Although breast MRI is an increasingly common complement to mammography because of its sensitivity in detecting suspicious lesions missed by mammography, two molecular imaging techniques—positron emission mammography (PEM) and breast specific gamma imaging (BSGI)—are moving up the ranks due to greater physiological detail and spatial resolution both techniques offer.
Imaging the uptake
“The problem with breast MRI is that it causes a lot of false alarms that result in increased patient anxiety, something not found with PEM for preoperative surgical staging,” says Kathy Schilling, MD, medical director of breast imaging and intervention at the Center for Breast Care at Boca Raton Community Hospital in Florida, which utilizes the Naviscan PEM scanner. She has seen breast MRI result in a number of prophylactic mastectomies—something that
PEM could possibly help cut down the prevalence of in the future.
PEM measures the accumulation of F-18 bound to FDG within cancer cells in an exam that takes about 40 minutes to complete (10 minutes per image). With a spatial resolution of 1.5 to 2 mm, it is the highest resolution biochemical modality that images breast ductal structures. “It’s about finding out how cancer cells function differently than normal cells,” Schilling says.
But PEM will not replace mammography or breast MRI; rather it will act as a complementary imaging technique, she notes. In 2008, Schilling presented the results of a study comparing whole-body PET, PEM and MRI for presurgical staging at the Radiological Society of North America (RSNA) meeting, which found that PEM had a higher specificity (73 percent) compared to MRI (43 percent) in detecting ductal carcinoma in situ. The findings, which were unaffected by menopausal status or breast density, suggested that in the future, PEM could be good for screening highest risk patients—BRCA1 and BRCA2—resulting in fewer unnecessary biopsies. However, biopsies are still sometimes required with PEM. Naviscan has FDA approval for breast PET-guided biopsy to localize lesions. With this capability, physicians can guide compatible interventional devices towards abnormalities visible on PET.
Getting specific with BSGI
Gamma imaging, a molecular-based tool that has been around for years, is re-emerging with renewed vigor as breast specific gamma imaging. With BSGI, the patient receives technetium 99 sestamibi; cancerous cells absorb more and appear as “hot spots.”
In women recently diagnosed with breast cancer, further testing using BSGI may find additional cancer in the same or opposite breast, with fewer false positives, according to a study published in February in the American Journal of Surgery. The researchers also found that BSGI is helpful in patients with dense breast tissue when additional evaluation of the remaining breast tissue is necessary.
Montgomery Breast Center in Alabama has been utilizing BSGI via the Dilon 6800 camera for the last year for a variety of reasons—including screening high-risk patients and patients with extremely dense breasts. “Mammography doesn’t detect up to 40 percent of lesions in dense breasts, which is unacceptable,” says Medical Director Cynthia Lorino, MD.
BSGI overcomes some of the inherent problems of breast MRI, such as the inability to image patients with pacemakers; claustrophobic patients; problems with pre-certification and, of course, the false positives.
However, BSGI, along with any other breast imaging study, “cannot be done in a vacuum. I have to have all available information from mammography, ultrasound, PET or breast MRI to come to the best decision for the patient,” Lorino says.
In an age of personalized medicine, having the right tools help to better assess patient treatment responses. “It’s an exciting time in breast imaging as we have a lot of new tools to help us find breast cancers earlier and earlier—even before they develop—and be able to offer our patients treatment or prophylactic options they never had before,” Schilling adds.