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  • br Contrast enhancement will make mammography an alternative

    2020-08-18


    Contrast-enhancement will make mammography an alternative to MRI in limited settings
    A major advantage of breast MRI is the use of an intravenous contrast agent which visualizes the vascularity of various lesions. However, contrast agents can also be used with mammography and the first studies are from early 2000s [10]. Malignant lesions are prone to show up after contrast injection due to their increased arterial and venous blood flow and highly permeable capillaries.
    The downside with contrast agent injection is that it involves an invasive procedure placing a needle into a vein in the arm, takes more time, makes it less easy to schedule patients due to large variability in the time it takes to place a needle, and it may cause oversensitivity reactions. The information from a contrast-enhanced mammography does not fully replace the contrast enhanced series from MRI [11]. First, there is the physiological problem of the Daptomycin pressure in regular mammography being higher than the venous pressure. In addition, with MRI you can visualize the contrast-enhancement between the left and right breast at the same time points, and you can assess the dynamics over time thanks to repeated examinations over a few minutes. Considering the time-requirements we do not believe this will become a standard screening modality for all women. Due to the disadvantages compared to MRI, including the potentially harmful use of ionization radiation among young women with BRCA mu-tations, we do not believe that it will replace MRI. However, in certain settings where MRI is not possible or too expensive, contrast-enhanced mammography could be a reasonable compro-mise [12].
    The usefulness of automated ultrasound will be determined
    Ultrasound relies on a different mechanism than x-rays to obtain the image of the breast tissue. Therefore, certain tumors that are not visible on mammography may be visualized on ultrasound. Ultrasound contrast agent, microbubbles, is not likely to be useful in screening settings due to the long time it takes to acquire images for the entire breast compared to the short time the microbubbles are visible. Since ultrasound is often acquired by the radiologist, it is a modality that requires large amount of radiologist time per ex-amination taking 25e30 min compared to 5 min or less for screening mammography [13]. Automated ultrasound mitigates the need for the radiologist to be present for image acquisition. A technologist then handles the device which involves automated movement of the transducer across the breast acquiring an image volume that can later be assessed by a radiologist. We believe that the use of hand-held ultrasound may increase in middle-low in-come countries. In high-income countries, where handheld ultra-sound is used at all breast centers, the jury is still out on automated ultrasound - will it prove cost-effective or will it be made obsolete by a combination of tomosynthesis and abbreviated MRI? In com-bination with mammography, MRI Daptomycin has a much higher sensitivity than ultrasound. Across four studies of high-risk women the sensitivity was more than 90% for MRI with mammography and around 50% for ultrasound with mammography [13]. In the thera-peutic setting, there is an opportunity for hand-held ultrasound to target the delivery of pharmacological agents contained in micro-bubbles [14].
    High-resolution diffusion and abbreviated protocols will enable MRI as a screening modality in certain subgroups
    MRI is a technique which exposes the human body to strong magnetic fields and forms images based on weak radiofrequency signals emitted by hydrogen atoms which are abundant in the body. MRI is without doubt the most sensitive imaging method to detect breast cancer. In a screening study of high-risk women, the sensitivity was 18%, 33% and 80% for clinical examination, mammography and MRI respectively [15]. The corresponding specificity was 98%, 95% and 90% respectively. The proportion of women that had metastatic spread to axillary lymph nodes was 52e56% in the mammography groups compared to 21% in the MRI group. However, MRI does require expensive equipment and the specificity is somewhat lower than mammography leading to more 
    biopsy procedures - most of which can be performed through second-look ultrasound. To address the economics, abbreviated protocols have been developed and shown to be as effective as full protocols in screening [16]. Current protocols for breast cancer detection and evaluation require the use of an intravenous contrast agent. As for contrast-enhanced mammography there are disad-vantages with the need to administer contrast agents intrave-nously. In addition, there are worries that certain, linear, gadolinium chelates might remain in the brain for a very long time, even though that does not seem to be the case with the cyclical compounds that are used today. Similar disadvantages as those listed above in the section on contrast-enhanced mammography as well as an additional worry that linear MRI contrast agents remain in the brain for a very long time, has sparked development of techniques that do not require contrast agent use. Diffusion MRI assess the rate of free movement of water molecules [17]. Malig-nant tumors are usually more disorganized compared to normal tissue, has less extracellular space and cells of more varying sizes, which translates into decreased diffusion of water molecules. The main issues that must be overcome are to increase the spatial resolution and to make the technique as well as the interpretation standardized across centers. Given current developments we may see diffusion protocols taking center stage in the next 5e10 years. By use of risk stratification to identify the women who are most likely to benefit, we believe that MRI screening, with or without contrast agents, will be incorporated into future population-based screening programs for specific subgroups.