K Kirk Shung

University of Southern California, Los Angeles, California, United States

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Publications (237)446.41 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Myocardial infarction results in scar tissue and irreversible loss of ventricular function. Unlike humans, zebrafish has the capacity to remove scar tissue after injury. To assess ventricular function during repair, we synchronized microelectrocardiogram (μECG) signals with a high-frequency ultrasound pulsed-wave (PW) Doppler to interrogate cardiac hemodynamics. μECG signals allowed for identification of PW Doppler signals for passive (early [E]-wave velocity) and active ventricular filling (atrial [A]-wave velocity) during diastole. The A wave (9.0±1.2 cm·s(-1)) is greater than the E wave (1.1±0.4 cm·s(-1)), resulting in an E/A ratio <1 (0.12±0.05, n=6). In response to cryocauterization to the ventricular epicardium, the E-wave velocity increased, accompanied by a rise in the E/A ratio at 3 days postcryocauterization (dpc) (0.55±0.13, n=6, p<0.001 vs. sham). The E waves normalize toward the baseline, along with a reduction in the E/A ratio at 35 dpc (0.36±0.06, n=6, p<0.001 vs. sham) and 65 dpc (0.2±0.16, n=6, p<0.001 vs. sham). In zebrafish, E/A<1 at baseline is observed, suggesting the distinct two-chamber system in which the pressure gradient across the atrioventricular valve is higher compared with the ventriculobulbar valve. The initial rise and subsequent normalization of E/A ratios support recovery in the ventricular diastolic function.
    Zebrafish 10/2014; 11(5):447-54. · 2.88 Impact Factor
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    ABSTRACT: Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state–of–art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will beaddressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN–PT and PIN–PMN–PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single–element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging, and microbeam applications of the single crystal transducers will be discussed.
    Progress in Materials Science 10/2014; · 23.19 Impact Factor
  • Source
    Hojong Choi, K Kirk Shung
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    ABSTRACT: The ultrasonic transducer is one of the core components of ultrasound systems, and the transducer's sensitivity is significantly related the loss of electronic components such as the transmitter, receiver, and protection circuit. In an ultrasonic device, protection circuits are commonly used to isolate the electrical noise between an ultrasound transmitter and transducer and to minimize unwanted discharged pulses in order to protect the ultrasound receiver. However, the performance of the protection circuit and transceiver obviously degrade as the operating frequency or voltage increases. We therefore developed a crossed SMPS (Switching Mode Power Supply) MOSFET-based protection circuit in order to maximize the sensitivity of high frequency transducers in ultrasound systems.The high frequency pulse signals need to trigger the transducer, and high frequency pulse signals must be received by the transducer. We therefore selected the SMPS MOSFET, which is the main component of the protection circuit, to minimize the loss in high frequency operation. The crossed configuration of the protection circuit can drive balanced bipolar high voltage signals from the pulser and transfer the balanced low voltage echo signals from the transducer.
    BioMedical Engineering OnLine 06/2014; 13(1):76. · 1.61 Impact Factor
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    ABSTRACT: We report a flexible shaft-based mechanical scanning photoacoustic endoscopy (PAE) system that can be potentially used for imaging the human gastrointestinal tract via the instrument channel of a clinical video endoscope. The development of such a catheter endoscope has been an important challenge to realize the technique's benefits in clinical settings. We successfully implemented a prototype PAE system that has a 3.2-mm diameter and 2.5-m long catheter section. As the instrument's flexible shaft and scanning tip are fully encapsulated in a plastic catheter, it easily fits within the 3.7-mm diameter instrument channel of a clinical video endoscope. Here, we demonstrate the intra-instrument channel workability and in vivo animal imaging capability of the PAE system.
    Journal of Biomedical Optics 06/2014; 19(6):66001. · 2.75 Impact Factor
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    ABSTRACT: We present a cross-beam nonlinear photoacoustic microscopy technique with enhanced axial resolution. By combining cross-beam illumination with optical nonlinearity, an axial resolution of 8.7 µm is measured experimentally.
