Calculate perfect textHeight which loads image with text

I have a dynamic textfield (with HTML = true) in stage. I am loading content into this textfield using HTML syntax.

I want to calculate the textfield height. The textfield height is showing perfectly when I am loading only text. But when I want to load some image using <img src> tag, it is not calculating the height of the image. How can I find the actual content height if there is image in it

abc_txt.htmlText = "the quick brown fox jumps over the<img src='mat1.gif' height='300'> lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog the quick brown fox jumps over the lazy dog ";
abc_txt._height=abc_txt.textHeight;

Thanks in Advance
Salim