A whistleblower lawsuit unsealed this week in Dallas accuses medical device manufacturer Guidant of marketing biliary stents to doctors for uses not approved by the Food and Drug Administration. In the lawsuit, Kevin N. Colquitt claimed that while he was employed with Guidant, he was instructed to market the stents to treat blocked blood vessels when they were designed to treat digestive cancers. The F.D.A. approval process for stents used in blood vessels is much more rigorous than the biliary devices marked by Guidant, the New York Times reported.