WordPress MU

I'm trying to show a list of blogs with the most posts along with the gravatar of the blog admin using the get_most_active_blogs function.

This code on its own spits out the email:

<?php
echo get_blog_option( $details[ 'blog_id' ], 'admin_email' ) ?>

How do I combine that above with

<?php echo get_avatar( ?????? , 64 ); ?>

I've tried lots of combinations but I'm not getting anywhere.

Thanks.

You seem so close,
I've used recently,
<?php echo get_avatar( get_blog_option($id, 'admin_email'), 32 ); ?>

Thanks.. while that didnt work for me, it gave me an idea of how it should be.

This works for me :)

<?php echo get_avatar( get_blog_option($details[ 'blog_id' ], 'admin_email'), 30 ); ?>

$id = $details[ 'blog_id' ];