Table 1.

Advantages and disadvantages of various neuroimaging techniques for collateral assessment.

Images	A good correlation with conventional angiographic collateral grade	Clinical Trials	Advantages	Disadvantages
Conventional angiography		None	Reference standard	Invasive
ASPECTS score	ASPECTS on both contrast-enhanced than non-enhanced CT31	ESCAPE23 SWIFT PRIME,25 REVASCAT26	Easy-to-use Routine study	Relatively low interrater reliability61 Collaterals not visualized
Multiphasic CT	Multiphasic perfusion CT collateral grades34,35	ESCAPE23	Easy-to-use	Radiation Needs contrast dye
Diffusion-weighted image	Infarct volume44 Infarct pattern45	BRASIL62 DEFUSE63	Routine MRI study	Many confounders Collaterals not visualized
FLAIR and gradient echo image	Distal hyperintense vessel on FLAIR46	Observational studies	Routine MRI study	Poor visualization
MR or CT perfusion	Tmax severity10,49	DEFUSE63 EPITHET64 MR RESCUE5 EXTEND-IA24 SWIFT PRIME25	Quantitative and good visualization	Needs post-processing Needs contrast dye More specific criteria for collateral assessment are needed
MR-based collateral image	Collateral map using DSC PWI source data65	Observational studies	Good visualization Simple post-processing performed at workstations; Covers the entire vascular phase	Needs validation
Arterial spin labeling	Vessel-encoded ASL56,55 Arterial transit artifact53	iCAS Other ongoing studies*	Vessel selective information No contrast dye	Contamination from the partial labeling of the nearby vessels or antegrade flow T1 decay of the label may limit the extent to which slow inflows can be imaged

ASPECTS, Alberta Stroke Program Early CT Score; ESCAPE, Endovascular treatment for small core and anterior circulation proximal occlusion with emphasis on minimizing CT to recanalization times; SWIFT PRIME, Solitaire with the intention for thrombectomy as primary endovascular treatment for acute ischemic stroke; REVASCAT, Endovascular revascularization with solitaire device versus best medical therapy in anterior circulation stroke within 8 hours; BRASIL, Bleeding risk analysis in stroke; DEFUSE, Diffusion and perfusion imaging evaluation for understanding stroke evolution imaging before thrombolysis; FLAIR, fluid attenuation inversion recovery; EPITHET, the echoplanar imaging thrombolysis evaluation trial; MR RESCUE, mechanical retrieval and Recanalization of stroke clots using embolectomy; EXTEND-IA, extending the time for thrombolysis in emergency neurological deficits-Intra-arterial; iCAS, imaging collarterals in acute stroke.

^*Quantifying collateral perfusion in cerebrovascular disease-Moyamoya disease and stroke patients (NCT01419275), Acute MRI in transient ischemic attack (NCT01531946), and A longitudinal study of multimodal resonance imaging in stroke patients (NCT02024503).