Publications by authors named "Howuk Kim"

12 Publications

  • Page 1 of 1

Dual-Frequency Intravascular Sonothrombolysis: an In-vitro Study.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Aug 9;PP. Epub 2021 Aug 9.

Thrombo-occlusive disease is one of the leading causes of death worldwide. There has been active research on safe and effective thrombolysis in pre-clinical and clinical studies. Recently, the dual-frequency transcutaneous sonothrombolysis with contrast agents (microbubbles) has been reported to be more efficient in trigging the acoustic cavitation which leads to a higher lysis rate. Therefore, there is increasing interest in applying dual-frequency technique for more significant effiacy improvement in intravascular sonothrombolysis since a miniaturized intravascular ultrasound transducer typically has a limited power output to fully harness cavitation effects. In this work, we demonstrated this efficacy enhancement by developing a new broadband intravascular transducer and testing dual-frequency sonothromblysis in vitro. A broadband intravascular transducer with a center frequency of 750 kHz and footprint size of 1.4 mm was designed, fabricated, and characterized. The measured -6 dB fractional bandwidth is 68.1%, and the peak negative pressure is 1.5 MPa under the driving voltage of 80 Vpp. By keeping one frequency component at 750 kHz, the second frequency component was selected from 450 kHz to 650 kHz with an interval of 50 kHz. The in-vitro sonothrombolysis tests were conducted with a flow model and the results indicated that the microbubble-mediated, dual-frequency (750 kHz + 500 kHz) sonothrombolysis yields an 85% higher lysis rate compared with the single-frequency treatment, and the lysis rate of dual-frequency sonothrombolysis increases with the difference between the two frequency components. These findings suggest a dual-frequency excitation technique for more efficient intravascular sonothrombolysis than conventional single-frequency excitation.
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http://dx.doi.org/10.1109/TUFFC.2021.3103409DOI Listing
August 2021

A multi-pillar piezoelectric stack transducer for nanodroplet mediated intravascular sonothrombolysis.

Ultrasonics 2021 Jul 9;116:106520. Epub 2021 Jul 9.

The Department of Mechanical and Aerospace Engineering at North Carolina State University, Raleigh, NC 27695, USA. Electronic address:

We aim to develop a nanodroplet (ND)-mediated intravascular ultrasound (US) transducer for deep vein thrombosis treatments. The US device, having an efficient forward directivity of the acoustic beam, is capable of expediting the clot dissolution rate by activating cavitation of NDs injected onto a thrombus. We designed and prototyped a multi-pillar piezoelectric stack (MPPS) transducer composed of four piezoelectric stacks. Each stack was made of five layers of PZT-4 plates, having a dimension of 0.85 × 0.85 × 0.2 mm. The transducer was characterized by measuring the electrical impedance and acoustic pressure, compared to simulation results. Next, in-vitro tests were conducted in a blood flow mimicking system using the transducer equipped with an ND injecting tube. The miniaturized transducer, having an aperture size of 2.8 mm, provided a high mechanical index of 1.52 and a relatively wide focal zone of 3.4 mm at 80 V, 0.96 MHz electric input. The mass-reduction rate of the proposed method (NDs + US) was assessed to be 4.1 and 4.6 mg/min with and without the flow model, respectively. The rate was higher than that (1.3-2.7 mg/min) of other intravascular ultrasound modalities using micron-sized bubble agents. The ND-mediated intravascular sonothrombolysis using MPPS transducers was demonstrated with an unprecedented lysis rate, which may offer a new clinical option for DVT treatments. The MPPS transducer generated a high acoustic pressure (~3.1 MPa) at a distance of approximately 2.2 wavelengths from the small aperture, providing synergistic efficacy with nanodroplets for thrombolysis without thrombolytic agents.
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http://dx.doi.org/10.1016/j.ultras.2021.106520DOI Listing
July 2021

Magneto-sonothrombolysis with combination of magnetic microbubbles and nanodroplets.

Ultrasonics 2021 Jun 6;116:106487. Epub 2021 Jun 6.

