OctoberCms - 在后端页面上使用媒体过滤器

I am trying to get full path of an image stored on media. In case of front end pages I have been using media filter.And it works fine. But the exact same code does not work on the backend pages.

<?php $imagepath = 'banner.jpg'; ?> <!--setting up a variable.--> 

<img src="{{imagepath|media }}"/>

Thanks in advance.