EIC on NCCT can appear within 6 hours of last known normal (LKN), and can be quantified using the Alberta Stroke Program Early CT Score (ASPECTS). However, there is lack of data describing when EIC first appear.

We leveraged our Mobile Stroke Unit (MSU) to determine the incidence of Early Ischemic Changes (EIC) on serial non-contrast computed tomography (NCCT).

Prospectively derived data from tissue plasminogen activator (tPA) eligible patients on MSU who had serial NCCT scans within 1 and 6 hours of LKN, and definite strokes on subsequent testing. EIC, defined as ASPECTS ≤ 7, were correlated to time from LKN, stroke severity (National Institutes of Health Stroke Scale, NIHSS), and large vessel occlusion (LVO) on neuroimaging. Scans were graded by Vascular Neurology fellow, with random scans compared with Vascular Neurology attending (Κ=0.69).

57 patients met above inclusion criteria. Of these, 54 had NCCT within 1 hour (median 46 minutes, IQR 39-52) and 31 within 6 hours (median 105 minutes, IQR 90-139) of LKN with sufficient diagnostic quality. Mean ASPECTS was 9.2 and 8.7 for each time point with average NIHSS 14.9. EIC were identified in 4 patients (7%; e.g. ASPECTS 6, 6, 7, 7) within 1 hour and 5 patients (16%; e.g. ASPECTS 2, 3, 7, 7, 7) within 6 hours of LKN. 2 patients had substantial change in ASPECT score (≥ 3 points) on NCCT within 6 hours. There was no association between ASPECTS score and time from LKN to CT (within 1 hour p=0.63, within 6 hours p=0.96). EIC detected within 6 hours correlated to presence of LVO (p=0.01) and stroke severity (p=0.03).

Though limited by small sample, substantial ASPECTS decay within 6 hours of LKN is rare. Close scrutiny of NCCT for EIC within this timeframe may not be necessary for determining eligibility for endovascular thrombectomy.