    Biomedical Optics; 04/2014
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    ABSTRACT: We have developed fully motorized optical-resolution photoacoustic microscopy (OR-PAM), which integrates five complementary scanning modes and simultaneously provides a high imaging speed and a wide field of view (FOV) with 2.6 μm lateral resolution. With one-dimensional (1D) motion-mode mechanical scanning, we measured the blood flow through a cross section of a blood vessel in vivo. With two-dimensional (2D) optical scanning at a laser repetition rate of 40 kHz, we achieved a 2 kHz B-scan rate over a range of 50 μm with 20 A-lines and 50 Hz volumetric-scan rate over a FOV of 50 μm×50 μm with 400 A-lines, which enabled real-time tracking of cellular dynamics in vivo. With synchronized 1D optical and 2D mechanical hybrid scanning, we imaged a 10 mm×8 mm FOV within three minutes, which is 20 times faster than the conventional mechanical scan in our second-generation OR-PAM. With three-dimensional mechanical contour scanning, we maintained the optimal signal-to-noise ratio and spatial resolution of OR-PAM while imaging objects with uneven surfaces, which is essential for quantitative studies.
    Optics Letters 04/2014; 39(7):2117-20. · 3.39 Impact Factor
  • Hojong Choi, K Kirk Shung
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    ABSTRACT: The purpose of protection circuits in ultrasound applications is to block noise signals from the transmitter from reaching the transducer and also to prevent unwanted high voltage signals from reaching the receiver. The protection circuit using a resistor and diode pair is widely used due to its simple architecture, however, it may not be suitable for very high frequency (VHF) ultrasound transducer applications (>100 MHz) because of its limited bandwidth. Therefore, a protection circuit using MOSFET devices with unique structure is proposed in this paper. The performance of the designed protection circuit was compared with that of other traditional protection schemes. The performance characteristics measured were the insertion loss (IL), total harmonic distortion (THD) and transient response time (TRT). The new protection scheme offers the lowest IL (-1.0 dB), THD (-69.8 dB) and TRT (78 ns) at 120 MHz. The pulse-echo response using a 120 MHz LiNbO3 transducer with each protection circuit was measured to validate the feasibility of the protection circuits in VHF ultrasound applications. The sensitivity and bandwidth of the transducer using the new protection circuit improved by 252.1 and 50.9 %, respectively with respect to the protection circuit using a resistor and diode pair. These results demonstrated that the new protection circuit design minimizes the IL, THD and TRT for VHF ultrasound transducer applications.
    Journal of Medical Systems 04/2014; 38(4):34. · 1.78 Impact Factor
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    ABSTRACT: Photoacoustic (PA) endoscopy for human urogenital imaging has the potential to diagnose many important diseases, such as endometrial and prostate cancers. We have specifically developed a 12.7 mm diameter, rigid, side-scanning PA endoscopic probe for such applications. The key features of this endoscope are the streamlined structure for smooth cavity introduction and the proximal actuation mechanism for fast scanning. Here we describe the probe's composition and scanning mechanism and present in vivo experimental results suggesting its potential for comprehensive clinical applications.
    Optics Letters 03/2014; 39(6):1473-6. · 3.39 Impact Factor
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    ABSTRACT: The purpose of the limiter circuits used in the ultrasound imaging systems is to pass low-voltage echo signals generated by ultrasonic transducers while preventing high-voltage short pulses transmitted by pulsers from damaging front-end circuits. Resistor-diode-based limiters (a 50 Ω resistor with a single cross-coupled diode pair) have been widely used in pulse-echo measurement and imaging system applications due to their low cost and simple architecture. However, resistor-diode-based limiters may not be suited for high-frequency ultrasound transducer applications since they produce large signal conduction losses at higher frequencies. Therefore, we propose a new limiter architecture utilizing power MOSFETs, which we call a power MOSFET-diode-based limiter. The performance of a power MOSFET-diode-based limiter was evaluated with respect to insertion loss (IL), total harmonic distortion (THD), and response time (RT). We compared these results with those of three other conventional limiter designs and showed that the power MOSFET-diode-based limiter offers the lowest IL (-1.33 dB) and fastest RT (0.10 µs) with the lowest suppressed output voltage (3.47 Vp-p) among all the limiters at 70 MHz. A pulse-echo test was performed to determine how the new limiter affected the sensitivity and bandwidth of the transducer. We found that the sensitivity and bandwidth of the transducer were 130% and 129% greater, respectively, when combined with the new power MOSFET-diode-based limiter versus the resistor-diode-based limiter. Therefore, these results demonstrate that the power MOSFET-diode-based limiter is capable of producing lower signal attenuation than the three conventional limiter designs at higher frequency operation.
