Exploration of the embolus to blood power ratio model (EBR) for characterizing microemboli detected in the middle cerebral artery

Sizing microemboli in flowing blood using pulse Doppler ultrasound has been investigated using the embolus-to-blood power ratio model (EBR). The EBR as a function of 1.6 MHz and 2.4 MHz carrier frequencies and of embolus size is explored for formed element emboli and gas bubbles, as a platform for characterizing microemboli in prosthetic heart valve patients, detected in the middle cerebral artery (MCA). Uncertainties in the backscatter coefficient of blood and Doppler sample volume size are explored, and shown to have a nominal effect on embolus sizing and characterization. Comparison of these theoretical EBR predictions with preliminary in vivo results from patients with embolizing prosthetic aortic valves, using a novel dual-frequency Doppler, indicate that microemboli from aortic prosthetic valves are particulate, and not cavitation bubbles generated at valve closure