Table 3 –

Potential benefits and challenges of acquiring CT perfusion routinely at primary stroke centers

Benefits:	Comment:

Increased diagnostic accuracy
• Reduced treatment of mimics • Increased treatment of stroke with atypical clinical presentation	Rapid decisions and limited on-site experience/telemedicine can lead to diagnostic errors and missed treatment opportunities. Artificial intelligence tools for decision assistance and automated alerts about treatable stroke are increasingly available.

Increased diagnostic and prognostic confidence
• Treatment of patients with mild deficits	Risk-benefit assessment in mild stroke is challenging and evidence limited, perfusion lesion/vessel occlusion may inform decision
• Treatment of patients with low ASPECTS but small ischemic core	Approximately 60% of patients with ASPECTS 0–5 have ischemic core <50mL and appear to benefit from reperfusion
• Balancing co-morbidities and imaging profile when considering potential therapeutic benefit	Patients in practice frequently have co-morbidities (not included in clinical trials) – favorable imaging improves likelihood of regaining current quality of life; unfavorable imaging in combination with comorbidities may indicate low probability of treatment benefit
• Familiarity that comes with routine acquisition	Faster, less technical errors, improved interpretation with regular use

Potential IV thrombolysis for patients presenting >4.5h	Evidence of benefit in patients with perfusion mismatch. Recommended in European⁵³ and Australian⁹ but not yet US guidelines. Note that only FLAIR-diffusion MRI mismatch has potential to identify patients with potentially treatable lacunar infarcts with unknown onset

Identify patients likely to meet >6h endovascular thrombectomy criteria
• Reduce futile transfers	Cost and dislocation from relatives

Identify patients at risk of large hemispheric infarction	Require transfer to neurosurgical center in case decompressive surgery needed

Aim for a single imaging session without repeating on arrival at comprehensive center	Requires immediate access to CT technician with CT angiography capability. Image transfer to comprehensive center essential.

Challenges:

Technician capability	Skill required is less than for acquiring CT angiography (no bolus timing needed)

Cost of processing software	Particularly relevant to smaller hospitals. Market competition between vendors may lead to reduced cost in future. Costs are potentially offset by reduction in futile transfers and retained reimbursement

Renal Function	Contrast nephropathy has been shown to be rare and reversible⁵²

Radiation in the setting of overutilization	Justifiable for diagnostically useful imaging, particularly in patients presenting in an extended time window

Time delay for extra imaging	Delays related to obtaining IV access also apply to CT angiography. CTP acquisition, reconstruction and processing should take no more than a few minutes if optimally configured. Best practice is to initiate thrombolysis in scanner after CT and prior to CTP and CTA acquisition.

Unjustified exclusion of patients who may benefit from therapy (overselection)	This risk relates to interpretation rather than acquisition of imaging and requires clinician education to synthesize all available information

ASPECTS – Alberta Stroke Program Early CT Score; CTP – CT Perfusion; FLAIR – Fluid-attenuated inversion recovery; IV – intravenous