This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Pathology
A decrease in cerebral blood flow to zero causes death of brain tissue within 
Select and explain. 
A. 4 -- 10 minutes, B. 20 -- 30 minutes, C. 50 -- 60 minutes, D. 80 -- 90 minutes
A: 4 -- 10 minutes
Answer: A: 4 -- 10 minutes 
Explanation: (A) 4-10 minutes # Decrease in cerebral blood flow to zero causes death of brain tissue within 4-10 minutes;> Values <16-18 mL/100 g tissue per minute cause infarction within an hour; and> Values <20 mL/100 g tissue per minute cause ischemia without infarction unless prolonged for several hours or days.> If blood flow is restored prior to a significant amount of cell death, the patient may experience only transient symptoms, and the clinical syndrome is called a TIA.> Tissue surrounding the core region of infarction is ischemic but reversibly dysfunctional and is referred to as the ischemic penumbra.> The penumbra may be imaged by using perfusion-diffusion imaging with MRI or CT