| Positron emission mammography | |
|---|---|
| Two PEM images, including sites of tracer uptake | |
| Purpose | imaging modality used to detect breast cancer |
Positron emission mammography (PEM) is a nuclear medicine imaging modality used to detect or characterise breast cancer. [1] Mammography typically refers to x-ray imaging of the breast, while PEM uses an injected positron emitting isotope and a dedicated scanner to locate breast tumors. Scintimammography is another nuclear medicine breast imaging technique, however it is performed using a gamma camera. Breasts can be imaged on standard whole-body PET scanners, however dedicated PEM scanners offer advantages including improved resolution. [2] [3]
PEM is not recommended for routine use or for breast cancer screening, in part due to higher radiation dose compared to other modalities. [4] Compared to breast MRI, PEM offers higher specificity. [5] Specific indications can include "high-risk patients with masses > 2 cm or aggressive malignancy and serum tumor marker elevation". [6] [7] 18F-FDG is the most common radiopharmaceutical used for PEM. [8]
PEM uses a specialised scanning system. Though some systems resemble a small PET scanner with a ring of detectors, others consist of a pair of gamma radiation detectors placed above and below the breast. [9] [10] On these systems, mild breast compression is applied to spread the breast and reduce its thickness. The detection process is identical to standard PET scanners. Positrons emitted by the injected 18F-FDG annihilate on interaction with electrons in tissue, leading to the emission of a pair of photons travelling in opposite directions. The detection of two simultaneous photons indicates the emission of a positron at a point on the line linking the two detection events. An image is the reconstructed from the collected emission data. [11] [1]
Mammography using positron emitters was first proposed in 1994. [12] PEM is now approved in the United States and Europe for post-diagnosis imaging, with multiple commercial systems available. [13] [14]
This article incorporates public domain material from Dictionary of Cancer Terms. U.S. National Cancer Institute.