Reply
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* Howard Yonas
* Peter J.  Jannetta
* Elad Levy

In regard to the comment by Lev and Ackerman concerning our article, *Reversible Ischemia Determined by Xenon-Enhanced CT After 90 Minutes of Complete Basilar Artery Occlusion,* we agree that the fogging effect may have initially introduced error into our ability to define infarction. Nonetheless, subsequent studies not cited in this article demonstrated retained tissue volume. Additionally, it must be noted that hemorrhage transformation of infarcted tissue occurred only on the left, where the PCA territory remained occluded despite attempted thrombolysis. The fact that hemorrhagic transformation was absent on the right, with Xe/CT and angiographic evidence of normal parenchymal blood flow, leads us to believe that this tissue was viable with intact perfusion regulatory mechanisms.

It should be clarified that the region with flow values less than 6 cc/100 g/min were primarily within the deep white matter of the occipital lobe. These therefore did not represent the more traditional mixed cortical flow values for the threshold of infarction that are more commonly referred to in the physiologic literature.

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