Table 3.

Wake-Up Stroke Imaging Modalities.

Parenchymal imaging	CT	Noncontrast CT	Screen for early ischemic changes	Time to ischemic change: variable; with MCA occlusion as little as 1 hour48 but often 3+ hours
		Perfusion CT CBV—total volume of  blood in a given  volume of brain  (mL/100 g) CBF—total volume of  blood moving through a  given volume of brain  (mL/100 g) MTT—the average transit  time of blood through a  brain region TTP—time from contrast  arrival-to-peak-intensity  flow through a brain  region	Screen for infarct/penumbra mismatch (see Figure 1)	Time to ischemic change: variable, depends on patient hemodynamics and CBV threshold for “infarct,” but is typically abnormal before clear signs on noncontrast CT
	MRI	Routine MRI	Screen for infarct volume, DWI/FLAIR mismatch (see Figure 2)	Time to ischemic change: DWI—3 minutes49; T2WI—1-4 hours50; FLAIR—3-6 hours51
		Perfusion (PWI) MRI CBV, CBF, and  MTT as defined  previously are the  basic sequences  of a PWI protocol	Screen for infarct/penumbra mismatch
Vascular imaging	CT	CT angiography	Screen for large artery occlusion
	MRI	MR angiography
	Ultrasound	Complete neurosonology (carotid duplex ultrasonography plus transcranial Doppler)

Abbreviations: CT, computed tomography; CBV, cerebral blood volume; CBF, cerebral blood flow; MTT, mean transit time; TTP, time to peak; MRI, magnetic resonance imaging; DWI, diffusion-weighted imaging; PWI, perfusion-weighted imaging; FLAIR, fluid attenuated inversion recovery.