Use global variables to pass values from the template to the header.
// in the template file
global $my_page_title;
$my_page_title="field value";
global $my_meta_description;
$my_meta_description = 'field value';
get_header();
// in the header file
global $my_page_title;
global $my_meta_description;
echo $my_page_title;
echo $my_meta_description;