The present study was approved by the institutional review board of the Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology and was conducted in compliance with the Health Insurance Portability and Accountability Act (HIPAA) of 1996.
Patients
We retrospectively searched database of CCTA that were performed from July 2017 to December 2019. The study population consisted of 346 consecutive patients who were suspected of CAD or CAD was included (Figure 1). General exclusion criteria were poor quality images could not be diagnosis, images couldn’t be recognized or analyzed by DL, patients with incomplete records or previously underwent percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) or other cardio surgery.
CCTA images acquisition and analysis
Multidetector row CT imaging was performed with dual-source CT scanner (Somatom Definition, Siemens Medical Solutions, Forchheim, Germany) and 256-slice CT scanner (Brilliance iCT; Philips Healthcare, Cleveland, OH). Heart rate control (HR≥65 beats/min) was performed with beta-blockers before the scan. Scanning parameters were as following: Detector collimation 128×2×6mm, tube voltage 120kV, tube current 280 mAs. For contrast enhancement, 60-80mL of iopromide (370mgI/mL, Bayer Schering Pharma,Germany) followed by 30-40 mL of pure saline with a flow rate of 4-5 mL/sec. The iodine contrast agent was automatically triggered into descending aorta of 100 HU threshold units. Then the scanning was performed during an inspiratory breath hold of 8 to 14 s after delay of 2s. The reconstruction images were automatic send to a workstation (CoronaryDoc, Shukun technology, Beijing, China) equipped with coronary analysis software tool (Computer Aided Diagnosis of Coronary Artery, Version 1.8, Shukun technology, Beijing, China).
Deep Learning
The patients in the test set were under ICA examination with an interval of less than 30 days after CCTA procedure. We have previously reported the validation of our deep learning system [13, 14]. Before training, the aorta, coronary artery and plaques were labeled on each image by a multi-layer manually annotation system consisting of multiple layers of trained graders. The first layer of graders is comprised of radiologists who had knowledge of medical imaging and coronary anatomy. The second layer of graders is comprised of radiologists with more than three years of work experience in radiology, which is a preliminary inspection of the accuracy of the label. The third and final layer of graders was consistence of experienced experts with over five years of work experience who verify the correctness of label of each image. In this study, we adopted an improved 3-dimensional (3-D) U-Net architecture added a Bottle-Neck model for segmentation coronary arteries and aorta, then a Growing Iterative Prediction Network (GIPN) model was developed to solve the problem of vascular segmentation fracture, final the full coronary tree segmentation was obtained [15]. Based on coronary tree segmentation, multiple planar reformat (MPR), curve planar reformat (CPR), maximum intensity projection (MIP) and volume rendering (VR) images were reconstructed. To detect stenosis, we developed a 3D segmentation neural network and a one-dimensional sequence checking hybrid technique [16]. Firstly, a 3D segmentation neural network was applied to MRP and CPR images to detect stenosis, and then a one-dimensional sequence checking algorithm was used to reduce false positive results (Figure 2).
Three readers with 5 years of experience in cardiac CT imaging diagnosis recorded the CAD-RADS classification based on the degree of coronary stenosis (CAD-RADS 0: 0%, CAD-RADS 1: 1-24%, CAD-RADS 2: 25-49%, CAD-RADS 3: 50-69%, CAD-RADS 4A: 70-99%, CAD-RADS 4B: Left main > 50% or 3-vessel disease, 70-99%, CAD-RADS 5: 100%) according to the CAD-RADS consensus document [6]. Structured report including CAD-RADS category was showed based on the model independently. 100 patients were randomly selected for time consumption (including post-processing, report-writing, typesetting and print) analysis. CAD was defined as stenosis > 50% in coronary artery segment ≥ 2mm in diameter.
Statistical Analysis
Continuous variables were presented as mean ± SD. Categorical variables were presented as percentages or absolute values. We used either the chi-square test, or Fisher’s exact test as appropriate for categorical variables. The diagnostic performance of CAD with DL-based CCTA was determined as sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy by comparison with ICA as the standard of reference. The agreement of the CAD-RADS categories was compared between Readers and the model using the linear weighted kappa identity test. P<0.05 was considered as statistical significance. All statistical analysis was performed using SPSS version 18 (SPSS, Inc., Chicago, IL) and MedCalc Statistical Software version16.8.4.0 (Ostend, Belgium).