A tunnel machine that's silent and they take pictures of various organs is called a CT Scanner.

A tunnel machine that makes a big noise like jack hammers is the MRI. That takes pictures of nerves... and is mostly used for pictures of the brain.... but is also used for pictures of the nerves in any other part of the body.

An EEG is were they take a graph of the electrical impulses of the brain. They just put electrodes on your head, and you just sit quietly while they take measurements, or a graph, of your brain waves.

I've had all of these, and all are pain free. All give different measurements that help your doctor in his/her diagnosis.