    Ultrasonic Imaging 03/2014; · 1.58 Impact Factor
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    ABSTRACT: We have developed a novel integrated optical coherence tomography (OCT)-intravascular ultrasound (IVUS) probe, with a 1.5 mm-long rigid-part and 0.9 mm outer diameter, for real-time intracoronary imaging of atherosclerotic plaques and guiding interventional procedures. By placing the OCT ball lens and IVUS 45MHz single element transducer back-to-back at the same axial position, this probe can provide automatically co-registered, co-axial OCT-IVUS imaging. To demonstrate its capability, 3D OCT-IVUS imaging of a pig's coronary artery in real-time displayed in polar coordinates, as well as images of two major types of advanced plaques in human cadaver coronary segments, was obtained using this probe and our upgraded system. Histology validation is also presented.
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    ABSTRACT: The natural history of atherosclerosis is marked by changes in the lipid biochemistry in the diseased arterial wall. As lesions become more vulnerable, different cholesterol species accumulate in the plaque. Understanding unstable atherosclerosis as a pharmacological and interventional therapeutic target requires chemically specific imaging of disease foci. In this study, we aim to image atherosclerotic plaque lipids and other vessel wall constituents with spectroscopic intravascular photoacoustics (sIVPA). sIVPA imaging can identify lipids in human coronary atherosclerotic plaque by relying on contrast in the near-infrared absorption spectra of the arterial wall components. Using reference spectra acquired on pure compounds, we analyzed sIVPA data from human coronary plaques ex vivo, to image plaque composition in terms of cholesterol and cholesterol ester content. In addition, we visualized the deeper lying connective tissue layers of the adventitia, as well as the fatty acid containing adipose cells in the peri-adventitial tissue. We performed simultaneous coregistered IVUS imaging to obtain complementary morphological information. Results were corroborated by histopathology. sIVPA imaging can distinguish the most prevalent lipid components of human atherosclerotic plaques and also visualize the connective tissue layers of the adventitia and the fatty acid containing adipose cells in the peri-adventitial tissue.
    Journal of Biomedical Optics 02/2014; 19(2):26006. · 2.75 Impact Factor
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    ABSTRACT: Photoacoustic ophthalmoscopy (PAOM) is a high-resolution in vivo imaging modality that is capable of providing specific optical absorption information for the retina. A high-frequency ultrasonic transducer is one of the key components in PAOM, which is in contact with the eyelid through coupling gel during imaging. The ultrasonic transducer plays a crucial role in determining the image quality affected by parameters such as spatial resolution, signal-to-noise ratio, and field of view. In this paper, we present the results of a systematic study on a high-frequency ultrasonic transducer design for PAOM. The design includes piezoelectric material selection, frequency selection, and the fabrication process. Transducers of various designs were successfully applied for capturing images of biological samples in vivo. The performances of these designs are compared and evaluated.
    Journal of Biomedical Optics 01/2014; 19(1):16015. · 2.75 Impact Factor
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    ABSTRACT: Multiparticle-trapping offers diverse opportunities and applications in biotechnology. It can be applied to creating various functional materials or organizing reactive particles. In this paper, we demonstrate that it is possible to trap and manipulate multi-particles in an annular pattern with a 24 MHz focused ring-type single element ultrasound transducer. Acoustic ring trap can be useful in undertaking biotropism studies due to an equal-distance condition from the center. Also, this ring trap could serve as a force shield to protect analysis area from other cells. The experimental results showed the capability of the proposed method as a multi-cell manipulator in formatting specific patterns of small cells like sperms.
    Applied Physics Letters 01/2014; 104(24):244107-244107-3. · 3.52 Impact Factor
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    ABSTRACT: Lipid deposition inside the arterial wall is a key indicator of plaque vulnerability. An intravascular photoacoustic (IVPA) catheter is considered a promising device for quantifying the amount of lipid inside the arterial wall. Thus far, IVPA systems suffered from slow imaging speed (~50 s per frame) due to the lack of a suitable laser source for high-speed excitation of molecular overtone vibrations. Here, we report an improvement in IVPA imaging speed by two orders of magnitude, to 1.0 s per frame, enabled by a custom-built, 2-kHz master oscillator power amplifier (MOPA)-pumped, barium nitrite [Ba(NO3)2] Raman laser. This advancement narrows the gap in translating the IVPA technology to the clinical setting.
