Breast Imaging Technology: Thinking Outside Mammography

More than 90 percent of mammograms in the United States are digital X-rays, a proliferation that Georgetown’s Amy Campbell, MD, traces to a 2005 paper published in the New England Journal of Medicine that found digital to be more accurate than film for women younger than 50 or with dense breasts.

Despite the advances, digital mammography still misses about 17 percent of breast cancers and as many as 30 percent depending on breast density and other factors, according to the Susan G. Komen Foundation

Radiologists and other researchers worldwide are working not only to improve the numbers but to create a technology that is quick, safe, cost effective, comfortable for both patients and radiologists and ideally non-invasive.

Here, we highlight a few technologies in the pipeline.

Tomosynthesis
Digital breast tomosynthesis mammography (DBT) was developed to improve cancer detection in women with dense breast tissue, and is “the current trend in breast imaging” as more facilities move to use this technology, according to Cleveland Clinic radiologist Laura Shepardson, MD.

While conventional digital X-rays have proven effective in detecting micro-calcifications, Shepardson says, tomosynthesis’ thin-section display should improve radiologists’ abilities to visualize and diagnose subtle areas of architectural distortion and small masses, which are often harder to see on conventional four-view mammography, particularly for patients with denser breasts.

Controversial and challenging, cancer detection in dense breasts has been described as “the Achilles Heel of screening mammography” by Mark A. Helvie, MD, in a September 2010 article in Radiology Clinics of North America. Nearly all cancers will show up in images of fatty breasts, but only half will be visible in extremely dense breasts, he says, describing the dense tissue as “masking or camouflaging” the cancer.

With tomosynthesis, explains Campbell, chief of breast imaging at MedStar Georgetown University Hospital, the machine first would take 2D digital X-ray images of the compressed breast as usual, and then move over the compressed breast in an arc taking multiple images, which allows the computer to produce a 3D image of the breast in one millimeter slices.

The additional tomosynthesis procedure does expose the patient to additional radiation, but Shepardson says the increase in dose likely would be offset by a decrease in need for additional diagnostic imaging to discern overlapping tissue from true pathology. 

Campbell says she expects tomosynthesis will become more widely available depending on the outcome of several, upcoming randomized trials. One vendor, Hologic Inc., received FDA approval for tomosynthesis in 2011; several other vendors are seeking approval.

Photon Counting
Developed in the 1980s, photon counting scans the breast using about one-third of the radiation dose of regular mammography--0.6mGy vs.1.7mGy for standard mammography, explains John M. Lewin, MD, a radiologist with Diversified Radiology of Colorado.

The exam requires a few extra seconds of breast compression, but Lewin says he is not convinced the lower radiation dose will benefit most women undergoing mammography.

“We know radiation given to the breast between puberty and age 30 increases your risk of breast cancer,” he says. Beyond age 30, he says, “there is no measurable effect.”

Photon counting had a 76 percent cancer detection rate compared with 59 percent for other screening units, according to data analysis from a 2014 study out of Germany and published in Radiology.

But Lewin points out that it’s impossible to know whether the results were because of the technology, the radiologists, the population or other factors.

Photon counting has been FDA-approved for one vendor, Royal Philips Electronics, and Shepardson points out that the technology would be costly since it requires an entirely new detector.

Breast CT
Photon counting and tomosynthesis potentially offer incremental, but not substantial advances in breast cancer detection, according to John M. Boone, radiology vice chair and professor of radiology and biomedical engineering, at the University of California Davis Medical Center.

After examining more than 600 patients in 10 years, “we do feel pretty strongly that breast CT will have a role in breast cancer screening,” Boone says.

Boone says breast CT is superior to digital mammography in detecting mass lesions even without contrast. Contrast-enhanced breast CT also is competitive with, if not superior to, digital mammography in detecting microcalcifications, he says.

And for women at high risk for breast cancer who might be candidates for breast MRI, breast CT might prove to be a preferred alternative, he says. When contrast agents are used with CT, “we can reap all the benefits of MRI,” Boone says, adding that the exam takes half as long as MRI and is less expensive. A disadvantage of CT is that it uses ionizing radiation, unlike MRI, which uses magnets and radio waves.

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While Boone does not have hard data on a technology his center is developing-along with a handful of others worldwide-he is optimistic that breast CT eventually will replace traditional mammography for routine screening.

With breast CT, the patient lies on her stomach with her breasts falling through a “hole” in the table-no compression necessary.

She holds her breath for 10 or 15 seconds while the machine under the table gathers 360 degrees of data in 500 individual images, which are used to reconstruct virtual slices of the breast.

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Georgetown’s Campbell explains that breast CT works under the same principle of tomosynthesis in looking at the breast in layers. Both technologies have “plusses and minuses,” she says, with CT possibly requiring a slightly higher radiation dose.

“As the two technologies evolve, we’ll have to see which of the two radiologists prefer to look at,” Campbell says. Breast CT still needs FDA approval and probably will find its niche, she says, “but it will be sometime before that happens.”

Breast US
Breast density laws in several states are the impetus behind the rise in breast ultrasound, Boone explains. Under these laws, a woman with a specific breast density may be eligible for additional screening technologies.

Like tomosynthesis, breast ultrasound is effective in picking up masses, while conventional mammography is better for visualization of micro-calcifications. A transducer placed over the entire breast, automatically creates images and reduces labor since a hand-held probe is used only if something suspicious appears.

Campbell explains that several groups are pushing for breast ultrasound for all women with dense breasts. She describes the technology as “heavily investigated.”

Photoacoustic Imaging
Another contender in the breast imaging arena, this one using sound and light, is being pursued by a partnership between the University of North Carolina and nearby OptoSonics.

The technology is described as photoacoustic imaging, in which the generation of sound from light absorption creates high-resolution, 3D images of the network of blood vessels in the breast, according to Cherie M. Kuzmiak, DO, director of breast imaging at North Carolina. Kuzmiak explains that tumors induce the creation of additional blood vessels feeding into a mass.

The patient lies face down on a table, with one breast placed in a clear plastic cup that is partially filled with water. An array of 500 ultrasonic detectors surrounds the cup, and a laser pulses approximately 2,000 times in one minute. A microsecond of light is absorbed, which creates one-thousandth of a degree of heating- enough to expand the tissue and create an acoustic wave. Blood vessels absorb more light than other tissue, and when the optical absorption is stronger, the sound wave is stronger, Kuzmiak says. The resulting ultrasonic waves travel through breast tissue and the surrounding water to the detector and a computer screen, which presents the image.

“We are working on developing another technology that does not use radiation or compression,” Kuzmiak says. So far four healthy patients have been imaged, she says, describing the technology as being in its very early stages.

These additional technologies in the pipeline should provide patients with more opportunities for accurate diagnoses, better detection when cancer is present and reduced risk of unnecessary biopsies.