Measure blood flow in mouse carotid artery - (Aug/30/2013 )

I am not sure in which tread I put this, so I just post it here.

I'm looking looking for a cheap method to determine blood flow in mouse carotid arteries. There are many sophisticated Doppler machines on the market, but starting at 30000. I would need a simple, cheap method just to get an idea about absence/presence of blood flow in the carotid artery.
I am looking forward to get some suggestions....

Invasive or non-invasive?

Non-invasive.

Could a pulse oxyimeter work?  might be a bit non-specific though.

I think this is a good idea and might be worth trying. I just need to find a probe which would be small enough. 

I was trying to use a fetal Doppler, but I am not sure so far how reliable this is....