hi,

i dont think that you have to study again.. If its 4 year degree, i think you are good....In order to get your licence for practice, you have to evaluate your degree from Educational evaluation agencies.. there are few such agneices ie wes, etc just google it.. you will find few....

they will evaluate your degree and send you the US degree equivalent degree.. with that degree  you can apply for your licence..

if you have Green Card, then i think you should do it that way... i dont know your status..