RESUMEN
Transcranial ultrasound imaging presents a significant challenge due to the intricate interplay between ultrasound waves and the heterogeneous human skull. The skull's presence induces distortion, refraction, multiple scattering, and reflection of ultrasound signals, thereby complicating the acquisition of high-quality images. Extracting reflections from the entire waveform is crucial yet exceedingly challenging, as intracranial reflections are often obscured by strong amplitude direct waves and multiple scattering. In this paper, a multiple wave suppression method for ultrasound plane wave imaging is proposed to mitigate the impact of skull interference. Drawing upon prior research, we developed an enhanced high-resolution linear Radon transform using the maximum entropy principle and Bayesian method, facilitating wavefield separation. We detailed the process of wave field separation in the Radon domain through simulation of a model with a high velocity layer. When plane waves emitted at any steering angles, both multiple waves and first arrival waves manifested as distinct energy points. In the brain simulation, we contrasted the characteristic differences between skull reflection and brain-internal signal in Radon domain, and demonstrated that multiples suppression method reduces side and grating lobe levels by approximately 30 dB. Finally, we executed in vitro experiments using a monkey skull to separate weak intracranial reflection signals from strong skull reflections, enhancing the contrast-to-noise ratio by 85 % compared to conventional method using full waveform. This study deeply explores the effect of multiples on effective signal separation, addresses the complexity of wavefield separation, and verifies its efficacy through imaging, thereby significantly advancing ultrasound transcranial imaging techniques.
Asunto(s)
Cráneo , Cráneo/diagnóstico por imagen , Animales , Humanos , Teorema de Bayes , Encéfalo/diagnóstico por imagen , Ultrasonografía Doppler Transcraneal/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Radón , AlgoritmosRESUMEN
A fully-sampled two-dimensional (2D) matrix array ultrasonic transducer is essential for fast and accurate three-dimensional (3D) volumetric ultrasound imaging. However, these arrays, usually consisting of thousands of elements, not only face challenges of poor performance and complex wiring due to high-density elements and small element sizes but also put high requirements for electronic systems. Current commercially available fully-sampled matrix arrays, dividing the aperture into four fixed sub-apertures to reduce system channels through multiplexing are widely used. However, the fixed sub-aperture configuration limits imaging flexibility and the gaps between sub-apertures lead to reduced imaging quality. In this study, we propose a high-performance multiplexed matrix array by the design of 1-3 piezocomposite and gapless sub-aperture configuration, as well as optimized matching layer materials. Furthermore, we introduce a sub-aperture volumetric imaging method based on the designed matrix array, enabling high-quality and flexible 3D ultrasound imaging with a low-cost 256-channel system. The influence of imaging parameters, including the number of sub-apertures and steering angle on imaging quality was investigated by simulation, in vitro and in vivo imaging experiments. The fabricated matrix array has a center frequency of 3.4 MHz and a -6 dB bandwidth of above 70%. The proposed sub-aperture volumetric imaging method demonstrated a 10% improvement in spatial resolution, a 19% increase in signal-to-noise ratio, and a 57.7% increase in contrast-to-noise ratio compared with the fixed sub-aperture array imaging method. This study provides a new strategy for high-quality volumetric ultrasound imaging with a low-cost system.
Asunto(s)
Imagenología Tridimensional , Transductores , Ultrasonografía/métodos , Relación Señal-Ruido , Electrónica , Fantasmas de ImagenRESUMEN
Coherent plane-wave compounding technique enables rapid ultrasound imaging with comparable image quality to traditional B-mode imaging that relies on focused beam transmission. However, existing methods assume homogeneity in the imaged medium, neglecting the heterogeneity in sound velocities and densities present in real tissues, resulting in noise reverberation. This study introduces the Reverse Time Migration (RTM) method for ultrasound plane-wave imaging to overcome this limitation, which is combined with a method for estimating the speed of sound in layered media. Simulation results in a homogeneous background demonstrate that RTM reduces side lobes and grating lobes by approximately 30 dB, enhancing the contrast-to-noise ratio by 20% compared to conventional delay and sum (DAS) beamforming. Moreover, RTM achieves superior imaging outcomes with fewer compounding angles. The lateral resolution of the RTM with 5-9 angle compounding is able to achieve the effectiveness of the DAS method with 15-19 angle compounding, and the CNR of the RTM with 11-angle compounding is almost the same as that of the DAS with 21-angle compounding. In a heterogeneous background, experimental simulations and in vitro wire phantom experiments confirm RTM's capability to correct depth imaging, focusing reflected waves on point targets. In vitro porcine tissue experiments enable accurate imaging of layer interfaces by estimating the velocities of multiple layers containing muscle and fat. The proposed imaging procedure optimizes velocity estimation in complex media, compensates for the impact of velocity differences, provides more reliable imaging results.
