Fast volumetric ultrasound facilitates high-resolution 3D mapping of tissue compartments

Volumetric ultrasound imaging has the potential for operator-independent acquisition and enhanced field of view. Panoramic acquisition has many applications across ultrasound; spanning musculoskeletal, liver, breast, and pediatric imaging; and image-guided therapy. Challenges in high-resolution human imaging, such as subtle motion and the presence of bone or gas, have limited such acquisition. These issues can be addressed with a large transducer aperture and fast acquisition and processing. Programmable, ultrafast ultrasound scanners with a high channel count provide an unprecedented opportunity to optimize volumetric acquisition. In this work, we implement nonlinear processing and develop distributed beamformation to achieve fast acquisition over a 47-centimeter aperture. As a result, we achieve a 50-micrometer -6-decibel point spread function at 5 megahertz and resolve in-plane targets. A large volume scan of a human limb is completed in a few seconds, and in a 2-millimeter dorsal vein, the image intensity difference between the vessel center and surrounding tissue was ~50 decibels, facilitating three-dimensional reconstruction of the vasculature.

2-D Array Design and Fabrication With Pitch-Shifting Interposer at Frequencies From 4 MHz up to 10 MHz

High element density and strict constraints of the element's size have significantly limited the design and fabrication of 2-D ultrasonic arrays, especially fully sampled 2-D arrays. Recently, 3-D printing technology has been one of the most rapidly developing fields. Along with the great progress of 3-D printing technology, complex and detailed 3-D structures have become readily available with a short iteration cycle, which allows us to reduce the complexity of routing and helps to ameliorate assembly problems in 2-D ultrasound array fabrication. In this work, we designed and fabricated 2-D ultrasound arrays for an array of applications with a pitch-shifting interposer, which allowed us to fit different array designs with the same circuit design and significantly reduce the requirements in routing and connection for 2-D array fabrication at frequencies from 4 to 10 MHz. Results demonstrated that this design would make 2-D arrays more available and affordable.

Erratum to "Highly Integrated Multiplexing and Buffering Electronics for Large Aperture Ultrasonic Arrays"

[This corrects the article DOI: 10.34133/2022/9870386.].

Highly Integrated Multiplexing and Buffering Electronics for Large Aperture Ultrasonic Arrays

Large aperture ultrasonic arrays can be implemented by tiling together multiple pretested modules of high-density acoustic arrays with closely integrated multiplexing and buffering electronics to form a larger aperture with high yield. These modular arrays can be used to implement large 1.75D array apertures capable of focusing in elevation for uniform slice thickness along the axial direction which can improve image contrast. An important goal for large array tiling is obtaining high yield and sensitivity while reducing extraneous image artifacts. We have been developing tileable acoustic-electric modules for the implementation of large array apertures utilizing Application Specific Integrated Circuits (ASICs) implemented using 0.35 μ m high voltage (50 V) CMOS. Multiple generations of ASICs have been designed and tested. The ASICs were integrated with high-density transducer arrays for acoustic testing and imaging. The modules were further interfaced to a Verasonics Vantage imaging system and were used to image industry standard ultrasound phantoms. The first-generation modules comprise ASICs with both multiplexing and buffering electronics on-chip and have demonstrated a switching artifact which was visible in the images. A second-generation ASIC design incorporates low switching injection circuits which effectively mitigate the artifacts observed with the first-generation devices. Here, we present the architecture of the two ASIC designs and module types as well imaging results that demonstrate reduction in switching artifacts for the second-generation devices.

