Feasibility and diagnostic accuracy of using brain attenuation changes on CT to estimate time of ischemic stroke onset
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DIAGNOSTIC NEURORADIOLOGY
Feasibility and diagnostic accuracy of using brain attenuation changes on CT to estimate time of ischemic stroke onset Grant Mair 1
&
Awad Alzahrani 2 & Richard I. Lindley 3,4
&
Peter A. G. Sandercock 2
&
Joanna M. Wardlaw 1
Received: 2 September 2020 / Accepted: 21 October 2020 # The Author(s) 2020
Abstract Purpose CT attenuation of ischemic brain reduces with time after stroke onset. We aimed to quantify this relationship and test the feasibility and accuracy of estimating stroke onset time using only CT attenuation of visible ischemic lesions, the CT-Clock Tool. Methods We selected CT scans with ischemic lesions representing a range of stroke-onset-to-scan times (elapsed time) from a well-defined stroke trial. We measured the attenuation of ischemic lesions and contralateral normal brain to derive attenuation ratio. We assigned scans to development (75%) or test (25%) datasets. We plotted the relationship between attenuation ratio and elapsed time in the development dataset and derived a best-fit curve. We calculated estimated time in the test dataset using only the attenuation ratio curve. We compared estimated time to elapsed time and derived absolute error for estimated time. We assessed area under the receiver operating characteristic (AUROC) curve for identifying scans ≤ 4.5 h elapsed time. Results We included 342 scans from 200 patients (41% male, median age 83 years). Elapsed time range: 22 min to 36 days. Estimation errors were least at early elapsed times (r = 0.82, p < 0.0001): median absolute error was 23, 106, 1030 and 1933 min for scans acquired ≤ 3, > 3–9, > 9–30 and > 30 h from stroke onset, respectively. AUROC was high at 0.955. Conclusions It is feasible to accurately estimate stroke onset time using simple attenuation measures of ischemic brain. Our method was most accurate 0–9 h from onset and may be useful for treatment eligibility assessment, especially where imaging resources are limited. Keywords Stroke . Ischemia . CT . Attenuation
Introduction In the first hours and days following the onset of an ischemic stroke, the CT attenuation of affected brain reduces with time.
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s00234-020-02591-w. * Grant Mair [email protected] 1
Edinburgh Imaging, and UK Dementia Research Institute at the University of Edinburgh and Centre for Clinical Brain Sciences, University of Edinburgh, Chancellor’s Building, 49 Little France Crescent, Edinburgh EH16 4SB, UK
2
Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
3
Westmead Applied Research Centre, University of Sydney, Sydney, Australia
4
The George Institute for Global Health, Newtown, Australia
Within a few hours of symptom onset, ischemic lesions are often not visible to the naked eye. By 3–6 h, subtle changes such as loss of normal grey-white matter differentiation are appreciable but can be challenging to detect [1]. In the 12– 48 h after onset, the ischemic lesion becomes
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