Mammography or -grafie is a method for early detection of breast cancer (breast cancer), the most common in most countries, cancer of women. Mammography is primarily a radiological procedure for diagnosing the female , but possibly also the male breast, and is used as a synonym for X-ray mammography . Alternative imaging methods are breast ultrasound, tomosynthesis and magnetic resonance mammography.
The surgeon Otto Kleinschmidt produced the world's first clinical mammography in 1927 at the Leipzig University Hospital . Another pioneer was Robert Egan at the University of Texas MD Anderson Cancer Center in the late 1950s, who published a book on mammography in 1964. However, the widespread use of mammography only began after an extensive clinical study in New York, which was published in 1966 (headed by Philip Strax ).
Technique of investigation
Classic 2D mammography
The examination is carried out on special X-ray machines . The X-ray radiation used is a soft radiation with an energy of approximately 25 to 35 keV (kiloelectron volts). In mammography, there are hardly any film-foil systems, but mainly digital X-ray devices. The latter are divided into image plate systems and flat panel detector systems. These in turn are divided into directly digital detectors, in which the X-ray radiation is converted directly into an electrical signal, and in indirect digital detectors, in which the X-ray radiation is first converted into visible light and then into an electrical signal. The X-ray images are viewed on a special mammography diagnostic station, which is essentially characterized by two gray-scale monitors with 5 megapixels each or one gray-scale monitor with at least 10 megapixels.
3D mammography / tomosynthesis
With classic 2D mammography, there is the problem that the superimposition of different tissue structures sometimes conceals pathological changes in the tissue, so that they can be overlooked. One tries to compensate for this by taking up the chest from two angles, namely “craniocaudal” and “mediolateral oblique”, i.e. H. once vertically and once at a 45-degree angle. This helps, but does not always solve the problem. With tomosynthesis , the breast is recorded from different angles, depending on the manufacturer over an angle of 15 to 50 degrees ( X-ray tomography ). Between 9 and 25 images are recorded with a low dose and a high acceleration voltage, so that the total dose roughly corresponds to that of a classic 2D image. Individual layers of the breast tissue are calculated from these recordings. For 1 mm layers, for example, 50 layers are calculated for a 5 cm thick compressed breast. Since the slices above and below the slice selected for viewing are now hidden during the diagnosis, changes in the tissue are easier to see. Since the conventional 2D image is also needed for diagnosis, but this should not be created in addition to the tomosynthesis, since additional X-rays are then required for the 2D image (double dose for one tomosynthesis and one 2D), some manufacturers are now using recalculated from the data set of the 3D tomosynhesis to a 2D image (synthetic 2D mammography).
The three largest studies on the subject are:
- The Oslo study.
- The four-year prospective study with the title "Two-View Digital Breast Tomosynthesis Screening with Synthetically Reconstructed Projection Images: Comparison with Digital Breast Tomosynthesis with Full-Field Digital Mammographic Images [Digital two-level tomosynthesis in preventive examinations of the breast with synthetic reconstructed projection images: Comparison with digital breast tomosynthesis with digital full-field mammography images] ”, which was carried out on the basis of 24,901 preventive examinations in a large hospital in Norway, evaluated the use of 2D images from 3D mammography slice images instead of the conventional 2D images that are part of the digital Breast tomosynthesis are required. Per Skaane, Department of Radiology, Oslo University Hospital Ullevaal, and his colleagues found that the use of 3D images and 2D images created from them reduced radiation dose by an average of 45% and reduced diagnostic accuracy over 3D and conventional mammography images No significant differences were found in 2D images. The study was published online prior to the January 24, 2014 print version of Radiology, a scientific journal of the Radiological Society of North America (RSNA).
- The UPMC study.
- The reader study, "Comparison of Two-dimensional Synthesized Mammograms versus Original Digital Mammograms Alone in Combination with Tomosynthesis Images [Comparison of two-dimensional synthetic mammograms with original digital mammograms alone in combination with tomosynthesis images]" also examined whether generated 2D images instead of conventional ones 2D images can be used in a 3D mammography. In this retrospective study, the authors compared the results of eight experts who evaluated different cases that covered the full range of lesions and the confounders identified in clinical practice. Margarita L. Zuley, Department of Radiology, Magee Women's Hospital, University of Pittsburgh Medical Center, and her colleagues concluded that the 2D images generated did not result in clinically meaningful differences in diagnostic accuracy and could therefore be used to determine the to replace conventional 2D mammography as part of routine 3D mammography exams. The study was published online prior to the January 21, 2014 print version of the journal Radiology.
- The Massachusetts General Hospital Study.
