Molybdenum target, rhodium target, tungsten target: Which breast X-ray examination is suitable for your breast?

Author: Qin Naishan, Chief Physician, Peking University First Hospital

Reviewer: Song Guohong, Chief Physician, Peking University Cancer Hospital

Mammography, as one of the important means of breast examination, has always attracted much attention. With its unique imaging technology and high sensitivity to breast cancer, it has become a trusted health partner for many women. Let us take a deeper look at the types, principles, applicable populations and related precautions of mammography to help you better understand this examination method and protect your health.

Mammography has undergone a transition from analog to digital (similar to the transition from traditional film photography to digital photography). Early mammography mainly used analog machines, which required film washing to see the image, which was a cumbersome and inefficient process. Today's digital mammography can directly transfer data to a computer, allowing doctors to obtain clear images at the first time, greatly improving the accuracy and efficiency of diagnosis. In addition, digital technology has brought more innovations, such as breast tomosynthesis technology (DBT) and enhanced mammography technology (CEM). The tomography technology is similar to CT scanning. It can cut the breast into multiple thin layers to achieve tomographic observation, which significantly improves the detection rate of tumors and the accuracy of differential diagnosis. Enhanced mammography requires the injection of contrast agents (the same contrast agents injected for enhanced CT) to enhance the lesions in the image, which helps doctors find lesions and more accurately determine the nature of the lesions.

In mammography, we often hear the terms "molybdenum target", "rhodium target" and "tungsten target". They actually refer to the material of the anode target surface that electrons bombard during the X-ray generation process. Different materials produce different qualities of X-rays and are suitable for different types of breasts.

The X-rays produced by molybdenum and rhodium targets are well matched to the absorption characteristics of film, so molybdenum and rhodium targets were used in the era of film mammography. Breasts can be divided into lipidic, fibroglandular, unevenly dense, and dense types according to their density (the ratio of glandular to fat content). For lipidic breasts, molybdenum targets are usually chosen because of their better imaging contrast; while for dense breasts, rhodium targets are often chosen because a larger amount of radiation is required to penetrate dense glandular tissue. Mammography equipment can detect the density of the breast and automatically switch between different target surfaces for imaging to ensure the best imaging quality.

In the era of digital mammography, digital detectors have a far better absorption performance for X-rays than film and can adapt to a wider range of X-ray exposures. The X-rays produced by tungsten targets are more compatible with the absorption performance of digital detectors, so they are widely used in digital mammography. The X-rays produced by tungsten targets have a relatively high average energy and strong penetrating power, which can reduce the breast's absorption of X-rays and reduce the radiation dose. In addition, in the era of digital mammography, the original image can be post-processed to adjust the contrast and brightness of the image, making it easier to display the lesions and their detailed features, allowing for more accurate qualitative diagnosis.

When performing a mammography examination, it is crucial to choose a suitable time. This is mainly related to the women's menstrual cycle. Before menstruation, due to the high estrogen level, women often feel discomfort from breast pain. At this time, the pain is more obvious for the patient, and it is difficult for the patient to cooperate with the examination. In addition, during this period, the breast density increases due to intercellular edema, which may cover up small lesions. Therefore, it is recommended to perform the examination within 3-7 days after menstruation. At this time, the estrogen level is relatively low, the intercellular edema of the breast subsides, and the breast is softer. Not only does the patient feel comfortable, but the imaging quality is better, and it is easier for the doctor to find the lesion.

Figure 1 Original copyright image, no permission to reprint

However, for young women, mammography may not be the first choice. Young women have abundant and dense breast glands. It is very difficult to find lesions in dense breasts. In addition, X-rays cause certain radiation damage to the human body, especially for young women. Excessive chest irradiation may increase the risk of breast cancer. Therefore, young women are more suitable to choose ultrasound examination as a means of examining breast diseases. With age, the glands in the breast gradually degenerate and are replaced by fat. At this time, the damage of radiation to the breast is significantly reduced, and X-ray examinations are more likely to find lesions.

Figure 2 Original copyright image, no permission to reprint

So, for women over 45 years old, how should mammography be performed? Generally speaking, it is recommended to conduct an examination every 1-1.5 years. However, if there are high-risk factors for breast cancer, such as family history, gene mutation, chest radiotherapy, or previous breast cancer, it is recommended to conduct breast cancer screening in advance and shorten the screening interval to once a year. Of course, if a woman does not have a high-risk factor for breast cancer, the screening interval can also be extended to one and a half years or even two years. During the examination, the doctor will choose the appropriate examination method according to the patient's specific situation and ensure the accuracy and safety of the examination.

Mammography is highly effective in screening and diagnosing breast cancer. It is particularly sensitive to calcification and can detect tiny calcification foci in some early breast cancers (carcinoma in situ).

Many women have concerns about the radiation from breast X-rays, and are concerned about the risk of radiation damage and radiation-induced cancer. In fact, the radiation from breast X-rays can damage human cells, but it is very small; and for women whose breasts have matured, the breast cells have differentiated, and the risk of X-rays causing cell gene mutations and cancer is basically zero.

Although the breast is a sex gland organ that is relatively sensitive to radiation, mammography once a year is safe for the human body. Radiation damage to the human body is an additive effect, so it is not recommended to have too frequent X-ray examinations. For women over 45 years old, since there are fewer glands in the breast and fat has a poor ability to absorb radiation, the impact of radiation is relatively small. But even so, you still need to follow the doctor's advice and guidance when conducting the examination to ensure the safety and effectiveness of the examination.

What is the specific process of breast X-ray examination? During the examination, the patient needs to stand in front of the X-ray camera and place the breast on the imaging board. In order to ensure the integrity and clarity of the image, the technician will use a compression plate to compress the breast. This process may cause some pain to the patient, but it is necessary. Compression can separate the glands in the breast and make the lesions appear more clearly; at the same time, compression can also reduce the impact of scattered rays on the image and reduce the patient's radiation dose; in addition, compression can also reduce the generation of blurring artifacts and improve the clarity of the image. In order to reduce pain, patients can fully communicate with the technician before the examination, relax their body and mind, and cooperate with the technician's positioning and operation.