Flexible ultrasound transceiver array for non-invasive surface-conformable imaging enabled by geometric phase correction

Development and testing of a deep learning algorithm to detect lung consolidation among children with pneumonia using hand-held ultrasound

BACKGROUND AND OBJECTIVES

Severe pneumonia is the leading cause of death among young children worldwide, disproportionately impacting children who lack access to advanced diagnostic imaging. Here our objectives were to develop and test the accuracy of an artificial intelligence algorithm for detecting features of pulmonary consolidation on point-of-care lung ultrasounds among hospitalized children.

METHODS

This was a prospective, multicenter center study conducted at academic Emergency Department and Pediatric inpatient or intensive care units between 2018-2020. Pediatric participants from 18 months to 17 years old with suspicion of lower respiratory tract infection were enrolled. Bedside lung ultrasounds were performed using a Philips handheld Lumify C5-2 transducer and standardized protocol to collect video loops from twelve lung zones, and lung features at both the video and frame levels annotated. Data from both affected and unaffected lung fields were split at the participant level into training, tuning, and holdout sets used to train, tune hyperparameters, and test an algorithm for detection of consolidation features. Data collected from adults with lower respiratory tract disease were added to enrich the training set. Algorithm performance at the video level to detect consolidation on lung ultrasound was determined using reference standard diagnosis of positive or negative pneumonia derived from clinical data.

RESULTS

Data from 107 pediatric participants yielded 117 unique exams and contributed 604 positive and 589 negative videos for consolidation that were utilized for the algorithm development process. Overall accuracy for the model for identification and localization of consolidation was 88.5%, with sensitivity 88%, specificity 89%, positive predictive value 89%, and negative predictive value 87%.

CONCLUSIONS

Our algorithm demonstrated high accuracy for identification of consolidation features on pediatric chest ultrasound in children with pneumonia. Automated diagnostic support on an ultraportable point-of-care device has important implications for global health, particularly in austere settings.

Wearable ultrasound devices: An emerging era for biomedicine and clinical translation

In recent years, personalized diagnosis and treatment have gained significant recognition and rapid development in the biomedicine and healthcare. Due to the flexibility, portability and excellent compatibility, wearable ultrasound (WUS) devices have become emerging personalized medical devices with great potential for development. Currently, with the development of the ongoing advancements in materials and structural design of the ultrasound transducers, WUS devices have improved performance and are increasingly applied in the medical field. In this review, we provide an overview of the design and structure of WUS devices, focusing on their application for diagnosis and treatment of various diseases from a clinical application perspective, and then explore the issues that need to be addressed before clinical translation. Finally, we summarize the progress made in the development of WUS devices, and discuss the current challenges and the future direction of their development. In conclusion, WUS devices usher an emerging era for biomedicine with great clinical promise.

Emerging Wearable Ultrasound Technology

This perspective article provides a brief overview on materials, fabrications, beamforming, and applications for wearable ultrasound devices, a rapidly growing field with versatile implications. Recent developments in miniaturization and soft electronics have significantly advanced wearable ultrasound devices. Such devices offer distinctive advantages over traditional ultrasound probes, including prolonged usability and operator independence, and have demonstrated their effectiveness in continuous monitoring, noninvasive therapies, and advanced human-machine interfaces. Wearable ultrasound devices can be classified into three main categories: rigid, flexible, and stretchable, each having distinctive properties and fabrication strategies. Key unique strategies in device design, packaging, and beamforming for each type of wearable ultrasound devices are reviewed. Furthermore, we highlight the latest applications enabled by wearable ultrasound technology in various areas. This article concludes by discussing the outstanding challenges within the field and outlines potential pathways for future advancements.

Flexible Ultrasonic Transducers for Wearable Biomedical Applications: A Review on Advanced Materials, Structural Designs, and Future Prospects

Due to the rapid developments in materials science and fabrication techniques, wearable devices have recently received increased attention for biomedical applications, particularly in medical ultrasound (US) imaging, sensing, and therapy. US is ubiquitous in biomedical applications because of its noninvasive nature, nonionic radiating, high precision, and real-time capabilities. While conventional US transducers are rigid and bulky, flexible transducers can be conformed to curved body areas for continuous sensing without restricting tissue movement or transducer shifting. This article comprehensively reviews the application of flexible US transducers in the field of biomedical imaging, sensing, and therapy. First, we review the background of flexible US transducers. Following that, we discuss advanced materials and fabrication techniques for flexible US transducers and their enabling technology status. Finally, we highlight and summarize some promising preliminary data with recent applications of flexible US transducers in biomedical imaging, sensing, and therapy. We also provide technical barriers, challenges, and future perspectives for further research and development.

