How Does Mammography Work?

Mammography is the most traditional method of mammography. In the past few decades, mammography technology has experienced from mammography to film-screen mammography and special screen-film photography. ) Until now, there has been a huge change in full-field digital mammography (FFDM). The image quality has been continuously improved and the radiation dose has been significantly reduced. It is mainly used for screening and diagnosis of breast cancer. It is the most basic and preferred imaging method for breast disease. It can detect early breast cancer with negative clinical palpation.

Li Jing

(Deputy Chief Physician)

Department of Imaging Diagnosis, Cancer Hospital, Chinese Academy of Medical Sciences

Introduction to mammography

Mammography is the most traditional method of mammography. It was first studied by German doctor Salomon in 1913, and first applied to the clinic by Egan in the United States in 1960. After a century of development, it has become an early discovery. Effective and feasible imaging methods for early diagnosis of breast cancer are widely used in screening and diagnosis of breast cancer. In the past few decades, mammography technology has gone from mammography to film-screen mammography to full-field digital mammography, FFDM), the image quality is continuously improved and the radiation dose is significantly reduced.

Full field digital mammography is also called breast DR (digital radiography), which has a large exposure latitude, wide dynamic range of photography, high contrast resolution, image contrast and calcification display are superior to traditional screen systems, and the radiation dose It is also lower than the traditional screen film system. Its main advantages are: 1. Image post-processing can be performed, brightness can be adjusted according to the situation, and the area of interest can be enlarged to observe and improve the contrast and sharpness of the photo; and it can help reduce improper technology, unsatisfactory images, or local needs Repeated radiographs caused by magnification. 2. It can transmit data to facilitate remote consultation. 3. Data can be stored, reducing the space for storing film. FFDM images are clear, and the diagnostic accuracy of dense breasts, women under 50 years old, and premenopausal women is better than that of traditional screen films.

Similar to ordinary X-ray photography, the imaging basis of mammography is that there is a density difference in the tissues that make up the mammary gland. The essence is that the absorption values of X-rays are different for each tissue. The mammary gland itself is a soft tissue component, mainly composed of fibrous gland tissue, adipose tissue, and skin. Its tissue density and linear absorption coefficient are very close. For this reason, the X-rays produced by mammography are unique, that is, they are low-energy soft X Line to increase the difference in X-ray absorption between breast tissues and enhance the contrast of the image.

The earliest anodes of mammography X-ray tube used molybdenum targets, so it is called "molybdenum target mammography" (referred to as "molybdenum target examination") in China, but with the development of technology, the anode materials are not limited to Molybdenum targets also include molybdenum-rhodium dual targets, molybdenum-tungsten dual targets, etc., as well as mammography cameras using tungsten targets alone. Therefore, the normative name should be "mammography".

In order to obtain high-quality images, the photography equipment used for mammography should have the performance requirements required for mammography, and the quality management of the equipment should be planned, and appropriate exposure conditions should be selected according to the size and density of the breast during photography. , Correctly implement positioning and oppression.

Each subject routinely irradiated bilateral breasts at four positions, namely bilateral medial and lateral oblique position (MLO position) and head and tail position (CC position). Patients are routinely used in standing or sitting positions. The medial and lateral oblique position is the most commonly used projection position, and this projection position exposes the most breast tissue. When the conventional photographic position is not good, you can choose to supplement the projection position according to your needs. In order to further evaluate the small nodules or fine calcifications displayed in conventional conventional photography of the mammary gland, point pressure photography, magnification photography or point pressure magnification photography may be further performed.

The mammary glands of fertile women will undergo periodic changes with reciprocating cycles such as rejuvenation, hyperplasia, and degradation during the menstrual cycle. Therefore, it is best to choose mammography and self-mammary physical examination after the breast tissue is restored or at the beginning of re-proliferation, that is, menstrual cramps The next 7 to 10 days. Before the examination, remove metal foreign objects from the chest, such as necklaces; do not apply topical liquids and skin care products on the chest to avoid artifacts.

New technologies and advances in mammography include digital breast tomosynthsis (DBT), contrast-enhanced digital mammography (CEDM), and dual-energy subtraction. However, these new technologies still need more experiments and research and experience accumulation to make them more mature ^[1] .