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA. Electronic address:

This paper reports a novel technique using the rotational magnetic field oscillation and low-intensity sub-megahertz ultrasound stimulation of magnetic microbubbles (MMBs) to promote the nanodroplets (NDs) phase transition and improve the permeation of NDs into the blood clot fibrin network to enhance the sonothrombolysis efficiency. In this study, the influence of different treatment methods with a combination of MMBs and NDs on the thrombolysis rate of both unretracted and retracted clots were investigated, including the stable and inertial cavitation, tPA effects, MMBs/NDs concentration ratio, sonication factors (input voltage, duty cycle) and rotational magnetic field factors (flux density, frequency). We demonstrated that tPA-mediated magneto-sonothrombolysis in combining NDs with MMBs could significantly enhance in vitro lysis of both unretracted clots (85 ± 8.3%) and retracted clots (57 ± 6.5%) in a flow model with 30 min treatment. The results showed that the combination of MMBs and NDs substantially improves in vitro lysis of blood clots with an unprecedented lysis rate.
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http://dx.doi.org/10.1016/j.ultras.2021.106487DOI Listing
June 2021

A 1.5-D Array for Acoustic Radiation Force (ARF)-Induced Peak Displacement-Based Tissue Anisotropy Assessment With a Row-Column Excitation Method.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Apr 26;68(4):1278-1287. Epub 2021 Mar 26.

Many biological tissues, including muscle or kidney, are mechanically anisotropic, and the degree of anisotropy (DoA) in mechanical properties is diagnostically relevant. DoA can be assessed either using the ratio of shear wave velocities (SWVs) or acoustic radio forced impulse (ARFI)-induced peak displacements (PD) measured longitudinal over transverse orientations. Whether using SWV or PD as a basis, DoA expressed as the ratio of values requires 90° transducer rotation when a linear array is employed. This large rotation angle is prone to misalignment errors. One solution is the use of a fully sampled matrix array for electronic rotation of point spread function (PSF). However, the challenges of matrix array are its high fabrication cost and complicated fabrication procedures. The cheaper and simpler alternative of matrix array is the use of a row-column array. A 3×64 elements 1.5-D array with a row-column excitation mode is proposed to assess DoA in mechanical properties using the PD ratio. Different numbers of elements in elevational and lateral directions were selected to have orthogonal ARFI excitation beams without rotating the transducer. A custom-designed flex circuit was used to fabricate the array with a simpler electrode connection than a fully sampled matrix array. The performance of the array was evaluated in Field II simulation and experiment. The output pressure was 0.57-MPa output under a 40- [Formula: see text] excitation with a -6-dB point spread dimension of 14×4 mm in orthogonal directions. The PD was measured to be [Formula: see text] in an isotropic elastic phantom with Young's modulus of 5.4 kPa. These results suggest that the array is capable of assessing DoA using PD ratio without physical rotation of the transducer. The array has the potential to reduce the misalignment errors for DoA assessment.
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http://dx.doi.org/10.1109/TUFFC.2020.3030040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8080255PMC
April 2021

Direct Acoustic Imaging Using a Piezoelectric Organic Light-Emitting Diode.

ACS Appl Mater Interfaces 2020 Aug 4;12(32):36409-36416. Epub 2020 Aug 4.

Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States.

Conventional ultrasonic imaging requires acoustic scanning over a target object using a piezoelectric transducer array, followed by signal processing to reconstruct the image. Here, we report a novel ultrasonic imaging device that can optically display an acoustic signal on the surface of a piezoelectric transducer. By fabricating an organic light-emitting diode (OLED) on top of a piezoelectric crystal, lead zirconate titanate (PZT), an acousto-optical piezoelectric OLED (p-OLED) transducer is realized, converting an acoustic wave profile directly to an optical image. Because of the integrated device architecture, the resulting p-OLED features a high acousto-optic conversion efficiency at the resonance frequency, providing a piezoelectric field to drive the OLED. By incorporating an electrode array in the p-OLED, we demonstrate a novel tomographic ultrasound imaging device that is operated without a need for conventional signal processing.
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http://dx.doi.org/10.1021/acsami.0c05615DOI Listing
August 2020

Examining the Influence of Low-Dose Tissue Plasminogen Activator on Microbubble-Mediated Forward-Viewing Intravascular Sonothrombolysis.

Ultrasound Med Biol 2020 07 7;46(7):1698-1706. Epub 2020 May 7.

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, USA. Electronic address:

Previous work revealed that a forward-viewing intravascular (FVI) transducer can be used for microbubble (MB)-mediated sonothrombolysis and that the clot lysis was dependent on MB concentration. This study examined the effects of combining tissue plasminogen activator (tPA) with MB-mediated FVI sonothrombolysis. In vitro clot lysis and passive cavitation experiments were conducted to study the effect of low-dose tPA in FVI sonothrombolysis with varying MB concentrations. Enhanced FVI sonothrombolysis was observed in cases in which ultrasound (US) was combined with tPA or MBs compared with control, tPA alone or US alone. The lysis rate of US + tPA + MBs was improved by up to 130%, 31% and 8% for MB concentrations of 106, 107 and 108 MBs/mL, respectively, compared with MBs + US alone. Changes in stable and inertial cavitation doses were observed, corresponding to changes in clot lysis in MB-mediated FVI sonothrombolysis with and without tPA.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2020.03.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293952PMC
July 2020

Stress-Sensing Method via Laser-Generated Ultrasound Wave Using Candle Soot Nanoparticle Composite.

