eja - think yourself lucky you did the right thing and went to see your doc after experiencing those symptoms. All to often they are ignored with a fatal result.
The nuclear stress test is a no-brainer. Technetium-90, a gamma emitter, has a half-life of 6 hours, so by the end of the day, it's all gone. CT scans are potentially much more harmful.

It looks like your asthma is well controlled if you can do 17+mph for 40+ miles. What meds do you use?

Good luck.