| Objective We assessed the effects of reducing temporal resolution on the accuracy of the results of CT perfusion of acute stroke patients by observing the change of Time-Density Curves,evaluating the quality of CT perfusion images and analyzing the result of CT perfusion parameters .Materials and Methods The CT perfusion data of 24 acute cerebral ischemic patients were investigated retroactively. All the patients received conventional non-enhanced CT and then PCT. A 45 ml bolus of Omnipaque(300mg/ml of iodine)was administered at an injection rate of 4.0ml/s.Dynamic CT scanning was initiated 5 seconds after the injection. The 8 adjacent 5mm thick perfusion slices were defined at the level of the basal ganglia.Scanning lasted for a cine duration of 50S,resulting in 792 imagines.For each group of patients,perfusion datasets were generated by analyzing PCT data with nine temporal resolutions.PCT images were analyzed with the brain stroke protocol of CT perfusion 3 analysis software. Time-Density Curves were compared,visual scoring about pseudo-color feature on the perfusion maps was carried out,and chose the same ROI on the CT perfusion images of different temporal resolutions to evaluate the variability of the parameters(CBF,CBV,MTT) by Friedman test,Kendall's W test and Wilcoxon test.Result With temporal resolution descending,Time-Density Curve is becoming steeper and steeper.The visual scoring of image quality of the perfusion maps (CBF,CBV,MTT)is gradually declining.This phenomenon is more significant in CBF and MTT.Analyze the perfusion parameters of 24 patients with cerebral ischemia whom were grouped according to different temporal resolutions:(1)All regions of interest: the temporal resolution down to 1 image / 1.0s had already effected the measurements of absolute value of perfusion parameters in CBF and MTT significantly,while absolute value of perfusion parameter in CBV was effected significantly until the temporal resolution down to 1 image / 5.0s.(2)Normal cerebral hemisphere:the decrease of temporal resolution didn't have a significant impact on the measurement of absolute value of perfusion parameter in CBV. The temporal resolution down to 1 image / 1.0s had already effected the measurements of absolute value of perfusion parameters in CBF and MTT significantly.(3)Ischemic cerebral hemisphere:the temporal resolution down to 1 image / 1.0s had already effected the measurements of absolute value of perfusion parameters in CBF and MTT significantly,while absolute value of perfusion parameter CBV was not effected significantly until the the temporal resolution down to 1 image / 5.0s.(4)The ratio of perfusion parameters in ischemic/healthy hemsiphere:there wasn't significant on the measurement of relative value of perfusion parameter in CBF and CBV while decreasing the temporal resolution. When the temporal resolution down to 1 image / 5.0s the effected of the measurement of relative value of perfusion parameter in MTT was significantly.(5)The cortex,white matter and basal ganglia:the temporal resolution down to 1 image / 1.0s had already effected the measurements of absolute value of perfusion parameters in CBF and MTT significantly,while absolute value of perfusion parameter CBV of white matter was effected significantly until the temporal resolution down to 1 image / 4.0s.Conclusion With temporal resolution descending,the shape of the Time-Density Curve changed.At the same time, the quality of the perfusion pseudo-color function maps gradually reduced. To obtain the accurate quantitative CT perfusion parameters, we still recommend using the temporal resolution of 1 image / 0.5S cine scan mode. The influence of temporal resolution descending on the relative value is fewer than that on the absolute value. Temporal resolution can be reduced to one image per four seconds without altering the precision of measurement of relative value. Among the three absolute value,the influence of temporal resolution descending on the value of CBV is the fewest.
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