IEEE Trans Ultrason Ferroelectr Freq Control 2020 09 22;67(9):1867-1876. Epub 2020 Apr 22.

This article aims to develop a semi-noncontact stress-sensing system using a laser-generated ultrasound (LGU) wave assisted by candle soot nanoparticle (CSNP) composite. While the acoustoelastic effect is commonly targeted to measure the stress level, efforts to combine it with the LGU wave signal have been lacking due to weak signal intensity. In this study, the CSNP-based transducer is designed to potentiate the photoacoustic energy conversion. To demonstrate the wave propagation with the designed parameters, a numerical simulation was first conducted. The experimental results showed that a laser intensity of 6.5 mJ/cm was enough to generate the subsurface longitudinal (SSL) wave from the CSNP composite transducer. The normal beam projection is the most effective wave-generation method, exhibiting the highest signal magnitude compared with inclined projection cases. Finally, the laser-assisted stress-sensing system was assessed by increasing the internal pressure of an air tank. The sensitivity of the developed sensor system was estimated to be 0.296 ns/MPa, showing a correlation of 0.983 with the theoretical prediction. The proposed sensing system can be used to monitor the structural integrity of nuclear power plants.
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http://dx.doi.org/10.1109/TUFFC.2020.2989035DOI Listing
September 2020

Adaptive signal decomposition and dispersion removal based on the matching pursuit algorithm using dispersion-based dictionary for enhancing damage imaging.

Ultrasonics 2020 Apr 31;103:106087. Epub 2020 Jan 31.

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA. Electronic address:

This paper aims to develop a method for high-resolution damage imaging for a sparsely distributed sensor network on a plate-like structure. Techniques for dispersion removal and signal decomposition are indispensable to accurate damage localization. By combining the dispersion-removed wave packets with the damage-imaging algorithm, a point-like damage can be precisely localized. In this article, a matching pursuit algorithm was utilized to decompose overlapping wave packets and then recompress the dispersion. The matching pursuit dictionary was constructed based on an asymptotic solution of the dispersion relation for Lamb waves in toneburst wave packets. The dispersion-based Hanning-window dictionary provided the parametric information for the extracted wave packets, such as propagation time-delay, dispersion extent, and phase. The parameters were leveraged for the dispersion-removal algorithm. Results of the simulation indicate that the proposed algorithm is capable of recompressing multiple dispersive wave packets with the different modes. Finally, the proposed approach was validated by the results of the experiment using a sparse array of piezoelectric wafers on an aluminum plate. Extracting the parameters of individual wave packets and removing the dispersion through matching pursuit, the algorithm for minimum-variance imaging produced a high-quality image with a fine spatial resolution. The image artifacts were significantly suppressed, and the accuracy was improved by 62.1% compared to conventional minimum-variance imaging.
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http://dx.doi.org/10.1016/j.ultras.2020.106087DOI Listing
April 2020

Miniaturized Intracavitary Forward-Looking Ultrasound Transducer for Tissue Ablation.

IEEE Trans Biomed Eng 2020 07 22;67(7):2084-2093. Epub 2019 Nov 22.

Objective: This paper aims to develop a miniaturized forward-looking ultrasound transducer for intracavitary tissue ablation, which can be used through an endoscopic device. The internal ultrasound (US) delivery is capable of directly interacting with the target tumor, resolving adverse issues of currently available US devices, such as unintended tissue damage and insufficient delivery of acoustic power.

Methods: To transmit a high acoustic pressure from a small aperture (<3 mm), a double layer transducer (1.3 MHz) was designed and fabricated based on numerical simulations. The electric impedance and the acoustic pressure of the actual device was characterized with an impedance analyzer and a hydrophone. Ex vivo tissue ablation tests and temperature monitoring were then conducted with porcine livers.

Results: The acoustic intensity of the transducer was 37.1 W/cm under 250 V and 20% duty cycle. The tissue temperature was elevated to 51.8 °C with a 67 Hz pulse-repetition frequency. The temperature profile in the tissue indicated that ultrasound energy was effectively absorbed inside the tissue. During a 5-min sonification, an approximate tissue volume of 2.5 × 2.5 × 1.0 mm was ablated, resulting in an irreversible lesion.