Clinical application and limitations of mammography

Imaging is the most important test for breast cancer. Early breast cancer with negative clinical palpation can be found. For patients with clinical symptoms, the characteristics of the lesion can be understood through imaging and the benign and malignant can be identified. Patients are accurately staged and used for follow-up after treatment; imaging performance can also be compared with other clinical indicators to show the biological behavior of tumors. The common examination methods are mammography and ultrasound, and the clinical application of breast MRI is becoming more and more widespread.

Clinical application of mammography

Mammography is mainly used for screening and diagnosis of breast cancer. It is the most basic and preferred imaging method for breast disease. It can detect early breast cancer with negative clinical palpation, especially in the detection of breasts with calcification as the main manifestation. In terms of cancer, there are advantages that other imaging methods cannot replace. For patients with clinical symptoms, the characteristics of the lesion can be understood through mammography, and the benign and malignant can be identified. Mammography is mainly used in two areas: screening mammography and diagnostic mammography.

(1) Screening mammography: It is a regular radiographic examination of asymptomatic people for the purpose of early detection of breast cancer. If suspicious is found, further inspection or treatment should be recommended.

Breast cancer can be detected early through organized breast cancer screening, and effective screening can reduce breast cancer mortality. In many countries, radiography has been widely used for breast cancer screening in women over the age of 40, and is by far the only screening method that has been proven to reduce breast cancer mortality. Screening of asymptomatic women over the age of 40 with mammography is generally recommended in China. Screening for the general population can be performed on the basis of clinical palpation and ultrasound. Mammography is performed every 1 to 2 years. Mammography is performed once a year in high-risk groups.

(2) Diagnostic mammography: Mammography is performed on patients with abnormal changes or symptoms and signs of breast disease during screening to provide more clinical information. The main indications include breast lump, sclerosis, abnormal nipple discharge, skin abnormality, local pain or swelling; abnormal changes found during screening; short-term follow-up of benign findings; guided interventional operation; breast reconstruction and reconstruction Subsequent patients; follow-up after treatment of breast tumors; other patients requiring radiologist examination or consultation.

Mammography is simple to operate, relatively inexpensive, and has a high diagnostic accuracy rate. If you are proficient in the correct projection technology and diagnostic skills, you can make early diagnosis of breast cancer ^[2] .

Limitations of mammography

There are still some limitations in mammography. Even under the best photography and diagnostic conditions, breast cancer sensitivity is only 85% to 90%, which is still 10% to 15 % Breast cancer is false negative due to various reasons such as lack of dense breasts, small tumors, and special tumor subtypes, so a negative X-ray image cannot exclude breast cancer. Masses located in the deep, high, or breast tail near the chest wall may be missed due to the lack of ingestion in the radiograph. Another major limitation of mammography is the differential diagnosis of benign and malignant lesions. Due to the variability of mammographic features and the fact that x-ray images are superimposed, there are also higher false positives in X-ray diagnosis of breast diseases. rate. In addition, the sensitivity and specificity of X-ray photography are affected by both breast tissue density and age, especially for dense breasts, and because of radiation damage, X-ray photography is not yet the first choice for pregnant women, lactating women and young patients. .

Abnormal signs of mammography

The main abnormalities found on mammography include masses, calcifications, distorted structures, and asymmetric dense images.

Mammography lump

Refers to a space-occupying lesion visible at two different projection locations. The characteristic analysis of the mass includes three aspects: shape (round, oval, lobular and irregular), edges (clear, fuzzy, micro-lobed, infiltrated, burr-like) and density (high density, equal density) , Low density, with fat density). The edge of the mass is most important in diagnosing the nature of the lesion. Micro-lobulation, infiltration, and burr-like edges are malignant signs. Benign masses are mostly clear-cut. Most breast cancers are high or equal density, and very few breast cancers can be low density; breast cancer does not contain fat density, and fat-containing masses must be benign.

Fig. 1. The oblique radiograph of the right and left breasts has lobular high-density nodules on the right upper quadrant with burrs on the edges, suggesting highly suspicious malignant lesions. Postoperative pathology: breast cancer.

