Clinically Relevant Reperfusion in Acute Ischemic Stroke: MTT Performs Better than Tmax and TTP

Abstract

Background While several MRI parameters are used to assess tissue perfusion during hyperacute stroke, it is unclear which is optimal for measuring clinically-relevant reperfusion. We directly compared MTT prolongation (MTTp), TTP, and time-to-maximum (Tmax) to determine which best predicted neurological improvement and tissue salvage following early reperfusion. Methods Acute ischemic stroke patients underwent three MRI's: <4.5hr (tp1), at 6hr (tp2), and at 1 month after onset. Perfusion deficits at tp1 and tp2 were defined by MTTp, TTP, or Tmax beyond four commonly-used thresholds. Percent reperfusion (%Reperf) was calculated for each parameter and threshold. Regression analysis was used to fit %Reperf for each parameter and threshold as a predictor of neurological improvement [defined as admission National Institutes of Health Stroke Scale (NIHSS) – 1 month NIHSS (ΔNIHSS)] after adjusting for baseline clinical variables. Volume of reperfusion, for each parameter and threshold, was correlated with tissue salvage, defined as tp1 perfusion deficit volume – final infarct volume. Results 50 patients were scanned at 2.7 hours and 6.2 hours after stroke onset. %Reperf predicted ΔNIHSS for all MTTp thresholds, for Tmax > 6s and > 8s, but for no TTP thresholds. Tissue salvage significantly correlated with reperfusion for all MTTp thresholds and with Tmax > 6s, while there was no correlation with any TTP threshold. Among all parameters, reperfusion defined by MTTp was most strongly associated with ΔNIHSS (MTTp>3s, p=0.0002) and tissue salvage (MTTp> 3s and 4s, P<0.0001). Conclusion MTT-defined reperfusion was the best predictor of neurological improvement and tissue salvage in hyperacute ischemic stroke.

Human Urinary Kallidinogenase Improves Outcome of Stroke Patients by Shortening Mean Transit Time of Perfusion Magnetic Resonance Imaging

“…So far, MTT, a timebased perfusion parameter, was proved to be a better predictor of reperfusion. 13 This study indicated that HUK shortened MTT in stroke patients 12 days after therapy using perfusion MRI. The MTT is used to predict the CBF of penumbra and to assess cerebral perfusion in acute ischemic stroke patients.…”

“…14 MTT-defined reperfusion also agreed with neurologic outcomes and tissue rescue after stroke. 13 Hypoperfusion is the main pathologic characteristic of ischemic stroke, which triggers a number of acute pathophysiological processes including oxygenic stress, inflammation, apoptosis, and so on. It is well known that the tissue plasminogen activator salvages brain tissue by recanalization and improving perfusion.…”

Technical considerations of multi-parametric tissue outcome prediction methods in acute ischemic stroke patients

“…This discrepancy may owe to the use of the block-circulant singular value decomposition method, which is delay-insensitive 62 . This interpretation is supported by additional studies showing that block-circulant singular value decomposition improves the predictive value of MTT compared to standard singular value decomposition 60 even to the point of outperforming Tmax 63 . While CBV may have utility in multi-parametric datasets, previous studies agree that CBV alone, also when derived from CT imaging, correlates poorly with final tissue outcome 64 .…”

Elevated brain oxygen extraction fraction measured by MRI susceptibility relates to perfusion status in acute ischemic stroke

“…For mismatch classification, hypo-perfusion was defined as MTT exceeding 6 s. 31 This definition was based on MTT instead of time-to-maximum (Tmax), because MTT has been shown to more strongly correlate with clinical outcomes and better reflect subtle changes in local tissue status than Tmax. 32 Patients were classified by visual inspection of the MTT and DWI maps as having no hypo-perfusion (no voxels with MTT > 6 s); a perfusion-diffusion match; or a perfusion-diffusion mismatch.…”