[themes] Alt text with preg_replace for accessibility

Hi, I'm creating a text only version of a site and would like to replace inline images with their alt text. In my template files I have: <?php print preg_replace("/<img[^>]+\>/i", "(image) ", $content) ?> which replaces all images with: (image) what code would I need to create output like: (Image description: THE ALT TEXT HERE) and is this best practice? Regards Mark