Inclusion Criteria:  Patients 18 years of age or older Among patients who visited the emergency department with symptoms related to lower extremities (e.g. lower extremity pain, swelling of the lower extremities, numbness of the lower extremities, redness of the lower extremities), the clinician judges that an ultrasonography of the lower extremity is necessary based on the medical history, physical examination, and blood test results. (or) Patients who need additional ultrasound of the lower extremity vein to check for deep vein thrombosis due to the detection of a pulmonary thromboembolism in an emergency department  Exclusion Criteria:  Do not agree to participate in the study Patients who refuse ultrasound of the lower extremities by an emergency physician or radiologist Patients who have already performed an ultrasound of the lower extremities at another hospital and have been diagnosed with DVT Patients with a history of chronic deep vein thrombosis Patients with hemodynamic instability to refer to diagnostic imaging facility for duplex exam