Breast Imaging Innovation Evokes View-Master, 3D Movies

David J. Getty, Ph.D., tests the stereoscopic system he helped to develop to aid radiologists in seeing the internal structure of the breast. Stereoscopic digital mammography acquires two digital radiographs of the breast, separated by about 8 degrees. The mammographer's visual system can then fuse the images at the workstation to view the breast in 3D. Photo courtesy of BBN Technologies.

Researchers at Emory University Breast Clinic in Atlanta report using 3D technology to help detect more breast cancers with fewer false positives.

The new stereoscopic digital mammography system is very much like seeing a picture from the View-Master children's toy or while wearing polarized 3D glasses, said lead researcher David J. Getty, Ph.D. "The image just leaps out at you," he said.

In an RSNA 2007 presentation, "Improved Accuracy of Lesion Detection in Breast Cancer Screening with Stereoscopic Digital Mammography," Dr. Getty discussed interim results of an ongoing clinical trial. He is a division scientist at BBN Technologies of Cambridge, Mass. BBN Technologies and Planar Systems developed the stereoscopic system to help radiologists see the internal structure of the breast.

Stereoscopic digital mammography acquires two digital radiographs of the breast, separated by about 8 degrees. The mammographer's visual system can then fuse the images at the workstation to view the breast in 3D. In the study presented by Dr. Getty, researchers used a full-field digital mammography unit slightly customized to acquire images in pairs.

"Standard mammography is one of the most difficult radiographic exams to interpret," said Dr. Getty, who has been developing the project for 12 years. "In a 2D image of the breast, subtle lesions may be masked by underlying or overlying normal tissue and can be missed. Normal tissue located at different depths can align, mimicking a lesion, leading to false-positive findings."

80 Percent Reduction in Missed Lesions Reported

As of July 2007, 1,093 patients at elevated risk for developing breast cancer were enrolled in the study. Each patient received full-field standard mammography and a full-field stereoscopic digital exam. Images were interpreted independently by different radiologists. In all, 259 suspicious findings were found by one or both procedures. Additional diagnostic tests, including biopsy, were also administered.

Of the 259 suspicious findings, 109 were true lesions. Standard mammography missed 40 of the 109 while the stereoscopic exam missed 24. Standard mammography missed 20 of 41 calcifications while stereo mammography missed only four—an 80 percent reduction in missed lesions.

The findings suggest that stereo digital mammography could lead to earlier detection of cancer, said Dr. Getty. "A small percentage of the additional lesions missed by standard mammography but detected by stereo mammography will turn out to be cancerous," he said.

There were 150 false positives among the 259 suspicious findings. Standard mammography detected 103 and stereo mammography 53. "Stereo digital mammography reduced false positives by 49 percent," said Dr. Getty. "This could have a significant impact by cutting in half the number of women who are needlessly recalled for additional diagnostic workups, resulting in reduced costs and reduced patient anxiety."

The trial recently ended with close to 1,500 women at elevated risk of breast cancer having received both screening exams. Final results will be issued soon, Dr. Getty said.

Equipment Advances Facilitate Stereo Technique

Institutions interested in participating in such research could easily update their equipment at a relatively low cost, said Dr. Getty. For the Emory study, researchers modified a collimator to improve the image. "With minor changes, most digital mammography equipment, or even a film mammography unit equipped with a digital cassette, is perfectly capable of taking stereo images," he said.

Other hospitals seeking to acquire the stereoscopic equipment may soon get help from manufacturers. Dr. Getty said three manufacturers are creating breast tomosynthesis machines with motorized movement of the X-ray tube, making it possible to automatically acquire stereo image pairs.

While the breast tomosynthesis unit could be used to acquire stereo mammograms, the basic intent of breast tomosynthesis is to reconstruct a stack of image sections through the breast, very much like a breast CT, said Dr. Getty. He said he now looks to improve standard scrolling through the stack of image sections by giving radiologists a stereo view through the volume of sections. If the technology works, he said, radiologists could selectively view only a “slab” of sections, rendering the remainder of the breast “invisible.” The slab could be moved interactively through the volume and the radiologist could even move the stereo point-of-view around to look at the tissue from different directions, he said.

"This could be incredibly powerful, with stereo viewing complementing the strengths of the viewing of individual tomosynthesis sections," Dr. Getty said. "The possibilities are very exciting."

Concern Raised Over Increasing Number of Radiologic Exams on Pregnant Women

Another study presented at RSNA 2007 indicated that the number of imaging studies using radiation in the pregnant population jumped by more than 125 percent in the last decade.

Elizabeth Lazarus, M.D.

Elizabeth Lazarus, M.D., discussed the results of the 10-year retrospective study to document the utilization of radiologic examinations in pregnant women at the Warren Alpert School of Medicine at Brown University in Providence, R.I.

Concerns about radiation exposure, imaging overuse and rising healthcare costs make it important to track utilization patterns, said Dr. Lazarus, and the pregnant population is of particular concern. "This patient population is vulnerable to adverse effects created by increased radiation," she said. "Fetal risks include central nervous system defects, increased incidence of childhood leukemia and other malignancies. There is a maternal risk associated with breast radiation."

At Brown University, every pregnant woman exposed to radiation during an imaging exam—whether an inpatient, outpatient or emergency department patient—is recorded in a database. A technologist completes a form for each one who receives a study with ionizing radiation and an estimated fetal radiation dose is calculated by a physicist. The forms are kept as a permanent record.

According to the study, 5,235 radiology examinations were performed on 3,249 pregnant patients between 1997 and 2006. Imaging tests included in the study were plain film radiography, nuclear medicine exams and CT. Fluoroscopy and interventional radiologic procedures were initially counted but later eliminated due to the small number of exams.

While the number of deliveries rose from 8,661 to 9,261, or 7 percent, during the study period, the number of pregnant patients increased by 94 percent and the total exam volume increased 125 percent.

The average yearly percent change was 6.8 percent for plain film and 17 percent for nuclear medicine, said Dr. Lazarus. The greatest average change, she said, was for CT at 25 percent each year. CT also results in the greatest amount of radiation exposure, she noted.

For all exams, the estimated radiation doses ranged from <0.01 to 40 mGy. These doses are below the medically allowable threshold during pregnancy of 50 mGy, said Dr. Lazarus.

"The two types of CT exams that have increased the most in utilization during our study, head and CT pulmonary angiography, have the lowest radiation doses to the fetus," she said. However, CT of the abdomen and pelvis with fetal exposure, averaging 20 mGy, also had large increases in volumes, she said.

"Doctors should use this information to explore other imaging modalities that don’t impart radiation," Dr. Lazarus said. "While CT can be a safe, effective test, pregnant patients should ask their doctors about other imaging or diagnostic tests that will not expose the fetus to radiation."

Dr. Lazarus said she hopes other institutions look at their own statistics as well. "I'm interested to see if they can duplicate them or if they come up with different results," she said.

The abstract for "Utilization of Radiological Examinations in Pregnant Women: A Ten Year Review–1997-2006" is available at RSNA2007.RSNA.org/rsna2007/v2007/conference/event_display.cfm?em_id=5001944.