This is a very interesting story. Medical software is exploding in many areas, and there are a number of competitors in the same boat. One quick question, how have you been in business this long and still maintained an unprofitable status? Have you been profitable in the past, and then the "hiccup" drained your resources?
My suggestion is that you put together a business plan and strategy that shows the allocation of resources and consider equity investment. With a potential 2008 of 4 million in sales, you could get a decent valuation on the company and 500K would not be a stake that would be anything more than 30% of the company if that. You could go the debt route, however it seems as that is not an option for you if you are not profitable at this point in time. Cash flow is key, which would seem to suggest an equity stake.
You have a proven model and sales traction, which would suggest that there are equity investors out there. One other question would be is your software copywritten or patented?