正则问题，为何只能匹配到一条数据

string sss = "<img width=\"499\" height=\"323\" title=\"asdfsadfasdf\" alt=\"\" src=\"http://images.xxxxxx.cn/2013/0522/20130522113854351.jpg\" border=\"0\" longdesc=\"asdfasdfsadfasdf\" /><img width=\"499\" height=\"323\" title=\"asdfsadfasdf\" alt=\"\" src=\"http://images.xxxxxx.cn/2013/0522/20130522113854351.jpg\" border=\"0\" longdesc=\"asdfasdfsadfasdf\" /><img width=\"499\" height=\"323\" title=\"asdfsadfasdf\" alt=\"\" src=\"http://images.xxxxxx.cn/2013/0522/20130522113854351.jpg\" border=\"0\" longdesc=\"asdfasdfsadfasdf\" /><img width=\"499\" height=\"323\" title=\"asdfsadfasdf\" alt=\"\" src=\"http://images.xxxxxx.cn/2013/0522/20130522113854351.jpg\" border=\"0\" longdesc=\"asdfasdfsadfasdf\" /><img width=\"499\" height=\"323\" title=\"asdfsadfasdf\" alt=\"\" src=\"http://images.xxxxxx.cn/2013/0522/20130522113854351.jpg\" border=\"0\" longdesc=\"asdfasdfsadfasdf\" />";



        string pattern = "<img.*title=\"(?<Title>.+?)\".*src=\"(?<SRC>.+?)\".*longdesc=\"(?<DESC>.+?)\" />";

        string title = string.Empty;

        string src = string.Empty;

        string longdesc = string.Empty;

        StringBuilder js = new StringBuilder();



        Regex rr = new Regex(pattern, RegexOptions.IgnoreCase);

        MatchCollection matches = rr.Matches(sss);

        int i = 1;

        foreach (Match match in matches)

        {

            title = match.Groups["Title"].Value;

            src = match.Groups["SRC"].Value;

            longdesc = match.Groups["DESC"].Value;



            js.Append("<li>");

            js.Append("<a href=\"javascript:void(0);\">");

            js.Append("<img src=\"\" width=\"120\" height=\"80\" alt=\"" + title + "\" />");

            js.Append("</a>");

            js.Append("</li>");

            i++;

        }

        Response.Write(matches.Count.ToString()+"<br />");

        Response.Write(js.ToString());

只能匹配到字符串的第一个img，后面的匹配不到，请高手做下修改。谢谢！