[Plugin: Yoast WordPress SEO] Call Keyword field to ALT Tag

Hi
I am using Yoast SEO in WordPress 3.7.1.
On my website I have a company logo in the header.php of the site and therefore this remains static for every page – however the ALT tag remains fixed being in the header file.

I would like to add a line of code in the header file in WordPress that calls on the Keyword field from YoastSEO so that my alt tag is dynamically updated depending on the keyword field of that page.

I’ve completed a search here, in the user guides and via Google and can’t find anyone that’s asked the same question – can anyone advise whether this is possible?
Thanks
Barkley1979