A few years ago, breast MR might have been good to offer-it might even have helped distinguish a women's health center from competitors-but it wasn't essential. That has begun to change, according to Dr. Rebecca Stough, clinical director of Breast MRI of Oklahoma, an outpatient clinic allied with its next-door neighbor, Mercy Women's Center in Oklahoma City.
Although Stough still occasionally scans on a general-purpose MR system, her clear favorite is a unit designed specifically for breast MR. The three acquisitions needed for a diagnostic exam on the 1.5T Aurora take five minutes each. Patients are on and off the table in 20 to 30 minutes.
The system, built by Aurora Imaging Technology of North Andover, MA, features a field-of-view that captures not only the axilla but also tissue in and beyond the chest wall, reaching in some cases all the way to the spine. Image quality has been good enough for Stough to make some unexpected diagnoses.
"I called one referring doctor and said, 'Your patient doesn't have breast cancer, but she does have a dissecting aortic aneurysm,'" she said.
The Aurora brand name hasn't always been held in such regard. The first unit, installed 10 years ago at the University of Texas, was underpowered, operating at just 0.5T. This unit, and those that followed at the same field strength, delivered images of conspicuously poor quality. Over the past several years, however, the system has been overhauled with an emphasis on delivering quality at least as good as the best 1.5T system. This modern configuration of Aurora lists for $1.3 million, about as much as other high-field systems. The dedicated breast MR system, however, is the better deal, said Debbie Thomas, vice president of marketing for Aurora.
"With this, you are getting an entire package designed specifically for breast imaging with CAD software and biopsy capabilities," she said. "You don't have to go further and buy add-on components."
The rejuvenated scanner can do no wrong by Stough, who cites one case after another in which breast MR changed patient management. One patient had a palpable mass negative for cancer on ultrasound and mammography. The lump was negative on MR also, but the other breast, scanned as part of a bilateral exam, showed an 8-mm cancer that was not seen on mammography even in retrospect, she said.
Another patient, who demonstrated a 1.5-cm cancer on mammography and was headed to surgery, was found on MR to have other lesions far away from where the lumpectomy was planned. These were proven cancerous on biopsy.
"She would have had radiation therapy and that would have knocked (the other cancers) back, but it wouldn't have killed them," Stough said. "Eventually, maybe five years from now, when she had brain and liver mets, everyone would have been wondering where they came from."
Driving image quality on the Aurora scanner is a novel commercial technique called bilateral RODEO (Rotating Delivery of Excitation Off-resonance). Using fat-suppressed magnetization transfer contrast, the proprietary pulse sequence, applied after contrast injection, reduces signal from normal ductal tissue and avoids false-positive enhancement from benign lesions and dense fibroglandular tissue.
RODEO excels at detecting two types of cancer that are difficult to pick up with x-ray mammography: ductal carcinoma in situ (DCIS) and lobular breast cancer.
"Because of its high contrast and spatial resolution, our machine can reliably see and determine the extent of both types of cancer," said Dr. Steven Harms, Aurora's medical director, who developed RODEO while serving as the director of imaging research at the University of Arkansas in Little Rock.
DCIS accounts for between 30% and 40% of cancers, according to Harms, who currently practices at the Breast Center of Northwest Arkansas in Fayetteville. Lobular cancer accounts for another 10%.
X-ray mammography picks up DCIS only if the disease is accompanied by calcifications. An estimated two-thirds of lesions, however, are not calcified. Data gathered by researchers at Memorial Sloan-Kettering Cancer Center in New York City and published in the November 2005 issue of The Breast Journal indicate that MR's sensitivity for DCIS is 88% versus 27% for mammography. Other published studies show a range from 20% to 95% in MR sensitivity for DCIS. This wide range may be due to differences in the acquisition technique as well as interpretation.
Advanced reconstruction software built into the Aurora scanner provides 2D and 3D renderings available simultaneously on split-screen displays. CAD software developed by Aurora further boosts productivity, according to Stough. But CAD takes the radiologist only so far. Morphology brings the diagnosis home.
"Is it smooth? Is it spiculated? Is it linear beaded or clumped? The appearance is what shows the most malignant characteristics," she said.
In cases with a high likelihood of cancer, Stough and colleagues move the patient to biopsy to confirm their diagnoses. But they also use MR to reduce the number of biopsies, when patients show negative diagnostic mammography and ultrasound.
"We use it to confirm a diagnosis when we are almost sure the lesions are benign, rather than doing three or four or five biopsies," she said.
Breast MR might only be starting to catch on in other parts of the country, but in Stough's backyard it is a routine approach. Whether proving the absence of disease, finding its extent, or uncovering cancer as an incidental finding, the value of MR can be summed up in one word. "Essential," Stough said.
