Women's Imaging

What is PEM?

PEM or Positron Emission Mammography is a relatively new imaging technology, very similar to PET—Positron Emission Tomography, in which an intravenous injection of a glucose based radioactive tracer (18F-FDG) is used. The FDG collects in inflammatory and cancerous cells because they have a higher metabolic rate than normal cells. However unlike a whole body PET scan which scans the whole body, PEM uses mild compression to capture localized images of the breasts or other small body parts producing very sharp, detailed images of abnormal tissue. With the close proximity of the detector heads, PEM allows visualization of cancers as small as 1.5—2 mm.

Studies have shown that the PEM’s sensitivity and specificity for characterizing suspicious lesions are both greater than 90%. Furthermore, the system has a positive predictive value of 92% for identifying breast cancer.

WHAT ARE THE BENEFITS OF PEM?

PEM serves as a legitimate substitute for patients who cannot undergo breast MRI for reasons including certain metallic or electronic medical implants, claustrophobia, or obesity.

PEM is particularly helpful in cases involving women with dense breast tissue that can make tumors hard to spot. In such patients, mammography has limitations in specificity and sensitivity.

Ultrasound can provide good anatomical information about where in the breast a tumor is located, but density still poses a challenge.

In patients with dense breasts, MRI may be the more viable alternative as it achieves a higher sensitivity. But it has a lower specificity which means MRI has a higher false positive rate.

Before surgery is undertaken, PEM provides physicians with one more imaging analysis to help determine whether there is multifocality and multicentricity.

HOW SHOULD THE PATIENT PREPARE FOR THE PROCEDURE?

Patients should not eat or drink for 6 hours prior to the exam, except for water and medications. Diabetic patients should discuss specific diet and glycemic medication guidelines with their physician to control glucose levels the day of the test. Patients should avoid heavy physical activity, alcohol, caffeine, nicotine and other stimulants for 24 hours prior to the exam. One should wear comfortable, loose-fitting clothes without metal for the examination. Female patients should be certain they are not pregnant for the examination, even if it requires having a pregnancy test. All patients should bring any pertinent outside imaging studies to MDR at the time of the exam to ensure the most accurate interpretation possible.

WHAT SHOULD THE PATIENT EXPECT DURING THE PROCEDURE?

About 1 hour prior to the actual scanning, the nurse or technologist will take a drop of blood from the patient’s finger to test the blood sugar level. Following the blood test, a radioactive compound, 18-fluorode-oxyglucose or 18-FDG, will be injected intravenously. There is no risk of allergic reaction or side effects of the radioactive substance.

The compound is similar to glucose, or normal blood sugar, and will be taken up by both normal and abnormal tissues according to their metabolic rate. More metabolically active tissues, such as tumors, will accumulate more radioactivity and will appear as a “hot spot” on the scan.

It takes approximately 45 minutes for the 18-FDG to be adequately taken up by the body. During this time, the patient is instructed to remain still, so as to avoid any excessive muscle uptake, which may make interpretation of the scan difficult.

If the patient is having a whole body PET scan along with the PEM scan, the whole body PET will be performed first.

The patient will be directed to the PEM scanning room and seated in a chair. The technologist will scan each breast separately, positioning each in the PEM scanner as for a mammogram but using far less pressure than a mammogram. Each breast will be gently immobilized for approximately 10 minutes per scan with multiple scan performed.

The images are then processed and displayed on a computer for evaluation by the radiologist. There are no restrictions on daily routine after the test, although you should drink plenty of fluids to flush the radioactive substance from your body.