A likelihood ratio map to predict infarct risk with the presence of ischemic penumbra.

Background The ischemic penumbra defines the cerebral tissue which can be salvaged with prompt reperfusion. This is defined by thresholded volumes of perfusion defect based on magnetic resonance image (MRI) or computer tomography (CT) perfusion. This volume based approach excludes consideration of regional difference such as variation in vascular supply relating to the degree of leptomeningeal anastomoses. Hence a voxel based method may help to clarify tissue fate in different brain regions. We hypothesis that the likelihood of tissue infarction differs depend on the brain region. Method Ischemic stroke patients presented within 4.5 hours of onset, received tissue plasminogen activator (tpa) with middle cerebral artery (MCA) occlusion on CT angiography and had CT perfusion (64 multirow scan) were recruited. Ischemic penumbra was defined as region of perfusion defect (Tmax > 2 seconds) not overlapped by the infarct core (cerebral blood volume > 2.5 seconds). Final infarct was assessed by MRI beyond 3 months from onset. Positive likelihood ratio for infarction (PLR) was generated at a voxel level, taking into account the relationship between the finding of penumbra and infarct at a given voxel. We defined voxels with PLR between 5-10 as providing useful clinical information with regards to risk of infarction; and voxels PLR > 10 as highly likely to progress to infarction. Result 19 patients were studied with median age of 66 years (10 males). The regions within the penumbra supplied by the deep MCA compartment (striatocapsular and internal watershed regions) had PLR values > 10 while the more superficial compartment has PLR range of 1.3-5.0. The posterior temporoparietal region had PLR < 2. Conclusion The deep compartment of the MCA territory has very high PLR and is most likely to progress to infarction despite receiving tpa. A likelihood ratio approach may help to refine the zone least likely to infarct, the penumbra and the infarct core on CT perfusion imaging.