K. Kirk Shung

Daegu Gyeongbuk Institute of Science and Technology, Daikyū, Daegu, South Korea

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Publications (377)609.58 Total impact

  • Changyang Lee · Hayong Jung · Kwok Ho Lam · Changhan Yoon · K. Kirk Shung ·

    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 11/2015; 62(11):1968-1978. DOI:10.1109/TUFFC.2015.007307 · 1.51 Impact Factor
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    ABSTRACT: Matching the acoustic impedance of high-frequency (≥100 MHz) ultrasound transducers to an aqueous loading medium remains a challenge for fabricating high-frequency transducers. The traditional matching layer design has been problematic to establish high matching performance given requirements on both specific acoustic impedance and precise thickness. Based on both mass-spring scheme and microwave matching network analysis, we interfaced metal-polymer layers for the matching effects. Both methods hold promises for guiding the metal-polymer matching layer design. A 100 MHz LiNbO3 transducer was fabricated to validate the performance of the both matching layer designs. In the pulse-echo experiment, the transducer echo amplitude increased by 84.4% and its -6dB bandwidth increased from 30.2% to 58.3% comparing to the non-matched condition, demonstrating that the matching layer design method is effective for developing high-frequency ultrasonic transducers.
    Applied Physics Letters 10/2015; 107(12):123505. DOI:10.1063/1.4931703 · 3.30 Impact Factor
  • Teng Ma · Bill Zhou · Tzung K Hsiai · K Kirk Shung ·
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    ABSTRACT: Catheter-based intravascular imaging modalities are being developed to visualize pathologies in coronary arteries, such as high-risk vulnerable atherosclerotic plaques known as thin-cap fibroatheroma, to guide therapeutic strategy at preventing heart attacks. Mounting evidences have shown three distinctive histopathological features-the presence of a thin fibrous cap, a lipid-rich necrotic core, and numerous infiltrating macrophages-are key markers of increased vulnerability in atherosclerotic plaques. To visualize these changes, the majority of catheter-based imaging modalities used intravascular ultrasound (IVUS) as the technical foundation and integrated emerging intravascular imaging techniques to enhance the characterization of vulnerable plaques. However, no current imaging technology is the unequivocal "gold standard" for the diagnosis of vulnerable atherosclerotic plaques. Each intravascular imaging technology possesses its own unique features that yield valuable information although encumbered by inherent limitations not seen in other modalities. In this context, the aim of this review is to discuss current scientific innovations, technical challenges, and prospective strategies in the development of IVUS-based multi-modality intravascular imaging systems aimed at assessing atherosclerotic plaque vulnerability.
    Ultrasonic Imaging 09/2015; DOI:10.1177/0161734615604829 · 0.91 Impact Factor
  • Min Gon Kim · Sangpil Yoon · Hyung Ham Kim · K Kirk Shung ·
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    ABSTRACT: An approach for the design of an impedance matching network (IMN) for high frequency ultrasonic transducers with large apertures based on impedance analysis for cellular applications is presented in this paper. The main objectives were to maximize energy transmission from the excitation source to the ultrasonic transducers for cell manipulation and to achieve low input parameters for the safe operation of an ultrasonic transducer because the piezoelectric material in high frequency ultrasonic transducers is prone to breakage due to its being extremely thin. Two ultrasonic transducers, which were made of lithium niobate single crystal with the thickness of 15μm, having apertures of 4.3mm (fnumber=1.23) and 2.6mm (fnumber=0.75) were tested. L-type IMN was selected for high sensitivity and compact design of the ultrasonic transducers. The target center frequency was chosen as the frequency where the electrical admittance (|Y|) and phase angle (θz) from impedance analysis was maximal and zero, respectively. The reference center frequency and reference echo magnitude were selected as the center frequency and echo magnitude, measured by pulse-echo testing, of the ultrasonic transducer without IMN. Initial component values and topology of IMN were determined using the Smith chart, and pulse-echo testing was analyzed to verify the performance of the ultrasonic transducers with and without IMN. After several iterations between changing component values and topology of IMN, and pulse-echo measurement of the ultrasonic transducer with IMN, optimized component values and topology of IMN were chosen when the measured center frequency from pulse-echo testing was comparable to the target frequency, and the measured echo magnitude was at least 30% larger than the reference echo magnitude. Performance of an ultrasonic transducer with and without IMN was tested by observing a tangible dent on the surface of a plastic petridish and single cell response after an acoustic pulse was applied on a target cell.
