Continuous blood flow monitoring using patch-type array transducer and portable ultrasound imaging system

Cerebrovascular and cardiovascular diseases such as stroke and coronary artery disease show a significant number of cases with a high mortality rate. Early detection of risk factors is important to prevent cerebrovascular and cardiovascular diseases. Measurements of carotid artery stenosis, blood flow rate, and the wall thickness of vessels by 2D and Doppler mode ultrasound are preferred choices due to advantages of their easy access, non-invasiveness, and safety. However, the current ultrasound imaging system with handheld type probes is not suitable for continuous monitoring and imaging, and the manual measurement is required by qualified personnel at a given time interval. Therefore, it is not an ideal solution for collecting continuous time-series data. We developed a 32-element, patch-type linear array transducer with a small footprint of 11.73 mm x 8 mm, which is an acceptable size to be attached over the carotid artery in the neck area. We evaluated the performance of the developed array transducer using the pulse-echo system and obtained its representative center frequency of 4.5 MHz, bandwidth (-6 dB) 64%, and sensitivity -47 dB. We also implemented a compact tabletop ultrasound system capable of 2D-mode real-time imaging of carotid artery and Doppler measurement of blood flow. In addition, with the tissue-mimicking phantom, we evaluated the performance of the developed system by collecting 2D images and Doppler spectrogram. The -6 dB lateral resolutions of the ultrasound system were 0.76, 0.61, and 1.33 mm at 15, 25, and 35 mm, respectively, and the peak velocity of the Doppler signal was close to 100 cm/s.