Since the introduction of mammography for breast cancer screening in the 1960s, breast screening technology has made great progress. Mammography machines have evolved from original film mammography machines to 2d mammography machine, and later to 3d mammography machine. So far, 2d mammography machine and 3d mammography machine are the most widely used in hospitals and communities.
This article compares the differences between 2D and 3D Mammography Machine in working principle, imaging effect, diagnostic performance and other aspects, providing clear reference for purchasers to help with reasonable selection.
1. Working Principle
2d mammography machine is also known as Full-Field Digital Mammography (FFDM). At present, 2D mammography is a routine method for observing breast tissue. The tube is fixed at a single angle, and the machine takes two X-ray films for each breast, one from top to bottom and the other from left to right. X-rays penetrate the breast through a single exposure to form a single two-dimensional projection image on the flat panel detector. After the two images are combined, a planar image of the breast is formed.
Three-dimensional mammography is also called Digital Breast Tomosynthesis (DBT). The DBT device moves in an arc above the breast and takes multiple consecutive low-dose exposures (about 10 to 30 times) during rotation, capturing multiple thin-layer X-ray films of each breast from different angles. The computer reconstructs a series of thin tomographic images through algorithms, which is equivalent to "cutting the breast into many thin slices" for layered observation, eliminating the overlap of front and rear tissues, thus generating clearer breast tissue images.
"2d mammography machine superimposes the entire breast tissue on one image, and some small lesions may be covered by normal tissues," said a radiologist with rich experience. "While 3d mammography machine can observe the thin-layer structure of the breast layer by layer, and can more easily find abnormal lesions that are easily missed in 2D examination."
2. Imaging Effect
The image of 2d mammography machine is only a planar view, with serious overlap of front and rear tissues, so small nodules and tiny masses are easily covered by normal glands.
3d mammography machine can display breast tissue more clearly regardless of breast density. Breast density affects the type of mammography recommended by doctors. For example, both dense breast tissue and cancerous tissue appear white on mammograms, and dense breast tissue may mask signs of cancer. Therefore, for dense breast tissue, 3d mammography machine can clearly display the layers of breast tissue and help clinicians distinguish dense tissue from cancerous tissue. Sometimes, doctors also recommend patients with extremely dense breast tissue to undergo other or additional examinations, such as ultrasound.
3. Differences in Diagnostic Performance
This is the core difference between 2d mammography machine and 3d mammography machine.
3.1 Cancer Detection Rate
Cancer detection rate is the proportion of people who are actually diagnosed with cancer among the people undergoing examination. Formula: Cancer Detection Rate = Number of people diagnosed with cancer / Total number of people undergoing examination × 100%
In a community practice, women who underwent 2d mammography machine examination and 3d mammography machine examination were investigated and analyzed within a period of time. The overall Cancer Detection Rate (CDR), expressed as the number of cancers found per 1000 patients examined, the CDR of 3D DBT (6.3/1000) was 28.6% higher than that of 2D DM (4.9/1000) (p = 0.035). The CDR of 3D DBT for invasive cancer (4.6/1000) was 43.8% higher than that of 2D DM (3.2/1000) (p = 0.0056).
It can be seen from the data that for women undergoing 3D DBT screening, the possibility of abnormal screening results finally diagnosed as cancer is higher than that of women undergoing 2D DM screening, indicating that the screening results of 3D DBT may be more accurate.
3.2 Positive Predictive Value of Screening Recall
When mammography results are abnormal or unclear, patients may need re-examination. Sometimes, these additional examination results show that everything is normal, which is called false positive. The positive predictive value of screening recall is the proportion of people who are finally diagnosed with cancer among those "recalled" for re-examination. Positive Predictive Value (PPV) of recall = Number of people diagnosed with cancer / Total number of people recalled for re-examination × 100%
The higher this value, the better, because a high PPV value means a high proportion of real cancers among the recalled people, accurate doctor judgment, fewer wronged people, and a low false positive rate. According to the above survey, the PPV1 of 3D DBT screening (4.6%) was statistically significantly different from that of 2D DM screening (3.0%) (p = 0.0003). This difference means that the PPV1 of abnormal results in 3D DBT screening is relatively increased by 53.3% compared with 2D DM screening. The estimated increase of PPV1 by the generalized linear mixed model is 51.14% (p = 0.0007). Therefore, for women undergoing 3D DBT screening, the possibility of abnormal screening results finally diagnosed as cancer is higher than that of women undergoing 2D DM screening.
