Early detection of breast cancer offers the best opportunity to find and treat small lesions before cancer spreads. However, the pinch that occurs when breasts are squeezed between two plates during a mammogram is enough to make some women avoid this potentially life-saving screening procedure.
A new approach to breast imaging – a dedicated breast scanner based on computed tomography (CT) – may someday offer women pain-free screening as well as more precise diagnosis and treatment options. Using x-rays taken from many different angles, breast CT provides a three-dimensional image of the breast using the same amount of radiation as that used for a mammogram. The scanner system, developed by researchers at the University of California, Davis (UC Davis), images the breast using cone beam geometry, a technique that radiates only the breast, protecting surrounding tissue in the lungs, heart, and back.
In order to be scanned, a woman lies face down on the special CT scanner table and places one breast through an opening in the table. The CT scanner and detector rotate 360? around the pendant breast, gathering 500 images. Data are sent to a computer that compiles the cross-sectional slices into a single three-dimensional image. “We can look at the breast from any angle using the same data set,” says UC Davis Medical Physicist John Boone, principal investigator of the project.
Potential Screening Tool
As a potential screening tool, the breast CT scanner surpasses conventional mammography in several ways: it provides three-dimensional images of the breast compared with just two-dimensional images for mammography, eliminates compression of the breast between two plates, and eliminates image artifacts (suspicious areas that result from normal breast structures overlaying each other when the breast compresses). Women with dense breasts may particularly benefit from this more detailed imaging, since dense breast tissue can obstruct lesions.
In a recent clinical study, Boone, collaborator Dr. Karen Lindfors, Chief of Breast Imaging at UC Davis, and their team showed that CT scans are comparable to x-ray mammography in identifying cancerous lesions. Additionally, women in the study found the CT technique significantly more comfortable. “We can see masses better than with mammography because there is no overlapping tissue. This improved clarity could reduce the number of women called back for further evaluation,” says Lindfors.
The study also found that mammography was better at distinguishing microcalcifications, tiny clusters of calcium that indicate breast cell activity and can sometimes be a sign of cancer. Imaging these clusters presents a challenge, but is a key to transforming the system into a viable clinical screening tool. “The third generation scanner will do better at identifying microcalcifications,” Boone says. “We’re hopeful the system can be used for screening, but the real niche may come in the area of diagnostics and therapy.”
Breast Imaging Suites
Boone envisions a breast imaging suite where women could be screened and, if needed, receive care the same day. Currently, clinics may have 8 to 10 mammography systems and a stereotactic biopsy machine. Women with suspicious lesions are often sent for further evaluation at a magnetic resonance imaging (MRI) facility where they compete for appointment times with patients waiting to have their knees, heads, and other body parts imaged. Getting an appointment can take up to 2 weeks, and the imaging is performed by an MR technologist rather than a breast imaging technologist. “A dedicated breast CT scanner in the breast center would allow imaging to be performed by a technologist familiar with the breast, and the breast could be biopsied immediately if needed,” says Boone. Lindfors adds that with contrast injection (a dye that enhances images) CT results would be equivalent or superior to breast MRI for staging tumors and screening for high-risk patients.
A dedicated scanning system could be a workhorse in a breast imaging suite, Boone says, since it could provide breast imaging as well as robotic biopsy guidance and therapies such as tumor ablation (destruction). To perform a biopsy, a radiologist could use the CT images to guide a needle holder into place near a tumor. A hollow biopsy needle would then be inserted into the holder and a core sample of the tumor removed. For tumor ablation, the CT images would provide a more precise method to visualize tumor location and guide a needle into place to deliver radio waves that destroy the tumor. He also notes that CT scans would be less expensive and more easily available than breast MRI. CT’s open design would also permit the use of metal needles and would reduce claustrophobia (fear of enclosed spaces), an impediment to imaging sometimes associated with MRI scanners.
New Ways of Seeing the Breast
Extending their work, the researchers, in collaboration with UC Davis PET physicist Ramsey Badawi, have developed a hybrid CT/positron emission tomography (PET) scanner that could determine the extent or progression of tumors (staging), monitor response to chemotherapy, and provide interventional procedures such as biopsy and tumor ablation. As with the breast CT scanner, images from the hybrid system would guide a radiologist’s needle to the tumor site for core sample removal or delivery of radio waves to destroy a tumor. Boone and Lindfors imaged their first patient in December and are continuing to gather preliminary data on the system. “We’re really in our infancy with all of this,” says Lindfors. “We still need to have trials with multiple observers and equipment at multiple sites.” Only a handful of groups are working on similar systems, including researchers at M.D. Anderson, the University of Rochester, the University of Massachusetts, Worcester, and Duke University.
Boone expects that within 3 to 5 years, the device could be available as a diagnostic tool. “This has the potential to replace the way we do breast imaging for cancer,” he says.
This work is supported by the National Institute of Biomedical Imaging and Bioengineering.
Lindfors KK, Boone JM, Nelson TR, Yang K, Kwan ALC, Miller DF. Dedicated breast CT: Initial clinical experience. Radiology. 2008 Mar 246(3):725-33. Published online before print January 14, 2008.