Statement.
This study received ethics approval by the ethics of the Affiliated Hospital of Qinghai University (AF-RHEC-0062-01). Each patient included in this study received written information and informed consent was obtained from all the participants. This research study was in accordance with the Declaration of Helsinski. All studies were performed under all relevant guidelines and regulations.
Patients.
The data were from October 2019 to December 2020. The clinical and imaging data of AIS patients with acute neurological impairment within 12 hours were analyzed by whole brain volume CT perfusion and CT angiography. Inclusion criteria: (1) one-stop CT scan within 12 hours of onset in our stroke center; (2) diagnosis of anterior circulation infarction based on imaging; (3) patients who underwent CT scan again within one week after clinical diagnosis after treatment (including conservative therapy, intravenous thrombolysis, intravascular therapy). (4) patients older than 18 years and living at 2000–2500 m elevation; (5) the image quality is good and there is no obvious motion artifact. Exclusion Criteria: (1) unable to undergo one-stop stroke screening due to kidney failure, sensitivity to contrast agents, or other reasons; (2) patients with malignant tumors; (3) patients with mental illness; and (4) patients who refused follow-up.
Imaging Protocol.
All patients were scanned on the 128 - slice multidetector CT scanner(Discovery CT 750 HD; GE Medical Systems, Milwaukee, Wis). The scanning parameters were as follows: tube voltage 120kv, tube current 300mA, scanning thickness 5mm, rotation time 1s/circle; Using 4D spiral adaptive scanning (volume shuttle mode) to acquire whole brain perfusion CT data, continuous acquisition 28 times, the total scanning time is 47.38s, the tube voltage is 100kv, the tube current is 80mA; the scanning thickness is 5mm, the time resolution is 1.6s; the pitch 0.984, rotation speed 0.4 s/circle, field of view 320×320 mm; matrix 512×512.
Contrast agent injection scheme: 50ml iopromide (370mgl / s) was injected at a flow rate of 4.5ml / s by high-pressure mechanical injector and 30ml normal saline was injected at the same flow rate for scanning. After injection of iodine contrast agent, perfusion scanning began after 5 s delay. Three-phase CTA was performed 5 min later, and 50 mL iopromide (370 mgl / s) was injected with a high-pressure injection at the injection rate of 4.5 mL / s. The first phase was the peak period of the head and neck artery. The scanning range was from the aortic arch to the parietal skull (Tube voltage100Kv, tube current200mA, rotating speed0.5s / cycle), scanning layer thickness5mm, reconstruction layer thickness0.625mm. The second phase was the peak period of the cranial vein, and the scanning was delayed by 8 s after the first phase scanning. The scanning range was from the skull base to the top of the skull. Phase 3 was the late stage of the cranial vein, which was delayed for 8 s after phase 2 scanning.
Contrast agent injection protocol: Inject 50ml of non-ionic contrast agent iopromide (370mgl/s) through a high-pressure syringe at an injection flow rate of 4.5ml/s and then inject 30ml of normal saline at the same flow rate for scanning. The perfusion scan was started after a delay of 5s after the injection of iodine contrast agent; after 5 minutes, a three-phase CTA examination was performed, and 50ml of non-ionic contrast agent iopromide (370mgl/s) was injected through a high-pressure syringe at an injection flow rate of 4.5ml/s. The first phase is the peak period of the head and neck arteries. The scanning range is from the aortic arch to the top of the skull. The scanning technology is used to automatically track and trigger the contrast agent. The monitoring level is the aortic arch level. The monitoring starts 10s after the injection of the iodine contrast agent. The threshold is set to 70HU; tube voltage ,100KV; tube current 200mA, rotation speed, 0.5 s/circle; scanning layer thickness, 5mm; reconstruction layer thickness, 0.625mm). The second phase is the peak period of cranial veins, after the first stage scan, the scan is delayed by 8 s, and the scan range is from the base of the skull to the top of the skull; the third stage is the late stage of the cranial veins, and the scan is delayed 8s after the second scan.
MRI data were collected by 3.0T magnetic resonance scanner (Magnetom Prisma, Siemens Healthineer) and 64 channel head coil. Conventional sequence scanning of head MR was performed: axial TIWI, T2WI, T2FLAIR and DWI. The specific scanning parameters were as follows:
TIWI: TR 150ms, TE 2.5ms, FOV 230mm, slice thickness 5.0mm.
T2WI: TR 5000ms, TE 117ms, FOV 230mm, slice thickness 5.0mm.
DWI: TR 3230ms, TE 65ms, FOV 230mm, slice thickness 5.0mm.
T2 FLAIR: TR 8000ms, TE 81ms, FOV 230mm, layer thickness 5.0mm.
Image Reconstruction and Analysis
All data post-processing is carried out in AW4.7 software. Peak arterial phase and peak venous phase were selected on the two time-density curves. The input artery and output vein were contralateral middle cerebral artery and superior sagittal sinus. Selecting the largest and most obvious abnormal perfusion level on the image of TTP to describe the region of interest (ROI) manually, CBV, CBF), TTP, MTT, Tmax and PS were collected automatically. The rCBF, rCBV, rMTT, rTTP, rTmax, rPS were calculated on the contralateral side as the normal control area. The ischemic core volume was defined as rCBF < 30% [8–9]. Low perfusion volume is defined as the volume of Tmax > 6s [9–10], which is calculated automatically by software. Fast-stroke software (GE Healthcare, Milwaukee, WI, USA) was used for automatic analysis of multi-phase CTA data, including arterial peak period and MIP image acquisition. According to the European cooperative acute stroke study (ECASS), patients were divided into HT and non-HT groups. The main outcome was a modified Rankin score[8] at 90 days, which defined good outcomes as 0–2 and poor outcomes as 3–6. The side branch score of mCTA was Bijoy K. Menon[9] and others put forward 0–5 score method, defining 0–2 as poor collateral circulation, 3–5 as good collateral circulation.
Statistical Analysis
Statistical analysis using SPSS25.0 software, Normality test and variance homogeneity test, consistent with the normal distribution using independent sample t test, skewness distribution using Wilcoxon rank sum test. The counting data were measured by chi-square test or exact probability method. The receiver operating characteristic (ROC) curve was used to assess the different risk factors for predicting HT. The test level was bilateral a = 0.05, with P < 0.05, the difference was statistically significant.