Volumetric ultrasound blood flow imaging in human brain phantoms

Cerebral blood flow is essential in maintaining brain function, and its disruption is related to various cerebrovascular diseases such as stroke. Transcranial doppler (TCD) has been used in clinics and hospitals for measuring the blood flow velocity of the basal arteries in human brain. Conventional TCD is performed using a single transducer through temporal windows, measuring blood flow spectrum in 1-D. B-mode TCD, also known as transcranial color-coded duplex (TCCD), combines the spectrum with 2-D anatomical contrast. However, the efficiency TCD/TCCD can be limited due to the demanding of prior anatomical knowledge and practical experience in probe positioning and angulation, making the techniques highly operator dependent. In this work, the feasibility of using a 2-D matrix array probe for volumetric transcranial blood flow imaging in human brain was demonstrated. The performance of the probe was evaluated using both numerical simulation and a 3-D printed calvaria phantom with flow in cross tubes embedded. In numerical simulation, an average spatial resolution of 1.35 mm was achieved transcranially at a central frequency of 2 MHz with an 3 × 3 × 8 cm3 field of view. Meanwhile, preliminary phantom results showed that the flow signals can be spatially resolved up to 8 cm deep through the highly attenuated calvaria, at a volume rate of up to 295 Hz, with a signal-to-noise ratio improvement of up to 10.5 dB using microbubble contrast agents.