MRI-guided selection of patients for treatment of acute ischemic stroke

Abstract

Purpose of review: To summarize what is known about the use of MRI in acute stroke treatment (predominantly thrombolysis), to examine the assumptions and theories behind the interpretation of magnetic resonance images of acute ischemic stroke and how they are used to select patients for therapies, and to suggest directions for future research.

Recent findings: Recent studies have been contradictory about the usefulness of MRI in selecting patients for treatment. New MRI models for selecting patients have emerged that focus not only on the ischemic penumbra but also on the infarct core. Fixed time-window selection parameters are being replaced by timing-based individualized MRI stroke features. New ways to interpret traditional MRI stroke sequences are emerging.

Summary: Although the efficacy of acute stroke treatment is time dependent, the use of fixed time windows cannot account for individual differences in infarct evolution, which could potentially be detected with MRI. Although MRI shows promise for identifying patients who should be treated, as well as excluding patients who should not be treated, definitive evidence is still lacking. Future research should focus on validating the use of MRI to select patients for intravenous therapies in extended time windows.

Figure 1

Panel A shows a schematic of how the infarcted core is hypothesized to grow into the ischemic penumbra if blood flow is not restored. Panel B shows a schematic of how diffusion and perfusion imaging is used to approximate the ischemic penumbra. Panel C shows a schematic of the unstable core in which restoration of blood flow to the infarcted core results in deleterious consequences.

Figure 2

DWI, PWI and FLAIR sequences from a single time point of an acute ischemic stroke patient are shown. Although the entire MCA territory is infarcted on DWI, the inferior division of the MCA territory (red circles) has experienced reperfusion on PWI, while the superior division territory (yellow circles) has not. On the FLAIR image the T2 signal change is much more advanced in the reperfused territory.

Figure 3

MRI scans are shown from two time points of an ischemic stroke patient. On the acute scan the DWI positive stroke does not show any blood-brain barrier damage on T1 post contrast imaging or any hemorrhagic transformation on hemosiderin imaging. However blood-brain permeability imaging (BBPI) detects an area of contrast leakage (yellow circle). Follow-up imaging demonstrates hemorrhagic transformation in the area of BBB damage (red circle) seen on BBPI.