how to get the real (unscaled) size of an embedded image in the svg document?!

I have a SVG document with the image entry in it:

<image id="image12975" x="30" y="40" width="30" height="45"
xlink:href="img/Akira1.jpg">    
</image>

I have fetched the SVG Image in Javascript by doing:

var imgE = document.getElementsByTagName('rect');
document.getElementById('test').innerHTML = imgE;

brings me the [object SVGImageElement] in Javascript.

By iterating the object I have a full subset of functions and attributes. height and width of the function "getBBox()" bring me only the attribut values defined as width (30), and height (45).

I am looking for the real parameters, like I would open the picture alone, which are in reality width="300" and height="430" pixels.

for any support I would kindly thank you

Tamer