Breast Density Changes the Breast-imaging Landscape

Cristen Bolan, MS

Disclosures

Appl Radiol. 2013;42(3):20-25. 

In This Article

Where Does MBI Fit in?

With the widespread availability of breast MRI, many radiologists may be wondering where MBI fits in. Much like breast MRI, MBI is a tool that is a supplement to mammography. But where MBI is especially useful in the clinical setting is for imaging patients who cannot have an MRI.

Figure 2.

The Discovery NM750b by GE Healthcare is a dedicated molecular breast-imaging device with solid-state cadmium zinc telluride (CZT) detectors for a compact device, enabling close imaging of the breast up to the chest wall in standard mammographic views.

In the study led by Dr. Berg,[5] she noted, "MRI detected additional invasive cancers not seen on mammography or ultrasound; however, we found that MRI was significantly less tolerable than mammography or ultrasound for many study participants. Of those participants offered an MRI, only 58% accepted the invitation."

Similarly, for patients at Karmanos Cancer Center, Detroit, MI, problems with undergoing MRI were the impetus for seeking out a solution in terms as a multidisciplinary approach to breast cancer. For Sharon Helmer, MD, clinical Service Chief, Imaging Department, and Director, Breast Imaging, Karmanos Cancer Center, 2 key scenarios encouraged her to consider MBI for screening her patients.

"We wanted to use another tool to examine their breasts with MR to see beyond mammography and ultrasound. But I practice with an urban population with rising obesity rates, and we found a significant number of patients who are candidates for MRI, but couldn't have MRI for various reasons: renal function, implants or pacemakers, claustrophobia, and weight issues," explained Dr. Helmer. "We were interested in MBI because about 20% of our patients are high-risk patients with dense breasts, who would normally get a biopsy and an MR for extent of disease."

While the center has a dedicated 3.0T MR, for a large number of patients, doctors could not provide surgeons with additional metabolic information for treatment planning. Therefore, doctors at Karmanos Cancer Center advocated for MBI as a solution, and implemented the Discovery* NM750b, a dual-head CZT unit by GE Healthcare. The CZT detectors fit into a compact device, allowing users to image the breast up close, right up to the chest wall. In a recent study,[9] comparing performance characteristics of dedicated dual-head gamma imaging and mammography in screening women with mammographically dense breasts, researchers found that the addition of gamma imaging to mammography significantly increased detection of node-negative breast cancer in dense breasts by 7.5 per 1000 women screened (95% CI: 3.6, 15.4). However, to be clinically important, gamma imaging will need to show equivalent performance at decreased radiation doses. Regarding radiation, Dr. Helmer points out that recent low-dose protocols developed by the Mayo Clinic have helped in safely conducting MBI procedures.

"The unit provides high-resolution imaging, and great functionality, and the patients are really comfortable walking into a room that looks very much like a mammogram unit. Also, there is very minimal compression of the breast, and the responses from patients have been very positive," said Dr. Helmer.

Both MRI and MBI are indicated for patients who have extremely dense breasts or have a strong family history of breast cancer. According to Dr. Helmer, MRI and MBI serve very similar functions. "MR gives you exquisite anatomic detail, but MBI also captures clear, precise images, even for those with dense breast tissue," she said.

"Obviously, MR gives you chest wall information in addition to the liver, which we can't get with MBI. As a radiologist, you look at all the film. You're not seeing the full extent of the anterior lungs and upper part of the liver that you would be able to include in your assessment on an MR. If the patient has an invasive carcinoma, the patient will be assessed and staged with CT and other exams," said Dr. Helmer.

But she noted that one of the unexpected benefits of MBI is that it is very good for lobular carcinoma. "That's good because often it's difficult to determine the exact extent of disease of a lobular carcinoma on a mammogram and ultrasound. Yet, unlike MRI, MBI is safe for those who have pacemakers, metal implants or other foreign bodies, and patients with renal challenges," she said.

Dr. Helmer believes MBI fits into the niche that complements mammography and ultrasound, and like breast MRI, provides data on the metabolic activity of an abnormality in the breast or an area of interest that may be of concern.

"Compared to mammography, MBI allows better detection of very small lesions in women with dense breast tissue. Not only will this help eliminate false positives, it may help to detect breast cancers earlier when the disease is highly survivable," she said. "It's not a replacement of mammography, but it does offer us another a chance to look at a patient with dense breasts or other problems with the breast. It's another tool in our armamentarium, and it gives us data, much like MRI."

MBI is also useful for following up response to noeadjuvent chemotherapy. "Sometimes when you follow patients with mammography or ultrasound to see response to their chemotherapy, the tumor may not appear that different size-wise because we are not able to really assess how it's responding to the chemotherapy. Whereas with MRI and MBI, we can see that it is less vascular, and that it is responding to the chemotherapy. MBI is a more cost-effective way to do that follow-up," she said.

For Dr. Helmer and the other radiologists at Karmanos Cancer Center, MBI is another tool in their imaging arsenal that enables them to offer more diagnostic and therapeutic services and to give patients more choices for better care.

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