如何判断ScrollViewer中的滚动时间？

Question

我有一个包含一些元素的ScrollViewer，例如图片。

 <ScrollViewer> 
    <Image x:Name="FlipViewImages" Grid.Row="0" Grid.ColumnSpan="3" Width="341" Height="236" Margin="0"> 
    <Button x:Name="MostraD1" Click="MostraD1_Click" Grid.Row="4" Grid.ColumnSpan="2" Grid.Column="1" BorderBrush="{x:Null}" Style="{StaticResource BottoneCuore}" Margin="2,0,0,0">
       <Button.Content>
             <TextBlock Text="MOSTRA DESCRIZIONE" FontSize="9" Foreground="Black" TextWrapping="Wrap" Height="26" HorizontalAlignment="Center"/>
        </Button.Content>
     </Button>
     <Button x:Name="MostraD2" Click="MostraD2_Click" Grid.Row="4" Grid.ColumnSpan="2" Grid.Column="1" BorderBrush="{x:Null}" Style="{StaticResource BottoneCuore}" Margin="0,0,60,0" HorizontalAlignment="Right"/>
         <Button.Content>
             <TextBlock Text="MOSTRA DESCRIZIONE" FontSize="9" Foreground="Black" TextWrapping="Wrap" Height="26" HorizontalAlignment="Center"/>
         </Button.Content>
     </Button>
</ScrollViewer>

您可以告诉ScrollViewer何时向下滚动并且图像不再可见？ 在那种情况下，我想在Grid的另一部分中显示图片