Breast Positron Emission Tomography 

Updated: May 15, 2018
Author: Thomas F Heston, MD, FAAFP, FASNC, FACNM; Chief Editor: Mahan Mathur, MD 

Overview

Background

Breast positron emission tomography (PET) is an organ-specific high-resolution technology that is used to visualize the metabolism of the breast. PET scanning is a nuclear medicine technique that images the flow of molecules in the body. This is made possible by attaching a radionuclide to a molecule that enters into metabolic pathways; the photons emitted when the radionuclide decays are then imaged. While anatomic imaging allows visualization of body structures, PET molecular imaging allows visualization of molecular flow and metabolic processes within the body.[1, 2, 3, 4, 5]

The primary benefit of PET imaging is that diseases such as cancer often first manifest as disordered metabolism before anatomic changes can be seen.[6, 7] In addition, dense breast tissue or scarring may cause anatomic techniques (mammography, MRI, ultrasonography) to be indeterminate. In such cases, knowing whether an anatomic structure is glucose hypermetabolic can be critical in the determination of proper medical management.[8, 9]

Breast PET typically utilizes the radiotracer F-18 fluorodeoxyglucose (F-18 FDG) to image glucose metabolism[10, 11] ; however, other radiotracers are under development.

Whole-body PET cameras are typically combined with a CT scanner to allow acquisition of anatomic and molecular information from a single procedure. These hybrid PET/CT cameras are donut-shaped. During the procedure, the patient is passed through the central hole of the camera. PET/CT cameras have the detector several centimeters away from the body surface, which limits scan resolution.

While PET/CT cameras are useful for whole-body imaging, breast-specific PET imaging, known as positron emission mammography (PEM), requires the PET camera to be configured like a mammography machine. PEM cameras utilize two small movable flat detectors that are pressed directly against the breast.

The camera technology utilized by PEM has been shown to be more sensitive than whole-body PET/CT imaging in the detection of breast tumors.[1, 4]

Grade III multifocal infiltrating ductal carcinoma Grade III multifocal infiltrating ductal carcinoma as seen on F-18 fluorodeoxyglucose positron emission tomography . This organ specific positron imaging technique results in a much higher resolution (down to 1 to 2 mm) compared to whole body PET/CT imaging.

Indications

Positron emission mammography (PEM) is particularly useful when other imaging scan results are indeterminate. It has a useful complementary role to mammography, ultrasonography, and MRI.

PEM can assist in presurgical planning in breast cancer, monitoring response to therapy, and evaluating for tumor recurrence. In some cases, it may be useful in breast cancer staging and in helping guide breast biopsies.

PEM has a sensitivity and specificity of over 90% in the detection of primary breast cancer.[2]

This image demonstrates the ability of positron em This image demonstrates the ability of positron emission tomography to quickly assess response to chemotherapy, as early as 1 week after the first cycle. (Images courtesy of Mary K. Hayes, MD, Memorial Healthcare System, Hollywood, FL)
This image shows the ability of positron emission This image shows the ability of positron emission mammography to help ensure a breast biopsy is taken in the best location. The most metabolically active tissue needs to be evaluated for malignancy. The top image is obtained right before performance of the biopsy. The bottom image shows the biopsy needle to be properly positioned.

 

Complication Prevention

Because F-18 FDG releases radiation, caution is urged when using in pregnant women or in nursing mothers.[12] Women who are pregnant or breastfeeding will only rarely undergo a nuclear medicine procedure such as F-18 FDG PEM. Although F-18 FDG PEM has not been shown to cause any harm to the fetus or breastfeeding infant, caution is urged.

For pregnant women in whom the benefits of PEM are thought to greatly outweigh any potential risks, the physician may modify the dose of the radiotracer.

Women who are breastfeeding typically will stop breastfeeding for an hour or two after the PEM scan has been completed. After this, breastfeeding is resumed as normal.

Outcomes

When required, a PET-guided breast biopsy has been found to be safe, effective, and associated with only minimal to mild discomfort.[13]

The camera technology utilized by PEM has been shown to be more sensitive than whole-body PET/CT imaging in the detection of breast tumors.[1]

PEM has a sensitivity and specificity of over 90% in the detection of primary breast cancer.[2]

In a retrospective study, Satoh et al determined that whole-body total lesion glycolysis (WTLG) on FDG PET/CT images is an independent prognostic factor for survival in breast cancer patients who have metastases on initial presentation.[14, 3, 15]

Although very rare, hypersensitivity allergic reactions to the radiotracer can occur.

 

Periprocedural Care

Patient Education & Consent

Prior to undergoing any medical procedure, patients need to be fully informed as to how to prepare, what to expect during the procedure, and the clinical benefits of the procedure. The alternatives, benefits, and risks should be fully understood.

Patient Instructions

Patients undergoing F-18 FDG PEM need to fast for 4-6 hours prior to the procedure.

Patients with diabetes should ensure that their blood sugar levels have been under control for several days before undergoing PEM. If it is elevated, the scan may need to be rescheduled. Following a low-carbohydrate, high-protein diet for a day or two prior to the scan is also recommended. After the procedure is completed, no further special precautions need to be taken.

 

Equipment

Breast PET scanning is currently performed with a portable PET camera, which consists of two flat camera plates between which the breast is placed during scanning. The camera plates are mobile in order to allow different imaging positions. The field of view is approximately 16 cm x 24 cm, and the spatial resolution is about 1-3 mm. Although the imaging plates are flat, 3-dimensional tomographic images are obtained.

PET scanners work by detecting photons released after a positron decay particle from the radionuclide annihilates with an electron. When the photons strike the detection crystal, a small amount of light is emitted. This light is then converted to digital form for interpretation. Currently, pixilated lutetium yttrium orthosilicate (LYSO) crystals are used for photon detection.[16]

 

Technique

Breast Positron Emission Tomography

Upon arrival at the clinic, the patient’s blood sugar is checked. If it is elevated, the scan may need to be rescheduled. If it is in an acceptable range (generally 7-8 mmol/L, ≤140 mg/dL), the patient is injected with approximately 370 MBq of F-18 FDG.

After tracer injection, the person will rest quietly for about an hour, to give time for the radiotracer to be taken up by hypermetabolic tissue.

After this uptake period, bilateral 10-minute craniocaudal and mediolateral oblique images of the breasts are obtained.[17]

 

Questions & Answers