What technology utilizes sound waves to evaluate blood flow in the heart and blood vessels?

Doppler ultrasound is the correct answer because it specifically employs sound waves to measure the velocity and direction of blood flow within the heart and blood vessels. This technique is particularly effective for assessing conditions such as blood clots, valve function, and identifying any potential blockages in the vascular system.

In contrast, while echocardiography also utilizes sound waves to visualize heart structures and assess their function, it primarily focuses on the images of the heart rather than the flow of blood. An electrocardiogram (ECG) monitors the electrical activity of the heart rather than blood flow, and an electrophysiological study (EPS) evaluates the electrical system of the heart to diagnose arrhythmias. Thus, Doppler ultrasound distinctly serves the purpose of analyzing blood flow, making it the appropriate choice in this context.