Breast CT scanner readies for RSNA meeting debut

October 1, 2006

Preliminary experience in small number of cases shows potential to visualize tiny calcifications

Preliminary experience in small number of cases shows potential to visualize tiny calcifications

CT is used in just about every part of the body except the breast. The reason is that traditional CT systems require patients to be scanned supine, flattening the breast and reducing resolution. But a new scanner installed at the University of Rochester in upstate New York is designed to address that problem.

"We are getting very fine image slices through the breast, which provide us with fabulous information," said Dr. Wende Logan-Young, the principal investigator of a study that is evaluating a prototype of the device.

A commercial version of the scanner, developed by Koning Corporation in West Henrietta, NY, will debut at the RSNA meeting. It will feature a horizontal gantry housing a conebeam CT imaging chain. The gantry, which includes a 30 x 40-cm flat-panel detector, is mounted under the patient table.

"The patient just lies down on the table," Logan-Young said. "You put something on the breast to keep it from moving, but you definitely don't compress firmly."

The CT device looks similar to a core-needle biopsy table. A major difference is the imaging chain that rotates once around a single, uncompressed breast, which extends through a table cut-out. Scan time is about eight seconds, Logan-Young said. Conebeam algorithms reconstruct the data into a volumetric image of the breast.

By mid-August, the system had been operating for only a few weeks. The 60-patient study will compare the CT images with those obtained using conventional mammography systems. Most of the 12 patients scanned to date have been normal cases, but in one instance, a cancer could be clearly seen on one of the slices.

"We are seeing tiny calcifications with this machine, which is unbelievable," she said.

The breast scanner might ultimately be used for screening mammography, but its near-term application will be as a diagnostic tool.

"This will be where you can send your 'head scratchers' or patients with a palpable mass, so you can zero in on that area," she said.

The system could prove advantageous in its ability to render 3D images, particularly in women with dense breasts.

"With dense breasts, we are always trying to figure out if there is really something there, or if what we are seeing is overlapping tissue," Logan-Young said.

Normal healthy tissue, particularly in dense glandular breasts, can overlie and obscure nearby cancers. The difference in contrast between a lesion and fibrous glandular background tissue is often so slight it cannot easily be identified on screen-film mammography. Digital mammography has an advantage in that its detectors capture data over a wide dynamic range, allowing the use of algorithms that enhance differences between lesions and normal tissue. Full-field digital mammography, however, requires compression and still produces a 2D image.

MRI has neither drawback. As with the Koning CT, MR delivers 3D images of the uncompressed breast. These images, however, must be acquired using a contrast medium whose wash-in, wash-out patterns are difficult to interpret. MR exams are also lengthy, requiring as much as 45 to 60 minutes to complete, whereas breast CT is done in seconds.

A commercial version of the CT scanner could be on the market by the end of the year, according to Koning. The company's RSNA meeting exhibit in Chicago will feature both normal cases and proven cancers.

The precedent set by CT and other modalities may allow the company to sidestep the intensive regulatory process that digital mammography systems must undergo, said John H. Neugebauer, CEO of Koning. That would allow speedy commercialization of the product. There are many instances in which other companies have done exactly that.

Whole-body CT was used as a precedent for CT systems dedicated to dental, head, and surgical applications, he said. MR devices have broadened their applications from general to breast-specific imaging, such as the dedicated device made by Aurora Imaging Technology. PET has achieved the same expansion with a dedicated breast imager from Naviscan PET Systems. All have been cleared through the FDA's 510(k) process.

"We hope it goes in this direction for market clearance, but it is up to the FDA, not us," he said.

Product labeling will make a big difference. The system will be marketed as a diagnostic rather than a screening tool. This should help make the case for 510(k) clearance, Neugebauer said.

Although optimized for breast imaging, the conebeam scanner might also be used to scan extremities, including hands and feet. The FDA submission will likely include these indications, he said.

The system is likely to be expensive, at a cost of about $800,000, but this price could decrease as the number of systems manufactured increases, according to Neugebauer. Maintenance is expected to be half of the cost of upkeep for a general-purpose CT, as the Koning system relies on a standard mammography x-ray tube.

Even at its initial price, however, the Koning CT costs only about 25% more than current digital full-field diagnostic mammography systems, which cannot perform volumetric reconstructions. These will be possible with digital mammography systems outfitted to support tomosynthesis, during which multiple exposures are acquired across an arc of a compressed breast. Hologic, GE, and Siemens are each developing such units.

Koning's system does tomosynthesis one better, however, in that it makes a full 360 degrees turn around the breast, capturing an entire volume and creating truly isotropic voxels, which are equal in size in all planes, Neugebauer said.

"This leads to very high spatial resolution," he said.

Dose will be approximately equivalent to a two-view mammogram, Neugebauer said. Unlike conventional CTs, chest tissue other than the breast largely avoids x-ray exposure, thanks to the horizontal gantry.

Images will be presented in 2D multislice, multiplanar, and 3D formats. A later version of the device, due for market about a year after the first, will support stereotactic biopsy. Both configurations are being designed to fit into a room no bigger than one needed to house a mammography system.