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1. Visualization of intracellular calcium transport between cells using high frequency ultrasound and FRET live-cell imaging

   https://doi.org/10.1109/IUS46767.2020.9251840  

   Rho, Sunghoon; Hwang, Gyoyeon; Kim, Jihun; Moon, Sunho; Yoon, Sangpil (September 2020, 2020 IEEE International Ultrasonics Symposium (IUS))

   The live visualization with fast kinetics of the interaction between cells has been long term challenges because of the lack of efficient stimulation methods. We propose an approach to achieve single cell resolution stimulation and FRET-base calcium live cell imaging to visualize fast kinetics of calcium transport between physically connect neighboring cells. Chemical stimulation stimulates cells within a dish at the same time and is not suitable for the study of cell-cell interaction. We replaced chemical stimulation with ultrasound-based mechanical stimulation approach to provide precise spatiotemporal resolution. To achieve this, we integrated 3D translation stages and epi-fluorescence microscope and a developed 150 MHz high frequency ultrasound with f number of 1 and aperture size of 1 mm. The 150 MHz transducer can focus within 10 micrometers in diameter and directly stimulate cells by disturbing cell plasma membranes without microbubbles. High frequency stimulation was used to introduce calcium ions into cytoplasm of cells. Results demonstrate calcium transport between cells, visualized by FRET calcium biosensor after only one cell was stimulated by the developed high frequency ultrasonic transducer. 

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2. Development of a Wearable Ultrasound Transducer for Sensing Muscle Activities in Assistive Robotics Applications

   https://doi.org/10.3390/bios13010134  

   Xue, Xiangming; Zhang, Bohua; Moon, Sunho; Xu, Guo-Xuan; Huang, Chih-Chung; Sharma, Nitin; Jiang, Xiaoning (January 2023, Biosensors)

   Robotic prostheses and powered exoskeletons are novel assistive robotic devices for modern medicine. Muscle activity sensing plays an important role in controlling assistive robotics devices. Most devices measure the surface electromyography (sEMG) signal for myoelectric control. However, sEMG is an integrated signal from muscle activities. It is difficult to sense muscle movements in specific small regions, particularly at different depths. Alternatively, traditional ultrasound imaging has recently been proposed to monitor muscle activity due to its ability to directly visualize superficial and at-depth muscles. Despite their advantages, traditional ultrasound probes lack wearability. In this paper, a wearable ultrasound (US) transducer, based on lead zirconate titanate (PZT) and a polyimide substrate, was developed for a muscle activity sensing demonstration. The fabricated PZT-5A elements were arranged into a 4 × 4 array and then packaged in polydimethylsiloxane (PDMS). In vitro porcine tissue experiments were carried out by generating the muscle activities artificially, and the muscle movements were detected by the proposed wearable US transducer via muscle movement imaging. Experimental results showed that all 16 elements had very similar acoustic behaviors: the averaged central frequency, −6 dB bandwidth, and electrical impedance in water were 10.59 MHz, 37.69%, and 78.41 Ω, respectively. The in vitro study successfully demonstrated the capability of monitoring local muscle activity using the prototyped wearable transducer. The findings indicate that ultrasonic sensing may be an alternative to standardize myoelectric control for assistive robotics applications. 

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3. Efficient Global Sensitivity Analysis of Model-Based Ultrasonic Nondestructive Testing Systems Using Machine Learning and Sobol’ Indices

   https://doi.org/10.1115/1.4051100  

   Nagawkar, Jethro; Leifsson, Leifur (November 2021, Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems)

   null (Ed.)

   Abstract The objective of this work is to reduce the cost of performing model-based sensitivity analysis for ultrasonic nondestructive testing systems by replacing the accurate physics-based model with machine learning (ML) algorithms and quickly compute Sobol’ indices. The ML algorithms considered in this work are neural networks (NNs), convolutional NN (CNNs), and deep Gaussian processes (DGPs). The performance of these algorithms is measured by the root mean-squared error on a fixed number of testing points and by the number of high-fidelity samples required to reach a target accuracy. The algorithms are compared on three ultrasonic testing benchmark cases with three uncertainty parameters, namely, spherically void defect under a focused and a planar transducer and spherical-inclusion defect under a focused transducer. The results show that NNs required 35, 100, and 35 samples for the three cases, respectively. CNNs required 35, 100, and 56, respectively, while DGPs required 84, 84, and 56, respectively. 

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4. Hydrogel-Fractal Piezoelectric Bilayer Transducer for Wireless Biochemical Sensing

   https://doi.org/10.1109/EMBC44109.2020.9175819  

   Islam, Sayemul; Park, Moonchul; Song, Seung Hyun; Kim, Albert (July 2020, 2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC))

   This paper reports on a novel transducer for wireless biochemical sensing. The bilayer transducer consists of a fractal piezoelectric membrane and pH-sensitive chemo-mechanical hydrogel, which overcomes many shortcomings in the chemical and biochemical sensing. The fractal design on the piezoelectric membrane enhances frequency response and linearity by employing periodically repeated pore architecture. As a basis of the pore, a Hilbert space-filling curve with modifications is used. On the surface of the fractal piezoelectric membrane, the hydrogel is laminated. When the bilayer transducer is introduced to a pH environment (e.g., pH = 4, 8, and 12), the hydrogel swells (or shrinks) and induces the curling of the bilayer transducer (10.47°/pH). The curvature then exhibits various ultrasound responses when the bilayer transducer was excited. The measured voltage outputs using an ultrasonic receiver were 0.393, 0.341, 0.250 mV/cm 2 when curvature angles were 30°, 60°, and 120°, respectively. Overall pH sensitivity was 0.017 mV/cm 2 /pH. Ultimately, the biochemical sensing principle using a novel bilayer ultrasound transducer suggests a simple, low-cost, battery-less, and long-range wireless readout system as compared to traditional biochemical sensing. 

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5. Thin-film optical-acoustic combiner enables high-speed wide-field multi-parametric photoacoustic microscopy in reflection mode

   https://doi.org/10.1364/OL.475373  

   Zhong, Fenghe; Hu, Song (January 2023, Optics Letters)

   Multi-parametric photoacoustic microscopy (PAM) is uniquely capable of simultaneous high-resolution mapping of blood oxygenation and flowin vivo. However, its speed has been limited by the dense sampling required for blood flow quantification. To overcome this limitation, we have developed a high-speed multi-parametric PAM system, which enables simultaneous acquisition of ∼500 densely sampled B-scans by superposing the rapid optical scanning across the line-shaped focus of a cylindrically focused ultrasonic transducer over the conventional mechanical scan of the optical-acoustic dual foci. A novel, to the best of our knowledge, optical-acoustic combiner (OAC) is designed and implemented to accommodate the short working distance of the transducer, enabling convenient confocal alignment of the dual foci in reflection mode. A resonant galvanometer (GM) provides stabilized high-speed large-angle scanning. This new system can continuously monitor microvascular blood oxygenation (sO₂) and flow over a 4.5 × 3 mm²area in the awake mouse brain with high spatial and temporal resolutions (6.9 µm and 0.3 Hz, respectively). 

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