How can I change an image source dynamically?

Hi to everyone,
I am developing a Silverlight web site. I have a small problem. I placed an Image control in the middle of the mainpage inside a scroll view control and I created a storyboard to animate that Image Control. What i'd like to do is only changing dynamically the source of that Image control, so,for example if I press a button I change the picture displayed in that Image control. I am programming in C#. I've tried something like ImageControl.Source=new BitmapImage(.....); but it doesn't work. I am using Expression Blend.
Thank you in advance.
Maurizio Di Vitto