69 research outputs found

    MEMS Technology for Biomedical Imaging Applications

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    Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

    Study of Various Detection Mechanisms for Photoacoustic Imaging

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    Photoacoustic imaging (PAI) is a developing imaging technique that has been researched for several clinical applications including oncology, neurology, dermatology and ophthalmology. PAI combines the benefits of pure optical and acoustic imaging to attain optical absorption contrast images. There are three different modalities in photoacoustic imaging which are categorized according to the type of image reconstruction and the focus. Photoacoustic computed tomography (PACT) uses reconstruction-based image formation while photoacoustic microscopy (PAM) uses focused-based image formation. Photoacoustic microscopy can be further divided into optical-focused imaging, optical-resolution photoacoustic microscopy (OR-PAM) and acoustic-focused imaging, acoustic resolution photoacoustic microscopy (AR-PAM). The two essential components in the photoacoustic imaging system are the excitation laser, which is typically implemented as a pulsed laser, and the detector. Various detection mechanisms have been investigated for photoacoustic imaging, ranging from contact mode physical sensors to non-contact forms of detection. In this research project, photoacoustic imaging with a piezoelectric transducer and a novel non-contact detection mechanism, photoacoustic remote sensing (PARS) were studied for optical-resolution photoacoustic microscopy, OR-PAM applications. Conventional photoacoustic imaging uses a piezoelectric transducer to pick up the pressure induced by the photoacoustic effect. PARS system, on the other hand, captures the changes in the elasto-optical refractive index modulation caused by the photoacoustic initial pressure. The photoacoustic signals can be detected in two modes, transmission and reflection modes. When the excitation laser hits the sample, the photoacoustic signals are generated in different directions. In transmission mode, photoacoustic signals are detected below the sample while reflection mode is the sensing of photoacoustic signals that have bounced off the sample. A 2.25 MHz piezoelectric transducer was used in transmission mode to image carbon fibers network. For the PARS system, the piezoelectric transducer was replaced with a 637 nm continuous-wave laser. The continuous-wave detection laser was co-focused and co-scanned with an excitation laser to image the same carbon fiber networks in reflection mode. The second objective of this research project focuses on the preliminary investigation of a micro-electro-mechanical system device, capacitive micromachined ultrasound transducers (CMUTs) for PAI applications. In comparison with conventional piezoelectric transducer, CMUTs generally have a larger bandwidth which will in turn attribute to a better axial resolution for applications such as PAM imaging. Furthermore, unlike piezoelectric transducer, CMUTs have a similar acoustic impedance as tissue. Therefore, there is no need for an additional matching layer. A 3.4 MHz CMUT fabricated with nitride-to-oxide wafer bonding technology was analyzed and characterized for PAI in this research project

    Piezoelectric Micromachined Ultrasound Transducer (PMUT) Arrays for Integrated Sensing, Actuation and Imaging

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    Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for integrated transducer arrays. This paper presents an overview of the current development status of PMUTs and a discussion of their suitability for miniaturized and integrated devices. The thin film piezoelectric materials required to functionalize these devices are discussed, followed by the microfabrication techniques used to create PMUT elements and the constraints the fabrication imposes on device design. Approaches for electrical interconnection and integration with on-chip electronics are discussed. Electrical and acoustic measurements from fabricated PMUT arrays with up to 320 diaphragm elements are presented. The PMUTs are shown to be broadband devices with an operating frequency which is tunable by tailoring the lateral dimensions of the flexural membrane or the thicknesses of the constituent layers. Finally, the outlook for future development of PMUT technology and the potential applications made feasible by integrated PMUT devices are discussed

    Innovations in Vascular Ultrasound

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    Innovations in Vascular Ultrasound

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    Semiconductor Infrared Devices and Applications

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    Infrared (IR) technologies—from Herschel’s initial experiment in the 1800s to thermal detector development in the 1900s, followed by defense-focused developments using HgCdTe—have now incorporated a myriad of novel materials for a wide variety of applications in numerous high-impact fields. These include astronomy applications; composition identifications; toxic gas and explosive detection; medical diagnostics; and industrial, commercial, imaging, and security applications. Various types of semiconductor-based (including quantum well, dot, ring, wire, dot in well, hetero and/or homo junction, Type II super lattice, and Schottky) IR (photon) detectors, based on various materials (type IV, III-V, and II-VI), have been developed to satisfy these needs. Currently, room temperature detectors operating over a wide wavelength range from near IR to terahertz are available in various forms, including focal plane array cameras. Recent advances include performance enhancements by using surface Plasmon and ultrafast, high-sensitivity 2D materials for infrared sensing. Specialized detectors with features such as multiband, selectable wavelength, polarization sensitive, high operating temperature, and high performance (including but not limited to very low dark currents) are also being developed. This Special Issue highlights advances in these various types of infrared detectors based on various material systems

    Optical Microring Resonators for Photoacoustic Imaging and Detection.

