Stacy Riggs of Fairfax, Va., is prepped for a screening for atrial fibrillation by Life Line Screening medical assistant Kennea Blake at Messiah United Methodist Church in Springfield, Va. Jenny Gold/Kaiser Health News hide caption

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Some images of lung cancer are clear cut. But in many others, a nodule on the screen turns out not to be cancer at all. iStockphoto.com hide caption

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