Hello,
I finally do the same with a sql query and a parsing :
$cck_path = JPATH_BASE . DS . 'components' . DS . 'com_cck';
if (file_exists($cck_path) && JComponentHelper::isEnabled('com_cck', true)):
// get text
$db =& JFactory::getDBO();
$query = "SELECT `introtext` FROM `#__content` WHERE `id` =" . $this->item->id;
$db->setQuery($query);
$text = $db->loadResult();
// Force parsing plugin if SEBLOD is used
if($this->config['parse_plugins'] == false) :
// clean sting
$parsed = array("::introtext::", "::/introtext::<br />", "::fulltext::", "::/fulltext::");
$fulltext = str_replace($parsed, "", $text);
$fulltext = preg_replace('%::cck::.+?::/cck::<br />%i','',$fulltext);
endif;
endif;