1. PERM Labor certification
A prospective employer files a request with the department of labor to certify that no able and willing american was available to fill your job. After a couple of months, DOL certifies that and your employer files an immigrant petition on your behalf.
++ once the LC is approved, the rest of the process is fairly routine
-- you are tied to this employer for a period extending 6 months after your immigrant petition is approved. Until that point, the employer can withdraw the petition and there is nothing you can do about it.
-- difficult if you are talking about a small practice as future employer. With larger practices/clinics, this is a pretty straight shot.
2. National Interest Waiver (standard, non-physician)
You or a prospective employer file a petition claiming that it would be in the public interest not to require labor certification because
- your work is national in scope
- the public interest would be violated if the employer was required to obtain LC
- your work requires an advanced degree
This can be an option if you are heavy into research and maybe fulfill a function in a nationwide study. There are subspecialists who managed to get this through.
++ it is sort of a personal petition. If you continue to work in the same field, you are not tied to an employer
-- chances to get this through depend on how much 'pull' from a university or big hospital you can get behind this. There is no percentage of success that anyone could give you.
3. National Interest Waiver for physicians
If you pledge to work in a medically underserved area or healthcare personnel shortage area for 5 years, you can file a NIW based on this. You need a 5 year employment contract, or a business plan for your own practice. Also you need a letter from the state department of health stating that your practice in this location is in the public interest.
-- The hook with this is the fact that the goverment gives you your green-card only at the end of the 5 years (and in your case more like the end of 6.5 years). For the entire time you have to depend on employment authorization documents for work and advance parole for travel. Lots of filing fees, lots of aggravation.
++ If you stick to the rules and stay in the medically underserved area, it is a pretty safe bet that they actually give you the GC at the end.
(in your case, all your paperwork would have to say 'internist' and couldn't say 'pulmonologist'. The physicians NIW is only for primary care)
4. Extraordinary ability/Outstanding researcher
If you have stacks of papers with your name on it, are member of professional societies that admit by invitation only, and 8 other criteria, you can apply under these categories. For the outstanding researcher thing, a university or research institution has to apply on your behalf. If they do, there is a pretty good chance that it goes through. In the EA category you can apply yourself, but it is a lot harder to prevail.
++ instant green-card, no strings attached. As long as you continue to work in your field, CIS won't bother you.
-- variable (-->slim) chances to prevail as a physician. CIS gets all these petitions from basic researchers who have nothing else to do but to publish papers. And all the credentials we amass as physicians are just considered to be 'qualifications incidental to the profession and not an expression of extraordinary ability in the arts and sciences'.