FLEX: FLexible Transducer With External Tracking for Ultrasound Imaging With Patient-Specific Geometry Estimation

Flexible array transducers can adapt to patient-specific geometries during real-time ultrasound (US) image-guided therapy monitoring. This makes the system radiation-free and less user-dependency. Precise estimation of the flexible transducer's geometry is crucial for the delay-and-sum (DAS) beamforming algorithm to reconstruct B-mode US images. The primary innovation of this research is to build a system named FLexible transducer with EXternal tracking (FLEX) to estimate the position of each element of the flexible transducer and reconstruct precise US images. FLEX utilizes customized optical markers and a tracker to monitor the probe's geometry, employing a polygon fitting algorithm to estimate the position and azimuth angle of each transducer element. Subsequently, the traditional DAS algorithm processes the delay estimation from the tracked element position, reconstructing US images from radio-frequency (RF) channel data. The proposed method underwent evaluation on phantoms and cadaveric specimens, demonstrating its clinical feasibility. Deviations in tracked probe geometry compared to ground truth were minimal, measuring 0.50 ± 0.29 mm for the CIRS phantom, 0.54 ± 0.35 mm for the deformable phantom, and 0.36 ± 0.24 mm on the cadaveric specimen. Reconstructing the US image using tracked probe geometry significantly outperformed the untracked geometry, as indicated by a Dice score of 95.1 ± 3.3% versus 62.3 ± 9.2% for the CIRS phantom. The proposed method achieved high accuracy (<0.5 mm error) in tracking the element position for various random curvatures applicable for clinical deployment. The evaluation results show that the radiation-free proposed method can effectively reconstruct US images and assist in monitoring image-guided therapy with minimal user dependency.

Flexible large-area ultrasound arrays for medical applications made using embossed polymer structures

With the huge progress in micro-electronics and artificial intelligence, the ultrasound probe has become the bottleneck in further adoption of ultrasound beyond the clinical setting (e.g. home and monitoring applications). Today, ultrasound transducers have a small aperture, are bulky, contain lead and are expensive to fabricate. Furthermore, they are rigid, which limits their integration into flexible skin patches. New ways to fabricate flexible ultrasound patches have therefore attracted much attention recently. First prototypes typically use the same lead-containing piezo-electric materials, and are made using micro-assembly of rigid active components on plastic or rubber-like substrates. We present an ultrasound transducer-on-foil technology based on thermal embossing of a piezoelectric polymer. High-quality two-dimensional ultrasound images of a tissue mimicking phantom are obtained. Mechanical flexibility and effective area scalability of the transducer are demonstrated by functional integration into an endoscope probe with a small radius of 3 mm and a large area (91.2×14 mm2) non-invasive blood pressure sensor.

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Shape estimation of flexible ultrasound arrays using spatial coherence: A preliminary study

A flexible ultrasound array can potentially provide a larger field-of-view, enhanced imaging resolution, and less operator dependency compared to conventional rigid transducer arrays. However, such transducer arrays require information about relative element positions for beamforming and reconstructing geometrically accurate sonograms. In this study, we assess the potential utility of using spatial coherence of backscattered radiofrequency data to estimate transducer array shape (inverse problem). The methodology is evaluated through 1) simulation of flexible arrays and 2) blinded in vivo experiments using commercial rigid transducer arrays on various anatomical targets (shoulder, forearm, scapular, posterior calf muscles, and abdomen) and multi-purpose ultrasound phantoms. The average Euclidean error of shape estimation is below 0.1 wavelengths for simulated arrays and below 1.4 wavelengths (median: 0.58 wavelengths) for real arrays. The complex wavelet structural similarity index between the B-mode images reconstructed with estimated and ground truth array shapes is above 99 % and 96 %, for simulations and experiments, respectively. These findings suggest that optimizing for spatial coherence may be an effective way to estimate the unknown shape of conformal ultrasound arrays.

Ultrasound-activatable and skin-associated minimally invasive microdevices for smart drug delivery and diagnosis

Ultrasound-activatable and skin-associated minimally invasive microdevices (USMIMs) have garnered significant attention in the domains of smart drug delivery and biomedical diagnosis for on-demand healthcare, owing to their outstanding wearability, flexibility, and comfort. In this review, we present a comprehensive overview of the noteworthy advancements in USMIMs, with a specific focus on device design, potential applications, challenges, and future prospects. The classification of such microdevices primarily encompasses biointerfacing microsystems, including skin-perforable US-assisted microneedles (MNs), skin-attachable sonophoresis and their combination with microbubbles, as well as non-biointerfacing microsystems for drug delivery. Additionally, US-mediated and skin-attached microtransducers utilized in biomedical diagnosis are classified into imaging-related microtransducers, diagramming detection devices, and their combinative systems with applications on diverse signal detection. Besides, the review also highlights the challenges associated with USMIMs, focusing on aspects such as safety, environmental tolerance, wearability/comfortability, and personalization. Furthermore, it offers insights into future perspectives that address these challenges and discuss potential advancements in the field. It is firmly believed that the proposed USMIMs possess immense potential to significantly improve human lives in the near future.