Transcranial Doppler (TCD) measurement of brain tissue pulsations generated by the major cerebral arteries: an in vitro study

Doppler ultrasound can be used to investigate brain tissue motion. The objective of this study was to construct a physiologically realistic vascular phantom of the brain to help elucidate invivo findings. A silicone cerebrovascular replica based on MRI data was incorporated into a flow circuit generating pulsatile flow (total 434ml/min, 60bpm) of a blood mimicking fluid. An electrical circuit analogue approach was used to achieve a 74:26 split of flow between the anterior and posterior circulations, pressure of ~90mmHg, and realistic flow rates in the major vessels. A polyvinyl-alcohol material mimicked the brain tissue. Ultrasound data were recorded from the phantom using a Spencer Technologies TCD system and analysed 'in house' to estimate tissue pulsation amplitude throughout the cardiac cycle. Properties of the tissue mimic were comparable to brain (speed of sound 1630m.s-1 , density 1.06kg.m-3 , Young’s Modulus 8kPa). Maximum displacements were ~250μm in the phantom (cf. ~200μm in healthy volunteers). Displacement/time curves were similar to in-vivo curves and the phantom helped elucidate features such as phase shifts and asymmetry. In conclusion, the phantom mimics tissue motion due to vessel pulsation, excluding ventricular flow, tissue perfusion and intracranial pressure. It is suitable for studying brain tissue pulsation and helps interpretation of in-vivo findings.