FormattedText.FormttedText is obsolete. Use the PixelsPerDip override

Try this:

FormattedText formattedText = new FormattedText(text, CultureInfo.GetCultureInfo("en-us"),
    FlowDirection.LeftToRight, new Typeface("Verdana"), 16, Brushes.Black,
    VisualTreeHelper.GetDpi(this).PixelsPerDip);