What is Molecular Breast Imaging? Purpose, Procedure & Results

Molecular breast imaging (MBI) is a specialized nuclear medicine scan that can detect breast cancer by highlighting areas where cancer cells are actively growing. This gentle imaging technique uses a small amount of radioactive tracer that's drawn to cancer cells, making them visible on special cameras that can spot problems regular mammograms might miss.

Think of MBI as giving your doctor a different lens to look through. While mammograms show the structure of your breast tissue, MBI shows the activity happening within your cells. This makes it particularly helpful for women with dense breast tissue, where cancers can sometimes hide behind normal tissue on standard mammograms.

What is molecular breast imaging?

Molecular breast imaging is a nuclear medicine test that uses a radioactive tracer to find breast cancer cells. The tracer, called technetium-99m sestamibi, is injected into your arm and travels through your bloodstream to areas where cells are dividing rapidly, which often indicates cancer.

The test works because cancer cells typically absorb more of the tracer than normal breast tissue. Special gamma cameras then capture images of this tracer distribution, creating detailed pictures that show your doctor exactly where any suspicious activity might be occurring. This process is completely painless and doesn't require any compression of your breast tissue.

MBI is also sometimes called breast-specific gamma imaging (BSGI), though the technology and approach are essentially the same. Both terms refer to this gentle, effective way of screening for breast cancer that complements your regular mammogram.

Why is molecular breast imaging done?

Your doctor might recommend MBI when you have dense breast tissue that makes mammograms harder to read accurately. Dense tissue appears white on mammograms, and so does cancer, which means small tumors can sometimes be missed in these cases.

MBI is particularly valuable for women who have an increased risk of breast cancer but aren't candidates for MRI screening. This might include women with a family history of breast cancer, previous breast biopsies showing high-risk changes, or genetic factors that elevate their cancer risk.

The test is also used when doctors need to get a clearer picture of suspicious areas found on mammograms or physical exams. Sometimes MBI can help determine whether a concerning spot is actually cancer or just dense tissue, potentially saving you from unnecessary biopsies.

Additionally, MBI can be helpful for monitoring how well breast cancer treatment is working. The tracer uptake can show whether tumors are responding to chemotherapy or other treatments, giving your medical team valuable information about your progress.

What is the procedure for molecular breast imaging?

The MBI procedure begins with a small injection of the radioactive tracer into a vein in your arm. This injection feels similar to any blood draw you've had, with just a quick pinch from the needle. The tracer takes about 5 to 10 minutes to circulate through your body and reach your breast tissue.

Once the tracer has had time to distribute, you'll be positioned comfortably in a chair next to the special gamma camera. The camera looks somewhat like a mammography machine, but it's designed to be much more comfortable since no compression is needed.

During the imaging, you'll need to remain still while the camera takes pictures from different angles. The entire imaging process typically takes about 30 to 40 minutes, with each view lasting about 8 to 10 minutes. You can breathe normally throughout the procedure.

The cameras will capture images of both breasts, even if only one breast is being investigated. This helps your doctor compare the two sides and ensures nothing is missed. The whole appointment, from injection to completion, usually takes about an hour.

How to prepare for your molecular breast imaging?

Preparing for MBI is straightforward and requires minimal changes to your routine. You can eat and drink normally before the test, and you don't need to stop taking any of your regular medications unless specifically instructed by your doctor.

You'll want to wear comfortable, two-piece clothing since you'll need to undress from the waist up for the procedure. A button-up shirt or blouse makes changing easier than a pullover. The imaging center will provide you with a hospital gown that opens in the front.

It's important to let your healthcare team know if you're pregnant or breastfeeding, as the radioactive tracer could potentially affect your baby. If you're breastfeeding, you may need to pump and discard breast milk for a day or two after the procedure.

Remove any jewelry, especially necklaces or earrings, before the test since metal can interfere with the imaging. You might also want to avoid using deodorant, powder, or lotion on your chest area the day of the test, as these products can sometimes show up on the images.

How to read your molecular breast imaging results?

Your MBI results will show whether the radioactive tracer accumulated in any areas of your breast tissue. Normal results mean the tracer was distributed evenly throughout your breast tissue without any concerning areas of increased uptake.