Conclusion: This miniaturized US transducer is a promising medical option for the precise tissue ablation, which can reduce the risk of unintended tissue damage found in noninvasive US treatments.

Significance: Having a small aperture (2 mm), the intracavitary device is capable of ablating a bio tissue in 5 min with a relatively low electric power (<17 W).
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http://dx.doi.org/10.1109/TBME.2019.2954524DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7269183PMC
July 2020

Stress Measurement of a Pressurized Vessel Using Ultrasonic Subsurface Longitudinal Wave With 1-3 Composite Transducers.

IEEE Trans Ultrason Ferroelectr Freq Control 2020 01 12;67(1):158-166. Epub 2019 Sep 12.

This article aims to develop a stress-sensing method for a pressurized vessel based on subsurface longitudinal (SSL) waves confined in a specific waveform by using 1-3 composite transducers. Although ultrasonic SSL waves have been commonly utilized for stress sensing, wave excitation under the predefined function using the composite-type transmitter is not well studied. In this article, composite-type transducers having a wide frequency bandwidth (> 60%) and a predominant thickness mode are utilized to enhance the signal intensity of the SSL wave and the accuracy of the sensor by incorporating a specific toneburst waveform. Finite element analysis demonstrates that the signal intensity of the composite-type transducer is up to 45.3% higher than that of a single-phase transducer. Pulse-echo tests reveal that the frequency bandwidth of the developed transducer reaches up to 60.7% and is, therefore, sufficient (> 57.0%) to transmit and receive Hanning-windowed toneburst signals. Results of stress sensing affirm a linear relationship between the time delay of SSL wave and the mechanical stress of a pressurized vessel (0.335 ns/MPa). Accordingly, the regression model is constructed via principal component regression (PCR) under temperature-varying condition. PCR has a less significant degree of error (0.62 MPa) compared to that of a typical least square regression (9.49 MPa).
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http://dx.doi.org/10.1109/TUFFC.2019.2941133DOI Listing
January 2020

Sonothrombolysis with magnetic microbubbles under a rotational magnetic field.

Ultrasonics 2019 Sep 10;98:62-71. Epub 2019 Jun 10.

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh 27695, NC, USA. Electronic address:

Thrombosis is an extremely critical clinical condition where a clot forms inside a blood vessel which blocks the blood flow through the cardiovascular system. Previous sonothrombolysis methods using ultrasound and microbubbles (MBs) often have a relatively low lysis rate due to the low microbubbles concentration at clot region caused by blood flow in the vessel. To solve this problem, the magnetic microbubbles (MMBs) that can be retained by an outer magnetic field against blood flow are used in this study. Here we report the development of a new method using the rotational magnetic field to trap and vibrate magnetic microbubbles at target clot region and then using an intravascular forward-looking ultrasound transducer to activate them acoustically. In this study, we investigated the influence of different blood flow conditions, vessel occlusion conditions (partial and fully occluded), clot ages (fresh, retracted), ultrasound parameters (input voltage, duty cycle) and rotational magnetic field parameters (amplitude, frequency) on the thrombolysis rate. The results showed that the additional use of magnetic microbubbles significantly enhances in vitro lysis of blood clot.
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http://dx.doi.org/10.1016/j.ultras.2019.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6710138PMC
September 2019

Candle Soot Carbon Nanoparticles in Photoacoustics: Advantages and Challenges for Laser Ultrasound Transmitters.

IEEE Nanotechnol Mag 2019 Jun 11;13(3):13-28. Epub 2019 Apr 11.

Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill and North Carolina State University, Raleigh.

This manuscript provides a review of candle-soot nanoparticle (CSNP) composite laser ultrasound transmitters (LUT), and compares and contrasts this technology to other carboncomposite designs. Among many carbon-based composite LUTs, a CSNP composite has shown its advantages of maximum energy conversion and fabrication simplicity for developing highly efficient ultrasound transmitters. This review focuses on the advantages and challenges of the CSNP-composite transmitter in the aspects of nanostructure design, fabrication procedure, and promising applications. Included are a brief description of the basic principles of the laser ultrasound transmitter, a review of general properties of CSNPs, as well as details on the fabrication method, photoacoustic performance, and design factors. A comparison of the CSNP-nanocomposite to other carbon-nanocomposites is provided. Lastly, representative applications of carbon-nanocomposite transmitters and future perspectives on CSNP-composite transmitters are presented.
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http://dx.doi.org/10.1109/MNANO.2019.2904773DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6553871PMC
June 2019
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