Barker code in TCD ultrasound systems to improve the sensitivity of emboli detection

In present research, Barker-coded excitation is applied to improve the sensitivity of emboli detection in transcranial Doppler (TCD) ultrasound systems. A 13-chip Barker code with a base pulse sequence that comprises two cycles at 2 MHz is used to compare with a 20-cycle pulse in both simulation studies and in vitro experiments. The results show that the system using coded excitation gains a 2.78-dB improvement in measured embolus-to-blood ratio (MEBR) while keeping a similar signal-to-noise ratio (SNR). The simulation results also indicate that the MEBR of the emboli are related to their velocities-a fast embolus has lower MEBR compared with a slow one with the same backscatter amplitudes, which makes fast emboli more difficult to detect. TCD system using coded excitation is more sensitive for faster and smaller emboli, which is significant for early diagnosis of stroke.