Breast Defense

From the time they are teenagers, women are taught that the best defense against breast cancer is early detection. It’s a fact: Women whose cancer is caught in the localized stage stand a 98.3 percent chance of survival five years after diagnosis.1 But just as early detection is key to survival, image quality is critical to early detection.

In February, Hologic Inc. received U.S. Food and Drug Administration (FDA) approval for its Selenia Dimensions Digital Tomosynthesis System, a machine capable of performing traditional two-dimensional (2-D) mammograms as well as three-dimensional (3-D) breast tomosynthesis, a new technology that, according to the company, gives radiologists the ability to more easily identify and characterize individual breast structures.

“In 2-D mammography, especially with dense breasts, areas of concern may be covered by overlying tissue,” Georgia Hitzke, vice president of product andclinical education at Hologic, told Medical Product Outsourcing. “Three-dimensional breast tomosynthesis mammography eliminates the tissue overlap and allows the doctors to see images of the breast at one millimeter slices.”

The Selenia Dimensions System offers three imaging modes: conventional 2-D digital mammography, 3-D tomosynthesis imaging, or a combination of both. In the combination mode, the breast is compressed in the typical way. The X-ray tube acquires a series of 15 low-dose projection images at multiple angles, which form a 3-D reconstruction. The scan then is transmitted to the imaging field, and the operator can view both a 2-D mammogram and a tomosynthesis scan under the same compression.

Being able to view images in this way is a big benefit for radiologists—in a clinical study reviewed by the FDA, radiologists read the combination scan generated by the Selenia Dimensions System and a 2-D mammography scan and agreed that the combination scan was superior. In addition, the scan, which demonstrated improved sensitivity, allowed radiologists to rule out breast cancer without summoning the patient for further study.

“We believe this to be a breakthrough in mammography screening and diagnosis,” Hitzke said. “Since the technology is the first of its kind in the United States, we had to pave the way to obtaining FDA approval.”

Hologic went before an FDA review panel of physicians, physicists and statisticians with the company’s claims. That panel later unanimously voted that the benefits for the Selenia Dimensions System outweighed the risks.

The image quality results from a combination of the system features, many of which also help keep patients at a low radiation dose. When the system is used in combination mode, the patient dose is similar to that of a digital mammogram, but less than that of an analog mammogram. The tungsten X-ray tube with rhodium and silver filters for 2-D imaging reduces the radiation dose by 30 percent; while the rhodium filter has been proven best for most breast sizes, the silver filtration provides better penetration of larger breasts without increased exposure time. In tomosynthesis imaging, the combination of the tube and aluminum filtration provides high-quality images at the lowest possible radiation dose. Other features that contribute to keeping the dose low are the conversion detector, which also eliminates the need to convert X-rays to light, and the High Transmission Cellular grid technology, which makes for higher-contrast images while significantly reducing radiation scatter, and without increasing the dose, officials from Bedford, Mass.-based Hologic noted. Automatic engagement for 2-D imaging takes about two seconds, making the tomosynthesis imaging exam time similar to that of a digital mammogram.

A common question regarding mammography is: if early detection is so critical to survival, why do so many women dread their first mammogram? The truth is, most women have been hearing mammogram “horror stories” almost since the time they are taught the importance of the self-exam. These stories usually focus on the high level of discomfort, and sometimes pain, women experience during a mammogram, which only compounds whatever anxiety already may exist because of a woman’s family history with breast cancer.

The Selenia Dimensions System has taken steps, from a design standpoint, to improve the patient experience and make the patient more comfortable where possible. Hologic enlisted Hollis, N.H.-based Farm Design Inc. to develop the system.

“Farm redesigned the entire gantry, including creating an entirely new ‘flush’ form to maximize patient comfort,” said Darrin Manke, director and program manager at Farm Design, told MPO.

Designers gave the device an ergonomic design, and indented spaces on the sides of the gantry give patients a natural place to rest their hands during the exam; this eliminates some potential awkwardness for the patient and also benefits the operator, who does not have to worry about inadvertent activation of controls by the patient during the exam. The system also features a retractable face shield, which makes patient positioning more comfortable for both parties.

“Hologic has learned a lot from our previous mammography systems, especially with respect to ergonomic design,” Hitzke said. “We also work closely with our customers for their feedback—we asked Farm to take these suggestions into consideration when developing their design, so that it meets everyone’s needs.”

Farm Design also developed an entirely new workstation, which features two displays—a high-resolution monitor for viewing and manipulating the X-ray image, and an enhanced graphical touch screen interface that allows for easy transition between imaging modules.

“Radiologists can also scroll through the X-ray 3-D reconstructed image by using a mouse scroll and they have the ability to play back the x-ray scan in cine mode (video playback),” Manke said. Prior breast imaging studies can be recalled on-screen, enabling the radiologist to view new and old images side by side.

“The reading time for the doctor will be longer than they are used to since there is additional detail available to go through when viewing the 3-D breast tomosynthesis images,” Hitzke explained. “While Hologic is continually working to improve that workflow to reduce the amount of time required, we believe that the reading time will decrease as doctors feel more comfortable with this state-of-the-art imaging modality.”

The workstation also features biometric login and ergonomically designed exposure levers, which can be configured for one- or two-lever activation.

“The technologist simply depresses a pair of levers on either side of the acquisition system to initiate exposure,” Manke said. “All of the fingers are used, which makes it much easier to initiate and eliminates the repetitive motion discomfort of existing single button controls.”

Another new design is the compression paddles, which are described by Hologic as “light and easy to handle.” Bulky components are eliminated in the new design, enabling each paddle to mount directly on the compression carriage. Hologic’s FAST Paddle conforms to the natural contour of the breast, allowing for a more even compression and providing another improvement in comfort for the patient.

Of course, new technology means a new regime to get used to, and additional training to be completed. Hologic offerstraining for technologists, radiologists and physicists, as required by the FDA.

Hologic also is looking to use the new technology in other ways, including as part of an upright biopsy system. The Affirm breast biopsy guidance system was designed to be used with the Selenia Dimensions System for minimally invasive breast biopsy. The Affirm received FDA 510(k) clearance in January.

“We are also exploring other avenues of use with breast tomosynthesis, but they are still in the early stages of research,” Hitzke said.

Reference:

1. Horner MJ, Ries LAG, Krapcho M, et al., eds. SEER Cancer Statistics Review, 1975-2006. National Cancer Institute. Bethesda, Md., http://seer.cancer.gov/csr/1975_2006/, based on November 2008 SEER data submission, posted to the SEER website, 2009.