Just for discussion's sake, I'm going to put something out here. These are 2007 stats for the US:
FASTSTATS - Leading Causes of Death
From what I can gather online, these scanners cost about $150,000 each (which I assume doesn't include initial training, maintenance and ongoing staffing to man the things, so I'd take it as a lower limit of the estimated cost) and there are about 200 currently in place.
That's $30,000,000. Imagine what $30,000,000 could do to prevent death and disability from stroke. In the case of stroke, reducing the impact isn't really a matter of working toward future cures or anything like that; the medical community knows exactly how to respond to them... the trick is making sure that the doctors, medicines and equipment are available to stroke victims immediately after the stroke occurs.
Imagine the benefit in human life if the federal government spent $30,000,000 to make sure that rapid care for stroke victims was available in rural areas. Now compare that to these scanners, where IMO, it's not even clear that they're going to save more people than they kill.