Professional Education


  • Master of Science, Duke University (2011)
  • Doctor of Philosophy, Duke University (2017)

Lab Affiliations


All Publications


  • High Sensitivity Liver Vasculature Visualization Using a Real-time Coherent Flow Power Doppler (CFPD) Imaging System: A Pilot Clinical Study Li, Y., Hyun, D., Durot, I., Willmann, J. K., Dahl, J. J., IEEE IEEE. 2018
  • Angular coherence in ultrasound imaging: Theory and applications JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA Li, Y. L., Dahl, J. J. 2017; 141 (3): 1582-1594

    Abstract

    The popularity of plane-wave transmits at multiple transmit angles for synthetic transmit aperture (or coherent compounding) has spawned a number of adaptations and new developments of ultrasonic imaging. However, the coherence properties of backscattered signals with plane-wave transmits at different angles are unknown and may impact a subset of these techniques. To provide a framework for the analysis of the coherence properties of such signals, this article introduces the angular coherence theory in medical ultrasound imaging. The theory indicates that the correlation function of such signals forms a Fourier transform pair with autocorrelation function of the receive aperture function. This conclusion can be considered as an extended form of the van Cittert Zernike theorem. The theory is validated with simulation and experimental results obtained on speckle targets. On the basis of the angular coherence of the backscattered wave, a new short-lag angular coherence beamformer is proposed and compared with an existing spatial-coherence-based beamformer. An application of the theory in phase shift estimation and speed of sound estimation is also presented.

    View details for DOI 10.1121/1.4976960

    View details for Web of Science ID 000398962500043

    View details for PubMedID 28372139

  • Coherence Beamforming and its Applications to the Difficult-to-Image Patient Dahl, J. J., Hyun, D., Li, Y., Jakovljevic, M., Bell, M. L., Long, W. J., Bottenus, N., Kakkad, V., Trahey, G. E., IEEE IEEE. 2017
  • COHERENT COLOR FLOW IMAGING: VELOCITY ESTIMATION USING COHERENT SIGNALS Dahl, J. J., Li, Y., IEEE IEEE. 2017: 240–43
  • Visualization of Small-Diameter Vessels by Reduction of Incoherent Reverberation With Coherent Flow Power Doppler. IEEE transactions on ultrasonics, ferroelectrics, and frequency control Li, Y. L., Hyun, D., Abou-Elkacem, L., Willmann, J. K., Dahl, J. J. 2016; 63 (11): 1878-1889

    Abstract

    Power Doppler (PD) imaging is a widely used technique for flow detection. Despite the wide use of Doppler ultrasound, limitations exist in the ability of Doppler ultrasound to assess slow flow in the small-diameter vasculature, such as the maternal spiral arteries and fetal villous arteries of the placenta and focal liver lesions. The sensitivity of PD in small vessel detection is limited by the low signal produced by slow flow and the noise associated with small vessels. The noise sources include electronic noise, stationary or slowly moving tissue clutter, reverberation clutter, and off-axis scattering from tissue, among others. In order to provide more sensitive detection of slow flow in small diameter vessels, a coherent flow imaging technique, termed coherent flow PD (CFPD), is characterized and evaluated with simulation, flow phantom experiment studies, and an in vivo animal small vessel detection study. CFPD imaging was introduced as a technique to detect slow blood flow. It has been demonstrated to detect slow flow below the detection threshold of conventional PD imaging using identical pulse sequences and filter parameters. In this paper, we compare CFPD with PD in the detection of blood flow in small-diameter vessels. The results from the study suggest that CFPD is able to provide a 7.5-12.5-dB increase in the signal-to-noise ratio (SNR) over PD images for the same physiological conditions and is less susceptible to reverberation clutter and thermal noise. Due to the increase in SNR, CFPD is able to detect small vessels in high channel noise cases, for which PD was unable to generate enough contrast to observe the vessel.