If there are areas where the tracer concentrated more heavily, these will appear as "hot spots" on your images. However, not all hot spots indicate cancer. Some benign conditions, like fibroadenomas or areas of inflammation, can also absorb more tracer than surrounding tissue.

Your radiologist will carefully analyze these images alongside your mammogram and any other imaging you've had. They'll look at the size, shape, and intensity of any abnormal areas to determine whether further investigation is needed.

The results are typically available within a few days, and your doctor will discuss them with you in the context of your overall breast health. If any areas need further evaluation, your doctor will explain the next steps, which might include additional imaging or a biopsy.

What affects molecular breast imaging accuracy?

Several factors can influence how well MBI detects breast cancer in your specific case. Dense breast tissue actually makes MBI more effective than mammograms, since the nuclear medicine technique isn't hindered by tissue density the way X-rays are.

The size of potential tumors plays a role in detection accuracy. MBI is excellent at finding cancers that are 1 centimeter or larger, but very small tumors might still be missed. This is why MBI works best as part of a comprehensive screening approach rather than as a standalone test.

Certain medications can potentially affect the uptake of the tracer. If you're taking heart medications, particularly those in the calcium channel blocker family, let your doctor know since these might influence how the tracer distributes in your body.

Your recent medical history can also impact results. If you've had a breast biopsy, surgery, or radiation therapy in the past few months, these procedures might cause inflammation that could affect tracer uptake and potentially lead to false-positive results.

What are the risks of molecular breast imaging?

The radiation exposure from MBI is comparable to what you'd receive from a CT scan of your chest. While this is more radiation than a mammogram, it's still considered a low dose and is generally safe for most women when used appropriately.

The radioactive tracer used in MBI has a very short half-life, meaning it breaks down quickly in your body. Most of the radioactivity will be gone within 24 hours, and you'll eliminate the tracer through your normal kidney function.

Allergic reactions to the tracer are extremely rare but possible. The injection site might experience minor bruising or soreness, similar to what you might feel after any blood draw or injection. Serious complications from the procedure itself are virtually unheard of.

Some women worry about the radioactive tracer affecting their family members, but the amount of radiation is so small that no special precautions are needed around family, pets, or coworkers after the test.

When should I consider molecular breast imaging?

You might be a good candidate for MBI if you have dense breast tissue and an elevated risk of breast cancer. This includes women with a strong family history of breast or ovarian cancer, particularly if genetic testing has shown you carry mutations in genes like BRCA1 or BRCA2.

Women who have had previous breast biopsies showing high-risk changes, such as atypical ductal hyperplasia or lobular carcinoma in situ, might also benefit from MBI screening. Your doctor might recommend it if you have multiple risk factors that put your lifetime breast cancer risk above average.

If you've had concerning findings on a mammogram that need further evaluation, MBI can provide additional information to help your doctor determine whether a biopsy is necessary. This can be particularly helpful in avoiding unnecessary procedures while ensuring nothing important is missed.

However, MBI isn't recommended for routine screening in average-risk women. The additional radiation exposure and cost make it most appropriate for women who have specific risk factors or clinical situations that warrant the enhanced detection capabilities.

How does molecular breast imaging compare to other tests?

Compared to mammography, MBI is significantly better at detecting cancer in dense breast tissue. While mammograms can miss up to 50% of cancers in very dense tissue, MBI maintains its accuracy regardless of breast density.

MRI is often considered the gold standard for high-risk breast cancer screening, but MBI offers several advantages. It's more comfortable for many women since there's no need to lie still in a confined space for 30-45 minutes, and it's generally less expensive than breast MRI.

Unlike MRI, MBI doesn't require an IV contrast injection that some people can't tolerate due to kidney problems or allergies. The radioactive tracer used in MBI rarely causes allergic reactions and is processed differently by your body than MRI contrast.

Ultrasound is another tool used to evaluate breast tissue, but it's typically used to investigate specific areas rather than for screening. MBI provides a more comprehensive view of both breasts and can detect cancers that might not be visible on ultrasound.