unable to iterate throughIEnumerable and List ???

Hi all,
i m new to asp.net 3.5 linq and dnt worked much on generics.
i m using IEnumerable to return set of results.
i m binding this IEnumerable type method directly to datagrid source then it works fine.
But i dnt knw how to iterate through this collection??
Same way i m using  List<String> to return columns like this
public List<String> FindImageData()
        {

            List<String> lst = new List<string> { "" };

            ISingleResult<Usp_Patient_Radiology_DisplayResult> imagedata = objimagedata.Usp_Patient_Radiology_Display(p_PatientID);


            foreach (Usp_Patient_Radiology_DisplayResult h in imagedata)
&nb ...