使用php simplexml从元素中获取价值

Im using PHP simplexml to get a VAST xml file from the web. I need to get the values of some elements.

My code is this:

<?php

 $myVAST = simplexml_load_file('http://mysite/ads/www/delivery/fc.php?script=bannerTypeHtml:vastInlineBannerTypeHtml:vastInlineHtml&zones=vimp_ads%3D5&nz=1&source=&r=323&block=1&format=vast&charset=UTF-8','SimpleXMLElement', LIBXML_NOCDATA);

 $result = $myVAST->xpath("//Impression/URL");

 print_r($result);

?>

Im getting this:

Array ( [0] => SimpleXMLElement Object ( [@attributes] => Array ( [id] => primaryAdServer ) [0] => http://mysite/ads/www/delivery/lg.php?bannerid=7&campaignid=3&zoneid=5&loc=1&cb=2c53ba2469 ) ) 

I need to get only the url value:

http://mysite/ads/www/delivery/lg.php?bannerid=7&campaignid=3&zoneid=5&loc=1&cb=2c53ba2469

But im not being able to do that. I tried to cast to string but with no success.

Any ideas?

thank you,

fwu