    Scientific reports. 01/2014; 4:6889.
  • JACC. Cardiovascular imaging 01/2014; 7(1):101-3. · 14.29 Impact Factor
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    ABSTRACT: We designed and developed a confocal acoustic radiation force optical coherence elastography system. A ring ultrasound transducer was used to achieve reflection mode excitation and generate an oscillating acoustic radiation force in order to generate displacements within the tissue, which were detected using the phase-resolved optical coherence elastography method. Both phantom and human tissue tests indicate that this system is able to sense the stiffness difference of samples and quantitatively map the elastic property of materials. Our confocal setup promises a great potential for point by point elastic imaging in vivo and differentiation of diseased tissues from normal tissue.
    Applied Physics Letters 01/2014; 104(12):123702-123702-4. · 3.52 Impact Factor
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    ABSTRACT: Phacoemulsification is a common surgical method for treating advanced cataracts. Determining the optimal phacoemulsification energy depends on the hardness of the lens involved. Previous studies have shown that it is possible to evaluate lens hardness via ultrasound parametric imaging based on statistical models that require data to follow a specific distribution. To make the method more system-adaptive, nonmodel-based imaging approach may be necessary in the visualization of lens hardness. This study investigated the feasibility of applying an information theory derived parameter - Shannon entropy from ultrasound backscatter to quantify lens hardness. To determine the physical significance of entropy, we performed computer simulations to investigate the relationship between the signal-to-noise ratio (SNR) based on the Rayleigh distribution and Shannon entropy. Young's modulus was measured in porcine lenses, in which cataracts had been artificially induced by the immersion in formalin solution in vitro. A 35-MHz ultrasound transducer was used to scan the cataract lenses for entropy imaging. The results showed that the entropy is 4.8 when the backscatter data form a Rayleigh distribution corresponding to an SNR of 1.91. The Young's modulus of the lens increased from approximately 8 to 100 kPa when we increased the immersion time from 40 to 160 min (correlation coefficient r = 0.99). Furthermore, the results indicated that entropy imaging seemed to facilitate visualizing different degrees of lens hardening. The mean entropy value increased from 2.7 to 4.0 as the Young's modulus increased from 8 to 100 kPa (r = 0.85), suggesting that entropy imaging may have greater potential than that of conventional statistical parametric imaging in determining the optimal energy to apply during phacoemulsification.
    PLoS ONE 01/2014; 9(4):e96195. · 3.53 Impact Factor
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    ABSTRACT: We describe how contactless high-frequency ultrasound microbeam stimulation (HFUMS) is capable of eliciting cytoplasmic calcium (Ca2+) elevation in human umbilical vein endothelial cells. The cellular mechanotransduction process, which includes cell sensing and adaptation to the mechanical micro-environment, has been studied extensively in recent years. A variety of tools for mechanical stimulation have been developed to produce cellular responses. We developed a novel tool, a highly focused ultrasound microbeam, for non-contact cell stimulation at a microscale. This tool, at 200 MHz, was applied to human umbilical vein endothelial cells to investigate its potential to elicit an elevation in cytoplasmic Ca2+ levels. It was found that the response was dose dependent, and moreover, extracellular Ca2+ and cytoplasmic Ca2+ stores were involved in the Ca2+ elevation. These results suggest that high-frequency ultrasound microbeam stimulation is potentially a novel non-contact tool for studying cellular mechanotransduction if the acoustic pressures at such high frequencies can be quantified.
