If you are really bringing someone here for treatment, you need the following:
1. A letter from the US based physician who would treat the patient.He/she should state the diagnosis and briefly outline the treatment plan and the anticipated duration of treatment. (eg., diagnosis of cancer with 6 cycles of chemotherapy or bypass surgery followed by 'x' weeks of anticipated recovery).
2.A letter from the finance department of the hospital stating the expected cost and an agreement signed by the payer that you(or whoever) would pay the money in full.
3.Financial statement from the bank of whoever is going to pay stating that they have the funds.
Please note that an american citizen, who has insurance does not pay the full amount for the hospital bill or the procedure.For example, medicare pays about 30% of what is billed.However, international patients have to pay the full amount PRIOR to the anticipated procedure. Therefore, it is very, very expensive for an average person.
bottom line: If you are planning on bringing someone without a proper medical reason, it is not worth doing all this. If you are really bringing someone for treatment, you better know a doctor or a high level financial administrator of a hospital or else it will be prohibitively expensive.Good luck.