$(document).ready(function() {
   		$(".icd_navigation > img").mouseover(function() {
			var new_bg = $(this).css("background-image").replace(/_off/,'_on');
			$(this).css("background-image", new_bg);
		});
		$(".icd_navigation > img").mouseout(function() {
			var new_bg = $(this).css("background-image").replace(/_on/,'_off');
			$(this).css("background-image", new_bg);
		});
 	});