- The multi-reader study, "Diagnostic Accuracy and Recall Rates for Digital Mammography and Digital Mammography Combined with One-view and Two-view Tomosynthesis: Results of an Enriched Reader Study [Diagnostic Accuracy and Recall Rates for Digital Mammography and Digital Mammography, Combined with One -Plane and two-plane tomosynthesis: results of an extended reader study] ", stated that the use of Hologic's single-plane 3D mammography in addition to conventional digital mammography significantly improves the accuracy of the diagnosis and reduces the recall rate, that the additional use of Hologic's two-level 3D mammography resulted in a double improvement in performance and further reduced the number of unnecessary patient recalls. The researchers concluded that "an approach that combines two-plane 3D mammography with digital mammography should be used in clinical practice." The researchers also found that the additional use of the two-plane Compared to conventional mammography, 3D mammography significantly increases the diagnostic accuracy of the imaging in women with dense breast tissue.
Each breast is recorded from two, possibly several directions. The two most common and commonly used projections are the cranio-caudal image (X-ray of the chest from above) and the MLO image (mediolateral oblique, X-ray of the chest from the center outwards). During the exposure, the breast is moderately compressed between the object table and a Plexiglas plate. This is necessary in order to keep the radiation dose low and to image the breast region to be examined in the best possible way. Some of the patients found the examination uncomfortable.
The soft radiation leads to higher-contrast images than would be possible with other X-ray examinations with hard radiation. The examination can detect small, non-palpable tissue formations as well as microcalcifications . The X-ray images are evaluated by the examining doctor, whereby in the European screening programs the double diagnosis is carried out by two doctors. Here can CAD systems (computer-assisted detection) assist radiologists in the evaluation of radiographs. You are billable in the US and the Netherlands.
Mammography as an individual examination
Mammography can be used to further clarify any suspicious tumor findings, usually a palpable lump or a secretion from the nipple. The term curative mammography is used for this among experts . The result of the examination flows into the planning of further therapy.
Mammography as a screening examination
Mammography is also used for the early detection of breast cancer. The aim of this screening measure is to extend the life expectancy of women with breast cancer by identifying them as early as possible. For this purpose, in some countries (the Netherlands, Sweden, Finland since 1974; Great Britain since 1979) organized screening is carried out on women without symptoms. This supposedly reduced mortality by 25-30%.
However, recent studies have put this benefit into perspective. A meta-analysis from 2013 attributes the originally found positive effects on mortality to inadequate randomization of patient groups. In contrast, the studies in which this was carried out correctly found no significant differences in cancer mortality after 10 years and in all-cause mortality after 13 years.
Furthermore, in a 25-year Canadian study with a random allocation of nearly 90,000 women to either an annual mammography and clinical examination group or an annual clinical examination group only, there was no significant difference in breast cancer mortality between the found in both groups.
The incidence of breast cancer increases by the screening because it overdiagnosis occurs, ie even cancers are discovered, where the woman had not died. Early detection cannot prevent breast cancer (such as vaccinations ). It is primarily used to detect breast cancer at an early stage and treat it in a less invasive manner.
In Germany, by resolution of the Bundestag, a national mammography screening program has been set up since 2005, taking into account the relevant European guidelines. In contrast to curative mammography, screening only takes place in a few highly specialized centers and with extremely complex quality management . Only specially trained radiologists or gynecologists, radiology assistants and pathologists are allowed to participate in the program. The qualification must be proven again by annual tests. The success rates are checked by special superordinate centers, the so-called reference centers.
The entire population of 50 to 69-year-old women is recorded in the population register. In December 2009, the last of the 94 units went into operation. By December 2009, 9.2 million women had been invited to the screening, 54% were examined. In order to reach women outside of metropolitan areas as well, the rural area is partly opened up by semi-trailers with built-in mammography devices, so-called mammobiles .
Double radiological and pathological findings ensure that the rate of small carcinomas and pre-invasive lesions (e.g. DCIS ) is high and, on the other hand, as few biopsies of benign breast tumors as possible are performed or these are surgically removed. The EUREF guideline requires at least 50% malignant tumors in biopsies; some programs achieve up to 80%.
The aim of quality assurance is to reduce the rate of false-positive or overlooked findings. Specially trained radiologists who are trained in assessing many mammograms can greatly improve both specificity and sensitivity . Specialized pathologists who histologically assess samples (e.g. vacuum biopsy ) are also an essential part of mammography screening . In addition to the individual diagnosis, they also provide the radiologist with feedback on the correctness of his interpretation of the findings ( correlation of the findings) in a so-called screening unit . These are centers that specialize in mammography screening and have a valid license (certificate) for this. Doctors who meet the strict criteria of the EuRef standard for mammography examinations are awarded a certificate that must be renewed annually. Women who want or need to have a mammogram should find out in advance whether the X-ray doctor has such a certificate. This gives you extensive security, both in terms of radiation risk and image quality, as well as in terms of the qualifications of the doctor and his staff. A breast cancer registry and quality assurance of the technical equipment also serve to ensure quality.
