You can enter small hack, something like this into your Admin->Edit wanted page->navigation title then:

<img src="assets/img/home-icon.png" alt="Home" />

If you want to hide it then in application\helpers\cms_helper.php, comment or remove this like:

$item['navigation_title'] = '<img src="assets/img/home-icon.png" alt="'.$item['navigation_title'].'" />';