Use of Imaging to Select Patients for Late Window Endovascular Therapy

Gregory W. Albers, MD

Stroke. 2018;49(9):2256-2260.

Technical Issues With CTP

To be confident about the accuracy of CTP volumes, it is important to have a technically adequate scan. CTP analysis programs typically require identification of the flow in a normal vessel that has early arrival of the contrast bolus (known as the arterial input function) and the flow through a venous sinus where the bolus departs the brain (known as the venous outflow function). The scan needs to be long enough in duration to capture the full arterial input waveform, as well as the venous output. In general, a scan time of 55 to 60 seconds is required to account for delayed and dispersed bolus arrival in patients with reduced cardiac output.^[11]

Patient movement is the most common cause of CTP artifacts. Artifacts can be minimized by making sure that the patient is tightly secured in the scanner and is relatively calm at the time that perfusion imaging begins. An adequate contrast bolus, with a large bore IV, is also required.

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Table 1. Key Imaging-Based Inclusion Criterial for DEFUSE 3 and DAWN
	DEFUSE 3	DAWN
Ischemic core volume	≤70 mL	≤20 mL if age >80
		≤30 mL if age <80 and NIHSS 10–20
		≤50 mL if age <80 and NIHSS >20
Mismatch volume	≥15 mL and a mismatch ratio of ≥1.8	Not required
Vessel occlusion	M1 or ICA (cervical and intracranial)	M1 or ICA (intracranial and cervical if stent not anticipated to be required)

DAWN indicates Triage of Wake-up and Late Presenting Strokes Undergoing Neurointervention With Trevo); DEFUSE 3, Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke 3; ICA, internal carotid artery; M1, the first segment of the middle cerebral artery; and NIHSS, National Institutes of Health Stroke Scale.

Table 2. MRI Versus CTP in Early and Late Window Thrombectomy Studies
Study	N	90-d mRS 0–2	90-d mRS 0–2	Absolute
Study	N	Control (%)	Thrombectomy (%)	Benefit (%)
SWIFT PRIME*
MRI	34	33	63	30
CTP	139	40	60	20
DEFUSE 3†
MRI	49	19	61	42
CTP	133	16	39	23
DAWN
MRI	83	35‡		NA
CTP	123	29‡		NA

CTP indicates computed tomography perfusion; DAWN, Triage of Wake-up and Late Presenting Strokes Undergoing Neurointervention With Trevo; DEFUSE 3, Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke 3; MRI, magnetic resonance imaging; mRS, modified Rankin Scale; and SWIFT PRIME, Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment for Acute Ischemic Stroke.
*SWIFT PRIME was an early window (<6 hours) study.
†CTP and MRI groups had statistically significant treatment effects on the studies primary outcome.
‡DAWN reported pooled data for the thrombectomy and control arms for the MRI and CTP subgroups.