Medical Device Daily

Mayo Clinic (Rochester, Minnesota) researchers reported last week that they have had success in finding smaller tumors in breasts than are typically found with mammograms using a specially designed gamma camera for molecular breast imaging.

The researchers reported the findings on the gamma camera, which would provide an alternative to mammograms, particularly in women with dense breast tissue, in a report in the January issue of Mayo Clinic Proceedings.

“By optimizing the camera to detect smaller breast lesions, this technique should aid in the detection of early stage breast cancer, something that was not possible with conventional gamma cameras,“ said Michael O'Connor, PhD, Mayo Clinic radiologist.

The camera, provided to Mayo about two years ago by GE Healthcare (Waukesha, Wisconsin), is a CZT (cadmium zinc teluride), or crystal, detector that was provided for the center to evaluate for breast imaging, Douglas Collins, MD, also a Mayo Clinic radiologist, told Medical Device Daily.

The CZT detector was put on a gantry and on a modified mammography unit.

The researchers' study began at that time and “slowly accrued“ 40 patients, Collins said. Ninety-six patients are now involved in the study, he said, noting that “It has really taken off.“

In the study, 40 women with suspicious findings on mammogram underwent molecular breast imaging. Twenty- six women had 36 malignant lesions confirmed at surgery. Molecular breast imaging detected 33 of the 36 lesions. In addition, the researchers said, four cancers were detected that were not seen on mammograms.

Stephen Phillips, MD, another Mayo Clinic radiologists involved in the study, said the technique yielded the “highest sensitivity yet reported for a gamma camera“ in the detection of small breast tumors of less than 1 centimeter, reporting an 86% rate of detection, or 19 of 22 cancers.

One key feature that distinguishes the technique from mammography, according to Mayo, is that it relies on differences in the metabolic behavior of tumors vs. normal breast tissue. In contrast, it said, mammography relies on differences in anatomic appearance of tumors vs. normal tissue, differences that can often be subtle and obscured by densities in the surrounding breast tissue.

“Mammographers do a lot of mammography in very dense breasts, and we know we miss a lot of cancers, so in dense breasts, it's not uncommon that these tumors are very large,“ Collins told MDD. “So, our goal is to try to find cancers two centimeters or less, hopefully at a centimeter or less. And for all tumors that were a centimeter or above . . . we found all of them [using the CZT camera].“

Although traditionally younger women have proved to have dense breasts, the advent of postponed childbearing until later years, as well as hormone therapy and the overall aging population has meant that it is not uncommon to find women in their 60s and 70s with dense breasts, Collins said. He estimated that 25% to 40% of women have dense breast tissue.

The American College of Radiology (Reston, Virginia) has four categories for density in breasts studied with mammograms, with D1 being the most clear breast tissue and therefore the easiest in which to find tumors. That goes up to D4, which means there is very dense breast tissue.

With the CZT camera, a cardiac drug modified for cardiac imaging was used. Collins explained that all people are made of molecules, and “every disease process is essentially a metabolic process,“ which means that the body is metabolizing molecules. In molecular breast imaging, the process involves injecting a molecule, or the imaging drug, and tumors metabolize that molecule.

“With this new camera and with nuclear medicine, we are very sensitive at finding very low concentrations of a molecule that concentrates in tumors,“ Collin said.

Those tumors found included some at 4 mm and 5 mm in size. Depending on the color of the screen, those tumors, or “hot spots,“ show up as a black dot on a white screen or a white dot on a black screen.

“It's amazing how conspicuous or obvious that spot is,“ said Collins.

In one example he experienced, Collins said one patient had a known breast cancer in her right breast. But using the camera, the researchers also found a 1 cm tumor in her left breast, to their surprise.

“It would have been completely missed and blown by because we just couldn't see through the breast tissue with a mammogram,“ he said.

Deborah Rhodes, MD, the Mayo Clinic physician who led the study, said the study's “early results suggest an important role for molecular breast imaging in filling this gap“ for women with dense breasts.

The camera is the only one of its kind at present, but the researchers hope that their work can be expanded to other medical centers to further explore molecular breast imaging.

Collins, who said he anticipates the growth of molecular breast imaging, said he expects that the cost of an evaluation using the CZT camera would be much less than MRI. While an MRI of the breasts costs about $4,500 — something he noted that Blue Cross and Blue Shield has recently agreed to cover — he suggested that the cost using the CZT camera would range from $500 to $1,000.