Can an x-ray of the head and neck after a carwreck pick up carotid blockages?

No: A plain x-ray may show calcification but it will not be able quantify stenosis in the carotid artery . A ct angiogram on the other hand will definitely be able to see "blockages". Other common test to evaluate the carotid arteries are ultrasonography ( carotid duplex).

No: If you have had a car crash and a whiplash type injury, small tears or dissections can occur in the carotid. Untreated, this can cause a stroke. A simple ultrasound promptly after the crash should be able to detect this, but an x-ray won't.