I having problem in getting the thumbnail image url for the items on the Magento Cart

Here is my code:

$quote = Mage::getSingleton('checkout/session')->getQuote();
$cartItems = $quote->getAllVisibleItems();
foreach ($cartItems as $item) {
echo $item->getThumbnail();
}

Does anyone know that why does it returns always blank.

php magento e-commerce magento-1.7
Edit
Report