Ultrasound Capsule Endoscopy With a Mechanically Scanning Micro-ultrasound:A Porcine Study

Wireless capsule endoscopy has been used for the clinical examination of the gastrointestinal (GI) tract for two decades. However, most commercially available devices only utilise optical imaging to examine the GI wall surface. Using this sensing modality, pathology within the GI wall cannot be detected. Micro-ultrasound (μUS) using high-frequency (>20 MHz) ultrasound can provide a means of transmural or cross-sectional image of the GI tract. Depth of imaging is approximately 10 mm with a resolution of between 40–120 μm that is sufficient to differentiate between subsurface histologic layers of the various regions of the GI tract. Ultrasound capsule endoscopy (USCE) uses a capsule equipped with μUS transducers that are capable of imaging below the GI wall surface, offering thereby a complementary sensing technique to optical imaging capsule endoscopy. In this work, a USCE device integrated with a ∼30 MHz ultrasonic transducer was developed to capture a full 360° image of the lumen. The performance of the device was initially evaluated using a wire phantom, indicating an axial resolution of 69.0 μm and lateral resolution of 262.5 μm. Later, in vivo imaging performance was characterised in the oesophagus and small intestine of anaesthetized pigs. The reconstructed images demonstrate clear layer differentiation of the lumen wall. The tissue thicknesses measured from the B-scan images show good agreement with ex vivo images from the literature. The high-resolution ultrasound images in the in vivo porcine model achieved with this device is an encouraging preliminary step in the translation of these devices toward future clinical use

A Digital Multigate Doppler Method for High Frequency Ultrasound

Noninvasive visualization of blood flow with high frequency Doppler ultrasound has been extensively used to assess the morphology and hemodynamics of the microcirculation. A completely digital implementation of multigate pulsed-wave (PW) Doppler method was proposed in this paper for high frequency ultrasound applications. Analog mixer was eliminated by a digital demodulator and the same data acquisition path was shared with traditional B-mode imaging which made the design compact and flexible. Hilbert transform based quadrature demodulation scheme was employed to achieve the multigate Doppler acquisition. A programmable high frequency ultrasound platform was also proposed to facilitate the multigate flow visualization. Experimental results showed good performance of the proposed method. Parabolic velocity gradient inside the vessel and velocity profile with different time slots were acquired to demonstrate the functionality of the multigate Doppler. Slow wall motion was also recorded by the proposed method

Retinal Ganglion Cell Responses to Low-frequency Focused Ultrasound Stimulation

PURPOSE: Acoustic retinal prosthesis has been put forward using high-frequency US with non-invasive and high-resolution advantages. But its application is limited by the difficulties in fabrication, energy consumption and acoustic attenuation. In the present study, low-frequency focused ultrasound stimulation (LFUS) had been demonstrated to activate retinal ganglion cells (RGCs) in rat retinas. The neurophysiological properties of RGC responses to LFUS were also investigated. METHODS: A 2.25 MHz focused ultrasound transducer (D=0.75 in., SF=2.0 in.) was used to stimulate the rat retina which was cultured in a multi-electrode array system (MEA2100, MCS , Fig. 1). The acoustic property was evaluated by hydrophone (UMS3, Precision acoustics). Ultrasound (US) stimulation was modulated at pulsed mode. Light stimulation was modulated in the same mode to give an uniform field flashes. The electrophysiological data collected from MEA was detected for neural spikes and sorted by Plexon Offline Sorter. Only channels recording single-cell activities were adopted for subsequent analysis. Peri-stimulus time histograms and raster plots were plotted for each RGC using Spike 2. RESULTS: In total, 116 retinal ganglion cells (RGCs) from 7 retinas were sorted and classified into four types according to light responses. The firing activity of 114 RGCs were modulated by repeated US stimulation. This suggested that low-frequency focused ultrasound stimulation (LFUS) could activate RGCs. The US responses didn&rsquo;t correspond to the standard light responses and varied greatly between cell types. Besides, dual-peak responses to US stimulation were observed which were not reported previously. The temporal response properties of RGCs, including latency, firing rate, and response type, could be modulated by changing acoustic intensity. CONCLUSIONS: These findings might imply a temporal neuromodulation effect of LFUS and provided an important foundation for the development of acoustic retinal prosthesis.</p

Effects of Non-Elevation-Focalized Linear Array Transducer on Ultrasound Plane-Wave Imaging

