Rosemary Thompson University of Sydney The Inside of Blood Vessels Wednesday 21st March 14:05-14:55pm, Eastern Avenue Lecture Theatre. Doppler ultrasound allows velocity measurements to be made within the lumen of a blood vessel, without disturbing the flow. The Doppler spectrum from an artery varies over the cardiac cycle, and contains a range of frequency shifts, corresponding to the velocity profile in the artery. It also depends on the ultrasound system and the intervening tissue which, inside a blood vessel, must include the vessel wall. In vascular disease plaques can develop within the vessel wall. Typically these are irregularly shaped, and neither very small nor very large compared to the ultrasound wavelength. We show that even with small physiological sound speed and density variations, such vessel wall inclusions can lead to complicated modulations of the nearby acoustic field.