Mammography calcification

The characteristics of calcification were analyzed from two aspects: morphology and distribution.

Morphology: There are three types of benign calcification, intermediate calcification (suspected calcification), and highly malignant possible calcification. (1) Typical benign calcifications: include skin calcification, vascular calcification, rough or popcorn-like calcification, thick rod-like calcification, round and point calcification, "ring-shaped" or "egg-like calcification", milk-like calcification, and suture calcification And hollow dystrophic calcification. (2) Intermediate calcification (suspected calcification): including irregular or fuzzy calcification, rough and heterogeneous calcification. (3) Highly malignant possible calcifications: including small polymorphic calcifications, linear or thin line branch calcifications (cast calcifications). Thin-line branched calcifications appear as thin, irregular lines, often discontinuous, and less than 0.5 mm in diameter. These signs suggest that calcifications are formed from the lumen of the ducts invaded by breast cancer.

Distribution: Including diffuse or scattered, regional, cluster, line-like and segment-like five ways of distribution. The line-like and segment-like distributions often indicate that the lesions originate from the ducts of the breast, most of which are malignant calcifications, but there are also a few benign calcifications that are distributed along the ducts. Both benign and malignant calcifications can be clustered and need to be considered in combination with calcification patterns. Regional distribution of calcification refers to the distribution of calcification in a wide range, rather than the distribution of the catheter. The possibility of malignancy is relatively small, but it also needs to be considered in combination with the calcification pattern. The most likely malignancy is diffuse or scattered calcifications, especially the punctate and amorphous calcifications of this distribution, which are often benign and often bilateral.

Figure 2 The right upper and lower oblique obliques of the right breast show irregularly shaped nodules and clusters of small polymorphic calcifications in and around it, suggesting highly suspicious malignant lesions. Postoperative pathology: breast cancer.

Mammography structure distortion

It means that the normal structure is distorted but no clear mass is visible, including radial shadows and focal contractions from one point, or distortion at the edges of the parenchyma. Structural distortion can also be a companion sign, which can be a companion sign of a mass, asymmetry, or calcification. If there is no history of local surgery and trauma, structural distortion may be a sign of malignant or radial scars, and a clinical biopsy should be submitted ^[3] .

Asymmetric dense mammography

Asymmetric shadows lack the outline of the boundary and the three-dimensional mass of the three-dimensional mass. They are divided into "spherical asymmetric shadows" and "focal asymmetric shadows." "Spherical asymmetric shadow" involves a large area of breast tissue, which is usually a normal mutation, but when a touchable mass is combined, it indicates a suspicious malignancy. The difference between "focal asymmetry shadow" and "spherical asymmetry shadow" is only in the scope of the affected breast. Compared with the latter, "focal asymmetry shadow" should be paid more attention to. The previous films are very important. When new or progressively increasing "focal asymmetric shadows" are discovered, the possibility of breast cancer should be considered. If further localized point pressure photography and / or ultrasound examination are performed, the actual A mass with unclear margins.

Other signs of mammography

Often combined with masses or signs of calcification, or separate changes without other abnormal signs. Including: skin depression, nipple depression, skin thickening, trabecular thickening, skin lesions projected in breast tissue, axillary lymph nodes, etc.

BI-RADS Breast X-ray Photography BI-RADS Classification

The Breast Imaging and Data Report System (BI-RADS), proposed and recommended by the American College of Radiology (ACR) in 1992, was not only used to guide breast X-ray diagnosis (4th edition) until 2003 ), Has also been extended to breast ultrasound and MRI diagnosis. The purpose is to standardize the diagnostic reports of all imaging normal and abnormal conditions of the breast as a whole organ, using uniform professional terms, standard diagnostic classification and inspection procedures, to help clinicians make a reasonable choice for the treatment of lesions. At present, China's mammography diagnostic report also recommends the use of this reporting system.

A very important part of the reporting system is the overall assessment and recommendations for breast lesions, which is commonly referred to as the breast imaging diagnostic classification (BI-RADS classification), as follows:

(1) The assessment is incomplete for unspecified categories.

