Parsing XML data with colon from Windows Phone Store

I am taking app details from the Windows Phone Store which throws an XML similar to this: http://ift.tt/X0SQi9

My code looks like this:

XElement app = XElement.Parse(e.Result);
var y = app.Descendants(XName.Get("feed", "http://ift.tt/r5ut6F")).First();

I am trying to get the value for "image" but can't proceed because of the XML tag with colon a:feed. I've read about XML namespaces so I tried using XName, using the URL found in the XML tag but it still does not work.