Oscar, try using
DotSpatial.Tools.RasterToPolygon
DotSpatial.Tools.RasterToPolygon
IFeatureSet fs = new FeatureSet(DotSpatial.Topology.FeatureType.Polygon);
IRaster r = Raster.Open("myraster.bgd");
DotSpatial.Tools.RasterToPolygon d = new DotSpatial.Tools.RasterToPolygon();
d.Execute(r, fs, null);