Category 0: Existing images cannot be evaluated, and other imaging examinations need to be added, including compression spotting, compression magnification, additional positions, or ultrasound and MRI. It is often used in screening situations and rarely used after a complete imaging examination and comparison with previous films.

(2) The final category, the evaluation is complete.

Category 1: Negative, no abnormal findings in mammography.

Category 2: Benign discovery, with clear benign lesions and no signs of malignancy. Includes calcified fibroadenomas, multiple secretory calcifications, fat-containing lesions (lipid cysts, lipomas, ductal cysts, and mixed density hamartomas), intramammary lymph nodes, vascular calcification, implants, surgery The structure of history is distorted and so on.

Category 3: benign and possibly large lesions, short-term follow-up is recommended. There is a high degree of benign possibility, and the lesion is expected to stabilize or shrink in short-term (usually 6 months) follow-up to confirm the judgment. The malignancy rate in this category is generally less than 2%. Palpation-negative masses with clear borders without calcification, focal asymmetry, clustered round or / and punctate calcifications fall into this category. It is recommended to perform X-ray review of the breast at the lesion side 6 months later, and X-ray review of both breasts at the 12th and 24th months. If the lesion remains stable, you can continue to follow up; if the lesion has Progress should be considered for biopsy.

Category 4: Suspicious abnormalities, but without typical malignant signs, biopsy should be considered. This category includes a large group of lesions that require clinical intervention. Such lesions have no characteristic breast cancer morphological changes but have the potential for malignancy. Then continue to divide into 4A, 4B, 4C, clinicians and patients can make final decisions on the treatment of lesions according to their different malignant possibilities.

4A: Lesions that require a biopsy but are less likely to be malignant. The benign results of biopsy or cytology can be trusted, and can be followed up routinely or six months later.

4B: Moderately malignant. It is important for the radiologist and pathologist to reach a consensus on the credibility of the biopsy results of this group of lesions.

4C: Further suspected as malignant. Irregular morphology, marginally infiltrating parenchymal masses, and newly emerged clusters of small polymorphic calcifications can be attributed to this category.

Category 5: Highly suggestive of malignant lesions, appropriate measures should be taken clinically (almost certainly malignant). There are imaging features of typical breast cancer with a malignancy probability greater than 95% and a biopsy should be performed. Irregular morphology, high-density masses with burr-shaped edges, fine linear and branched calcifications with segmental or linear distribution, irregular burr-shaped masses with irregular and polymorphic calcifications fall into this category.

Category 6: Biopsy confirmed malignancy, and appropriate measures should be taken clinically. This classification is used in the evaluation of images that have been confirmed to be malignant by biopsy but have not been treated. It is mainly to evaluate the image changes after biopsy or to monitor the image changes of neoadjuvant chemotherapy before surgery.

The correct assessment of mammography requires the combination of relevant clinical information, including the subject's symptoms, course and signs, related laboratory tests, previous medical history, marriage and childbirth history, menstrual cycle, family history, other imaging test results and The purpose of this inspection is ^[4] .

X Mammography x-ray performance of breast cancer

X-ray manifestations of breast cancer are divided into direct signs and indirect signs. Direct signs include masses, calcifications, focal asymmetry and dense structures, and structural distortion. Indirect signs include thickened or retracted skin, abnormal nipples and areolas, edema around the tumor, and abnormally thickened blood vessels. Lumps and microcalcifications are the most common X-ray signs of breast cancer

Mammography lump

Mass is the most common and basic X-ray sign of breast cancer, and is the main basis for the diagnosis of breast cancer. Irregular masses with marginal burrs are often indicated as malignant.

Masses vary in size. X-rays show that the mass is much smaller than clinical palpation, which is one of the malignant signs. Skin edema, inflammation around the cancer, and invasion of cancerous tumors are the main causes of clinically encountered masses larger than those seen on X-rays. The mass density is denser in most cases, and is similar to or slightly higher than that of the adjacent breast. The morphology of the mass was mostly round, lobulated or irregular. The edges of most lumps are not smooth, the state is fuzzy, and slight and obvious burrs or infiltration are visible. Sometimes the outline can be clear and partially blurred. The length of the burr varies, it can be several centimeters, or it can be short like a brush.