    Ultrasound in Medicine & Biology. 01/2014;
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    ABSTRACT: Viewing individual cells and ambient microvasculature simultaneously is crucial for understanding tumor angiogenesis and microenvironments. We developed a confocal fluorescence microscopy (CFM) and photoacoustic microscopy (PAM) dual-modality imaging system that can assess fluorescent contrast and optical absorption contrast in biologic samples simultaneously. After staining tissues with fluorescent dye at an appropriate concentration, each laser pulse can generate not only sufficient fluorescent signals from cells for CFM but also sufficient photoacoustic signals from microvessels for PAM. To explore the potential of this system for diagnosis of bladder cancer, experiments were conducted on a rat bladder model. The CFM image depicts the morphology of individual cells, showing not only large polygonal umbrella cells but also intracellular components. The PAM image acquired at the same time provides complementary information on the microvascular distribution in the bladder wall, ranging from large vessels to capillaries. This device provides an opportunity to realize both histologic assay and microvascular characterization simultaneously. The combination of the information of individual cells and local microvasculature in the bladder offers the capability of envisioning the viability and activeness of these cells and holds promise for more comprehensive study of bladder cancer in vivo.
    Molecular Imaging 12/2013; 12(8):491-6. · 3.41 Impact Factor
  • Hojong Choi, Hao-Chung Yang, K Kirk Shung
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    ABSTRACT: High performance limiters are described in this paper for applications in high frequency ultrasound imaging systems. Limiters protect the ultrasound receiver from the high voltage (HV) spikes produced by the transmitter. We present a new bipolar power transistor (BPT) configuration and compare its design and performance to a diode limiter used in traditional ultrasound research and one commercially available limiter. Limiter performance depends greatly on the insertion loss (IL), total harmonic distortion (THD) and response time (RT), each of which will be evaluated in all the limiters. The results indicated that, compared with commercial limiter, BPT-based limiter had less IL (-7.7dB), THD (-74.6dB) and lower RT (43ns) at 100MHz. To evaluate the capability of these limiters, they were connected to a 100MHz single element transducer and a two-way pulse-echo test was performed. It was found that the -6dB bandwidth and sensitivity of the transducer using BPT-based limiter were better than those of the commercial limiter by 22% and 140%, respectively. Compared to the commercial limiter, BPT-based limiter is shown to be capable of minimizing signal attenuation, RT and THD at high frequencies and is thus suited for high frequency ultrasound applications.
    Ultrasonics 10/2013; · 2.03 Impact Factor

Publication Stats

1k Citations
446.41 Total Impact Points


  • 2003–2014
    • University of Southern California
      • Department of Biomedical Engineering
      Los Angeles, California, United States
  • 2013
    • University of California, Davis
      • Department of Radiology
      Davis, CA, United States
  • 2010–2013
    • Beckman Research Institute
      Duarte, California, United States
    • Southern California University of Health Sciences
      Whittier, California, United States
  • 2012
    • Kwangwoon University
      • School of Electronic Engineering
      Seoul, Seoul, South Korea
    • Cedars-Sinai Medical Center
      • Cedars Sinai Medical Center
      Los Angeles, CA, United States
  • 2011–2012
    • Dongguk University
      • Department of Medical Biotechnology
      Seoul, Seoul, South Korea
    • Wuhan University
      Wu-han-shih, Hubei, China
    • Tsinghua University
      • School of Materials Science and Engineering
      Beijing, Beijing Shi, China
    • Chang Gung University
      • Department of Medical Imaging and Radiological Sciences
      Taoyuan, Taiwan, Taiwan
    • Sogang University
      Sŏul, Seoul, South Korea
  • 2007–2012
    • Washington University in St. Louis
      • Department of Biomedical Engineering
      Saint Louis, MO, United States
    • Academia Sinica
      • Research Center for Applied Sciences
      Taipei, Taipei, Taiwan
    • Institute of Electrical and Electronics Engineers
      Washington, Washington, D.C., United States
    • National Taiwan University
      • Institute of Applied Mechanics
      T’ai-pei, Taipei, Taiwan
  • 2006–2012
    • University of California, Los Angeles
      Los Angeles, California, United States
  • 2004–2010
    • Jeju National University
      • Department of Ocean System Engineering
      Cheju, Jeju, South Korea
  • 2009
    • Fu Jen Catholic University
      • Department of Electronic Engineering
      T’ai-pei, Taipei, Taiwan
  • 2008
    • Cheju Halla University
      Tse-tsiu, Jeju, South Korea
  • 2005
    • I-Shou University
      Kao-hsiung-shih, Kaohsiung, Taiwan
  • 1999–2003
    • Pennsylvania State University
      • • College of Engineering
      • • Department of Bioengineering
      University Park, MD, United States