Prof. Hae Gyun Lim Profile

Prof. Hae Gyun Lim

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Publications (2)

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Proceedings Article | 15 February 2021 Poster + Presentation + Paper

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

Kyungmin Kim, Miji Kim, Yeonseong Park, Hae Gyun Lim, Changhan Yoon, Hyung Ham Kim

Proceedings Volume 11602, 116021B (2021) https://doi.org/10.1117/12.2582071

KEYWORDS: Ultrasonography, Imaging systems, Transducers, Blood circulation, Doppler effect, Arteries, Safety, Real time imaging, Neck

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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.

Proceedings Article | 15 February 2021 Poster + Presentation + Paper

Frequency-dependent calcium dynamics in ultrasound mechanotransduction

Jinhee Yoo, Hae Gyun Lim, Hyung Ham Kim

Proceedings Volume 11602, 116021E (2021) https://doi.org/10.1117/12.2581558

KEYWORDS: Ultrasonography, Calcium, Transducers, Tissues, Cell mechanics, Cancer, Calibration, Alzheimer's disease

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Calcium signaling is a second messenger that triggers physiological changes at the cellular level, such as proliferation, differentiation, or apoptosis. It was recently found that calcium dynamics play a vital role in many studies, including cancer, Alzheimer’s disease, and Parkinson’s disease, and we studied how intracellular signaling pathways work by ultrasound mechanotransduction. However, since ultrasound mechanotransduction does not yet have many experimental results by the quantified ultrasound parameters, little is known about the mechanism between ultrasound parameters and calcium dynamics. We investigate calcium level changes using different frequencies of ultrasound to study intracellular signal pathways of fibroblasts, which may function as one of the contributing factors of tissue repair. We quantified a few major ultrasound stimulation parameters, i.e., operating frequency, beam width, and acoustic pressure. Three 40 MHz ultrasound transducers with different f-numbers (0.8, 1.0, and 1.5) were designed and fabricated. During the cell stimulation, ultrasound waves with different frequencies (36, 45, and 69 MHz) but the same beam width and same acoustic pressure were exerted on the cells. The cell lines used were NIH/3T3 fibroblasts. At the fixed acoustic pressure and beam width, intracellular calcium level increased more rapidly at higher frequencies, which shows that the intracellular signal pathways of fibroblasts may be mainly dependent upon the frequency used for stimulation.

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