Mammography microcalcification

Calcification plays a particularly important role in the diagnosis of breast cancer. As a major sign of breast cancer, it can not only help the diagnosis of breast cancer, but also in a large number of clinically asymptomatic cases that cannot reach the mass, only the special signs of calcification can be found early by mammography. ,Early diagnosis.

Calcification is not malignant when found on X-ray photography. Most of the calcified lesions detected by X-ray photography are benign. Doctors can make benign and malignant assessments based on the morphology and distribution of calcifications. Morphological manifestations are small polymorphism, thin line-like or thin line branch-like calcifications suggesting highly suspicious malignant calcifications; line-like, segment-like, and clustered distributions are more common in malignancy. Vessel calcification, coarse or popcorn-like calcification, rod-shaped calcification, dot-shaped calcification, translucent calcification, and eggshell-shaped calcification are typical benign calcifications; irregular or fuzzy calcifications, rough and heterogeneous Calcification is suspicious calcification, which can be seen in benign and malignant lesions, which needs to be considered in combination with the distribution. For calcified lesions that are difficult to characterize, mammography biopsy is required when malignancy is not excluded.

Focal asymmetry dense mammography

Sometimes breast cancer does not appear as a mass, but only as a focal asymmetric dense.

Usually bilateral breast tissue is basically symmetrical, but slight asymmetry is very common. In most cases, this asymmetric dense shadow is a benign lesion, such as hyperplasia, chronic inflammation, cysts, etc., and some are caused by cancerous tumors, especially lobular cancer. . Most of the cancerous lesions are denser than normal glands, especially at its central part, which gradually fades outward and is submerged in the shadow of normal glands. The boundary with normal tissue is often difficult to determine, and there is little or no fat in it. organization. The infiltration form can be flaky, irregular or round. The local compression magnification of the spot may show burr and micro-calcification in the infiltration area.

Mammography structure distortion

Sometimes the mass of breast cancer is small and difficult to find, but its fibroblast response pulls on adjacent tissues, causing local structural distortions and disorders. On the X-ray film, there were changes in the normal contours of the parenchyma of the mammary gland and the horny, stellate, and burr-like changes caused by the interstitial components. It is important to carefully check the structure of the bilateral breasts and to compare with a series of past breast films. It should be noted that scars, fat necrosis, sclerosing adenopathy, and localized fibrosis after biopsy or surgery can also cause distortion of the local structure of the breast parenchyma, which is easily confused with malignant lesions. Local compression spot films can more clearly show the structural distortion, which is helpful for diagnosis and differential diagnosis.

Indirect signs of mammography

Including thickened or retracted skin, sunken nipples, edema around the tumor, abnormally thickened blood vessels, etc. Nipple retraction, localized skin thickening, or retraction often occur in the later stages of the lesion. X-ray films show that there is a cord-like or band-shaped dense shadow between the lump and the nipple. Skin thickening is most clearly displayed at the tangent line, as The tumor area is localized or diffusely thickened or retracted, and the skin and the mass can be seen as a strip of shadow. When you see nipple retraction, you should first ask a medical history to rule out congenital changes and sequelae of inflammation.

X Mammography X-ray Quality Control

The density difference of the breast tissue itself is very small, and many lesions show microcalcifications. Therefore, mammography is the most difficult examination method in traditional radiological diagnosis, and it also has the most stringent requirements for machinery and technology. X-ray photography is a kind of damage examination. The mammary glands are highly susceptible to radiation. In order to minimize the risk of radiation damage and ensure the safety and effectiveness of screening practices, scientific image quality control procedures must be carefully implemented. Obtaining high-quality images is a prerequisite for correct diagnosis, and strict quality control is a guarantee for obtaining images.

The goals of quality control mainly include two points:

1. Ensure that when appropriate imaging techniques are used, high-quality images that provide rich diagnostic information can be obtained;

2. Make sure the radiation dose is the lowest under the premise of meeting the requirements of diagnostic information. A qualified breast X-ray examination team requires the close cooperation of radiologists, radiographers, and maintenance physics personnel. The staff should preferably be relatively fixed to ensure quality.