Узнать, изменилось ли поле при изменении элемента?

$db_props = CIBlockElement::GetProperty($arFields["IBLOCK_ID"], $arFields['ID'], "sort", "asc", Array("CODE"=>"NEWS_PHOTO"));
                $arrPhoto = array();
                while($ar_props = $db_props->Fetch())
                {
                    if ($ar_props["VALUE"])
                    {
                        $ar_val = $ar_props["VALUE"];
                        $ar_val_id = $ar_props["PROPERTY_VALUE_ID"];
                        $img_path = CFile::GetPath($ar_props["VALUE"]);
                        if (!empty($img_path)){
                            $arrPhoto[] = $img_path;
                        }
                        else{
                            continue;
                        }
                    }
                }