Array separator question

I'm using Genesis themes which I'm not having a direct issue with. I have the following code to display my CustomPress values:
<?php global $post; if ( get_post_meta( $post->ID, '_ct_checkbox_4f4d6559d90f2', true ) ) { foreach ( get_post_meta( $post->ID, '_ct_checkbox_4f4d6559d90f2', true ) as $value ) { echo $value . ', '; }} ?>

So it displays an item from the array, then a comma, then another item, then a comma, then another item and so on.

The problem is with the last item in the array. It still gets a comma at the end.

Is there a way to tell it to output the comma for every value except the last one?