Is a head mri or a neck mri needed in case of a stiff neck?

Not usually: Not usually. You usually just need heat, massage, or rest. But if you have a stiff neck (the kind the hurts if you try to touch your chin to your chest) with headache or fever, you need to see a doctor right away.

Usually not needed: Most problems are self limiting and can be diagnosed and treated without imaging. For those that persist in spite of treatment, imaging may then be indicated.

Stiff neck: Probably neither, you probably has a muscle spasm which self limited, warm compress , analgesic may help.