What are some statistics regarding medical tourism?

I'm one of those odd people who allows facts to support their decision making. What are the numbers behind medical tourism (high and low estimates)? How many come to the US, how many US leave the US, where do they most often go? Which countries are the top importers of medical tourism? I read that Thailand takes in about 600,000/year and India 200,000, but I haven't found all the numbers consolidated in one place. Please support your findings with references so I can verify them.

I'm not getting out of a school project, but rather just trying to find the facts behind the statements politicians make. Thanks!