Figure 4
From: Aneurysmal subarachnoid haemorrhage from a neuroimaging perspective
Effect of the angle between the ultrasound beam and blood flow. (1) Ultrasound beam is parallel to blood flow, acquiring an optimal, high-frequency Doppler signal. (2) Ultrasound beam forms an angle <20°, leading to a good signal. (3) Ultrasound beam is almost at 90°, resulting in a damped waveform. (4) Blood flow direction is away from ultrasound beam, which results in a negative Doppler signal.