Xin Sun

Large aperture 2D arrays improve ultrasound imaging by increasing lateral resolution at depth, owing to the inverse relationship between beamwidth and aperture size, and by enabling higher contrast resolution through electronic focusing in elevation. We present a 4,096-element (128 × 32) large-aperture 2D ultrasound array with element pitches of 0.65 mm (azimuth) and 0.5 mm (elevation), operating at a 2.4 MHz center frequency with over 80% –6 dB bandwidth. The active aperture measures 83.2 mm × 16 mm and is integrated with custom multiplexing ASICs, local preamplifiers for sensitivity enhancement, and an FPGA-based control interface, forming a fully reconfigurable imaging platform. Phantom experiments using a commercial CIRS 054GS tissue-mimicking phantom demonstrated penetration beyond 120 mm. The system achieved axial and lateral resolutions of 0.40 mm and 0.46 mm respectively at depths of 51 mm, with a maximum CNR of 2.13 and gCNR of 0.94 for cyst targets. These results validate the effectiveness of the large aperture 2D array for high-resolution volumetric ultrasound imaging and underscore the promise for future clinical translation.

Objective: This study aims to facilitate a sequential excitation 4-dimensional (4D) ultrasound shear wave elastography (SWE) method for volumetric characterization of mechanical properties of ocular tissue using a 2D matrix array with a standard 256-channel ultrasound system. Impact Statement: Sequential elastography (SE) enables cost-effective 4D volumetric elastography without requiring an equal channel-count system. The swept-cross strategy improves volumetric imaging quality and, for the first time, enables 4D SWE-based differentiation of tissue anisotropy, with in vivo ocular applications. Introduction: Volumetric SWE remains challenging because of the limited channel counts of the acquisition system. Methods: SE applies a 32 × 32 matrix array and divides it into four 8 × 32 subpanels, connected with a Vantage 256 system through 4-1 multiplexing. An optimized sequential excitation and swept-cross compounding method is used to reduce the interpanel gap influence and improve elevational performance. Results: Validated using wire targets, point target, ex vivo chicken breast, and in vivo rabbit cornea, SE improved volumetric imaging performance compared with conventional subpanel compounding. It improved the elevational resolution from 0.84 mm to 0.35 mm at 10-mm depth and the 3D point spread function from 1 × 2.1 × 4.7 λ ³ to 1 × 2.2 × 2.1 λ ³ . In chicken breast, it differentiated tissue anisotropy and estimated muscle fiber direction. In rabbit cornea, it enabled volumetric shear wave velocity mapping. Conclusion: SE enables 4D shear wave elastography and provides a promising approach for volumetric assessment of tissue biomechanics, anisotropy, and ocular stiffness.

The purpose of this study is to enable in-vivo three-dimensional (3-D) ultrasound localization microscopy (ULM) of posterior ocular microvasculature using a 256-channel system and a 1024-element matrix array, and to overcome limitations of restricted transmit angles, sound speed mismatch caused by the crystalline lens and surrounding tissues, and the low signal-to-noise ratio (SNR) of microbubble signals. To address phase distortions from the crystalline lens, which has a higher speed of sound (SOS) than surrounding tissues, a region-dependent SOS beamforming approach was implemented to improve microbubble resolution. A 4-D non-local means filter was subsequently applied to suppress background noise and enhance microbubble contrast. The proposed method improved localization accuracy and image quality, achieving a spatial resolution of 63 um, while Fourier shell correlation (1/2-bit threshold) confirmed a global resolution of approximately 59 um. Higher mean normalized cross-correlation coefficients between the microbubbles and the system point-spread function, obtained with the proposed method (approximately 0.67), compared with those without the proposed method (approximately 0.60), indicate enhanced microbubble signal quality. Furthermore, the 3-D bi-directional vessel density and flow-velocity maps were reconstructed, capturing detailed choroidal vascular and hemodynamic patterns. These results demonstrate that region-dependent SOS beamforming combined with spatiotemporal denoising enables high-resolution posterior ocular ULM and provides a practical pathway toward quantitative 3-D assessment of retinal and choroidal microvasculature for potential clinical use.

Medical ultrasound technology provides zero-radiation, non-invasive, high-penetration and high-resolution evaluation of body organs for diagnosing various diseases. However, challenges remain for emerging ultrasonic bioelectronics in terms of novel material exploration, structural flexibility, wearable integration. Here, we present a 64-channel lead-free ultrasound line imaging array transducer developed from biofriendly potassium sodium niobate-based ceramics, which enables wearable multimodal imaging through the incorporation of multilevel material structure engineering and flexible device design. On the materials engineering aspect, the lead-free ceramics exhibits superior piezoelectricity (d₃₃ ~ 630 pC N⁻¹, k₃₃ ~ 0.66) by restoring long range ferroelectric ordering and suppressing excessive polar nanoregions. In terms of device architecture, the miniaturized array integrates 64 lead-free 1-3 piezo-elements on a flexible printed circuit board and a bioadhesive hydrogel layer for acoustic coupling and robust adhesion to the skin, enabling portable, high-precision operation with a center frequency of 8.36 MHz and a −6 dB bandwidth of over 40%. In wearable applications for the human body, this array demonstrates real-time high-resolution vascular imaging, blood flow dynamics, and elastography of muscle dynamics, advancing the next generation of wearable ultrasound technologies.

