Wordpress - get all defined thumbnail sizes

list_thumbnail_sizes.php

<?php
    function list_thumbnail_sizes() {
        global $_wp_additional_image_sizes;
        $sizes = array();
        $rSizes = array();
        foreach (get_intermediate_image_sizes() as $s) {
            $sizes[$s] = array(0, 0);
            if (in_array($s, array('thumbnail', 'medium', 'large'))) {
                $sizes[$s][0] = get_option($s . '_size_w');
                $sizes[$s][1] = get_option($s . '_size_h');
            } else {
                if (isset($_wp_additional_image_sizes) && isset($_wp_additional_image_sizes[$s]))
                    $sizes[$s] = array($_wp_additional_image_sizes[$s]['width'], $_wp_additional_image_sizes[$s]['height'],);
            }
        }

 
        foreach ($sizes as $size => $atts) {
            $rSizes[$size] = $size . ' ' . implode('x', $atts);
        }
        return $rSizes;
    }

Thank you so much!