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.
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.
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 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.”
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.