Recommendations regarding the age of the examination
According to the current state of knowledge, screening mammography does not seem to be of any advantage for women under 40 to 50 years of age, since the younger the woman, the higher the proportion of false positive results. This can be explained, among other things, by the higher tissue density of the breasts of younger women, which makes the general assessment of the X-ray more difficult. The German screening program therefore invites all residents between the ages of 50 and 69 to have an examination every two years.
Criticism of mammography screening
Criticism of the general benefit of X-ray screening
Critics argue that the relative risk reduction is often misunderstood, or the expected benefit for the participants is overestimated and conclude from this that unnecessary investigations when taking radiation exposure into account. Similar to the undisputed preventive medical check-up for slowly growing cervical cancer (so-called "smears"), it is very likely that a woman who regularly goes to mammography will never develop cancer and thus will not benefit from the examination. Participation in a mammography screening program does not change the overall mortality of women from cancer (all types). There is no effective way to determine which woman will benefit from mammography. A major problem with breast cancer and its precursors is that it is usually only recognized (relatively large) when the tumor has reached a more advanced stage . However, the goal of radiation-free breast ultrasound and mammography screening is not only to reduce the general mortality rate from breast cancer, but above all to detect tumors at an earlier stage and thus to improve the survival time and quality of life of the woman concerned. Cochrane Nordic writes that it no longer seems to make sense to take part in breast cancer screenings.
Criticism of overdiagnosis due to false-positive results
Like any test, mammography also gives false positive results , i.e. a suspicion of cancer even though no cancer is present. According to Christa Halbwachs from the Austrian Breast Imaging Study Group , mammography has a sensitivity (true-positive rate) of 83% and a specificity (true-negative rate) of 97%. Each screening finding suspicious for cancer should be clarified as standard, either by means of a vacuum or punch biopsy or by a prompt mammographic check-up (e.g. in six months). Only in exceptional cases is an open biopsy (i.e. an operation) performed to confirm the diagnosis. These false-positive findings can be very stressful for the woman in question. Many women find a histological evaluation with a final all-clear (i.e. a confirmation of the diagnosis) to be a relief, even if the examination afterwards was unnecessary. In the German screening program, the ratio of benign to malignant biopsies is 1: 2.3; it is much less favorable in magnetic resonance imaging.
Criticism of radiation exposure
Mammography itself, since it involves ionizing radiation , can at least statistically cause carcinomas. However, the frequency cannot be measured directly; there is only data from historical studies that estimate the theoretical risk to be 0.01%.
Criticism of "harmless carcinomas" and unnecessary operations
The breast cancer is not a single disease, but rather consists of a heterogeneous group of various tumors with different prognosis. Basically, the survival rate depends on certain factors. These include tumor size, settlements in the armpit lymph nodes, distant metastases ( TNM classification ), histological degree of differentiation and the type of tumor therapy.
Screening critics point out that, among other things, the mammographic screening can also detect carcinomas which - if they had not been detected in the mammography - could take a life-threatening course ( indolent tumor ). According to the criticism, this would lead to unnecessary operations and cancer therapies being carried out, which would reduce the patient's quality of life, even if she had not died of breast cancer if she had not been treated. Since the individual course of cancer cannot be predicted with sufficient certainty, this attitude is highly controversial among experts. According to Italian researchers, the benefits of screening outweigh the risks of overdiagnosis. Proponents of the screening program refer to the lower mortality (mortality) since the introduction of screening. However, it does not reduce mortality among women over the age of 70; H. the women did not benefit from the study because of their age. The upper age limit for participation in mammography screening is therefore 70 years.
In connection with indolent tumors, there is often talk of unnecessary operations that could lead to stigmatization or mutilation. In fact, the female breast makes special demands on the surgeon in order to achieve an oncologically compatible and at the same time cosmetically appealing result in breast-conserving therapy as well as in a mastectomy . The claim to achieve the best possible cosmetic result with every operation is also anchored in the S3 guidelines for the treatment of breast cancer. Treatment in a certified breast center is therefore generally recommended.
- With a participation rate of 70 percent, the costs in Germany amount to around 300 million euros, which are borne by the statutory health insurance companies . The examination is free of charge for the participating women.
Research on other methods
The imaging of the breast with the help of microwaves is being researched for detection and observation, screening and chemotherapy monitoring. The potential of such methods lies in the different dielectric properties that can be observed between healthy and cancerous tissue.
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