A theranostic 3D ultrasound imaging system for high resolution image-guided therapy

Microbubble contrast agents are a diagnostic tool with broad clinical impact and an increasing number of indications. Many therapeutic applications have also been identified. Yet, technologies for ultrasound guidance of microbubble-mediated therapy are limited. In particular, arrays that are capable of implementing and imaging microbubble-based therapy in three dimensions in real-time are lacking. We propose a system to perform and monitor microbubble-based therapy, capable of volumetric imaging over a large field-of-view. To propel the promise of the theranostic treatment strategies forward, we have designed and tested a unique array and system for 3D ultrasound guidance of microbubble-based therapeutic protocols based on the frequency, temporal and spatial requirements. Methods: Four 256-channel plane wave scanners (Verasonics, Inc, WA, USA) were combined to control a 1024-element planar array with 1.3 and 2.5 MHz therapeutic and imaging transmissions, respectively. A transducer aperture of ~40×15 mm was selected and Field II was applied to evaluate the point spread function. In vitro experiments were performed on commercial and custom phantoms to assess the spatial resolution, image contrast and microbubble-enhanced imaging capabilities. Results: We found that a 2D array configuration with 64 elements separated by λ-pitch in azimuth and 16 elements separated by 1.5λ-pitch in elevation ensured the required flexibility. This design, of 41.6 mm × 16 mm, thus provided both an extended field-of-view, up to 11 cm x 6 cm at 10 cm depth and steering of ±18° in azimuth and ±12° in elevation. At a depth of 16 cm, we achieved a volume imaging rate of 60 Hz, with a contrast ratio and resolution, respectively, of 19 dB, 0.8 mm at 3 cm and 20 dB and 2.1 mm at 12.5 cm. Conclusion: A single 2D array for both imaging and therapeutics, integrated with a 1024 channel scanner can guide microbubble-based therapy in volumetric regions of interest.

2-D Ultrasonic Array-Based Optical Coherence Elastography

Acoustic radiation force optical coherence elastography (ARF-OCE) has been successfully implemented to characterize the biomechanical properties of soft tissues, such as the cornea and the retina, with high resolution using single-element ultrasonic transducers for ARF excitation. Most currently proposed OCE techniques, such as air puff and ARF, have less capability to control the spatiotemporal information of the induced region of deformation, resulting in limited accuracy and low temporal resolution of the shear wave elasticity imaging. In this study, we propose a new method called 2-D ultrasonic array-based OCE imaging, which combines the advantages of 3-D dynamic electronic steering of the 2-D ultrasonic array and high-resolution optical coherence tomography (OCT). The 3-D steering capability of the 2-D array was first validated using a hydrophone. Then, the combined 2-D ultrasonic array OCE system was calibrated using a homogenous phantom, followed by an experiment on ex vivo rabbit corneal tissue. The results demonstrate that our newly developed 2-D ultrasonic array-based OCE system has the capability to map tissue biomechanical properties accurately, and therefore, has the potential to be a vital diagnostic tool in ophthalmology.

The effective coupling coefficient for a completed PIN-PMN-PT array

The computation of the electromechanical coupling coefficient (EMCC) of a fully assembled medical ultrasound transducer array is directly computed with closed form expressions. The Levenberg-Marquardt non-linear regression algorithm (LMA) is employed to help confirm the EMCC calculated prediction (k_EFF) and provide statistical insights. The complex electrical impedance spectra of a 1-3 composite array with two matching layers operating at a 3.75 MHz center frequency using PIN-PMN-PT single crystal material is measured in air both before and after oven heating at 160 °C for 15 min. The oven heating produces changes in the EMCC of -4.9%, clamped dielectric constant of -11%, and effective transducer longitudinal velocity of -2.5%. Utilizing the pre- and post-heating array impedance data, the calculated EMCC values from the new closed form expressions agree well with the complete KLM model based LMA, and also exhibit approximately one tenth the error as compared to the formulas for a flat, unloaded transducer.

Current Ultrasound Technologies and Instrumentation in the Assessment and Monitoring of COVID-19 Positive Patients

