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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2023)

Ultrasonography has been widely applied in imaging tissues and organs for diagnosing diseases due to its capability of serving as a real-time, non-invasive, portable, and radiation-free tool. Ultrasound imaging has demonstrated significant value in diagnosing and monitoring periodontitis that can improve the limitations of conventional methods such as radiography and periodontal probing. While radiography provides excellent sensitivity to hard tissues, it uses ionizing radiation and is limited in stratifying disease in soft tissues. Periodontal probing is time-consuming and painful for patients, and inter-operator variation in probing can exceed 40%.In this dissertation, the first part reviews the materials and mechanisms of ultrasound transducers. The second part includes our work that developed a wearable skin-conformal ultrasonic phased array patch for continuous haemodynamics monitoring in deep tissue. The penetration depth is up to 14 cm beneath the skin, allowing accessing biological signals from central organs. The third part includes our work that developed a toothbrush-shaped ultrasound transducer to image all 28 human teeth with its miniaturized size and side-facing design. The results showed that the full-mouth imaging process by the miniaturized transducer is reproducible in a small cohort of five subjects. Besides imaging anatomical structures, blood flow of the supraperiosteal artery in human gingiva was measured by color and spectral Doppler to provide hemodynamic information. The fourth part includes our work that mapped the location and physiology of the greater palatine artery (GPA) in a 3D manner. Mapping the trajectory of the GPA in the hard/soft palate is clinically important to evaluate the available palate donor tissue during soft tissue autografting and to avoid sectioning of the GPA during the surgery. The fifth part summarizes our work of reconstructing sparse array ultrasound imaging with deep learning algorithms. Sparse array ultrasound imaging has presented potential in reducing the fabrication cost, energy consumption and electrical system complexity. However, sparse array imaging suffers from inevitable artifacts due to grating lobes. We developed a convolutional neural network (CNN)-assisted sparse array using only 16 channels out of a 128-channel transducer, in which the pitch is eight times that of the dense array.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2022)
    Synchronization is important for photoacoustic (PA) tomography, but some fixed delays between the data acquisition (DAQ) and the light pulse are a common problem degrading imaging quality. Here, we present a simple yet versatile method named Scissors to help synchronize ultrasound open platforms (UOPs) for PA imaging. Scissors is a programed function that can cut or add a fixed delay to radio frequency (RF) data and, thus, synchronize it before reconstruction. Scissors applies the programmable metric of UOPs and has several advantages. It is compatible with many setups regardless of the synchronization methods, light sources, transducers, and delays. The synchronization is adjustable in steps reciprocal to the UOPs sampling rate (20-ns step with a 50-MHz sampling rate). Scissors works in real-time PA imaging, and no extra hardware is needed. We programed Scissors in Vantage UOP (Verasonics, Inc., Kirkland, WA, USA) and then imaged two 30- [Formula: see text] nichrome wires with a 20.2-MHz central frequency transducer. The PA image was severely distorted by an 828-ns delay; over 90% delay was caused by our Q -switch laser. The axial and lateral resolutions are 112 and [Formula: see text], respectively, after using Scissors. We imaged a human finger in vivo, and the imaging quality is tremendously improved after solving the 828-ns delay by using Scissors.
      Cover page: Synchronization of RF Data in Ultrasound Open Platforms (UOPs) for High-Accuracy and High-Resolution Photoacoustic Tomography Using the Scissors Programming Method.
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2022)
      Periodontitis is a public issue and imaging periodontal pocket is important to evaluate periodontitis. Regular linear transducers have limitations in imaging the posterior teeth due to their geometry restrictions. Here we characterized a transducer that can image the posterior teeth including assessment of periodontal pockets via a combination of photoacoustic and ultrasound imaging. Unlike conventional transducer design, this device has a toothbrush-shaped form factor with a side-view transducer to image molars (total size: 1 ×1.9 cm). A laser diode was integrated as the light source to reduce the cost and size and facilitates clinical transition. The in vivo imaging of a molar of a periodontal patient demonstrated that the transducer could image in the posterior area of gum in vivo; the value determined by imaging was within 7 % of the value measured clinically.
