WPF/Silverlight rendering blur effect in realtime

In my WPF project I've done with clicking some UI element such stuff:

void vb1_click(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
    DispatcherTimer dt = new DispatcherTimer();
    dt.Interval = new TimeSpan(0, 0, 0, 0, 1000);
    dt.Tick += new System.EventHandler(dt_Tick);
    dt.Start();
}

void dt_Tick(object sender, System.EventArgs e)
{
    for(int i = 0; i < 20; i++)
    {
        this.vb2_blur_eff.Radius = (double)i;
    }
}

The main problem is: "I can't see the each step of blur-effect per second. The program is idling and when the process is complete it gives me the final step of bluring the UI element.

I don't want it, cause both program idling is looking ugly and I want actually see the rendered result at the each period.

Tags: WPF, Silverlight, Multi-threading