    Ultrasonics 09/2015; 65. DOI:10.1016/j.ultras.2015.09.016 · 1.94 Impact Factor
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    ABSTRACT: Intravascular photoacoustic imaging at 1.7 μm spectral band has shown promising capabilities for lipid-rich vulnerable atherosclerotic plaque detection. In this work, we report a high speed catheter-based integrated intravascular photoacoustic/intravascular ultrasound (IVPA/IVUS) imaging system with a 500 Hz optical parametric oscillator laser at 1725 nm. A lipid-mimicking phantom and atherosclerotic rabbit abdominal aorta were imaged at 1 frame per second, which is two orders of magnitude faster than previously reported in IVPA imaging with the same wavelength. Clear photoacoustic signals by the absorption of lipid rich deposition demonstrated the ability of the system for high speed vulnerable atherosclerotic plaques detection.
    Applied Physics Letters 08/2015; 107(8):083701. DOI:10.1063/1.4929584 · 3.30 Impact Factor
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    ABSTRACT: We demonstrate a jitter noise reduction technique for acoustic radiation force impulse microscopy via photoacoustic detection (PA-ARFI), which promises to be capable of measuring cell mechanics. To reduce the jitter noise induced by Q-switched pulsed laser operated at high repetition frequency, photoacoustic signals from the surface of an ultrasound transducer are aligned by cross-correlation and peak-to-peak detection, respectively. Each method is then employed to measure the displacements of a target sample in an agar phantom and a breast cancer cell due to ARFI application, followed by the quantitative comparison between their performances. The suggested methods for PA-ARFI significantly reduce jitter noises, thus allowing us to measure displacements of a target cell due to ARFI application by less than 3 μm.
    Optics Express 07/2015; 23(15):19166. DOI:10.1364/OE.23.019166 · 3.49 Impact Factor
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    ABSTRACT: Extracellular matrix proteins such as fibronectin (FNT) play crucial roles in cell proliferation, adhesion, and migration. For better understanding of these associated cellular activities, various microscopic manipulation tools have been used to study their intracellular signaling pathways. Recently, it has appeared that acoustic tweezers may possess similar capabilities in the study. Therefore, we here demonstrate that our newly developed acoustic tweezers with a high-frequency lithium niobate ultrasonic transducer have potentials to study intracellular calcium signaling by FNT-binding to human breast cancer cells (SKBR-3). It is found that intracellular calcium elevations in SKBR-3 cells, initially occurring on the microbead-contacted spot and then eventually spreading over the entire cell, are elicited by attaching an acoustically trapped FNT-coated microbead. Interestingly, they are suppressed by either extracellular calcium elimination or phospholipase C (PLC) inhibition. Hence, this suggests that our acoustic tweezers may serve as an alternative tool in the study of intracellular signaling by FNT-binding activities. Copyright © 2015 Elsevier B.V. All rights reserved.
    Ultrasonics 06/2015; 63. DOI:10.1016/j.ultras.2015.06.017 · 1.94 Impact Factor
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    ABSTRACT: RE1-Silencing Transcription factor (REST) has a well-established role in regulating transcription of genes important for neuronal development. Its role in cancer, though significant, is less well understood. We show that REST downregulation in weakly invasive MCF-7 breast cancer cells converts them to a more invasive phenotype, while REST overexpression in highly invasive MDA-MB-231 cells suppresses invasiveness. Surprisingly, the mechanism responsible for these phenotypic changes does not depend directly on the transcriptional function of REST protein. Instead, it is driven by previously unstudied mid-size (30-200 nt) non-coding RNAs (ncRNAs) derived from the first exon of an alternatively spliced REST transcript: REST-003. We show that processing of REST-003 into ncRNAs is controlled by an uncharacterized serine/arginine repeat-related protein, SRRM3. SRRM3 expression may be under REST-mediated transcriptional control, as it increases following REST downregulation. The SRRM3-dependent regulation of REST-003 processing into ncRNAs has many similarities to recently described promoter-associated small RNA-like processes. Targeting ncRNAs that control invasiveness could lead to new therapeutic approaches to limit breast cancer metastasis.
