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Wednesday, July 16, 2014

What is a the difference between a Regular Mammogram and a "3-D Mammogram"?

Every year, 200,000 women in the U.S. are diagnosed with Breast Cancer, and 40,000 lose their lives to the disease. 40 Million mammograms are performed to screen women for Breast Cancer. Over 1 Million of them will have biopsy procedures. These numbers tell the story of a devastating disease and the importance of having accurate and widely available screening tools to detect Breast Cancer early.

The traditional screening tool, a mammogram, has been used to screen women for Breast Cancer since the 1960's. It became widely used in the 1970s as more and more hospitals adopted the technology. In the 1980s and 90s, major improvements of the technology became available in the form of lower radiation doses, and the advent of digital images and computers which could detect abnormalities. Despite these advances, Mammograms remain controversial and are not the ideal Breast Cancer screening tool.

A regular, conventional screening mammogram involves taking two X-Ray Images of each Breast from a side-view and top-to-bottom view respectively. Each Image essentially looks through the entire Breast, detecting tissues with different densities along the way. The final Image is essentially a summary of all the information it gathers as the X-Ray beam travels through the Brest. A 3-D mammogram, also called "tomosynthesis", on the other hand rotates the X-Ray tube around the Breast, taking a series of pictures, similar to a CT Scan. The series of Images essentially creates layers or slices of Breast tissue which are computer processed into 3-D equivalent Images.

The Image below shows some of the differences between conventional and 3-D mammograms. The Image on the left, a 2-D mammogram essentially adds all the information gathered by the X-Ray beam together, while the 3-D mammogram just uses information obtained from one X-Ray beam at a time. This allows the Radiologist to see thin slices of Breast tissue across the Breast vertically and horizontally. Notice that the Image itself is not 3-Dimensional. Rather, the Radiologist can get a 3-Dimensional impression of the Breast after reviewing multiple Image slices. Notice how the circle in the Image below points to a specific abnormality which can be seen on a specific 3-D slice, whereas the 2-D Image shows too much overlapping tissue to isolate the abnormality.

Comparison of 2-D and 3-D Mammogram Images of the same Breast

The FDA approved 3-D mammography in 2011 as an "adjunct" to a conventional mammogram, meaning the two studies would have to be combined. A patient would get both a conventional and 3-D mammogram in one setting. This approval implied that the conventional screening mammogram would still be the standard test, while the 3-D mammogram would be an additional test if patients desired it. However, this also meant that patients would be exposed to two sources of radiation, one from each type of mammogram. This could potentially double the radiation dose to the patient. However the "double dose" of radiation was still considered within the safe radiation limits defined by the FDA.

In 2013, the FDA approved software which would allow patients to receive one single mammogram, which can be used to generate the 2-D and 3-D Images. This approval did not mean that 3-D mammograms were taking the place of the 2-D version, but rather if would allow the data needed for a 2-D mammogram to be extracted from the 3-D version. Again, this implies that 2-D mammograms are still the time-proven test. However, both the 2-D and 3-D version could now be generated through one radiation exposure to the patient. The software is not yet available to many Radiology Centers which have 3-D mammography units. This means many patients still have to undergo two separate studies.

The FDA approval of the technology has thus far not impacted on the insurance approval for the 3-D test. At this point the majority of insurers consider 3-D mammography experimental and do not cover the cost of the test. Patients who desire the 3-D mammogram have to pay out of pocket, which typically varies between $50-$100 per test.

3-D mammography equipment is more expensive than the standard equipment, roughly double that of a digital mammography unit. Currently approximately 10% of mammography centers offer 3-D units, which are available in 48 States. It is estimated that 6 Million U.S. women will undergo 3-D mammography this year.

What prompted the surge in interest and popularity of 3-D mammography were several studies which were published in recent years. In the next Blog we will take a close look at these studies to review the potential risks and benefits of 3-D mammography.

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