如何从Google新闻RSS获取缩略图

Question

当我以XML格式查看Google News feed时，我无法告诉如何获取缩略图图片网址。有谁知道怎么样？

$news = simplexml_load_file('https://news.google.com/news?output=rss&topic=n');

foreach($news->channel->item as $item) {
    $title = $item->title . "\n";
    $link = $item->link . "\n";
    $pubDate = $item->pubDate . "\n";
    $image = $item-> ???? 

    echo $title . ' - ' . link . ' - ' . $image;
    echo strip_tags($item->description) ."\n";
    echo '<br><br>';
}