Study population and design
The patients with confirmed AD according to guidelines [19] and who visited the Radiology Department of our Hospital from December 2018 to December 2019 were retrospectively included. The exclusion criteria were 1) no CTA examination within 48 h from admission, 2) patients who underwent thoracic endovascular aortic repair (TEVAR) within 48 h of admission, 3) the intimal flap involved the kidney vessels or did not reach the plane under the renal artery origin, or 4) patients with a history of renal injury. This study was approved by the Ethics Committee of our Hospital. The requirement for informed consent was waived by the committee.
Technical Parameters Of Dynamic Angiography
All patients were examined using a Siemens third-generation dual-source CT (SOMATOM Force, Siemens, Erlangen, Germany). Each patient was placed in the supine position, headfirst, and the scan range was from 3 cm above the arch of the aorta to the symphysis pubis. The DynMulti 4d-xl package was used for multiphase scanning. The contrast agent was iodomyrine (400 mgI/ml), a non-ionic iodine contrast agent (40 ml). The contrast agent was injected at a 4-ml/s flow rate through the cubital vein, and then 40 ml of isotonic saline was injected at a 4-ml/s flow rate. The tube rotation time was 0.25 s/rotation. The tube voltage was 80 kV. The current was automatically set by the caredose4D system. The collimator was set at 48×12 mm with eight phases of scanning.
Dynamic vascular imaging was performed with multiphase scanning (DynMulti 4d-XL package) consisting of eight sessions of scanning with imaging delay times of 10 s, six periods before each scan time of 2.5 s, two phases after the scan time for each period for 5 s, and a scanning time of 25 s. The examinations were completed within 35–38 s. The scanning data were transmitted to the post-processing workstation, the CTA sets were chosen, and all patients had eight images for every CT value measurement. The measurements consisted of the main artery true lumen, false lumen, liver, pancreas, left kidney, the density of the right kidney and intestine, and true and false lumen measurement location. The opposing aortic celiac axis branches above were selected, and the right liver lobe liver measurement was selected to avoid the portal vein and hepatic vein. The pancreas carotid body measurement was selected to avoid the splenic vein and in some patients according to the measurement of the pancreatic duct. The kidney was measured for renal cortex perfusion in the normal area. The small intestines were measured at the duodenum and jejunum for transitional measure thickness.
Image Scanning And Post-processing
After the CT scan, all the original data were stored in DICOM 3.0 format and transmitted to a syngo. Via CB20A (Siemens, Erlangen, Germany) post-processing workstation. The aortic CTA was reconstructed in 3D and post-processed using the CT vascular software package. The dynamic angiography software was used for post-processing, and the post-processing images were transferred to a Neusoft PACS database for storage. Post-processing methods included bone removal (BR), volume rendering (VR), multiple planar reconstructions (MPR), curved planar projection (CPR), and maximum intensity projection (MIP).
Image Result Analysis
All cases were analyzed by two graduate students and a resident in combination with the original image and the post-processing data analysis. For the analysis of the Neusoft PACS data, the resident combined the reading of the original image and part of the post-processing image (MPR, CPR, and MIP) with wide window position adjustments, and the diagnosis was reviewed by a senior attending physician or a deputy chief physician. If there were no agreement on the diagnosis of images by the three above attending physicians, consultation and further discussion were used to reach a conclusion.
AD analysis mainly included a judgment of the affected scope of the AD: looking for AD tears (including the positioning of the tear, the tear form, and the number of tears), observing the AD true and false lumen line, and determining all branches of the aorta vascular blood flow organ involvement. At the same time, according to the density changes of the true and false lumens of the AD, the optimal phase observation in dynamic angiography was sought. The difference of the true and false lumen density was the largest among the phases of 300–450 HU.
Patients with unilateral renal artery involvement were selected, and their uninvolved kidneys were used as a control to analyze the correlation between the density of the false lumen and the density of the renal artery in AD to explore the optimal scanning phase for evaluating the hemodynamic changes in the pseudolumen and changes of organ blood supply to the pseudolumen after AD.
Data Collection
Demographic and clinical data (age, sex, body mass index (BMI), hypertension, hyperlipidemia, smoking, diabetes, coronary heart disease, blood pressure, and heart rate), imaging data (ulcer numbers and characteristics, aortic diameter, pleural effusion, and pericardial effusion), and drugs (antiplatelets, β-blockers, calcium antagonists, angiotensin-converting enzyme inhibitors (ACEIs), and angiotensin receptor blockers (ARBs)) were collected from the patient charts.
Statistical analysis
SPSS 22.0 (IBM, Armonk, NY, USA) was used for statistical analysis. The continuous data are presented as means ± standard deviation and were analyzed using the paired t-test, analysis of variance, and Spearman correlation analysis. The categorical data are presented as n (%) and were analyzed using the chi-square test. P-values < 0.01 were considered statistically significant.