YouTube Video Gallery

[MAAU]

Sorry for the language but i speak spanish.
I need to use something like {$GLOBALS['threadfields']['ytvgalid']} on my portal.php because im editing the lastthreads block tu show the lastest videos of my gallery. Specifically i use:          <img src="http://img.youtube.com/vi/{$GLOBALS['threadfields']['ytvgalid']}/mqdefault.jpg" class="panel-image-preview"> to try that the block show the video thumb. ¿How can i get this?