Min Su

Modulated Excitation Imaging System for Intravascular Ultrasound

Advances in methodologies and tools often lead to new insights into cardiovascular diseases. Intravascular ultrasound (IVUS) is a well-established diagnostic method that provides high-resolution images of the vessel wall and atherosclerotic plaques. High-frequency (>50xa0MHz) ultrasound enables the spatial resolution of IVUS to approach that of optical imaging methods. However, the penetration depth decreases when using higher imaging frequencies due to the greater acoustic attenuation. An imaging method that improves the penetration depth of high-resolution IVUS would, therefore, be of major clinical importance. Modulated excitation imaging is known to allow ultrasound waves to penetrate further. This paper presents an ultrasound system specifically for modulated-excitation-based IVUS imaging. The system incorporates a high-voltage waveform generator and an image processing board that are optimized for IVUS applications. In addition, a miniaturized ultrasound transducer has been constructed using a Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal to improve the ultrasound characteristics. The results show that the proposed system was able to provide increases of 86.7% in penetration depth and 9.6 dB in the signal-to-noise ratio for 60 MHz IVUS. In vitro tissue samples were also investigated to demonstrate the performance of the system.

Noninvasive Ultrasonic Neuromodulation in Freely Moving Mice

Neuromodulation is a fundamental method for obtaining basic information about neuronal circuits for use in treatments for neurological and psychiatric disorders. Ultrasound stimulation has become a promising approach for noninvasively inducing neuromodulation in animals and humans. However, the previous investigations were subject to substantial limitations, due to most of them involving anesthetized and fixed small-animal models. Studies of awake and freely moving animals are needed, but the currently used ultrasound devices are too bulky to be applied to a freely moving animal. This study is the first time to design and fabricate a miniature and lightweight head-mounted ultrasound stimulator for inducing neuromodulation in freely moving mice. The main components of the stimulator include a miniature piezoelectric ceramic, a concave epoxy acoustic lens, and housing and connection components. The device was able to induce action potentials recorded in situ and evoke head-turning behaviors by stimulating the primary somatosensory cortex barrel field of the mouse. These findings indicate that the proposed method can be used to induce noninvasive neuromodulation in freely moving mice. This novel method could potentially lead to the application of ultrasonic neuromodulation in more-extensive neuroscience investigations.

A Portable Ultrasound System for Non-Invasive Ultrasonic Neuro-Stimulation

Fundamental insights into the function of the neural circuits often follows from the advances in methodologies and tools for neuroscience. Electrode- and optical- based stimulation methods have been used widely for neuro-modulation with high resolution. However, they are suffering from inherent invasive surgical procedure. Ultrasound has been proved as a promising technology for neuro-stimulation in a non-invasive manner. However, no portable ultrasound system has been developed particularly for neuro-stimulation. The utilities used currently are assembled by traditional functional generator, power amplifier, and general transducer, therefore, resulting in lack of flexibility. This paper presents a portable system to achieve ultrasonic neuro-stimulation to satisfy various studies. The system incorporated a high voltage waveform generator and a matching circuit that were optimized for neuro-stimulation. A new switching mode power amplifier was designed and fabricated. The noise generated by the power amplifier was reduced (about 30 dB), and the size and weight were smaller in contrast with commercial equipment. In addition, a miniaturized ultrasound transducer was fabricated using Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) 1–3 composite single crystal for the improved ultrasonic performance. The spatial peak temporal average pressure was higher than 250 kPa in the range of 0.5–5 MHz. In vitro and in vivo studies were conducted to show the performance of the system.

Local field potentials responses of ultrasonic neuromodulation in freely moving mouse

Ultrasound (US) brain stimulation has been demonstrated to be a promising approach for noninvasive neuromodulation. However, traditional methods always demand animals to be under anesthesia and body constraint to achieve stable operation with bulky US transducer, while those demands would result in interference to the neural activity related to perception, cognition, and behavior. Appling a miniature US stimulator in freely moving mouse will greatly benefit for obtaining credible neural response from brain modulation. This study investigates the local field potentials (LFPs) responses of ultrasonic neuromodulation on freely moving mouse with a customized head-mounted US transducer. The stimulator mainly consist of a tiny piezoelectric ceramic, a concave epoxy acoustic lens, and some affiliated accessories for housing and connecting. The decrease of power spectral density at theta band and increase of power at delta band of local field potentials, indicate that the proposed head-mounted ultrasound stimulator can perform noninvasive neuromodulation on freely moving mouse. The proposed head-mounted US device could potentially promote the development of ultrasonic neuromodulation to more extensive neuroscience studies.

