Mammography

Mammography device performing routine mammogram

About

Mammography is the process of using low-energy X-rays (usually around 30 kVp) to examine the human breast and is used as a diagnostic and a screening tool. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses and/or microcalcifications.

Like all X-rays, mammograms use doses of ionizing radiation to create images. Radiologists then analyze the images for any abnormal findings. It is normal to use lower-energy X-rays (typically Mo-K) than those used for radiography of bones. Ultrasound, ductography, positron emission mammography (PEM), and magnetic resonance imaging (MRI) are adjuncts to mammography. Ultrasound is typically used for further evaluation of masses found on mammography or palpable masses not seen on mammograms. Ductograms are still used in some institutions for evaluation of bloody nipple discharge when the mammogram is non-diagnostic. MRI can be useful for further evaluation of questionable findings as well as for screening pre-surgical evaluation in patients with known breast cancer to detect any additional lesions that might change the surgical approach, for instance from breast-conserving lumpectomy to mastectomy. New procedures, including breast tomosynthesis, may offer benefits in years to come.

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 Canadian Task Force on Preventive Health Care (2012) and the European Cancer Observatory (2011) recommends mammography every 2–3 years between 50 and 69.[2][3] 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.

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.

Regulatory Standards

Mammography facilities in the United States and its territories (including military bases) are subject to the Mammography Quality Standards Act (MQSA) aas well as regulated by the FDA. The act requires annual inspections and accredition every 3 years through an FDA-approved body. Facilities found deficient during the inspection or accreditation process can be barred from performing mammograms until corrective action has been verified or, in extreme cases, can be required to notify past patients that their exams were sub-standard and should not be trusted.

At this time MQSA applies only to traditional mammography and not related scans such as breast ultrasound, stereotactic breast biospy, or breast MRI.

Qualitative measurements

Performance checks include but not limited to...

Image receptor sizes.

• Systems using screen-film image receptors shall provide, at a minimum, for operation with image receptors of 18 x 24 centimeters (cm) and 24 x 30 cm.
• Systems using screen-film image receptors shall be equipped with moving grids matched to all image receptor sizes provided.
• Systems used for magnification procedures shall be capable of operation with the grid removed from between the source and image receptor.

Light fields. For any mammography system with a light beam that passes through the X-ray beam-limiting device, the light shall provide an average illumination of not less than 160 lux (15 foot candles) at 100 cm or the maximum source-image receptor distance (SID), whichever is less.

Magnification.

• Systems used to perform nonintervention problem solving procedures shall have radiographic magnification capability available for use by the operator.
• Systems used for magnification procedures shall provide, at a minimum, at least one magnification value within the range of 1.4 to 2.0.

Focal spot selection.

• When more than one focal spot is provided, the system shall indicate, prior to exposure, which focal spot is selected.
• When more than one target material is provided, the system shall indicate, prior to exposure, the preselected target material.
• When the target material and/or focal spot is selected by a system algorithm that is based on the exposure or on a test exposure, the system shall display, after the exposure, the target material and/or focal spot actually used during the exposure.

Compression. All mammography systems shall incorporate a compression device.

• Application of compression. Effective October 28, 2002, each system shall provide:
• An initial power-driven compression activated by hands-free controls operable from both sides of the patient; and
• Fine adjustment compression controls operable from both sides of the patient.

Compression paddle.

• Systems shall be equipped with different sized compression paddles that match the sizes of all full-field image receptors provided for the system. Compression paddles for special purposes, including those smaller than the full size of the image receptor (for "spot compression") may be provided. Such compression paddles for special purposes are not subject to the requirements of paragraphs (b)(8)(ii)(D) and (b)(8)(ii)(E) of this section.
• Except as provided in paragraph (b)(8)(ii)(C) of this section, the compression paddle shall be flat and parallel to the breast support table and shall not deflect from parallel by more than 1.0 cm at any point on the surface of the compression paddle when compression is applied.
• Equipment intended by the manufacturer's design to not be flat and parallel to the breast support table during compression shall meet the manufacturer's design specifications and maintenance requirements.
• The chest wall edge of the compression paddle shall be straight and parallel to the edge of the image receptor.
• The chest wall edge may be bent upward to allow for patient comfort but shall not appear on the image.

Technique factor selection and display.

• Manual selection of milliampere seconds (mA's) or at least one of its component parts (milliampere (mA) and/or time) shall be available.
• The technique factors (peak tube potential in kilovolt (kV) and either tube current in mA and exposure time in seconds or the product of tube current and exposure time in mA's) to be used during an exposure shall be indicated before the exposure begins, except when automatic exposure controls (AEC) are used, in which case the technique factors that are set prior to the exposure shall be indicated.
• Following AEC mode use, the system shall indicate the actual kilovoltage peak (kVp) and mA's used during the exposure. The mA's may be displayed as mA and time.

Automatic exposure control.

• Each screen-film system shall provide an AEC mode that is operable in all combinations of equipment configuration provided, e.g., grid, nongrid; magnification, nonmagnification; and various target-filter combinations.
• The positioning or selection of the detector shall permit flexibility in the placement of the detector under the target tissue.
• The size and available positions of the detector shall be clearly indicated at the X-ray input surface of the breast compression paddle.
• The selected position of the detector shall be clearly indicated.

(iii) The system shall provide means for the operator to vary the selected optical density from the normal (zero) setting.

X-ray film. The facility shall use X-ray film for mammography that has been designated by the film manufacturer as appropriate for mammography.

Intensifying screens. The facility shall use intensifying screens for mammography that have been designated by the screen manufacturer as appropriate for mammography and shall use film that is matched to the screen's spectral output as specified by the manufacturer.

Film processing solutions. For processing mammography films, the facility shall use chemical solutions that are capable of developing the films used by the facility in a manner equivalent to the minimum requirements specified by the film manufacturer.

Lighting. The facility shall make special lights for film illumination, i.e., hot-lights, capable of producing light levels greater than that provided by the view box, available to the interpreting physicians.

Film masking devices. Facilities shall ensure that film masking devices that can limit the illuminated area to a region equal to or smaller than the exposed portion of the film are available to all interpreting physicians interpreting for the facility.

Kilovoltage peak (kVp) accuracy and reproducibility.

• The kVp shall be accurate within +/- 5 percent of the indicated or selected kVp at:
• The lowest clinical kVp that can be measured by a kVp test device;
• The most commonly used clinical kVp;
• The highest available clinical kVp, and
• At the most commonly used clinical settings of kVp, the coefficient of variation of reproducibility of the kVp shall be equal to or less than 0.02.