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Figure 2. Perfusion maps from an acute posterior circulation stroke causing left posterior cerebral artery infarction at 7 h and 15 min after last known well time. Maps are from the Siemens syngo.CT Neuro perfusion package which include (A) MTT, (B) Tmax, (C) CBV and (D) CBF. Images demonstrate an acute left occipital perfusion lesion involving the posterior cerebral artery vascular territory. The vessel occlusion was not seen on CT angiography. Changes are most prominent on the (A) MTT and (B) Tmax and (D) CBF maps. Perfusion maps from the same acute posterior circulation stroke seen in Figure 2A-D. Map outputs are from the MiStar neuro perfusion package which include; (E) MTT, (F) DT, (G) CBV and (H) CBF. Images demonstrate an acute left occipital lesion most evident on the (E) Tmax, (F) DT and (H) CBF maps. Similar to the Siemens syngo.CT Neuro perfusion package, the acute lesion is not well visualised on the CBV map. There is a notable difference in the volume of the perfusion lesion seen across the packages. This reflects the different algorithms employed by the two software proprietors in determination of the perfusion maps. Evolution of the acute posterior circulation stroke demonstrated in Figure 2. (I) Initial non-contrast CT at 7 h and 15 min after last known well time demonstrates no acute change. (J) Initial summary map from the MiStar neuro perfusion package using the conventional thresholds for core and penumbra of CBV < 30% and DT > 3 s does not demonstrate a detectable perfusion lesion. (K) Delay time map demonstrates a perfusion lesion at the threshold of DT > 2 s (but below the DT 3 s threshold for “penumbra”. (L) Progress diffusion weighted magnetic resonance imaging at 24 h and 40 min after last known well time demonstrating an established right posterior cerebral artery infarct. Discordance with the automated map and similarity to the DT > 2 lesion suggest conventional perfusion thresholds are not optimised for posterior circulation strokes. Both cases also highlight the need not to simply rely on the core/penumbra maps, but to look at all the perfusion maps. MTT: Mean transit time; CBV: cerebral blood volume; CBF: cerebral blood flow; DT: delay time.