Molecular breast imaging proves effective and less expensive than MRI for women with dense breast tissue.
It can be tough being the new modality on the block—even more so if it’s a new breast imaging technique. This is due in part to safety and economic factors—including cost and reimbursement issues—that make women’s imaging among the most challenging in the entire health care enterprise.
But molecular breast imaging (MBI) is proving itself to be a valuable adjunct to traditional mammography for women with dense breasts. And research indicates it is effective for finding cancers in all women regardless of breast density.
Even more important is the fact that the radiation dose is only slightly higher than that of a traditional mammogram and that it costs significantly less than an MRI, which in many institutions is the current go-to adjunct screening method.
Although MBI is fairly new, the concept is decades old.
Birth of a New Modality
According to Michael K. O’Connor, PhD, FAAPM, professor of radiologic physics at the Mayo Clinic, Rochester, Minn, research into what became MBI started in the 1990s.
The technology, called scinti-mammography, used a conventional gamma camera and even had a radioisotope approved by the US Food and Drug Administration (FDA). Unfortunately, the technology didn’t work because the resolution of the conventional gamma camera was inadequate to visualize small tumors. In addition, the dose was 10 times as much as a mammogram. And that cast a pall over the more effective and safer MBI of today. “People remember that nuclear medicine [for breast imaging] didn’t work,” said O’Connor. “But it was the technology that was bad, not the technique.”
The breakthrough that led to MBI’s success came by accident, said Craig Thiessen, MD, director of radiology at West Houston Radiology, LLP, and North Cypress Medical Center in Houston. Radiologists noticed that when they were imaging women using sestamibi, they would also occasionally find that it would light up breast tissue. Upon querying the women, the radiologists often found that the patient had either a suspected cancer or had been diagnosed with breast cancer.
Research followed, which led to FDA-approved systems from Dilon and Gamma Medica. Both of these systems have solved the dose problem, are catching more cancers earlier, and, best of all, are more economical than MRI.
A Tale of Two Systems
Thiessen has worked primarily with the Dilon 6800, a digital high-resolution, compact gamma camera optimized to perform breast specific gamma imaging (BSGI), and says that he uses it primarily because of the timing—it was the first system approved for market use. He likes that the device can be positioned right on the breast and that it only has a single detector.
For him, the biggest advantage of Dilon’s system is that he can take a gamma-guided biopsy immediately after a lesion has been detected.
Gamma Medica’s LumaGEM MBI system was approved about a year ago. It features a planar, dual-head, fully solid state digital imaging system, and utilizes cadmium zinc telluride (CZT) technology. The CZT detectors are arranged in a dual-head configuration to optimize detector geometry from the typical 3 to 4 mm resolution expected from such a camera to 1.6 mm. Each square hole in the tungsten collimator is matched with a pixel in the detector and optimized for imaging objects within 3 cm of the collimator surface.
The LumaGEM, like the Dilon 6800, uses technetium-99m (Tc-99m) sestamibi, which concentrates in cells with increased mitochondrial density. While the two systems have some fundamental differences, they both have one big advantage: low radiation dose.
Low Dose, Big Rewards
In a recent presentation at the National Consortium of Breast Centers Annual Meeting, Thiessen noted that both position sensitive photomultiplier tubes (PSPMT) and CZT systems—thanks to improved photon sensitivity—should be capable of reducing BSGI/MBI dosing by 75%. Ironically, this requires an off-label use of the radiopharmaceutical, which makes it unreimbursable.
The radiotracer—sestamibi—is still being dosed at the level it was for cardiology testing, 20 mCi, but Thiessen said that his research has shown that it can be effective with half that rate. The reason: The BSGI/MBI detector is closer to the breast than the cardiac gamma camera is to the heart.
Even still, O’Connor notes that the amount of radiation is still quite low, about twice as much as a mammogram. In his own research, O’Connor has been able to reduce the radiation dose of the LumaGEM and General Electric’s Alcyone MBI system by up to fivefold so that the dose is now comparable to that of mammography.
And because of the higher sensitivity and specificity, women typically don’t have to have the aggressive follow-up—including additional imaging tests—which they had to have before the advent of BSGI/MBI, said Thiessen.
Of course, while safety is one of the biggest pieces of the new technology puzzle for women’s imaging, its effectiveness is the bottom line, since, O’Connor notes, a patient’s fear of cancer will most often outweigh the fear of high radiation dose.
And, according to O’Connor and Thiessen’s research and experience, BSGI/MBI is quite effective.
In a recent article published in the Journal of Nuclear Medicine, MBI was shown to be effective in the preoperative evaluation of women with biopsy-proven breast cancer. Typically, MBI is used as an adjunct for women with dense breasts. This study, which was led by O’Connor, showed that women with normal density could also benefit from adjunct screening by MBI.
