Sub Focus-1: Computational Ultrasound and Medical Technology 

Through novel device design, real-time image analysis and machine intelligence, understanding of diagnostic techniques, and system design we work to improve the usability, diagnostic capability, and workflow productivity of freehand ultrasound imaging. Freehand ultrasound instruments are a low cost, versatile, safe (i.e. non-ionizing radiation), imaging technique – suitable for diverse medical practices.

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  • Non-contact and Quantitative Ultrasound Imaging

Non-contact and quantitative ultrasound images of bone and soft tissue are produced from original algorithms applied to observational data sets collected using a water immersion ultrasound tomography (UST) and laser ultrasound (LUS) imaging systems. These systems and algorithms could improve the quality, cost and safety of osteoporosis diagnosis and tracking, prosthetic fitting, bone fracture detection and tracking, intraoperative imaging and volumetric imaging in intensive care units. The images are quantitative in that the distribution of sound speeds and dimensionally accurate geometry of tissue structures are reconstructed. The experiments completed with the LUS system demonstrate its capability to generate ultrasound images without contacting or treating the skin surface. Further, soft tissue (weak reflector), as well as strong reflectors are resolved at skin safe optical exposures. The full waveform inversion (FWI) algorithms developed for the UST system yield quantitative (sound speed and geometry) bone and soft tissue ultrasound images.

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  • Ultrasound Imaging

Ultrasound shear wave elastography (SWE)

Ultrasound shear wave elastography qunatifies tissue elasticity by generating shear wave and measuring the speed of its propagation. Clinical ultrasound platforms implement acoustic radiation force impulse (ARFI) for shear wave generation, which requires upgraded electronics and is therefore only available on premium systems. In our lab, we are developing a low-cost portable miniature SWE system using external mechanical vibration (EMV). Our miniature EMV system can be mounted to an ultrasonic probe and robustly launch high-amplitude shear waves in various patterns with low power consumption. Current work involves system validation both ex vivo and in vivo, as well as integration with force sensing/control probe.

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Quantitative musculoskeletal tissue assessment and improved prosthetic interface design

For persons living with lower extremity amputation, the prosthetic socket – the cup-like interface connecting the residuum to prosthesis – is considered the most critical component. It must be custom-made and tailored to each individual user, and if not fit properly can significantly hinder the quality of life. As an alternative to conventional fabrication practices that involve subjective input from a clinician, computational modeling-based socket design practices have emerged.  Despite early success, its clinical implementation and potential for broad accessibility are limited since it relies on expensive imaging technologies and robotic indentation devices. Medical ultrasound imaging, a cost-effective modality that can be used at the bedside, is a promising and clinically-viable solution.

In order for an ultrasound to become a viable scanning method for this application, technological development was necessary that allows for three-dimensional acquisition of (1) limb geometry and (2) mechanical tissue properties. Toward this goal, we first present the design of a novel multi-modal imaging system for rapidly acquiring volumetric ultrasound imagery of human limbs. Second, we present results of two studies that evaluate the use of ultrasound indentation and shear wave elastography (SWE) to characterize tissue biomechanics: the former to investigate how SWE is affected by transducer force, and the latter presenting a novel approach for constitutive parameter identification using a combination of finite element analysis (FEA), indentation, and SWE. Finally, we demonstrate that SWE may be performed using a non-contact approach, allowing for human limb data to be collected under discrete transducer-independent loading conditions.

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Sub-focus-II: Smart Manufacturing

Optical digital-imaging techniques offer a fast, high-resolution, and wide-range metrology capability for measuring semi-transparent and transparent polymer-based devices during manufacture. We create novel instrumentation for in-process statistical control and metrology capable of measuring a complete macroscale part (~25 mm) down to its microscale features (~50 µm).

  • Optical Metrology

Fiber manufacturing process has been an integral part of the optical fiber communications. The optical fiber manufacturing processes involve high precision quality control and large volume production. However, the conventional fiber drawing manufacturing technologies are not flexible and highly specialized. This prevents innovative ideas such as flexible fiber manufacturing and small-scale prototypes. We are working to design and test a desktop fiber manufacturing kit. Proportional control can be used to adjust fiber diameters very precisely.

