Final answer:
Comparing cortical blood flow in white matter during CTP is done to evaluate the blood distribution across various brain regions, which is crucial for diagnosing and understanding various brain pathologies.
Step-by-step explanation:
The purpose of comparing cortical blood flow in white matter during CT perfusion (CTP) scans is to evaluate the distribution of blood in different brain regions. CTP is useful in assessing various brain conditions, including the detection of ischemic areas in stroke patients and contributing to the evaluation of various brain tumors or other pathologies. Functional MRI (fMRI) similarly measures changes in blood flow related to neural activity, leveraging the fact that active nervous tissue has greater blood flow. The Circle of Willis is an important structure in ensuring constant cerebral perfusion, even during an event of an artery blockage. In the event of a blockage just posterior to the middle cerebral artery on the left, blood would still reach the area through the collateral circulation provided by the Circle of Willis.