Mammography: X-ray and Breast Tissue
Wilhelm Conrad Roentgen discovered x-rays while working with a Crookes tube in his laboratory on November 8, 1895. Eighteen years later mammography got its rudimentary beginnings due to these ionizing x-rays. In 1913, Berlin Albert Soloman, a German surgeon, was among the first to discover that breast cancer could be radiographed. In a 1927 medical textbook the first instance of a radiograph of a living person’s breast taken by Otto Kleinschmidt was published. Although these recordings of mammography appeared in early years, it wasn’t until the late 50’s that it was popularized by Robert Egan, from the United States and Professor Charles M.
Gros, from Germany. These men started using mammography for the diagnosis and evaluation of breast cancer. With this popularity of mammography came vast improvements with technology. Before 1969, many machines were not designed for imaging exclusively breast tissue. For example, imaging units from the past were comprised of tungsten targets, which were primarily used for imaging anatomy that required relatively higher doses of radiation. These units also worked off of a large focal spot which decreases the detail of the image. This was not ideal for imaging something as minute as a breast calcification.
Mammography: X-ray and Breast Tissue Essay Example
In the 60’s direct exposure x-ray film was the film of choice. This film often required a long exposure time which causes a higher dose of radiation to the patient and increased motion blur. Some units utilized substandard compression paddles that didn’t distribute pressure evenly, which produced a radiograph with uneven contrast. This all resulted in a poor diagnostic film. In 1969 dedicated mammography units were employed with low kilovoltage x-ray tubes and molybdenum targets making the units more efficient in x-ray production. The dedicated mammography units have more latitude for positioning as well as minimal discomfort for the patient.
Smaller focal spots for imaging little objects with increased detail were also designed. These units were accompanied with their own compression cone. Industrial grade, high-detail film became available that year also. Xeromammography became popular by John Wolfe and Ruzicka in the 60’s. This type of mammography greatly reduced the radiation dose received by the patient compared to the earlier direct film and was easier to understand and evaluate. 1972 was a turning point for mammography when Dupont announced their production of higher-resolution faster speed x-ray films in conjunction with intensifying screens.
These intensifying screens contained calcium tungstate phosphor materials that convert x-rays into light. This concept caused the film to be exposed with less radiation, therefore reducing the amount of radiation to the patient. Rare earth elements, a faster, more efficient phosphor, began replacing the use of calcium tungstate in 1976, making this intensifying screen combination the most efficient combination until early 2000. In 1990, a number of advances were employed including: grid technique, emphasis on compression, high-frequency generators, and automatic exposure controls.
In the early 2000’s digital technology was incorporated with mammography. It replaced the screen-film system with a charged-coupled device (CCD). The CCD converts visible light photons to electrons. Electrons are sent to a computer where it is converted into a digital format and a radiographic image is produced on a CRT monitor. Together these developments have given mammography the ability to produce diagnostic radiographic images with greater detail and considerably reduced patient radiation dose.
Digital mammography has given the physicians the capability to adjust contrast, transmit images, and to magnify suspicious areas of the breast. This technology has also given the radiologist the capacity to digitally mark areas of concern directly onto the digitalized image which is conveniently stored on the computer for easy retrieval for the next mammogram for comparison. A mammography unit is a rectangular box that houses a vacuum tube in which x-rays are produced. The unit is designed to rotate to optimally image all angles of the breast tissues.
These units are integrated with a compression device that firmly holds the breast in place. This act of flattening the breast is extremely important to improve optical density, contrast, and spatial resolution and lower the patient’s radiation dose. Most importantly, to ensure that small abnormalities won’t be covered by overlying breast tissue. In routine screening procedures, each breast should be screened using the craniocaudal (CC) and mediolateral oblique (MLO) projections; however, there are 13 projections that can be performed.
Once the breast is positioned, a low dose of ionizing radiation is sent through the tissue from the vacuum tube to produce black and white images of the tissue on x-ray film. Different parts of the body absorb the x-rays in varying degrees. Bone absorbs much of the radiation while soft tissue allows more of the x-ray to pass through. As a result, bones appear white on an x-ray, soft tissue shows up in shades of gray and air appears black. Therefore, a dense microcalcification of the breast will appear whiter than the rest of the breast tissue. For that reason both breasts are examined for comparison purposes.
Once the screening is complete, the radiologist looks for evidence of cancer or non-cancerous conditions that may require further testing, follow-up or treatment by looking at the density and shapes of the tissues on the radiograph. Their findings could include things such as calcium deposits in ducts and other tissues, masses or lumps, distorted tissues or dense areas appearing in only one breast and/or that have appeared since last mammogram. Calcifications can be the result of cell secretions, cell debris, inflammation, trauma, previous radiation or foreign bodies.
Tiny, irregular deposits with sharp edges called microcalcifications may be associated with cancer. Larger, coarser deposits called macrocalcifications may be caused by a benign condition known as fibroadenoma. Dense areas indicate tissue with many glands and can make calcifications and masses more difficult to identify. They could also represent cancer. Distorted areas suggest tumors that may have invaded tissues. If any of these abnormal conditions are found the patient is referred for further testing, possibly a diagnostic mammogram, MRI, ultrasound or a biopsy.
Radiation safety is a concern with all parties involved. The doctor and the technologist should see that proper safety guidelines are adhered to so that the benefits of the exam far outweigh the risk of radiation. Mammogram screenings should begin at the age of 40, unless a patient possesses high risk factors. The American College of Radiology, the American Cancer Society, and the American Medical Association recommend annual mammography screenings at least every other year for women between the ages of 40 and 49 and yearly thereafter.
High risk factors put a patient at an increased risk of developing cancer and should begin screenings at an earlier age. These factors include but not limited to: early onset of menses, immediate family members with a history of cancer and a first born child after the age of 30. The patient should always be assessed for the possibility of pregnancy. Depending on the stage in development of the fetus radiation could cause birth and genetic defects that can be passed to the fetus’ offspring. Lead shielding should always be worn at the waist level though pregnancy is not suspected.
The technologist should expose only the area of interest to the radiation. This is done by restricting the field size of radiation; this is called collimation. The technologist should also give clear instructions, such as “don’t move” and “hold your breath” to reduce the amount radiographs that will need to be repeated because of blurred images due to motion. This will reduce the radiation to the patient. Breast cancer is now a disease that is far from fatal. Because of early, advanced mammography screening procedures, more than 90 % of patients are cured.
However there are limitations. Mammograms may present false-positive or false-negative readings about 5-15% of the time. This occurs on occasion because the procedure is not as sensitive for the denser breast tissue such as in younger women. These false readings occur more often in women under age 50. Another setback is that silicone and/or saline breast implants are radiopaque which block breast tissue that would otherwise show up on x-rays, especially if the implant was laid in front of the pectoral muscle instead of beneath it.
And lastly, not all of the tumors found by mammography can be cured. Certain types of cancers are aggressive, grow rapidly and metastasize to other parts of the body. Mammography has greatly enhanced the quality of life for women by making it easier for radiologists to detect anomalies in the breast tissue. This makes for a faster and more accurate diagnosis of malignancies so patients can be treated before metastasis occurs to other parts of their body. It has also reduced the radiation dose to the patient and the possibilities of genetic mutations to future generations.