Breast imaging

Positron emission mammography is one of several methods of breast imaging.

In medicine, breast imaging is the representation or reproduction of a breast's form. There are various methods of breast imaging.

X-ray

Mammography

The best mammographic images are produced when the breast is compressed.

Mammography is the process of using low-energy X-rays (usually around 30 kVp) to examine the human breast, which 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 microcalcifications. For the average woman, the U.S. Preventive Services Task Force recommended (2009) mammography every two years in women between the ages of 50 and 74.^[1] The American College of Radiology and American Cancer Society recommend yearly screening mammography starting at age 40.^[2] The Canadian Task Force on Preventive Health Care (2012) and the European Cancer Observatory (2011) recommends mammography every 2–3 years between 50 and 69.^[3][4] These task force reports point out that in addition to unnecessary surgery and anxiety, the risks of more frequent mammograms include a small but significant increase in breast cancer induced by radiation.^[5][6] Additionally, mammograms should not be done with any increased frequency in people undergoing breast surgery, including breast enlargement, mastopexy, and breast reducation.^[7] The Cochrane Collaboration (2013) concluded that the trials with adequate randomisation did not find an effect of mammography screening on total cancer mortality, including breast cancer, after 10 years. The authors of systematic review write: "If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings." The authors conclude that the time has come to re-assess whether universal mammography screening should be recommended for any age group.^[8] They thus state that universal screening may not be reasonable.^[9] The Nordic Cochrane Collection, which in 2012 reviews updated research to state that advances in diagnosis and treatment make mammography screening less effective today. They state screening is “no longer effective.” They conclude that “it therefore no longer seems reasonable to attend” for breast cancer screening at any age, and warn of misleading information on the internet.^[9]

Mammography has a false-negative (missed cancer) rate of at least 10 percent. This is partly due to dense tissues obscuring the cancer and the fact that the appearance of cancer on mammograms has a large overlap with the appearance of normal tissues. A meta-analysis review of programs in countries with organized screening found 52% over-diagnosis.^[9]

Digital breast tomosynthesis

Digital breast tomosynthesis (DBT) can provide a higher diagnostic accuracy compared to conventional mammography. In DBT, like conventional mammography, compression is used to improve image quality and decreases radiation dose. The laminographic imaging technique dates back to the 1930s and belongs to the category of geometric or linear tomography.^[10]

Because the data acquired are very high resolution (85 - 160 micron typical ), much higher than CT, DBT is unable to offer the narrow slice widths that CT offers (typically 1-1.5 mm). However, the higher resolution detectors permit very high in-plane resolution, even if the Z-axis resolution is less. The primary interest in DBT is in breast imaging, as an extension to mammography, where it offers better detection rates with little extra increase in radiation.^[11][12]

Tomosynthesis is now Food and Drug Administration (FDA) approved for use in breast cancer screening.^[13]

Xeromammography

Xeromammography is a photoelectric method of recording an x-ray image on a coated metal plate, using low-energy photon beams, long exposure time, and dry chemical developers. It is a form of xeroradiography.^[14]

Galactography

Galactography is a medical diagnostic procedure for viewing the milk ducts. The standard treatment of galactographically suspicious breast lesions is to perform a surgical intervention on the concerned duct or ducts: if the discharge clearly stems from a single duct, then the excision of the duct (microdochectomy) is indicated;^[15] if the discharge comes from several ducts or if no specific duct could be determined, then a subareolar resection of the ducts (Hadfield's procedure) is performed instead.^[15] To avoid infection, galactography should not be performed when the nipple discharge contains pus.^[16]

MRI

A color-enhanced MRI of a breast

Breast MRI, an alternative to mammography, has shown substantial progress in the detection of breast cancer. The available literature suggests that the sensitivity of contrast-enhanced breast MRI in detection of cancer is considerably higher than that of either radiographic mammography or ultrasound and is generally reported to be in excess of 94%.^[17]

The specificity (the confidence that a lesion is cancerous and not a false positive) is only fair ('modest'),^[18] (or 37%-97%^[17]) thus a positive finding by MRI should not be interpreted as a definitive diagnosis.

The reports of 4,271 breast MRIs from eight large scale clinical trials were reviewed in 2006.^[19]

Ultrasound

Breast ultrasounds may be used with or without a mammogram.

Breast ultrasound is the use of medical ultrasonography to perform imaging of the breast. It can be considered either a diagnostic or a screening procedure.^[20] It may be used either with or without a mammogram.^[21]

Scintimammography

Scintimammography is a type of breast imaging test that is used to detect cancer cells in the breasts of some women who have had abnormal mammograms, or for those who have dense breast tissue, post-operative scar tissue or breast implants, but is not used for screening or in place of a mammogram. Rather, it is used when the detection of breast abnormalities is not possible or not reliable on the basis of mammography and ultrasound. In the scintimammography procedure, a woman receives an injection of a small amount of a radioactive substance called technetium 99 sestamibi.^[22]

Tactile imaging

Tactile images of breast lesions

Breast cancer is one of the most common causes of death from cancer. The lifetime probability of developing breast cancer in the next 10 years is evaluated as 13%.^[23] A critical key to a continued reduction in mortality is early detection and accurate diagnosis made in a cost-effective manner. Figure 3 shows a general view of Breast Tactile Imager (BTI). The device includes a probe with a pressure sensor array, an electronic unit, and a laptop computer. BTI can quantitatively evaluate multiple mechanical and structural properties of breast and breast lesions, such as Young’s modulus, elasticity contrast, tissue nonlinearity (strain hardening), heterogeneity index, nodule size, shape and mobility, which could be altered by cancer development.^[24] Clinical data collected at four different sites for 179 cases have demonstrated BTI's capability for characterizing and differentiating benign and malignant breast lesions.^[25] Histologically confirmed malignant breast lesions demonstrated increased hardness and strain hardening as well as decreased mobility in comparison with benign lesions. Statistical analysis of data on 147 benign and 32 malignant lesions revealed BTI's sensitivity of 91.4% and specificity of 86.8%. Examples of cysts and ductal carcinoma images recorded by BTI are shown in Figure 4. BTI has the potential to be used as a cost effective device for cancer detection as a diagnostic modality. It was estimated that the use of the BMI after standard screening procedures (mammography alone or combination of mammography and conventional ultrasound) could significantly reduce the benign biopsy rate.^[25]

References