Custom Icon in Wordpress Admin

gistfile1.php

<?php

function as_custom_logo() {
   echo '
	  <style type="text/css">
		 #header-logo { background-image: url('.get_bloginfo('template_directory').'/images/myIcon.png) !important; }
	  </style>
	';
}

add_action('admin_head', 'as_custom_logo');

?>