Introduction: Stroke is the third most common cause of disability and the second leading cause of death worldwide. The diagnosis requires a multidisciplinary medical approach, including computed tomography (CT) imaging. The imaging protocol consists of a non-contrast head CT, CT angiography (CTA) of the intracranial and carotid arteries, and CT perfusion (CTP). The imaging always begins with a non-contrast head CT, followed by the other two examinations. Purpose: The aim of the study was to identify the advantages and disadvantages of a different order of imaging protocols. We have investigated whether the calculated CTA-based delay would have a significant impact on the optimal performance of the CTP. We were interested in which CTA reference time point is the most optimal for calculating the additional delay for CTP. Methods: The study consisted of 120 patients who were randomly assigned to 4 groups. The reference time point of the group was determined by a case study of 30 patients, where the required average time for contrast to reach the measured spot was measured. The first group was assigned with the average time with subtracted standard deviation, the second group with the average time, and the third group with the sum of the average and standard deviation. In the fourth group, CTP was performed before CTA. The calculated delays were added to the initial CTP imaging delay and the time to peak (TTP) values were measured after the examination and compared with the optimal value. Results: The second group was proven to be the most successful with the smallest relative deviation of 9,17 %. This was followed by the first group with the average relative deviation of 10,5 %. Much less successful were the third group with 28,67 % and the fourth group with 27,5 % average value of relative deviations. The analysis showed statistically significant differences between all groups, which means that the reference time for the calculation of delay is an important factor for performing optimal CTP. Discussion and conclusion: The average value of the time (16,03 s) is the most appropriate for calculating the additional delay. The least appropriate reference value is when standard deviation is added to the mean values, and when the CTP is performed before the CTA, which means that no additional delay is added. In conclusion, the calculated delay of perfusion imaging based on a previously performed CTA has a significant impact on the performance of CTP and thus the quality of CT imaging in suspected acute ischemic stroke.
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