A relaxed, undrugged dog patiently waits its turn in the MRI scanner. The scientists' trick: Make it seem fun. Enikő Kubinyi/Science hide caption

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How A Dog In An MRI Scanner Is Like Your Grandma At A Disco

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Breasts deemed "dense" in a mammogram tend to have less fatty tissue and more connective tissue, breast ducts and glands, doctors say. About 40 percent of women between the ages of 40 and 74 have dense breasts. Lester Lefkowitz/Getty Images hide caption

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Researchers have used MRI scanners to learn that preemies are born with weak connections in some critical brain networks. iStockphoto hide caption

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Weak Brain Connections May Link Premature Birth And Later Disorders

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Leaks in a barrier between blood vessels and brain cells could contribute to the development of Alzheimer's. VEM/Science Source hide caption

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Leaky Blood Vessels In The Brain May Lead To Alzheimer's

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Spinal MRIs similar to these found infections that many patients hadn't realized they had. Stefano Raffini/iStockphoto.com hide caption

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Who's there? A radiologist studies digital X-rays in a viewing room at what is now called the Walter Reed National Military Medical Center in Bethesda, Md. Seth Rossman/U.S. Navy hide caption

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The warmer orange colors show parts of the brain most active during improvisational rap. The blue regions are most active when rappers performed a memorized piece. NIDCD hide caption

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Do you really need that MRI, or is your doctor just trying to make a buck? iStockphoto.com hide caption

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