How do I read AJAX elements on a web page?

I am trying to write code for a class that is able to download the page source of a web page. However, for pages that contain AJAX elements, the request comes back without them. Here is the code I have so far:

Code:

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'''<summary>Gets the page source of a page located at the specified Url</summary>
Function PageSource(ByVal Url As String) As String
Dim req As System.Net.WebRequest = System.Net.WebRequest.Create(Url)
Dim res As System.Net.WebResponse = req.GetResponse
Dim reader As New System.IO.StreamReader(res.GetResponseStream)
Return reader.ReadToEnd
End Function

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This code works awesome for simple pages, but how is one supposed to read the page source within an AJAX element? Basically I need the WebRequest to render the AJAX element before returning the stream. Is a WebRequest the correct way to do this, or should I be using another method to get the page?

I'm sure the solution is simple, I just haven't been able to find any information on it at all. So any hints, tips, or partial answers would be most helpful.