    View details for PubMedID 27824565

    View details for PubMedCentralID PMC5154731

  • Coherent Flow Power Doppler (CFPD): Flow Detection Using Spatial Coherence Beamforming IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL Li, Y. L., Dahl, J. J. 2015; 62 (6): 1022-1035

    Abstract

    Power Doppler imaging is a widely used method of flow detection for tissue perfusion monitoring, inflammatory hyperemia detection, deep vein thrombosis diagnosis, and other clinical applications. However, thermal noise and clutter limit its sensitivity and ability to detect slow flow. In addition, large ensembles are required to obtain sufficient sensitivity, which limits frame rate and yields flash artifacts during moderate tissue motion. We propose an alternative method of flow detection using the spatial coherence of backscattered ultrasound echoes. The method enhances slow flow detection and frame rate, while maintaining or improving the signal quality of conventional power Doppler techniques. The feasibility of this method is demonstrated with simulations, flow-phantom experiments, and an in vivo human thyroid study. In comparison with conventional power Doppler imaging, the proposed method can produce Doppler images with 15- to 30-dB SNR improvement. Therefore, the method is able to detect flow with velocities approximately 50% lower than conventional power Doppler, or improve the frame rate by a factor of 3 with comparable image quality. The results show promise for clinical applications of the method.

    View details for DOI 10.1109/TUFFC.2014.006793

    View details for Web of Science ID 000356162000005

    View details for PubMedID 26067037

    View details for PubMedCentralID PMC4467462

  • Coherence Beamforming Applied to Velocity Estimation and Partially Coherent Signals 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) Dahl, J. J., Li, Y., Hyun, D., Doherty, J. R. 2015
  • Small-diameter Vasculature Detection with Coherent Flow Power Doppler Imaging IEEE International Ultrasonics Symposium (IUS) You, L., Dahl, J. J. 2015

    View details for DOI 10.1109/ULTSYM.2015.0012

  • Flow Detection based on the Spatial Coherence of Backscattered Echoes Li, Y., Dahl, J. J., IEEE IEEE. 2014: 428–31
  • Quantitative Surface-Enhanced Resonant Raman Scattering Multiplexing of Biocompatible Gold Nanostars for in Vitro and ex Vivo Detection ANALYTICAL CHEMISTRY Yuan, H., Liu, Y., Fales, A. M., Li, Y., Liu, J., Vo-Dinh, T. 2013; 85 (1): 208–12

    Abstract

    Surface-enhanced Raman scattering (SERS)-active plasmonic nanomaterials have become a promising agent for molecular imaging and multiplex detection. To produce strong SERS intensity while retaining the nonaggregated state and biocompatibility needed for bioapplications, we integrated near-infrared (NIR) responsive plasmonic gold nanostars with resonant dyes for resonant SERS (SERRS). The SERRS on nanostars was several orders of magnitude greater than signals from SERRS on nanospheres and nonresonant SERS on nanostars. For the first time, we demonstrated quantitative multiplex detection using four unique nanostar SERRS probes in both in vitro solutions and ex vivo tissue samples under NIR excitation. With further optimization, in vivo tracking of multiple SERRS probes is possible.

    View details for DOI 10.1021/ac302510g

    View details for Web of Science ID 000313156500031

    View details for PubMedID 23194068

    View details for PubMedCentralID PMC4022299

  • Multispectral nanoparticle contrast agents for true-color spectroscopic optical coherence tomography BIOMEDICAL OPTICS EXPRESS Li, Y., Seekell, K., Yuan, H., Robles, F. E., Wax, A. 2012; 3 (8): 1914–23

    Abstract

    We have recently developed a novel dual window scheme for processing spectroscopic OCT images to provide spatially resolved true color imaging of chromophores in scattering samples. Here we apply this method to measure the extinction spectra of plasmonic nanoparticles at various concentrations for potential in vivo applications. We experimentally demonstrate sub-nanomolar sensitivity in the measurement of nanoparticle concentrations, and show that colorimetric imaging with multiple species of nanoparticles produces enhanced contrast for spectroscopic OCT in both tissue phantom and cell studies.

    View details for DOI 10.1364/BOE.3.001914

    View details for Web of Science ID 000307116800013

    View details for PubMedID 22876354

    View details for PubMedCentralID PMC3409709