Time-Dependent Computed Tomographic Perfusion Thresholds for Patients With Acute Ischemic Stroke

Abstract

P rogression to infarction after acute ischemic stroke onset is time-sensitive and has substantial intersubject variability. 1,2 Computed tomographic (CT) perfusion (CTP) measurement of brain parenchyma can be used to estimate ischemic core and penumbra and, therefore, provide immediate information for treatment decision-making. Current CTP thresholds that estimate these tissue states are generally derived either by comparison with magnetic resonance (MR) diffusion-weighted imaging (DWI), often done within an hour of CTP, or with follow-up infarction in patients who have reperfused sometime within 24 hours.3-11 Because infarcts grow over time and final tissue fate depends greatly on what happens in the minutes to hours immediately after this imaging snapshot, CTP thresholds predicting infarction are likely to depend on the time from stroke symptom onset to imaging, time from imaging to reperfusion, and the quality of reperfusion.Background and Purpose-Among patients with acute ischemic stroke, we determine computed tomographic perfusion (CTP) thresholds associated with follow-up infarction at different stroke onset-to-CTP and CTP-to-reperfusion times. Methods-Acute ischemic stroke patients with occlusion on computed tomographic angiography were acutely imaged with CTP. Noncontrast computed tomography and magnectic resonance diffusion-weighted imaging between 24 and 48 hours were used to delineate follow-up infarction. Reperfusion was assessed on conventional angiogram or 4-hour repeat computed tomographic angiography. T max , cerebral blood flow, and cerebral blood volume derived from delayinsensitive CTP postprocessing were analyzed using receiver-operator characteristic curves to derive optimal thresholds for combined patient data (pooled analysis) and individual patients (patient-level analysis) based on time from stroke onset-to-CTP and CTP-to-reperfusion. One-way ANOVA and locally weighted scatterplot smoothing regression was used to test whether the derived optimal CTP thresholds were different by time. Results-One hundred and thirty-two patients were included. T max thresholds of >16.2 and >15.8 s and absolute cerebral blood flow thresholds of <8.9 and <7.4 mL•min −1•100 g −1 were associated with infarct if reperfused <90 min from CTP with onset <180 min. The discriminative ability of cerebral blood volume was modest. No statistically significant relationship was noted between stroke onset-to-CTP time and the optimal CTP thresholds for all parameters based on discrete or continuous time analysis (P>0.05). A statistically significant relationship existed between CTP-to-reperfusion time and the optimal thresholds for cerebral blood flow (P<0.001; r=0.59 and 0.77 for gray and white matter, respectively) and T max (P<0.001; r=−0.68 and −0.60 for gray and white matter, respectively) parameters. Conclusions-Optimal CTP thresholds associated with follow-up infarction depend on time from imaging to reperfusion.

Ischemic core thresholds change with time to reperfusion: A case control study

“…However, the likely infarct growth in the interval between treatment and infarct measurement in the alteplase group reinforces the concept that ischemic core thresholds are likely to vary with time to reperfusion, and that further refinement of "reperfusion time-dependent" thresholds may be required. 16 Indeed, it possible that the CBF threshold for ischemic core may be even lower with even faster times to reperfusion and possibly with very short stroke onset to CTP times. However, we have no data on patients imaged and recanalized within 60 minutes of stroke onset on which to test this theory.…”

“…Baseline National Institutes of Health Stroke Scale (median, 15; interquartile range [IQR], [11][12][13][14][15][16][17][18][19], age (median, 65; IQR, 59-80), and time to intravenous treatment (median, 153 minutes; IQR, 82-315) were well matched (all p > 0.05). Despite similar baseline CTP ischemic core volumes using the previously validated measure (relative cerebral blood flow [rCBF], <30%), thrombectomy patients had a smaller median 24-hour infarct core of 17.3ml (IQR, 11.3-32.8) versus 24.3ml (IQR, 16.7-42.2; p 5 0.011) in alteplase-treated controls.…”

Use of Noncontrast Computed Tomography and Computed Tomographic Perfusion in Predicting Intracerebral Hemorrhage After Intravenous Alteplase Therapy

“…11 The following CTP variables were then calculated from the CTP functional maps: (1) rvlCBV determined by calculating the CBV value from the lower 2.5th percentile of the contralesional hemisphere CBV distribution and then applying this value to the ipsilesional hemisphere within an ischemic territory denoted by a T max ≥8 s to get a brain volume. The rvlCBV (a ratio standardized to CTP z axis coverage) was obtained by dividing this volume by total ipsilesional hemisphere volume from 4 cm or 8 cm coverages, (2) relative volume of low CBF (rvCBF) determined by calculating the ipsilesional hemisphere volume with CBF ≤7 mL/min•per 100 g again standardized to z axis coverage, 11 (3) relative volume of prolonged T max determined by calculating the ipsilesional hemisphere volume with T max ≥16 s standardized to z axis coverage, 11 (4) PS ischemia -mean PS values (mL/min per•100 g) from within the T max ≥8 s volume (ie, permeability within ischemic tissue), and (5) PS total -mean PS values (mL/min per•100 g] within the entire ipsilesional hemisphere. Gray matter and white matter values were obtained separately for all CTP variables by applying patient-specific HU thresholds to the CTP average map, while excluding cerebrospinal fluid, ventricles, choroid plexus, and large vessels.…”

Segabrottnám við brátt blóðþurrðarslag er mesta framför í læknisfræði í áraraðir

“…Staðfest hefur verið að þröskuldur <30% af blóðflaeði í heilbrigðum heila á TSG í samanburði við flaeðisvigtaða segulómun sé gagnlegur til að greina óafturkraefan skaða með þeim töfum sem eru á endurflaeðismeðferð í dag. 7,39,40 Ef endurflaeði naest hins vegar innan 90 mínútna gaeti þröskuldur <20% verið meira viðeig-andi. 39 Spennandi þróun vaeri ef haegt vaeri að bjarga hinum áður "óbjarganlega" heilavef, einfaldlega með því að meðhöndla fyrr.…”

“…7,39,40 Ef endurflaeði naest hins vegar innan 90 mínútna gaeti þröskuldur <20% verið meira viðeig-andi. 39 Spennandi þróun vaeri ef haegt vaeri að bjarga hinum áður "óbjarganlega" heilavef, einfaldlega með því að meðhöndla fyrr.…”