In this study, Carotid duplex ultrasound data will be collected. These scans are done as per usual clinical and investigational protocol in National Heart Centre Singapore. The scan images are usually acquired by sonographers, and supervised or verified by physician(s). The data is stored in NHCS Cardiology Image and Information Management System. This system is meant to be a long-term storage, or at the very least, provide at least 7 years of data storage. The nature of the data acquired is part of the clinical assessment of the patient. Hence the data will not be destroyed even after completion of the study.