Can physicians detect carotid artery thinning with an ultrasound?

Yes: Yes. Ultrasounds of the carotid arteries are very accurate. We typically look for blockages in the artery. We actually like to see "thin" (non-diseased) walls of the arteries. When we see thickened carotid artery walls in patients, this considered a marker for cardiovascular disease. (carotid intima-media thickness).

All seeing : While ultrasound is not necessarily "all seeing" it can be and is used by most physicians to diagnose and follow most conditions involving the extracranial carotid artery. While I am not certain what carotid "thinning" is, ultrasound can detect stenosis, dissection, aneurysm formation, occlusion, etc and is typically the initial test of choice.