It can be seen from the above data that 3D imaging technology can help us detect cancer as early as possible before it spreads and help reduce the need for additional examinations. The above data shows that the false positive rate of 3d mammography machine examination is lower than that of 2d mammography machine examination, which can help patients avoid unnecessary pressure and potential costs of follow-up examinations. However, in some cases, such as after biopsy, when less detailed images are needed, 2d mammography machine examination may be useful (low cost), and the radiation dose of 2d mammography machine is slightly lower than that of 3d mammography machine.
3.3 Number of Mammograms Required for Recall
Analysis of the frequency distribution of the number of additional mammograms taken during re-examination showed that women diagnosed with breast cancer after 3D DBT screening had fewer additional mammograms taken than those undergoing 2D DM screening (p < 0.001). Among patients diagnosed with cancer after re-examination, 74.1% of 3D DBT patients had no more than two mammograms taken, while this proportion was 51.0% for 2D DM patients. In addition, 35.1% of patients in the 3D DBT group did not need additional mammograms, compared with 6.3% in the 2D DM group. This finding indicates that re-examination after 3D DBT screening may be more efficient than 2D DM.
4. Differences in Radiation Dose and Examination Speed
The dose of 2d mammography machine is lower, about 0.3–0.4 mSv for a single examination. 3d mammography machine has a slightly higher dose of 10%–30% due to multiple exposures, but the radiation doses used in both 2D and 3D mammography are considered safe.
In terms of examination speed, 2d mammography machine has fast exposure, fast imaging and fast film reading; 3d mammography machine has a slightly longer exposure time, requires time for reconstruction, has more layers for film reading, and takes slightly longer time.
5. Differences in Equipment Price and Examination Cost
5.1 Price
The price difference between 2d mammography machine (FFDM) and 3d mammography machine (DBT) is mainly reflected in technical cost, diagnostic accuracy, data processing and other aspects. Usually, the purchase price of a 3D system is 2 to 3 times that of a 2D system.
| Equipment type |
Entry-level/Standard (USD) |
Mid-to-high-end/flagship models (USD) |
| 2d mammography machine (FFDM) |
$50,000 - $70,000 |
$142,000 - $250,000 |
| 3d mammography machine (DBT) |
$90,000 - $165,000 |
$250,000 - $500,000+ |
Refurbished 3D systems (such as Hologic Dimensions) usually cost between $50,000 and $100,000, saving about $50,000 to $100,000 compared with buying new machines. Top brands such as Hologic, GE (General Electric) and Siemens 3D flagship models can cost up to $265,000 or even higher.
5.2 Examination Cost
For patients, 3D examination is usually more expensive than 2D examination, mainly due to higher equipment depreciation, longer doctor's film reading time and larger data storage requirements.
Although 3d mammography machine is becoming more and more popular, not all breast imaging centers can provide this examination. If both types of mammography are available, the appointment process may be different. Moreover, the medical insurance coverage of 3d mammography machine may not be as extensive as that of 2d mammography machine. In the United States, the out-of-pocket or insurance bill cost of 3D examination is usually $40 - $100 higher than that of 2D.
6. Differences in Applicable Populations
2d mammography machine is applicable to:
- Fatty breast
- Postoperative re-examination, follow-up of known benign lesions
- Limited budget, primary screening
3d mammography machine is the first choice for:
- Dense breast (mainstream in Asian women)
- High-risk groups of breast cancer (family history, past medical history)
- Previous suspicious 2D results, requiring accurate diagnosis
- Those who want to reduce recalls and improve diagnostic confidence
7. Conclusion
In summary, the difference between 2d mammography machine and 3d mammography machine is essentially the improvement of diagnosis and treatment experience and accuracy brought by the iterative upgrading of imaging technology. With the advantages of maturity, economy and high efficiency, 2d mammography machine has become the basic choice for routine breast screening, meeting the basic screening needs of large-scale populations. 3d mammography machine, relying on the core advantage of tomographic imaging, solves the pain points of tissue overlap and high missed diagnosis rate of dense breasts of 2D models, showing significant advantages in accurate diagnosis and early detection, providing a more reliable screening scheme for high-risk groups and dense breast groups. The two have different focuses and complement each other, not a simple replacement relationship. In clinical practice, it is necessary to reasonably select the appropriate examination method according to the breast type, disease risk, medical budget and other factors of the screening population, relying on 2d mammography machine to achieve wide coverage and 3d mammography machine to improve diagnostic accuracy, and finally achieve the goal of early detection, early diagnosis and early treatment of breast cancer, providing more comprehensive and accurate protection for women's breast health.
