取出字符串中的数字----正则表达式

string img="{"treeId":11498,"treeName":"冲绳","imgId":11424,"imgName":"冲绳"}";  
                                string regex = @"(d+)";  
                                System.Text.RegularExpressions.Match mstr = Regex.Match(img, regex);  
                                string imgId = mstr.Groups[1].Value.ToString();