In the United States, Pulmonary Embolism (PE) accounts for 100,000-200,000 deaths annually. Early identification and treatment of the presence of emboli in the systemic vasculature could decrease mortality.  Detection of emboli with Doppler ultrasonography is a method in which efficacy is dependent upon embolus size, flow rate, and user error.  The objective of this study is to quantify the efficiency of Doppler ultrasound at detecting emboli of various sizes over a range of physiological conditions.