What are the key specifications should I care when choose a x-ray ?

Now in the market all the suppliers sell the machines with almost the same functions and performance. Most of the numbers on the brochures are meaningless, but some numbers are important:

1- Tunnel size, this means which size of the machine you choose. Because different sizes machines are much different in the prices.

2- X-ray generator, in the market even the same size of the machines, they use generator in 80KV, 90KV ,100KV, 140KV, 160KV,180KV, 200KV and 300KV etc. The bigger KV, the higher price. See clearly the voltage of the generator is most important.

3-Other numbers are not much important.