    Scientific Reports 06/2015; 5:11207. DOI:10.1038/srep11207 · 5.58 Impact Factor
  • Hung Cao · Bong Jin Kang · Chia-An Lee · K Kirk Shung · Tzung K Hsiai ·
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    ABSTRACT: Inadequate replacement of lost ventricular myocardium from myocardial infarction leads to heart failure. Investigating the regenerative capacity of mammalian hearts represents an emerging direction for tissue engineering and cellbased therapy. Recent advances in stem cells hold promise to restore cardiac functions. However, embryonic or induced pluripotent stem cell-derived cardiomyocytes lack functional phenotypes of the native myocardium, and transplanted tissues are not fully integrated for synchronized electrical and mechanical coupling with the host. In this context, this review highlights the mechanical and electrical strategies to promote cardiomyocyte maturation and integration, and to assess the functional phenotypes of regenerating myocardium. Simultaneous microelectrocardiogram and high-frequency ultrasound techniques will also be introduced to assess electrical and mechanical coupling for small animal models of heart regeneration.
    05/2015; 8. DOI:10.1109/RBME.2015.2431681
  • Zhengyao He · Fan Zheng · Yuanliang Ma · Hyung Ham Kim · Qifa Zhou · K Kirk Shung ·
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    ABSTRACT: A method is proposed to suppress sidelobe level for near-field beamforming in ultrasound array imaging. An optimization problem is established, and the second-order cone algorithm is used to solve the problem to obtain the weight vector based on the near-field response vector of a transducer array. The weight vector calculation results show that the proposed method can be used to suppress the sidelobe level of the near-field beam pattern of a transducer array. Ultrasound images following the application of weight vector to the array of a wire phantom are obtained by simulation with the Field II program, and the images of a wire phantom and anechoic sphere phantom are obtained experimentally with a 64-element 26 MHz linear phased array. The experimental and simulation results agree well and show that the proposed method can achieve a much lower sidelobe level than the conventional delay and sum beamforming method. The wire phantom image is demonstrated to focus much better and the contrast of the anechoic sphere phantom image improved by applying the proposed beamforming method.
    The Journal of the Acoustical Society of America 05/2015; 137(5):2785. DOI:10.1121/1.4919318 · 1.50 Impact Factor
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    ABSTRACT: We report on a novel acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE) technique for imaging shear wave and quantifying shear modulus under orthogonal acoustic radiation force (ARF) excitation using the optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A shear wave induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF-induced vibration. For analysis of the shear modulus, the Doppler variance method is utilized to visualize shear wave propagation instead of Doppler OCT method, and the propagation velocity of the shear wave is measured at different depths of one location with the M scan. In order to quantify shear modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the shear wave propagating to the same OCT imaging depth. We also quantitatively map the shear modulus of a cross-section in a tissue-equivalent phantom after employing the B scan.
    Optics Letters 05/2015; 40(9):2099-102. DOI:10.1364/OL.40.002099 · 3.29 Impact Factor
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    ABSTRACT: Using tape-casting technology, 35 μm free-standing (100)-textured Li doped KNN (KNLN) thick film was prepared by employing NaNbO3 (NN) as template. It exhibited similar piezoelectric behavior to lead containing materials: a longitudinal piezoelectric coefficient (d33) of ∼150 pm/V and an electromechanical coupling coefficient (kt ) of 0.44. Based on this thick film, a 52 MHz side-looking miniature transducer with a bandwidth of 61.5% at −6 dB was built for Intravascular ultrasound (IVUS) imaging. In comparison with 40 MHz PMN-PT single crystal transducer, the rabbit aorta image had better resolution and higher noise-to-signal ratio, indicating that lead-free (100)-textured KNLN thick film may be suitable for IVUS (>50 MHz) imaging.
