get_post_meta and displaying string once

Hello,
To be explicit, here is my code.

<?php global $meta_box, $post;
foreach ($meta_box['fields'] as $field) {
$check = get_post_meta( $post->ID, $field['id'], true );
$output = '';
if ( ($check == 'on' ) ) {
$output .= 'text: ' . $field['name'] ;
$output .= '<br />' ;
 }
echo $output;
} ;   ?>

Actually works fine. The result is:
text: result1
text: result2
in case I have 2 boxes checked.

Now, I would like to have:
text: result1, result2
I can see two issues:
– first, the coma to avoid at the end of the string. I precise that implode doesn’t work at all
– and I am unable to find out a way to display “text:” only once.

Is anybody can help, would be much appreciated.
Thx in advance.
Mad.