Honors & Awards

  • K99 Pathway to Independence, Eunice Shriver Kennedy National Institute of Child Health and Human Development (NICHD) (2021)
  • New Investigator Award for Basic Science, American Institute of Ultrasound in Medicine (2021)


  • Jeremy Dahl, You Li. "United States Patent 10,111,644 Method of coherent flow imaging using synthetic transmit focusing and acoustic reciprocity", Leland Stanford Junior University, Oct 30, 2018

Lab Affiliations

All Publications

  • A Physics-Based Neural Network (PNN) Approach to Solving the Heterogeneous Nonlinear Fullwave Equation Li, Y., Pinton, G., IEEE IEEE. 2022
  • Real-Time In Vivo Imaging of Human Liver Vasculature Using Coherent Flow Power Doppler: A Pilot Clinical Study IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL Li, Y., Hyun, D., Ducey-Wysling, J., Durot, I., D'Hondt, A., Patel, B., Dahl, J. J. 2021; 68 (9): 3027-3041


    Power Doppler (PD) is a commonly used technique for flow detection and vessel visualization in radiology clinics. Despite its broad set of applications, PD suffers from multiple noise sources and artifacts, such as thermal noise, clutter, and flash artifacts. In addition, a tradeoff exists between acquisition time and Doppler image quality. These limit the ability of clinical PD imaging in deep-lying and small-vessel detection and visualization, particularly among patients with high body mass indices (BMIs). To improve the Doppler vessel detection, we have previously proposed coherent flow PD (CFPD) imaging and demonstrated its performance on porcine vasculature. In this article, we report on a pilot clinical study of CFPD imaging on healthy human volunteers and patients with high BMI to assess the clinical feasibility of the technique in liver imaging. In this study, we built a real-time CFPD imaging system using a graphical processing unit (GPU)-based software beamformer and a CFPD processing module. Using the real-time CFPD imaging system, the liver vasculature of 15 healthy volunteers with normal BMI below 25 and 15 patients with BMI greater than 25 was imaged. Both PD and CFPD image streams were produced simultaneously. The generalized contrast-to-noise ratio (gCNR) of the PD and CFPD images was measured to provide the quantitative evaluation of image quality and vessel detectability. Comparison of PD and CFPD image shows that gCNR is improved by 35% in healthy volunteers and 28% in high BMI patients with CFPD compared to PD. Example images are provided to show that the improvement in the Doppler image gCNR leads to greater detection of small vessels in the liver. In addition, we show that CFPD can suppress in vivo reverberation clutter in clinical imaging.

    View details for DOI 10.1109/TUFFC.2021.3081438

    View details for Web of Science ID 000690441000022

    View details for PubMedID 34003748

  • Blood Flow Imaging in the Neonatal Brain Using Angular Coherence Power Doppler IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL Jakovljevic, M., Yoon, B., Abou-Elkacem, L., Hyun, D., Li, Y., Rubesova, E., Dahl, J. J. 2021; 68 (1): 92–106


    Using ultrasound to image small vessels in the neonatal brain can be difficult in the presence of strong clutter from the surrounding tissue and with a neonate motion during the scan. We propose a coherence-based beamforming method, namely the short-lag angular coherence (SLAC) beamforming that suppresses incoherent noise and motion artifacts in Ultrafast data, and we demonstrate its applicability to improve detection of blood flow in the neonatal brain. Instead of estimating spatial coherence across the receive elements, SLAC utilizes the principle of acoustic reciprocity to estimate angular coherence from the beamsummed signals from different plane-wave transmits, which makes it computationally efficient and amenable to advanced beamforming techniques, such as f-k migration. The SLAC images of a simulated speckle phantom show similar edge resolution and texture size as the matching B-mode images, and reduced random noise in the background. We apply SLAC power Doppler (PD) to free-hand imaging of neonatal brain vasculature with long Doppler ensembles and show that: 1) it improves visualization of small vessels in the cortex compared to conventional PD and 2) it can be used for tracking of blood flow in the brain over time, meaning it could potentially improve the quality of free-hand functional ultrasound.

    View details for DOI 10.1109/TUFFC.2020.3010341

    View details for Web of Science ID 000602706700010

    View details for PubMedID 32746214

  • Human Placental Vasculature Imaging Using Long Ensemble Angular-coherence-based Doppler Li, Y., Chueh, J., Ness, A., Hyun, D., Jakovljevic, M., Lyell, D., Winn, V., Dahl, J. J., IEEE IEEE. 2020
  • An Open Source GPU-Based Beamformer for Real-Time Ultrasound Imaging and Applications Hyun, D., Li, Y., Steinberg, I., Jakovljevic, M., Klap, T., Dahl, J. J., IEEE IEEE. 2019: 20–23
  • Vector Flow Velocity Estimation from Beamsummed Data Using Deep Neural Networks Li, Y., Hyun, D., Dahl, J. J., IEEE IEEE. 2019: 860–63
  • 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


    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
  • 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


    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


    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


    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


    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