        Cover page: Posterior photoacoustic/ultrasound imaging of the periodontal pocket with a compact intraoral transducer
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2022)
        SIGNIFICANCE: Photoacoustic imaging has shown advantages over the periodontal probing method in measuring the periodontal probing depth, but the large size of conventional photoacoustic transducers prevents imaging of the more posterior teeth. AIM: Our aim is to develop a photoacoustic imaging system to image the more posterior periodontal pocket. APPROACH: We report a clinical hockey-stick-style transducer integrated with fibers for periodontal photoacoustic imaging. Cuttlefish ink labeled the periodontal pocket as the photoacoustic contrast agent. RESULTS: We characterized the imaging system and then measured the pocket depth of 35 swine teeth. Three raters evaluated the performance of the hockey-stick transducer. The measurements between the Williams probing (gold standard) and the photoacoustic methods were blinded but highly correlated. We showed a bias of ∼0.3  mm for the imaging-based technique versus Williams probing. The minimum inter-reliability was over 0.60 for three different raters of varying experience, suggesting that this approach to measure the periodontal pocket is reproducible. Finally, we imaged three pre-molars of a human subject. We could access more upper and posterior teeth than conventional linear transducers. CONCLUSIONS: The unique angle shape of the hockey-stick transducer allows it to image more posterior teeth than regular linear transducers. This study demonstrated the ability of a hockey-stick transducer to measure the periodontal pocket via photoacoustic imaging.
          Cover page: Photoacoustic imaging of posterior periodontal pocket using a commercial hockey-stick transducer.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2023)
          3D-bioprinted skin-mimicking phantoms with skin colors ranging across the Fitzpatrick scale are reported. These tools can help understand the impact of skin phototypes on biomedical optics. Synthetic melanin nanoparticles of different sizes (70-500 nm) and clusters are fabricated to mimic the optical behavior of melanosome. The absorption coefficient and reduced scattering coefficient of the phantoms are comparable to real human skin. Further the melanin content and distribution in the phantoms versus real human skins are validated via photoacoustic (PA) imaging. The PA signal of the phantom can be improved by: 1) increasing melanin size (3-450-fold), 2) increasing clustering (2-10.5-fold), and 3) increasing concentration (1.3-8-fold). Then, multiple biomedical optics tools (e.g., PA, fluorescence imaging, and photothermal therapy) are used to understand the impact of skin tone on these modalities. These well-defined 3D-bioprinted phantoms may have value in translating biomedical optics and reducing racial bias.
            Cover page: 3D‐Bioprinted Phantom with Human Skin Phototypes for Biomedical Optics
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2023)
            Aromatic interactions are commonly involved in the assembly of naturally occurring building blocks, and these interactions can be replicated in an artificial setting to produce functional materials. Here we describe a colorimetric biosensor using co-assembly experiments with plasmonic gold and surfactant-like peptides (SLPs) spanning a wide range of aromatic residues, polar stretches, and interfacial affinities. The SLPs programmed in DDD-(ZZ)x -FFPC self-assemble into higher-order structures in response to a protease and subsequently modulate the colloidal dispersity of gold leading to a colorimetric readout. Results show the strong aggregation propensity of the FFPC tail without polar DDD head. The SLPs were specific to the target protease, i.e., Mpro , a biomarker for SARS-CoV-2. This system is a simple and visual tool that senses Mpro in phosphate buffer, exhaled breath condensate, and saliva with detection limits of 15.7, 20.8, and 26.1 nM, respectively. These results may have value in designing other protease testing methods.
              Cover page: Peptide Amphiphile Mediated Co‐assembly for Nanoplasmonic Sensing
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2022)
              Electronic patches, based on various mechanisms, allow continuous and noninvasive monitoring of biomolecules on the skin surface. However, to date, such devices are unable to sense biomolecules in deep tissues, which have a stronger and faster correlation with the human physiological status than those on the skin surface. Here, we demonstrate a photoacoustic patch for three-dimensional (3D) mapping of hemoglobin in deep tissues. This photoacoustic patch integrates an array of ultrasonic transducers and vertical-cavity surface-emitting laser (VCSEL) diodes on a common soft substrate. The high-power VCSEL diodes can generate laser pulses that penetrate >2 cm into biological tissues and activate hemoglobin molecules to generate acoustic waves, which can be collected by the transducers for 3D imaging of the hemoglobin with a high spatial resolution. Additionally, the photoacoustic signal amplitude and temperature have a linear relationship, which allows 3D mapping of core temperatures with high accuracy and fast response. With access to biomolecules in deep tissues, this technology adds unprecedented capabilities to wearable electronics and thus holds significant implications for various applications in both basic research and clinical practice.
                Cover page: A photoacoustic patch for three-dimensional imaging of hemoglobin and core temperature
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