6.1.5 Data registration and preservation: Every time after the follow-up visit, researchers should record the required information in the case report sheet timely. After the end of each subjects' observed period, researchers should accurately record relevant information from original records in the form of data in the CRF within 7 days. CRF, informed consent and other documents should be examined and signed by the project leader, then saved in the archive office of institution. If a problem is found, it should be timely dealt with and recorded.