Should perfusion imaging be the standard of care in cases of a severe symptomatic intracranial stenosis?  

I would say no until we prove that perfusion imaging helps risk stratify patients with symptomatic ICAD and select them for reperfusion therapies.

I agree with Dr. @Yaghi that not all patients should undergo perfusion studies. In vascular neurology, few things (if anything) are one size fits all. There are no set guidelines regarding this subject since it is an understudy population but some physicians get perfusion studies on symptomatic foc...

To my knowledge, there is no evidence that CTP can reliably guide decisions in a way that it impacts meaningful patient outcomes and therefore, does not justify the significant radiation dose (3.5 to 7.5x an NCCT) (Zensen et al., PMID 32901338).

Very interesting question indeed. In the acute setting, distinguishing between chronic severe stenosis and acute occlusion can be challenging. In this setting, CTP can provide valuable information by showing more tmax <4 (more benign oligemia) with tmax >4/tmax >6 equal to or more than 2. ...

If the symptomatic issue is acute ischemic stroke, then definitely. However, if it's a TIA, I'm not sure it would change my decision-making.