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]
Positron emission mammography | |
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Purpose | imaging modality used to detect breast cancer |
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.[citation needed] 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.[9][10]
Mammography using positron emitters was first proposed in 1994.[11] PEM is now approved in the United States and Europe for post-diagnosis imaging, with multiple commercial systems available.[12][13]
This article incorporates public domain material from Dictionary of Cancer Terms. U.S. National Cancer Institute.