Plane-wave ultrasound imaging (PWUS) has become an important method of ultrasound imaging in recent years as its frame rate has exceeded 10,000 frames per second, allowing ultrasound to be used for two-dimensional shear wave detection and functional brain imaging. However, compared to the traditional focusing and scanning method, PWUS images always suffer from a degradation of lateral resolution and contrast. To improve the image quality of PWUS, many different beamforming algorithms have been proposed and verified. Yet the influence of transducer structure is rarely studied. For this paper, the influence of using an acoustic lens for PWUS was evaluated. Two linear array transducers were fabricated. One was not self-focalized in the elevation direction (non-elevation-focalized transducer, NEFT); the other one was a traditional elevation-focalized transducer (EFT). An initial simulation was conducted to show the influence of elevation focusing. Then the images obtained with NEFT on a standard ultrasound imaging phantom were compared with those obtained with EFT. It was demonstrated that, in a relatively deep region, the contrast of an NEFT image is better than that of an EFT image. These results indicate that a more sophisticated design of ultrasound transducer would further improve the image quality of PWUS

Retina stimulation with low-frequency ultrasound in vivo

PURPOSE: More and more researches are exploring the neuromodulation effect of ultrasound (US) on the central nervous system (e.g. brain and retina) and the peripheral nervous system (such as skin). US stimulation has been regarded as a new noninvasive neurostimulation approach by many researchers. Our previous studies had shown that the temporal response patterns of RGCs could be modulated by US in vitro. In this article, we studied US stimulation to the retina in vivo. This study attempted to use low-frequency (2.25 MHz) focused US to stimulate the rat eyes and investigate the effect on the primary visual cortex. METHODS: Experiments were conducted on adult male and female Sprague Dawley rats (250&ndash;300 g). A 2.25 MHz focused US transducer (D = 0.75 in., SF = 2.0 in., Olympus, Waltham, MA, USA) was used to stimulate the rat eyes in vivo. Rats were anaesthetized with urethane (5 ml/kg, 20% aqueous solution, intraperitoneally; Sigma-Aldrich, Munich, Germany). Next, the rat was laid prone on an automatic heating pad (69002, RWD Life Science Co.) at 37℃ and with its head gently immobilized using a stereotaxic frame (68028, RWD Life Science Co.). The skin on the head was swabbed with iodine and then a local anesthetic (lidocaine hydrochloride, Lidocaine 0.5%, 1mL) was injected subcutaneously along the incision line. The skull was exposed and trephined in an area (4x4 mm2) overlaying the monocular visual cortex: 6.0 mm posterior to bregma, and 3.0 mm lateral from the midline, the depth of multi-electrode arrays implantation were 300-500&micro;m below the pia surface. US stimulation was modulated in the pulsed mode, which parameters included: pulse repetition frequency (PRF) = 1 kHz, tone burst duration (TBD) = 0.5 ms, sonication duration (SD) = 300 ms, and inter-stimulus interval (ISI) = 3 s. In each experiment, 40 trials (stimulus trains) were delivered, and there were 2-min intervals between each experiment. The neural activities from the primary visual cortex was amplified, filtered and digitized by Cerebus 64-Channel system (Animal Use). RESULTS: As shown in Fig. 1a, the low-frequency focused US (2.25 MHz) transducer was used to stimulate the rat left eye and a 4x4 multi-electrode array was used to record neural activities from the right primary visual cortex. Some preliminary experimental results showed that the local field potentials and the single neuron spikes recorded from the primary visual cortex were both changed by US stimulation. Fig. 1b showed the responses of local field potentials that were recorded by 13 electrodes to US stimulation. The average latency of these responses was about 250 ms, which was consistent with the previous study. The peri-stimulus time histogram (PSTH) of a single spiking unit that was sorted by Offline Sorter showed that the neuron responded to US stimulation at the offset Fig. 1c. CONCLUSIONS: Such influence on the neural activities in brain demonstrated that the low-frequency focused US was capable of stimulating retinas in vivo, which might become a novel therapy tool for ophthalmic diseases. Figure 1. US influenced on the neural activities of visual cortex. (a) The experimental paradigm. US stimulation to the rat left eye and multi-electrode arrays recording from the right primary visual cortex. (b) The local field potentials responded to US stimulation. X-axis is time (ms) and Y-axis is recording channels. (c) The PSTH of a single spiking unit that was sorted by Offline Sorter. X-axis is time (ms) and Y-axis is firing rate (Hz) .</p

Piezoelectric single crystal ultrasonic transducers for biomedical applications

Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state-of-art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will be addressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN–PT and PIN–PMN–PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single-element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging and microbeam applications of the single crystal transducers will be discussed