CakePHP: Define an image URL into a Variable

I'm trying to define a variable for an Image URL which is something like this:

http://MyWebSite.com/app/webroot/upload/foods/2/beef_wellington_thumb.jpg

The number 2 digit in the link is an $id and also represents the folder number. The image file name is originally beef_wellington.jpg. But I have to display it using an additional underscore:_thumb for each image file name due to an upload component (plugin) I'm using in Cake. So how should I go about in defining a variable for that: e.g.

$itemImageurl = "/app/webroot/upload/foods/".$id开发者_开发问答./$item['Food']['image'];

What about the _thumb ? could we place it somewhere in the line of code above?

UPDATE:

Assuming I have changed the upload plugin so I can also add my original image file name in my folder as this:

http://MyWebSite.com/app/webroot/upload/foods/2/beef_wellington.jpg

without needing _thumb

How to write the correct variable, I'm not sure about this:

$itemImageurl = "/app/webroot/upload/foods/".$id./$item['Food']['image'];

How about finding the last dot in $item['Food]['image] and replace it with "_thumb."?

e.g. (not tested):

$newName = basename("/app/webroot/upload/foods/".$id./$item['Food']['image'],".jpg");
$newName = newName."_thumb.jpg";

does it work?