    Applied Physics Letters 04/2015; 106(17):173504. DOI:10.1063/1.4919387 · 3.30 Impact Factor
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    ABSTRACT: We report photoacoustic and ultrasonic endoscopic images of two intact rabbit esophagi. To investigate the esophageal lumen structure and microvasculature, we performed in vivo and ex vivo imaging studies using a 3.8-mm diameter photoacoustic endoscope and correlated the images with histology. Several interesting anatomic structures were newly found in both the in vivo and ex vivo images, which demonstrates the potential clinical utility of this endoscopic imaging modality. In the ex vivo imaging experiment, we acquired high-resolution motion-artifact-free three-dimensional photoacoustic images of the vasculatures distributed in the walls of the esophagi and extending to the neighboring mediastinal regions. Blood vessels with apparent diameters as small as 190 μm were resolved. Moreover, by taking advantage of the dual-mode high-resolution photoacoustic and ultrasound endoscopy, we could better identify and characterize the anatomic structures of the esophageal lumen, such as the mucosal and submucosal layers in the esophageal wall, and an esophageal branch of the thoracic aorta. In this paper, we present the first photoacoustic images showing the vasculature of a vertebrate esophagus and discuss the potential clinical applications and future development of photoacoustic endoscopy.
    PLoS ONE 04/2015; 10(4):e0120269. DOI:10.1371/journal.pone.0120269 · 3.23 Impact Factor
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    ABSTRACT: Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Dual frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced intravascular ultrasound (CE-IVUS) platform with the capability of vasa vasorum imaging. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with low frequency transmitter performance. In this paper, transducer designs encompassing different transducer layouts, transmitting frequencies, and transducer materials are compared for optimization of imaging performance. In the layout selection, the stacked configuration showed superior super-harmonic imaging compared with the interleaved configuration. In the transmitter frequency selection, a decrease in frequency from 6.5 MHz to 5 MHz resulted in an increase of CTR from 15 dB to 22 dB when receiving frequency was kept constant at 30 MHz. In the material selection, the dual frequency transducer with the lead magnesium niobate-lead titanate (PMN-PT) 1-3 composite transmitter yielded higher axial resolution compared to single crystal transmitters (70 μm compared to 150 μm pulse length). These comparisons provide guidelines for the design of intravascular acoustic angiography transducers.
    Physics in Medicine and Biology 04/2015; 60(9):3441-3457. DOI:10.1088/0031-9155/60/9/3441 · 2.76 Impact Factor
  • Hojong Choi · Hayong Jung · K. Kirk Shung ·
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    ABSTRACT: Power amplifiers (PAs) are used to produce high-voltage excitation signals to drive ultrasonic transducers. A larger dynamic range of linear PAs allows higher contrast resolution, a highly desirable characteristic in ultrasonic imaging. The linearity of PAs can be improved by reducing the nonlinear harmonic distortion components of high-voltage output signals. In this paper, a linearizer circuit is proposed to reduce output signal harmonics when working in conjunction with a PA. The PA performance with and without the linearizer was measured by comparing the output power 1-dB compression point (OP1dB), and the second- and third-order harmonic distortions (HD2 and HD3, respectively). The results show that the PA with the linearizer circuit had higher OP1dB (31.7 dB) and lower HD2 (−61.0 dB) and HD3 (−42.7 dB) compared to those of the PA alone [OP1dB (27.1 dB), HD2 (−38.2 dB), and HD3 (−36.8 dB)] at 140 MHz. A pulse-echo measurement was also performed to further evaluate the capability of the linearizer circuit. The HD2 of the echo signal received by the transducer using a PA with the linearizer (−24.8 dB) was lower than that obtained for the PA alone (−16.6 dB). The linearizer circuit is capable of improving the linearity performance of PA by lowering harmonic distortions.
    Journal of Medical and Biological Engineering 04/2015; 35(2):226-235. DOI:10.1007/s40846-015-0026-7 · 0.97 Impact Factor
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    ABSTRACT: A dual-element needle transducer for intravascular ultrasound imaging has been developed. A low-frequency element and a high-frequency element were integrated into one device to obtain images which conveyed both low- and high-frequency information from a single scan. The low-frequency element with a center frequency of 48 MHz was fabricated from the single crystal form of lead magnesium niobate-lead titanate solid solution with two matching layers (MLs) and the high frequency element with a center frequency of 152 MHz was fabricated from lithium niobate with one ML. The measured axial and lateral resolutions were 27 and [Formula: see text], respectively, for the low-frequency element, and 14 and [Formula: see text], respectively, for the high-frequency element. The performance of the dual-element needle transducer was validated by imaging a tissue-mimicking phantom with lesion-mimicking area, and ex vivo rabbit aortas in water and rabbit whole blood. The results suggest that a low-frequency element effectively provides depth resolved images of the whole vessel and its adjacent tissue, and a high-frequency element visualizes detailed structure near the surface of the lumen wall in the presence of blood within the lumen. The advantages of a dual-element approach for intravascular imaging are also discussed.
