Our study demonstrated three major findings. First, there was no significant difference in time consumption for NCCT scan between CTA and CTP- based imaging assessment strategy. However, CTP- based imaging assessment strategy needed significant longer time for imaging scan and reconstruction than CTA- based strategy. The time delayed for CTP- based strategy was approximately 10 minutes. Second, we found that CTP scan showed a higher failure rate than CTA scan. The failure rate of CTP scan was 11%, and motion was the most common cause. Third, we found the admission NIHSS were significantly associated with CTP scan failure.
In our study, CTP- based imaging assessment strategy showed relatively longer time consumption than CTA- based strategy. Multiphase CTA included a three-time phases scan, while CTP scan contained 30 consecutive spiral scans of the brain. More images raw data would be obtained from CTP scan, and subsequent transform of raw data from scan workstation to reconstruction workstation might be one reason of time delay in CTP- based strategy. Besides that, compared with reconstruction of vascular image from CTA, reconstruction of CTP parametric maps seemed to be a more complicated process. This situation might also be associated the time delay of CTP- based strategy. Currently, automated perfusion analysis software has been widely used in large comprehensive stroke centers. It may dramatically shorten the time usage of CTP reconstruction and subsequent analysis [11–13]. While in primary stroke center, the automated reconstruction software was still not popularized. The decision to open up an advanced CTP examination to assess the AIS patients should be taken into careful consideration for the potential longer time consumption of CTP imaging strategy.
Besides longer time consumption, CTP also showed higher failure rate than CTA in our study. Kauw et al reported a CTP failure rate of 11%, and they found that motion was the leading cause, followed by streak artifacts and poor contrast bolus arrival, which was in line with our study [9]. The main reason for the higher failure rate of CTP might be that it was difficult for the patients to remain stationary during the longer scan time than CTA. In consistent with the prior study, we found that baseline NIHSS was the risk factor that significantly associated with CTP failure [9]. Patients with higher baseline NIHSS would be neurologically more severe, more restless, and more likely to be mobile during the scanning process. We recommended to take caution on the patients with high NIHSS score, and to take effective measures such as fixed band and sedation drugs to keep them static during CTP scan.
When CTP scan failure occurred, usually repeated CTP scan was not suggested because of that waiting the clearance of the contrast retention within the brain would increase the time consumption. Therefore, some previous studies tried to find fungible imaging biomarkers. Nannoni et al reported that NCCT ASPECTS correlated significantly with the CTP infarct core, especially in the AIS patients with late window and large-vessel occlusion. Therefore, they concluded that the use of ASPECTS could be a surrogate maker of CTP core in late-arriving AIS patients with large-vessel occlusion [14]. In addition, simulated multiphase CTA reconstructed from CTP raw data was also reported to be useful in reflecting the perfusion information to a certain extent. Better collateral circulation was tightly correlated with small ischemic core volumes. A multiphase CTA collateral score more than 3 could optimally predict a target mismatch on CTP and a good clinical outcome in AIS patients [15].
Our study had some limitations. First, our study was a retrospective study conducted in single center. As different imaging modalities and different post-processing software were used in different centers, further multi-center trials were needed to be performed. Second, the sample size was relatively small and may limit the reliability of results. Third, the time duration of CTA and CTP post-processing could be influenced by the experience of different radiologists, so a unified post-processing train standard should be taken in further studies.