Get Image Size from New Image

Hi:
I have an ASP.net application where I have a dropdown box and it fires an event to load a new image from my  SQL Server 2005 database.  I am able to show the image but would like to show the dimensions as a label but not able to do this.
 My code looks like this
//This works fine - can load the image
imgLargePic.ImageUrl = "~/Controls/Fetch_Pic.ashx?ProductPicID=" + iProductPicID + "&Size=Large";

//Can't get this to work... - next line of code...
lblPicSize.Text=imgLargePic.Width.Value.ToString() + "X" + imgLargePic.Height.ToString();
 Any help greatly appreciated.
Roger

...