Asunto(s)
Procesamiento de Imagen Asistido por Computador , Fantasmas de Imagen , Ultrasonografía , Ultrasonografía/métodos , Animales , Porcinos , Procesamiento de Imagen Asistido por Computador/métodos , Algoritmos , Simulación por Computador , Procesamiento de Señales Asistido por ComputadorRESUMEN
Acoustic droplet ejection (ADE) uses the acoustic energy produced by a focused ultrasound beam to provide a noncontact, highly precise, automatic, and cost-effective liquid transfer method for life science applications. The reported minimum precision of the current acoustic liquid transfer technology is 1 nL. Since precision improvement always brings valuable results in biological research, it is highly necessary to develop pico-liter precision liquid transfer technology. In this work, we developed a 40-MHz ultrahigh -frequency focused ultrasound transducer with a large aperture of 7×7 mm2 and a wide bandwidth of 76.4%. The designed transducer can successfully eject pico-liter droplets, and the droplet ejection accuracy ranges from 28 to 439 pL. The effects of the acoustic parameters, including excitation amplitude, pulsewidth, and frequency, on the size of the ejected droplet were studied. A wide range of ejected droplet sizes could be obtained by adjusting the acoustic parameters, thereby making liquid transfer flexible. The flexible pico-liter liquid transfer based on the wide-bandwidth, high-frequency ultrasound transducer is easier to achieve automatically, and thus it has broad prospects in biological research and industrial applications.
Asunto(s)
Acústica , TransductoresRESUMEN
High-frequency ultrasound imaging (at >20 MHz) has gained widespread attention due to its high spatial resolution being useful for basic cardiovascular and cancer research involving small animals. The sampling rate of the analog-to-digital converter in a high-frequency ultrasound system usually needs to be higher than 120 MHz in order to satisfy the Nyquist sampling-rate requirement. However, the sampling rate is typically within the range of 40-60 MHz in a traditional ultrasound system, and so we propose a delayed-excitation method for performing high-frequency ultrasound imaging with a traditional data acquisition scheme. In this method, the transmitted pulse is delayed by a certain time period so that the ultrasound echo data are aligned into high-sampling-rate slots. Wire and tissue-mimicking phantoms were imaged to evaluate the performance of the proposed method, whereas a porcine small-intestine specimen and an excised rabbit eyeball were used for in vitro imaging evaluations. The test results demonstrate that the proposed method allows high-frequency ultrasound imaging to be implemented using a traditional ultrasound sampling system.
Asunto(s)
Procesamiento de Imagen Asistido por Computador/métodos , Procesamiento de Señales Asistido por Computador , Ultrasonografía/métodos , Animales , Ojo/diagnóstico por imagen , Intestino Delgado/diagnóstico por imagen , Fantasmas de Imagen , Conejos , PorcinosRESUMEN
Wireless capsule endoscopy has opened a new era by enabling remote diagnostic assessment of the gastrointestinal tract in a painless procedure. Video capsule endoscopy is currently commercially available worldwide. However, it is limited to visualization of superficial tissue. Ultrasound (US) imaging is a complementary solution as it is capable of acquiring transmural information from the tissue wall. This paper presents a mechanical scanning device incorporating a high-frequency transducer specifically as a proof of concept for US capsule endoscopy (USCE), providing information that may usefully assist future research. A rotary solenoid-coil-based motor was employed to rotate the US transducer with sectional electronic control. A set of gears was used to convert the sectional rotation to circular rotation. A single-element focused US transducer with 39-MHz center frequency was used for high-resolution US imaging, connected to an imaging platform for pulse generation and image processing. Key parameters of US imaging for USCE applications were evaluated. Wire phantom imaging and tissue phantom imaging have been conducted to evaluate the performance of the proposed method. A porcine small intestine specimen was also used for imaging evaluation in vitro. Test results demonstrate that the proposed device and rotation mechanism are able to offer good image resolution ( [Formula: see text]) of the lumen wall, and they, therefore, offer a viable basis for the fabrication of a USCE device.
Asunto(s)
Endoscopía Capsular , Animales , Diseño de Equipo , Fantasmas de Imagen , Porcinos , Transductores , UltrasonografíaRESUMEN
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 (>50 MHz) 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.