Since the emergence of the COVID-19 pandemic in December of 2019, clinicians and scientists all over the world have faced overwhelming new challenges that not only threaten their own communities and countries but also the world at large. These challenges have been enormous and debilitating, as the infrastructure of many countries, including developing ones, had little or no resources to deal with the crisis. Even in developed countries, such as Italy, health systems have been so inundated by cases that health care facilities became oversaturated and could not accommodate the unexpected influx of patients to be tested. Initially, resources were focused on testing to identify those who were infected. When it became clear that the virus mainly attacks the lungs by causing parenchymal changes in the form of multifocal pneumonia of different levels of severity, imaging became paramount in the assessment of disease severity, progression, and even response to treatment. As a result, there was a need to establish protocols for imaging of the lungs in these patients. In North America, the focus was on chest X-ray and computed tomography (CT) as these are widely available and accessible at most health facilities. However, in Europe and China, this was not the case, and a cost-effective and relatively fast imaging modality was needed to scan a large number of sick patients promptly. Hence, ultrasound (US) found its way into the hands of Chinese and European physicians and has since become an important imaging modality in those locations. US is a highly versatile, portable, and inexpensive imaging modality that has application across a broad spectrum of conditions and, in this way, is ideally suited to assess the lungs of COVID-19 patients in the intensive care unit (ICU). This bedside test can be done with little to no movement of the patients from the unit that keeps them in their isolated rooms, thereby limiting further exposure to other health personnel. This article presents a basic introduction to COVID-19 and the use of the US for lung imaging. It further provides a high-level overview of the existing US technologies that are driving development in current and potential future US imaging systems for lung, with a specific emphasis on portable and 3-D systems.

Co-Integrated PIN-PMN-PT 2-D Array and Transceiver Electronics by Direct Assembly Using a 3-D Printed Interposer Grid Frame

Tiled modular 2-D ultrasound arrays have the potential for realizing large apertures for novel diagnostic applications. This work presents an architecture for fabrication of tileable 2-D array modules implemented using 1-3 composites of high-bandwidth (BW) PIN-PMN-PT single-crystal piezoelectric material closely coupled with high-voltage CMOS application-specific integrated circuit (ASIC) electronics for buffering and multiplexing functions. The module, which is designed to be operated as a λ -pitch 1.75-D array, benefits from an improved electromechanical coupling coefficient and increased Curie temperature and is assembled directly on top of the ASIC silicon substrate using an interposer backing. The interposer consists of a novel 3-D printed acrylic frame that is filled with conducting and acoustically absorbing silver epoxy material. The ASIC comprises a high-voltage switching matrix with locally integrated buffering and is interfaced to a Verasonics Vantage 128, using a local field programmable gate array (FPGA) controller. Multiple prototype 5 ×6 element array modules have been fabricated by this process. The combined acoustic array and ASIC module was configured electronically by programming the switches to operate as a 1-D array with elements grouped in elevation for imaging and pulse-echo testing. The resulting array configuration had an average center frequency of 4.55 MHz, azimuthal element pitch of [Formula: see text], and exhibited average -20-dB pulsewidth of 592 ns and average -6-dB fractional BW of 77%.

Fabrication and Characterization of a Miniaturized 15-MHz Side-Looking Phased-Array Transducer Catheter

This paper describes the development of a miniaturized 15-MHz side-looking phased-array transducer catheter. The array features a 2-2 linear composite with 64 piezoelectric elements mechanically diced into a piece of PMN-30%PT single crystal and separated by non-conductive epoxy kerfs at a 50-μm pitch, yielding a total active aperture of 3.2 mm in the azimuth direction and 1.8 mm in the elevation direction, with an elevation natural focal depth of 8.1 mm. The array includes non-conductive epoxy backing and two front matching layers. A custom flexible circuit connects the array piezoelectric elements to a bundle of 64 individual 48-AWG micro-coaxial cables enclosed within a 1.5-m long 10F catheter. Performance characterization was evaluated via finite element analysis simulations and afterwards compared against obtained measurement results, which showed an average center frequency of 17.7 MHz, an average bandwidth of 52.2% at -6 dB, and crosstalk less than -30 dB. Imaging of a tungsten fine-wire phantom resulted in axial and lateral spatial resolutions of approximately 90 μm and 420 ìm, respectively. The imaging capability was further evaluated with colorectal tissue-mimicking phantoms, demonstrating the potential suitability of the proposed phased-array transducer for the intraoperative assessment of surgical margins during minimally invasive colorectal surgery procedures.