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  • Precise Multimaterial Fiber Extrusion using Acoustic Radiation Force

Carbon nanofibers in polymer-based composites reduce the electrical resistivity of the composite but can be up to 100 times more expensive than the bulk polymer. This work uses acoustic focusing to organize and compact carbon nanofibers in a mineral oil mixture. The result is a decrease in the composite electrical resistivity without an increase in the global volume fraction of the fibers in the composite and associated material cost.

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Sub-focus-III: Micro and Nanotechnology

  • Integrated Photonics for Point-of-Care Diagnostic Sensors

Optical imaging, sensing, and testing are ubiquitous in biology, offering elegant solutions for diagnostic, therapeutic, and theranostic applications. At present, there is not a single biomedical application where optical components are not applied.  If these optical systems can be built using complex miniaturized photonic systems, then scalability, portability, lower cost, and higher performance can be obtained for real-time monitoring and bedside treatment. On these lines, we propose bio-photonic integrated circuits (Bio-PICs) for point-of-care diagnostics. These circuits rely on moving photons in photonic waveguides (similar to electrons in your electronic chips) to provide on-chip sensing solution. Specifically, we are working on developing Bio-PICs for following three foci:

  • Neurophotonic Probes for Deep Brain Photoacoustic Imaging: Conventionally, the implantable probe technology is based on an array of patterned electrodes to monitor electrical signals in the extracellular matrix of deep neural cells. The state-of-art design can successfully record only ~100 neurons simultaneously, making it rather slow progress to reach the ultimate goal of probing 100 billion neurons in the human brain! To overcome this bottleneck, we are working an implantable neurophotonic photoacoustic probe architecture that could image ~10000 neurons with cellular resolution. Realized on Michigan style MOEMS technology, the probe consists of photonic waveguide-based meta illuminators for photoacoustic excitation and high-frequency ultrasonic transducers for acoustic detection. The probe is a miniaturized implantable sensing system that improves the depth of penetration ( 8-10 mm) and resolution ( 1-5 um) in neural imaging. We will discuss imaging feasibility, engineering different optical excitation beam profiles using nanophotonic structures, and will demonstrate an ultrasound detector using an integrated photonics platform.
  • Integrated Optofluidic Sensors for Aerosol Sensing and Blood Coagulometry: We are working on optofluidic sensors for in-situ characterization (size, count, and chemistry) of aerosol and bio-aerosol particles. These photonic sensor designs based on Near-IR and Mid-IR platforms can extract the physical and chemical nature of interacting particles over a broad range of sizes (100 nm to 2 um in diameter) compared to current integrated photonics-based sensors, that are restricted to molecular or nanoparticle sensing. We also explore these photonic sensors for on-chip blood coagulometry.
  • Machine Learning for Nanophotonic Design: The ever-growing applications like ones mentioned above require complex photonic structures that can manipulate and guide light waves at the nanoscale. The design space of such nanostructures is often high-dimensional, where conventional design optimization methods fail. We employ machine learning to capture a global optimum in functionality.
  • MEMS-based Flexible Ultrasonic Transducer

Wearable ultrasound sensing could lead to novel medical diagnostics by enabling continuous, real-time, and direct measurement of physiological phenomena, such as blood pressure. Currently, ultrasound is not used in wearable health sensing applications because clinical ultrasound systems are expensive, bulky, and require high operating power. Realizing wearable ultrasound, therefore, requires significant reductions in cost, size, and power consumption. Manufacturing cost was of particular concern because sensors are frequently incorporated into consumer goods, where cost is a key driver of technology adoption. Toward that goal, we are exploring the opportunity to fabricate low-cost ultrasound transducers by contact printing. Contact printing is chosen because it could be scalable for high-throughput manufacturing, and it could be performed at ambient temperature and pressure.  a capacitive microscale ultrasound transducer is fabricated by contact printing a gold-parylene composite flexible membrane onto a silicon chip substrate. We have shown that flexible membrane ultrasound transducers have the potential to in the future enable ultrasound to be used for wearable health sensing.