Temporal Neuromodulation of Retinal Ganglion Cells by Low-Frequency Focused Ultrasound Stimulation

Significant progress has been made recently in treating neurological blindness using implantable visual prostheses. However, implantable medical devices are highly invasive and subject to many safety, efficacy, and cost issues. The discovery that ultrasound (US) may be useful as a noninvasive neuromodulation tool has aroused great interest in the field of acoustic retinal prostheses (ARPs). We have investigated the responsiveness of rat retinal ganglion cells (RGCs) to low-frequency focused US stimulation (LFUS) at 2.25 MHz and characterized the neurophysiological properties of US responses by performing in vitro multielectrode array recordings. The results show that LFUS can reliably activate RGCs. The US-induced responses did not correspond to the standard light responses and varied greatly among cell types. Moreover, dual-peak responses to US stimulation were observed that have not been reported previously. The temporal response properties of RGCs, including their latency, firing rate, and response type, were modulated by the acoustic intensity. These findings suggest the presence of a temporal neuromodulation effect of LFUS and potentially open a new avenue in the development of ARP.

Local field potentials responses to ultrasonic neuromodulaton on freely moving mouse

Ultrasound (US) brain stimulation has been demonstrated to be a promising approach for noninvasive neuromodulation. However, traditional methods always demand animals to be under anesthesia and body constraint to achieve stable operation with bulky US transducer, while those demands would result in interference to the neural activity related to perception, cognition, and behavior. Appling a miniature US stimulator on freely moving mouse will greatly benefit for obtaining credible neural response from ultrasonic neuromodulation. This study investigates the local field potentials (LFPs) responses to ultrasonic neuromodulation on freely moving mouse by using a customized head-mounted US transducer.

Dual-mode imaging catheter for intravascular ultrasound

Intravascular ultrasound (IVUS) is a well-established diagnostic method that has been applied frequently for providing high-resolution images of vessel wall and atherosclerotic plaques. Side looking transducer has been employed in a catheter for delineating the structure of vessel wall and lesions. However, it is difficult to get the flow distribution in the vessel by side looking transducer as the ultrasound wave is transmitted perpendicularly to the flow. Doppler ultrasound wire has been proposed and applied to measure the flow information. In this study, we propose a new design of dual mode imaging method by combining side looking transducer together with the forward looking Doppler transducer in one catheter. It could be potentially used for the measurement of both morphology and flow information simultaneously in one catheter.

High frequency array transducer for intravascular ultrasound

Atherosclerotic plaque rupture will cause acute coronary syndrome and sudden cardiac death, so that the diagnosis of this kind disease is crucial in clinical studies. Intravascular ultrasound (IVUS) imaging is an effective means of detecting atherosclerotic plaques. In general, two kinds of transducers were used for IVUS imaging, i.e. single-element transducer and radial array transducer. It should be noted that imaging resolution of single-element transducer was reduced in the deep area. In this study, we propose a high frequency array transducer targeted for IVUS applications.

Noninvasive neurostimulation on mice by 5 MHz ultrasound

Ultrasound has been demonstrated to be an effective approach for noninvasive neurostimulation. Low frequency ultrasound (<;1 MHz) is preferable as its low ultrasonic attenuation when passing through the skull. High frequency ultrasound is able to provide reduced size of focal region. However, the performance of stimulation with high frequency ultrasound is not proved yet. This study examines the feasibility and effectiveness of using high frequency, i.e. 5 MHz, focused ultrasound to perform the neurostimulation on mice. The acoustic properties of 1 MHz and 5 MHz ultrasound on mouse skull were evaluated by a 3D acoustic scanning system. By performing proper acoustic compensation, 1 MHz and 5 MHz ultrasound can present the same acoustic intensity level after passing the skull. They were used to do the brain stimulation with same group of mice. Electromyography (EMG) signals collected from tail muscles and videos of motion responses were analyzed for the evaluation of neurostimulation. The results illustrated that 5 MHz ultrasound can successfully achieve the neurostimulation by monitoring the EMG and motion responses. The equivalent diameter (D) of stimulus for 5 MHz is significantly smaller than that of 1 MHz. Focused ultrasound with higher frequency can provide smaller size of stimulation region, which offers precise control of the neurostimulation in a non-invasive manner.

Design and fabrication of cylindrical transducer based on 2–2 piezoelectric composite

A cylindrical transducer based on PZT-5H/epoxy 2-2 piezoelectric composite with 40 elements is designed and fabricated in this paper. The prepared PZT-5H/epoxy 2-2 piezoelectric composite shows a single thickness mode, low acoustical impedance (25.8MRayls) and high electromechanical coupling coefficient (0.72). A pulse-echo method is utilized to test the performance of the cylindrical transducer. The center frequency for a representative element is calculated to be 5.02MHz and -6dB bandwidth is 62.9%. The elevation focal length is approximately 4.9cm. It indicates the bend-and-combine method proposed is feasible.