In January of 2011, Radiology magazine released results of an NIH study indicating a new technique, Positron Emission Mammography (PEM) as being more accurate in identifying cancerous and benign breast lesions than breast imaging using MRI. PEM’s 13% higher PPV (Positive Predictive Value) results in a possible reduction in unnecessary breast biopsies.1 Not only can this mean a reduction in patient trauma, but could significantly lower costs associated with breast cancer detection and staging.
PEM Effective Dose (2)
PEM uses dedicated scanners (manufactured by Naviscan since 2007) and F18 labeled FDG to determine the metabolic activity of suspicious lesions in the breast. PEM scanners are similar in size to an ultrasound machine, with 16cm x 24cm FOV and spatial resolution of 2mm. Using a 10mCi dose, Whole Body Radiation Dose has been calculated at 6.2 to 7.1 mSv (effective dose)2 which is comparable to that of a chest, abdomen, or pelvic CT, and is 23 times higher than the effective dose of an Xray mammogram (0.44 to 0.56 mSv).3 This could be the primary reason that PEM is currently being used for staging and assessment after a breast cancer diagnosis, and is not being used as a screening tool.
One way to decrease the effective dose received in PEM would be to decrease the dose of F18 FDG administered for the study. Although most US sites currently use 10mCi doses, studies with phantom imaging have determined that doses as low as 3mCi could be administered without losing accuracy in detection of lesions. The Journal of Nuclear Medicine has validated a dose of 5mCi for clinical use, and sites performing PEM in Japan are currently using this dosing protocol. 4
Breast MRI has been the traditional modality used for assessing breast lesions prior to a biopsy, but with recent findings that PEM’s equal in sensitivity to Breast MRI (83%) and has an increased specificity (80% with PEM vs. 63% with MRI), the ‘gold standard’ in lesion assessment could be changing. Other notable benefits to PEM over breast MRI include PEM’s easily tolerable procedure for patients with claustrophobia, less likelihood for artifacts due to patient movement (because of the increased comfort of the PEM procedure) and that women’s menopausal state and breast density do not affect the results of PEM images. Additionally, Dr. Wendie Berg points out that PEM images are easier to interpret than MRI images (24 total images produced in PEM vs. 1,000 to 2,000 images in MRI). MRI accuracy also relies on successful contrast injection during imaging.5
Currently, Nuclear Medicine Technologists and Mammography professionals are carrying out PEM scans. Although a certified Nuclear Medicine Technologist must inject the radioactive isotope and be responsible for radiation protection procedures post-injection, a trained breast imager would be the most appropriate professional for positioning accuracy. Some sites are using Nuclear Techs for injection and monitoring while trained breast imaging professionals carry out the scanning. Other sites use Nuclear Medicine Technologists to carry out the entire procedure after receiving specified training from a certified mammography professional.
It should also be mentioned that PEM can be used in conjunction with Whole Body PET imaging, using the same injected dose to perform both imaging procedures.
Images and case studies of PEM can be viewed here.
By Jennifer Lilly, CNMT, RT(N)(CT)
References
1 Berg, W. A., K. S. Madsen, et al. (2011). “Breast Cancer: Comparative Effectiveness of Positron Emission Mammography and MR Imaging in Presurgical Planning for the Ipsilateral Breast.” Radiology 258(1): 59-72.
2 Berg, W.A., Clinical Applications of Positron Emission Mammography, Webinar, presented on April 29th, 2011.
3 Hendrick, R. E. (2010). “Radiation Doses and Cancer Risks from Breast Imaging Studies1.” Radiology 257(1): 246-253.
5 A Conversation with Wendie Berg, MD, PhD. Image: www.rt-image.com
6 New studies show PEM may reduce unnecessary breast biopsies
“PEM’s 26% higher PPV results in a possible reduction in unnecessary breast biopsies.”<– It' a very useful report. Could you please tell me how to use Ref1 to get this conclusin ? thank you1
Hi Janet,
The 26% higher PPV statistic is actually from this source http://dicardiology.com/article/new-study-shows-pem-scanners-may-reduce-unnecessary-breast-biopsies, not from the Berg/Madson study reference (where there is reported 13% increase in PPV declared in the abstract). We’re editing accordingly! Thanks!