CMOS High-Voltage Analog 1-64 Multiplexer/Demultiplexer for Integrated Ultrasound Guided Breast Needle Biopsy

Ultrasound guided needle biopsy is an important method for collection of breast cancer tissue. In this paper, we report on the design and testing of a high-voltage 1 to 64 Multiplexer/Demultiplexer (MUX/De-MUX) integrated circuit (IC) for ultrasound-guided breast biopsy applications implemented in a high-voltage CMOS process. The IC is intended to be incorporated inside the breast biopsy needle and is designed to fit inside the needle inner diameter of 2.38 mm. The MUX/De-MUX electronics are made up of three parts, including a low-voltage 6 to 64 decoder, a level shifter to convert from low voltage to high voltage, and analog high-voltage switches. Experimental results show a -3-dB bandwidth of over 70 MHz, Rds (on) of , -2.279-dB insertion loss, and -17.5-dB off isolation at 70 MHz with low-voltage input. Finally, we present results obtained via synthetic aperture imaging using the fabricated MUX/De-Mux device and a high-frequency ultrasound array. This device and technique hold promise for high-frequency imaging probes where a limited number of elements are used and the depth of penetration is short such as in breast biopsy and intravascular applications.

Reconfigurable mosaic annular arrays

Mosaic annular arrays (MAA) based on reconfigurable array (RA) transducer electronics assemblies are presented as a potential solution for future highly integrated ultrasonic transducer subsystems. Advantages of MAAs include excellent beam quality and depth of field resulting from superior elevational focus compared with 1-D electronically scanned arrays, as well as potentially reduced cost, size, and power consumption resulting from the use of a limited number of beamforming channels for processing a large number of subelements. Specific design tradeoffs for these highly integrated arrays are discussed in terms of array specifications for center frequency, element pitch, and electronic switch-on resistance. Large-area RAs essentially function as RC delay lines. Efficient architectures which take into account RC delay effects are presented. Architectures for integration of the transducer and electronics layers of large-area array implementations are reviewed.

Packaging and modular assembly of large-area and fine-pitch 2-D ultrasonic transducer arrays

A promising transducer architecture for largearea arrays employs 2-D capacitive micromachined ultrasound transducer (CMUT) devices with backside trench-frame pillar interconnects. Reconfigurable array (RA) application-specified integrated circuits (ASICs) can provide efficient interfacing between these high-element-count transducer arrays and standard ultrasound systems. Standard electronic assembly techniques such as flip-chip and ball grid array (BGA) attachment, along with organic laminate substrate carriers, can be leveraged to create large-area arrays composed of tiled modules of CMUT chips and interface ASICs. A large-scale, fully populated and integrated 2-D CMUT array with 32 by 192 elements was developed and demonstrates the feasibility of these techniques to yield future large-area arrays. This study demonstrates a flexible and reliable integration approach by successfully combining a simple under-bump metallization (UBM) process and a stacked CMUT/interposer/ASIC module architecture. The results show high shear strength of the UBM (26.5 g for 70-μm balls), high interconnect yield, and excellent CMUT resonance uniformity (s = 0.02 MHz). A multi-row linear array was constructed using the new CMUT/interposer/ASIC process using acoustically active trench-frame CMUT devices and mechanical/ nonfunctional Si backside ASICs. Imaging results with the completed probe assembly demonstrate a functioning device based on the modular assembly architecture.

Large Area MEMS Based Ultrasound Device for Cancer Detection

We present image results obtained using a prototype ultrasound array which demonstrates the fundamental architecture for a large area MEMS based ultrasound device for detection of breast cancer. The prototype array consists of a tiling of capacitive Micro-Machined Ultrasound Transducers (cMUTs) which have been flip-chip attached to a rigid organic substrate. The pitch on the cMUT elements is 185 um and the operating frequency is nominally 9 MHz. The spatial resolution of the new probe is comparable to production PZT probes, however the sensitivity is reduced by conditions that should be correctable. Simulated opposed-view image registration and Speed of Sound volume reconstruction results for ultrasound in the mammographic geometry are also presented.