Large aperture 2D arrays benefit from improved lateral resolution at depth, due to the dependence of beamwidth on the inverse of the aperture width, and improved contrast resolution due to electronic focusing. We have been developing modular large aperture multi-row 1,024 (64 azimuth × 16 elevation) element, 2D arrays based on custom-designed and locally integrated Application Specific Integrated Circuit (ASIC) multiplexing devices. The implemented handheld large array prototype probe for human imaging consists of multiple rows with multiplexed synthetic aperture in elevation and planewave transmits in azimuth. The pitch of the acoustic array is 650 μm in azimuth by 1,000 μm in elevation, with a 2.4 MHz (FBW=88%) center frequency and total active aperture of 42 mm × 16 mm. We interfaced the large aperture array and multiplexing ASICs, along with local preamplifier devices for improved sensitivity, and a local FPGA for digital ASIC control, to a configurable ultrasound imaging platform and demonstrate 2D orthogonal and full 3D-beamformed imaging. The implemented imaging prototype includes local buffering for improved sensitivity of the high impedance 2D array elements, and realizes penetration down to 140 mm, experimental lateral/axial resolution at 67 mm of 1.1 mm/0.4 mm, and maximum experimental CNR of 2.1 for 8 mm cylindrical cysts, and 1.7 for 10 mm spherical cysts. We demonstrate in-vivo imaging of liver in human volunteers utilizing a hermetically-sealed and safety-validated handheld prototype of the large 2D array. Preliminary results are promising for clinical imaging in future studies.

Wearable ultrasound has been widely developed for long-term, continuous imaging without the need for bulky system manipulation and repeated manual locating. To potentially lead to more accurate and reliable imaging monitoring, this work presents the design, fabrication, and evaluation of a novel high-frequency wearable ultrasound array belt (WUAB) for small animal echocardiography. The fabrication process involved precise dicing technology for a λ-pitch design. The 20 MHz WUAB consists of two matching layers, piezoelectric composite with 128 channels, customized flexible circuit substrate, acoustic backing layer, and customized belt structure with designed end tip and insertion point for wearability. The resulting WUAB demonstrates sensitivity of -5.69 ± 2.5 dB and fractional bandwidth of 57 ± 5 %. In vivo experiments on rat model showed expected echocardiography and B-mode images of rat heart. These results represent significant promise for future longitudinal studies in small animals and real-time physiological monitoring.

Objective: Current shear wave elastography methods primarily focus on 2D imaging. To explore mechanical properties of biological tissues in 3D, a four-dimensional (4D, x, y, z, t) ultrasound shear wave elastography is required. However, 4D ultrasound shear wave elastography is still challenging due to the limitation of the hardware of standard ultrasound acquisition systems. In this study, we introduce a novel method to achieve 4D shear wave elastography, named sequential-based excitation shear wave elastography (SE-SWE). This method can achieve 4D elastography implemented by a 1024-element 2D array with a standard ultrasound 256-channel system. Methods: The SE-SWE method employs sequential excitation to generate shear waves, and utilizes a 2D array, dividing it into four sub-sections, to capture shear waves across multiple planes. This process involves sequentially exciting each sub-section to capture shear waves, followed by compounding the acquired data from these subsections. Results: The phantom studies showed strong concordance between the shear wave speeds (SWS) measured by SE-SWE and expected values, confirming the accuracy of this method and potential to differentiate tissues by stiffness. In ex vivo chicken breast experiments, SE-SWE effectively distinguished between orientations relative to muscle fibers, highlighting its ability to capture the anisotropic properties of tissues. Conclusion: The SE-SWE method advances shear wave elastography significantly by using a 2D array divided into four subsections and sequential excitation, achieving high-resolution volumetric imaging at 1.6mm resolution. Significance: The SE-SWE method offers a straightforward and effective approach for 3D shear volume imaging of tissue biological properties.

Ultrasound A-scan is an important tool for quantitative assessment of ocular lesions. However, its usability is limited by the difficulty of accurately localizing the ultrasound probe to a lesion of interest. In this study, a transparent LiNbO₃ single crystal ultrasound transducer was fabricated, and integrated with a widefield fundus camera to guide the ultrasound local position. The electrical impedance, phase spectrum, pulse-echo performance, and optical transmission spectrum of the ultrasound transducer were validated. The novel fundus camera-guided ultrasound probe was tested for in vivo measurement of rat eyes. Anterior and posterior segments of the rat eye could be unambiguously differentiated with the fundus photography-guided ultrasound measurement. A model eye was also used to verify the imaging performance of the prototype device in the human eye. The prototype shows the potential of being used in the clinic to accurately measure the thickness and echogenicity of ocular lesions in vivo.

Optical imaging and phototherapy in deep tissues face notable challenges due to light scattering. We use encoded acoustic holograms to generate three-dimensional acoustic fields within the target medium, enabling instantaneous and robust modulation of the volumetric refractive index, thereby noninvasively controlling the trajectory of light. Through this approach, we achieved a remarkable 24.3% increase in tissue heating rate in vitro photothermal effect tests on porcine skin. In vivo photoacoustic imaging of mouse brain vasculature exhibits an improved signal-to-noise ratio through the intact scalp and skull. These findings demonstrate that our strategy can effectively suppress light scattering in complex biological tissues by inducing low-angle scattering, achieving an effective depth reaching the millimeter scale. The versatility of this strategy extends its potential applications to neuroscience, lithography, and additive manufacturing.