    04/2015; 2(2):027001. DOI:10.1117/1.JMI.2.2.027001
  • Hongwei Liu · Wei Ren · Jinyan Zhao · Huifeng Zhao · Xiaoqing Wu · Peng Shi · Qifa Zhou · K. Kirk Shung ·
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    ABSTRACT: Intravascular ultrasound (IVUS) has been used for diagnosis of coronary diseases. According to the outstanding transducer performance, Ba0.5Na0.5TiO3 (BNT)-based piezoelectric materials are good candidates for the IVUS applications. In this paper, lead-free BNT piezoelectric thick film has been used to fabricate a linear array transducer. The BNT based transducer array has a 2×16-element pattern. In the fabrication process of transducers, micro-machining technologies have been adopted. Wet etching was used to pattern the silicon substrate. The thin layers of Si3N4 and SiO2, are used as etching masks, and patterned by reactive etching and buffered oxide etch (BOE), respectively. After that, the part of Si not covered by the patterned masks is etched by 30% KOH solution. BNT slurry prepared by mixing BNT solution and BNT powder has been deposited on the substrate by spin coating and then thermally treated to obtain the thick film. The PiezoCAD software has been employed to analyze the performance of the array, and the simulation results show that the BNT film array has a center frequency of 82.84 MHz and a −6 dB bandwidth of 46.77%.
    Ceramics International 04/2015; 41. DOI:10.1016/j.ceramint.2015.03.256 · 2.61 Impact Factor
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    ABSTRACT: Capitalizing on the optical absorption of hemoglobin, photoacoustic microscopy (PAM) is uniquely capable of anatomical and functional characterization of the intact microcirculation in vivo. However, PAM of the metabolic rate of oxygen (MRO2) at the microscopic level remains an unmet challenge, mainly due to the inability to simultaneously quantify microvascular diameter, oxygen saturation of hemoglobin (sO2), and blood flow at the same spatial scale. To fill this technical gap, we have developed a multi-parametric PAM platform. By analyzing both the sO2-encoded spectral dependence and the flow-induced temporal decorrelation of photoacoustic signals generated by the raster-scanned mouse ear vasculature, we demonstrated—for the first time—simultaneous wide-field PAM of all three parameters down to the capillary level in vivo.
    Optics Letters 03/2015; 40(6). DOI:10.1364/OL.40.000910 · 3.29 Impact Factor

Publication Stats

4k Citations
609.58 Total Impact Points


  • 2015
    • Daegu Gyeongbuk Institute of Science and Technology
      • Department of Information and Communication Engineering
      Daikyū, Daegu, South Korea
  • 2004-2015
    • University of California, Los Angeles
      • Department of Bioengineering
      Los Ángeles, California, United States
  • 2003-2015
    • University of Southern California
      • • Department of Biomedical Engineering
      • • Department of Ophthalmology
      Los Ángeles, California, United States
  • 2011
    • The University of Hong Kong
      Hong Kong, Hong Kong
  • 2010-2011
    • Taipei Veterans General Hospital
      T’ai-pei, Taipei, Taiwan
    • Sogang University
      Sŏul, Seoul, South Korea
  • 2008
    • Washington University in St. Louis
      • Department of Biomedical Engineering
      San Luis, Missouri, United States
  • 2007
    • National Taiwan University
      • Institute of Applied Mechanics
      T’ai-pei, Taipei, Taiwan
  • 2006
    • American Institute of Ultrasound in Medicine
      LUL, Mississippi, United States
  • 1992-2003
    • Pennsylvania State University
      • Department of Bioengineering
      University Park, Maryland, United States
  • 2000-2001
    • William Penn University
      University Park, Florida, United States