In the United States, 32 percent of mammography clinics now have at least one digital machine, up from only 10 percent in 2006. Eventually, film will be phased out, but progress is causing some centers to repeat mammogram tests for some patients. During this transition period, doctors are learning to interpret digital mammograms and compare them to patients’ previous X-ray films. The digital and film versions can sometimes be hard to reconcile, and radiologists may be more likely to play it safe by requesting additional X-rays and/or biopsies.