Rss feed filter SimplePie

Hi,
I'm rather new to php so...I use simplepie to parse rss feed but i want to filter them by keywords
i made this code :
$feed = new SimplePie();
$feed->set_feed_url(website/rss);
$feed->init();
$feed->set_cache_duration (3600);
$feed->set_timeout(30);
$feed->handle_content_type();
$countItem = 0;
foreach ($feed->get_items() as $item){
$checktitle = $item->get_permalink();
//Regex keyword filter
$pattern = '/keyword1|keyword2/';
//If the there is a keyword match, store in $matches array
if (preg_match($pattern, $checktitle)) {
$news[$countItem]= $item;
$countItem++;
}
}
This is the filtering part it does it work but, i want all the items that contains both keywords.
I'm not sure that preg_match is the right way to do this but it;s the only thing i got, so please!

If keyword1 and keyword2 are regular expressions, call preg_match twice.

If they are not, use strpos twice instead (it's faster).

ie:

he keyword are words, like "world news"