mammogram. Ultrasound helps to differentiate between different types of lumps, such as liquid-filled cysts and a solid mass. It is also used to find out the size, shape, texture and density of a breast lump.
3D automated ultrasound
A hand held 2D ultrasound is operator dependent and a lengthy procedure. Hence it is only used as an adjunct to mammography. However, a 3D automated ultrasound device has changed the scenario by reducing operator dependent bias. Pre-programmed trajectories ensure that images of every part of the breast are obtained and ensuing data are evaluated by at a 3D workstation by analysing the images of the breast in any desired direction. Thus, automated breast ultrasound (ABUS) reduces the subjectivity of ultrasound and makes it easier to verify results and compare them with mammographic and 3D-MRI findings. Studies are in progress to prove this as an effective screening tool.
Elastography
Breast elastography is a new sonographic technique that provides additional characterisation information on breast lesions over conventional sonography and mammography. This technique provides information on the strain or hardness of a lesion, similar to a clinical palpation examination. Two techniques are now available for clinical use: strain (compression-based elastography) and shear wave elastography.
Breast MRI
A breast MRI uses magnetic fields to create an image of the breast. It can sometimes find cancers in dense breasts that are not seen on mammograms. Breast MRI is often used with mammography for screening some women at a high risk of breast cancer. However, it can be costly and often finds something that looks abnormal, but turns out to be benign (false positive).
Image guided biopsies
Advent of newer breast-screening protocols has led to an increase in the detection of small or impalpable breast lesions.
The ability to achieve an accurate histopathologic diagnosis of these lesions is crucial to any screening programme in terms of appropriate treatment planning and patient counselling. This can be performed via ultrasounds, as fine needle aspiration or core biopsy, but lesions better seen on mammography images, particularly microcalcifications, require stereotactic localisation.
Stereotactic breast needle biopsy
It refers to the sampling of non-palpable or indistinct breast lesions by using techniques that enable spatial localisation of the lesion within the breast. Compared with open surgical biopsy, needle biopsy causes less trauma and disfigurement and is performed as an outpatient procedure with the patient under local anesthetic.
Vacuum-assisted biopsy
This is a type of biopsy in which a vacuum-powered instrument is inserted through the skin to the site of an abnormal growth to collect and remove a sample of cells for analysis. Using vacuum pressure, the abnormal cells and tissue are removed without having to withdraw the probe after each sampling as in core needle biopsy.
Wire localisation
Guided by an imaging modality such as ultrasound or MRI, a wire is inserted through a hollow needle to a lesion or suspicious area of cells and tissue. The wire then guides the surgeon to the area so that the abnormal tissue can be surgically removed for examination.
Breast-specific gamma imaging (BSGI)
BSGI is a functional imaging technique designed to assess changes in tissue function rather than in anatomical structure. It is most commonly used for patients who have equivocal mammography or ultrasound findings. It is also used to help determine the extent of breast cancer involvement and to help clarify lymph-node involvement. The breast is compressed between two camera heads and a small dose of radioactive material is injected intravenously (sestamibi). BSGI can help to differentiate cancer from other structures.
Computer-aided detection
Computer-aided detection (CAD) technology uses a computer to provide a second read or assist radiologists in making an accurate diagnosis. CAD systems have been approved by the US FDA for use in mammography, lung computed tomography, virtual colonoscopy, and breast MRI. They help increase sensitivity for detecting small lesions and calcifications in the breast.
To summarise, continuously emerging advancements in technology present new challenges and possibilities for the field of breast imaging. Such innovations in technology are helping clinicians detect and diagnose breast cancer in its earliest stage, thus saving the lives of countless women yearly.