I finally found the answer:
$articleId = JFactory::getApplication()->getRouter()->getVar("id");
$db = JFactory::getDbo();
$query = $db->getQuery(true)
->select($db->quoteName('images'))
->from($db->quoteName('#__content'))
->where('id = '. $db->Quote($articleId));
$db->setQuery($query);
$result = $db->loadResult();
$images = json_decode($result);