MR imaging of the breast: indications, established technique, and new directions

Abstract

IntroductionThis article summarizes the principles and major technical aspects of dynamic magnetic resonance (MR) imaging of the breast with particular emphasis on pulse sequence parameters, contrast agent dosage, and image postprocessing. A detailed list of clinical indications for dynamic breast MR imaging is given, and an interpretation score system provided. The performance of the MR examination in terms of sensitivity and specificity for lesion detection and characterization is discussed in detail, as are the pharmacokinetics and safety of the twocompartment Gd-based contrast agents. The effects of stressing temporal and spatial resolution are also discussed. Finally, intriguing new directions in breast MR imaging are presented in terms of the potential for Gdchelates with high T1-relaxivity, blood-pool contrast agents, and proton MR spectroscopy.Breast MR imaging: technique, tips, and tricksThe first applications of magnetic resonance (MR) imaging to the breast were disappointing. Classic spin-echo T1-, proton-density-, or T2-weighted sequences were not able to distinguish malignant from benign tumors [1,2]. This scenario changed dramatically with the introduction of intravenously administered paramagnetic gadoliniumbased contrast agents: tumors showed greater contrast enhancement than normal gland parenchyma, and strong enhancement was observed for malignant, invasive tumors in particular [3]. This behavior is due to the neoangiogenesis related to the growth of the tumor: breast malignancies are more highly vascular (more and larger vessels) and have increased permeability (up to eightfold more) compared to normal parenchyma. Moreover, an increased interstitial space (between three-and fivefold more than normal parenchyma) functions as a large distribution space for the contrast agent [4]. The advent of rapid MR sequences together with field gradients of increased power and slew rate have permitted the definition of a dynamic technique that today is considered standard for MR imaging of the breast.MR imaging of the breast needs to be performed during the second week of the menstrual cycle in premenopausal women and 2-3 months after the interruption of hormone replacement therapy in postmenopausal women. An earlier recommendation to wait 6 months after surgery and 12-18 months after radiation therapy in order to avoid false-positive findings is no longer relevant [5]: MR imaging performed about 1 month after surgery was shown to have a sensitivity of 95% and a positive predictive value of 92% for malignancy [6].Imaging is performed with patients in the prone position using a dedicated bilateral breast coil and a longline venous access to a cubital or hand vein. In order to avoid misregistration artifacts on subtracted images, patients should be carefully instructed not to move during the 10-15 min required for the full examination.Dynamic imaging is performed after obtaining scout views and, optionally, short-time fast inversion recovery or T2-weighted fat-saturated fast spin-echo images. The dynamic sequen...

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