Most Boston hospitals offer 3-D mammograms routinely to all women, saying the new technology saves more lives than traditional mammograms. But a major insurance company is telling customers it won't pay for the more advanced screenings. "I think it would be a step backwards in both technology and standard of care," said Newton-Wellesley Hospital Dr. Michael Misialek. Misialek can't imagine relying on 2-D mammograms, especially now that he's seen what 3-D images can catch. "It's very similar to a CAT scan in the sense that multiple slices or images of the breast are taken and individually can be looked at versus just one flat image," Misialek said.