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    This work is to utilize the superior characteristics of polymer microring resonators in ultrasound detection to push the application of photoacoustic imaging to an entirely new level. We first demonstrated significantly improved imaging quality for photoacoustic tomography (PAT) using microring detectors. For wideband PAT, the microring detectors were able to faithfully detect both the boundaries and the inner structure, while piezoelectric detectors can only preserve one of the two aspects. For high-resolution PAT over a large imaging area, we imaged 50 µm black beads and found that microrings produced high-resolution imaging over a 16-mm-diameter imaging area while the 500 µm piezoelectric detectors only obtained high-resolution imaging over a small area around center. Pure optical photoacoustic microscopy (PAM) has been demonstrated. Microring ultrasonic resonators were applied in in vivo photoacoustic imaging for the first time. Good imaging signal-to-noise ratio and high axial resolution of 8 µm were calibrated. As a comparison, a commercial hydrophone with similar sensitivity produced a low axial resolution of 105 µm. A 5 mm miniaturized probe consisting of a fiber to deliver excitation laser pulses and microring detectors for ultrasound detection has been fabricated for photoacoustic endoscopy. The calibrated high radial resolution of 21 µm was higher than other types of endoscopic photoacoustic probes, around 40 µm or larger. A photoacoustic correlation spectroscopy (PACS) technique was proposed. In a proof-of-concept experiment, we demonstrated low-speed flow measurement of ~15 µm/s by the PACS technique. We also demonstrated in vivo flow speed measurement of red blood cells in capillaries in a chick embryo model by PACS. Other techniques might have difficulties to measure it due to the low signal contrast and/or poor resolutions. We also proposed terahertz electromagnetic pulse detection by photoacoustic method. We used carbon nanotube composites as efficient photoacoustic transmitters and microrings as sensitive detectors. The photoacoustic method provides low-cost and real-time terahertz detection (~µs), which is difficult by conventional terahertz detectors, such as a bolometer or a pyroelectric detector.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91497/1/chensll_1.pd

    A comprehensive review on photoacoustic-based devices for biomedical applications

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    The photoacoustic effect is an emerging technology that has sparked significant interest in the research field since an acoustic wave can be produced simply by the incidence of light on a material or tissue. This phenomenon has been extensively investigated, not only to perform photoacoustic imaging but also to develop highly miniaturized ultrasound probes that can provide biologically meaningful information. Therefore, this review aims to outline the materials and their fabrication process that can be employed as photoacoustic targets, both biological and non-biological, and report the main components’ features to achieve a certain performance. When designing a device, it is of utmost importance to model it at an early stage for a deeper understanding and to ease the optimization process. As such, throughout this article, the different methods already implemented to model the photoacoustic effect are introduced, as well as the advantages and drawbacks inherent in each approach. However, some remaining challenges are still faced when developing such a system regarding its fabrication, modeling, and characterization, which are also discussed.This work was supported by Fundação para a Ciência e Tecnologia national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020

    Integrated Circuits for Medical Ultrasound Applications: Imaging and Beyond

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    Medical ultrasound has become a crucial part of modern society and continues to play a vital role in the diagnosis and treatment of illnesses. Over the past decades, the develop- ment of medical ultrasound has seen extraordinary progress as a result of the tremendous research advances in microelectronics, transducer technology and signal processing algorithms. How- ever, medical ultrasound still faces many challenges including power-efficient driving of transducers, low-noise recording of ultrasound echoes, effective beamforming in a non-linear, high- attenuation medium (human tissues) and reduced overall form factor. This paper provides a comprehensive review of the design of integrated circuits for medical ultrasound applications. The most important and ubiquitous modules in a medical ultrasound system are addressed, i) transducer driving circuit, ii) low- noise amplifier, iii) beamforming circuit and iv) analog-digital converter. Within each ultrasound module, some representative research highlights are described followed by a comparison of the state-of-the-art. This paper concludes with a discussion and recommendations for future research directions
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