Get only URL from URL field

Hi, I would like to get only the URL of the URL field of a list but it returns the URL and also the description (ex: "http://www.url.com, description"). How can I do that pls?

IEnumerable<BannieresItem> res = this.List.GetItems(query).Cast<SPListItem>().Select(item => new BannieresItem(
                item.ID,
                item.Title,
                item["URL_Image"] as string, <<< HERE
                item["URL_Lien"] as string <<< HERE
));

thanks