A total of 98 patients with biopsy-proven breast cancer were enrolled in the study and underwent preoperative MBI and completed surgical resection. MBI detected additional disease greater than that identified by the combination of mammogram and ultrasound, which altered the surgical treatment in 12 patients. In seven of the 98 patients, MBI detected additional foci of cancer not seen on the mammogram. This resulted in a change in their surgical treatment plan from breast conservation to mastectomy. In these patients, final pathology confirmed that mastectomy was warranted. Contralateral breast cancer was detected in one patient that was not detected with mammography. A second-look mammogram and ultrasound with biopsy demonstrated invasive breast cancer, and the patient underwent surgery on both breasts. Two patients had uptake in the contralateral breast on MBI. Surgical excision demonstrated atypical ductal hyperplasia and atypical lobular hyperplasia. Another patient had an abnormality detected on MBI, which, at the time of the planned bilateral mastectomy, was found to represent an atypical ductal hyperplasia.
The researchers concluded that MBI can detect invasive ductal carcinoma, ductal carcinoma in situ, and invasive lobular carcinoma and can “play a valuable role in evaluating the extent of disease and the presence of multifocal disease in the breast for surgical treatment planning.”
During the Society of Nuclear Medicine’s Breast Imaging Meeting in April 2011, O’Connor and his colleagues presented additional findings about the benefits of low-dose MBI as a diagnostic tool. Of the 440 women screened in this ongoing study, six patients were diagnosed with cancer. MBI detected cancer in five of the six patients and mammography detected none of the cancers. A total of 79 women were recalled for diagnostic evaluation of findings; 35 due to MBI alone, 40 due to incident mammogram alone, and four due to both tests. The reduced dose was comparable to screening mammography.
O’Connor’s research not only has proven the clinical efficacy of MBI, but it has economic implications as well. “When you’re screening earlier, you catch the cancers earlier, when they’re smaller. And the costs of smaller cancers are less,” he said. So, while MBI may cost about 1.5 times more than a standard mammogram, it may have a net savings to the health care enterprise, the patient, and the payor.
Thiessen adds that because MBI has a 98% negative predictive rate, this will cut down, for instance, on unnecessary biopsies. “Every modality has its advantage,” he said. “Breast imaging is like painting a picture, and each modality helps you fill in the background.”
These initial studies make a strong case for MBI as an adjunct screening modality, but it does have competition already from an older, proven imaging sibling—MRI.
Why Not MRI?
O’Connor, who has spent the last decade of his life helping to develop and prove the efficacy of MBI, says that MRI is a “very, very good technique.” It is very sensitive, although its specificity isn’t quite as good. But an experienced radiologist can overcome the specificity issue with experience.
But MRI has one problem that MBI doesn’t have—it’s expensive, about seven times more expensive than mammography, while MBI costs only 1.5 times more than mammography. “If MRI was inexpensive, it would be game over [and we wouldn’t be talking about MBI],” he said.
Ideally, O’Connor would follow this taxonomy when evaluating women for breast cancer: mammography, MBI, and then MRI. However, because it is the established modality, typically MRI follows mammography with only women with dense breasts or other risk factors receiving MBI screening.
Thiessen says that one of the reasons why MRI still is ahead of MBI is because the older modality is a moneymaker and is easier to read. But that’s not the only stumbling block to getting MBI as the go-to adjunct to mammography.
O’Connor’s Mayo radiologist colleague Amy Conners, MD, notes that part of the problem is that there’s still a question as to how MBI fits into the diagnostic algorithm and the technical issues are still being worked out, such as the dose. “How do we prudently and appropriately image patients? We want to get it right and that takes time,” she said.
Thiessen said in his experience it’s a question of logistics. Many nuclear imaging departments are separate from the rest of imaging, and many radiologists aren’t rated to read a BSGI study.
Reimbursement is an issue as well, and because mammography is one of the only tests regulated by the federal government, it may take an act of Congress to finally legitimate MBI—or at least make it easily reimbursable. And that could be “several years away,” said O’Connor.
But these are only hurdles along the way. Thiessen, O’Connor, and Conners all agree on one thing—MBI is here to stay.
Here to Stay
Conners is enthusiastic about the modality. “MBI is generally straightforward and fun to read. Some of the cases can be tricky, but you only get eight images [as opposed to many more for other types of scans] and you get good information from those images. MBI has a lot of potential and could be a really great thing,” she said.
Thiessen sees BSGI/MBI moving more to the forefront and helping to individualize care at the genetic level. “Every individual is different. There’s no doubt in my mind that molecular imaging is the way to go; it’s here to stay,” he said.
O’Connor sees a bright, evolving future for MBI, including new and better radiopharmaceuticals and technological improvements. This includes a new hybrid modality akin to PET/CT. “I think what will happen is that we will develop an MBI/ultrasound with the former looking at the function and the latter at the anatomy,” he said. “No technique is perfect, and the combined effect is better than one by itself.”
C.A. Wolski is a contributing writer for Axis Imaging News.