Standard loop?

Hi, I have a simple loop question:

I have 5 custom variables that are accessed with:

<?php echo get_field('image_1'); ?>

they contain a URL as their value. How can I loop through these variables and display this: 

<a href="<?php echo get_field('image_1'); ?>" rel="lightbox[<?php the_title(); ?>]"><img src="<?php echo get_field('image_1'); ?>"/></a>

if the value is true.

yet nothing if its not.

Thanks

By the way: this is within a wordpress WHILE loop

get_field() is a function, image1 is a parameter.

If you have all the parameters in an array then you can loop like this:

$images = array('image1', 'image2', 'image3');
foreach ($images as $row) {
   get_field($row);
}

Here's what I've got...

<?php

for($i=1; $i<6; $i++){              //loop 5 times

if(get_field('image_' . $i)){      //check if there is an image on each iteration of the loop

echo' <a href="' . get_field('image_' . $i) . '" rel="lightbox[ ]"><img src="' . get_field('image_' . $i) . '"/>';  //output results

}

}

?>

now my problem is adding this:    rel="lightbox[<?php the_title();?>]" inside that echo. any idea?