in the breast parenchyma during the menstrual cycle [4][5][6]. Estrogen has been shown to exert a histamine-like effect that causes an increase in microvascular permeability and vasodilation, and progesterone exerts a mitogenic effect that may increase metabolic activity, also resulting in an increase in perfusion [7,8].The detection of malignancy at MRI is based on the fact that tumors show neovascularity, with increased blood flow and increased vascular leakiness, and relies on the differential enhancement between neoplastic tissue and normal breast parenchyma [9][10][11][12][13]. It has been postulated that benign enhancement may obscure the detection of small cancers by masking this difference. In addition, although MRI is very sensitive for the detection of malignancy, specificity is somewhat Wo m e n's I m ag i ng • O r ig i n a l R e s e a rc h CMEThis article is available for CME credit. See www.arrs.org for more information. 2011; 196:218-224 0361-803X/11/1961-218 © American Roentgen Ray Society B ackground parenchymal enhancement on breast MRI refers to the normal enhancement of the patient's fibroglandular tissue seen on the first contrast-enhanced image. Background enhancement is due to the increase in T1 relaxation of tissue that occurs after gadolinium administration, and the degree of enhancement is directly related to vascular supply and permeability. Background parenchymal enhancement is thought to be related to endogenous hormone status and fluctuates with the menstrual cycle, being highest during weeks 1 and 4 and lowest during week 2 [1,2]. It increases in postmenopausal women receiving hormone replacement therapy (HRT) [3]. Changes in background parenchymal enhancement likely correlate to hormone-dependent histopathologic changes that occur Keywords: background parenchymal enhancement, BI-RADS category 3, MRI breast biopsy rate, screening breast MRI DOI:10.2214/AJR.10.4550 AJRReceived March 3, 2010; accepted after revision June 6, 2010. W O M E N ' S I M A G I N GOBJECTIVE. Background parenchymal enhancement on breast MRI refers to normal enhancement of the patient's fibroglandular tissue. The aim of this study was to determine the effect of background parenchymal enhancement on short-interval follow-up, biopsy, and cancer detection rate on baseline screening MRI in a high-risk group.MATERIALS AND METHODS. Two hundred fifty baseline high-risk screening MRI examinations were reviewed. For each, the background parenchymal enhancement pattern was recorded (minimal, ≤ 25%; mild, 26-50%; moderate, 51-75%; and marked, > 75%), as were BI-RADS category, biopsy rate, and final pathology result. Results were compared for each enhancement category.RESULTS. Of the 250 MRI examinations, 24.8% showed minimal enhancement; 34%, mild; 24%, moderate; and 17.2%, marked enhancement. Women with minimal enhancement had a significantly higher number of BI-RADS categories 1 and 2 examinations (64.5%) than women with mild (38.8%), moderate (40%), or marked (25.6%) enhancement. The BI-RADS category 3 rate was 43....

FFDM resulted in significantly higher cancer detection and recall rates than screen-film mammography in women 50-64 years old. The PPVs of FFDM and screen-film mammography were comparable. The results of this study suggest that FFDM can be safely implemented in breast cancer screening programs.

Our study illustrates a method to evaluate the standard of practice for thyroid nodule assessment among radiologists within an ultrasound group. Application of a 5-point malignancy rating scale to select nodules for biopsy is feasible and shows good diagnostic accuracy.