determine width and height of an image while it isn't inserted to the dom

determine width and height of an image while it isn't inserted to the dom

I'm receiving images inside a long string from a server using an ajax call
The url of the image is inside result[1] for sure. I've used
width/naturalWidth and height/naturalHeight and on occasion they return 0
and in other cases they return the right size in pixels
var imgElement = jQuery("<img>").attr("src", result[1]);
var width = imgElement[0].naturalWidth;
var height = imgElement[0].naturalHeight;
if (width >= that.minImgPixels && height >= that.minImgPixels) {
image = result[1];
}
How is the right way to check image width and height without inserting it
to the dom?