Intra-cardiac echography (ICE) probes (Fig. 32.2.1) are widely used in electrophysiology for their good procedure guidance and relatively safe application. ASICs are increasingly employed in these miniature probes to enhance signal quality and reduce the number of connections needed in mm-diameter catheters [1]-[5]. 3D visualization in real-time is additionally enabled by 2D transducer arrays with, for each transducer element, a high-voltage (HV) transmit (TX) part, to generate acoustic pulses of sufficient pressure, and a receive (RX) path, to process the resulting echoes. To achieve the required reduction in RX channels, micro-beamforming (BF), which merges the signals from a subarray using a delay-and-sum operation, has been shown to be an effective solution [3], [4]. However, due to the frame-rate reduction that is associated with BF, these designs cannot serve emerging high-frame-rate imaging modes (1000 volumes/s) like 3D blood-flow and elastography imaging. In-probe digitization has recently been investigated to provide further channel-count reduction, make data transmission more robust, and enable pre-processing in the probe [1]-[3]. However, these earlier designs have either no TX functionality [2], [3] or only low-voltage (LV) TX [1] integrated. Combining BF and digitization with area-hungry HV transmitters in a pitch-matched scalable fashion while supporting high-frame-rate imaging remains an unmet challenge. The work presented in this paper meets this target, enabled by a hybrid ADC, the small die size of which allows for co-integration with 65V element-level pulsers.

@en

We proposed a high frame rate 3D imaging scheme for carotid imaging applications. We optimized the transmit and receive sub-aperture sizes to reduce the data rate while providing a sufficient frame rate and image quality for carotid pulse wave and blood flow 3D imaging. In addition, a specific angular weighting function was used in coherent compounding of intermediate images to suppress grating lobes. @en

We present an ultrasound transceiver ASIC designed for an ultrasound probe for 3-D carotid artery imaging. We propose an improved switch design to minimize the charge-injection effects of high-voltage MOSFETs. @en

This article quantitatively analyzes the impact of bit errors in digitized RF data on ultrasound image quality. The quality of B-mode images in both linear array and phased array imaging is evaluated by means of three objective image quality metrics: peak signal-to-noise ratio, structural similarity index, and contrast-to-noise ratio, when bit errors are introduced to the RF data with different bit-error rates (BERs). The effectiveness of coding schemes for forward error detection and correction to improve the image quality is also studied. The results show that ultrasound imaging is inherently resilient to high BER. The image quality suffers unnoticeable degradation for BER lower than 1E-6. Simple 1-bit parity coding with 9% added redundancy helps to retain similar image quality for BER up to 1E-4, and Hamming coding with 33.3% added redundancy allows the BER to increase to 1E-3. These results can serve as a guideline in the datalink design for ultrasound probes with in-probe receive digitization. With much more relaxed BER requirements than in typical datalinks, the design can be optimized by allowing fewer cables with higher data rate per cable or lower power consumption with the same cable count.

@en

Shear wave elastography can potentially be used to diagnose an increased stiffness of the myocardium for patients with diastolic heart failure. This study focusses on the shear waves induced by aortic valve closure in the interventricular septum. The propagation speed of these shear waves is expected to be related to the stiffness of the myocardium and is determined along a manually-drawn M-line over the myocardium. In this study the effect of M-line location and angle is systematically investigated. In-vitro, measurements were performed using a PV A slab phantom, and in-vivo using three pigs with open chest. We found large global differences in propagation speed for different M-line locations over the interventricular septum, possibly having physiological causes. To avoid these physiological effects, we averaged the propagation speed of 10M-lines manually drawn at the endocardial side of the interventricular …@en

Until now, no matrix transducer has been realized for 3D transesophageal echocardiography (TEE) in pediatric patients. In 3D TEE with a matrix transducer, the biggest challenges are to connect a large number of elements to a standard ultrasound system, and to achieve a high volume rate (>200 Hz). To address these issues, we have recently developed a prototype miniaturized matrix transducer for pediatric patients with micro-beamforming and a small central transmitter. In this paper we propose two multiline parallel 3D beamforming techniques (μBF25 and μBF169) using the micro-beamformed datasets from 25 and 169 transmit events to achieve volume rates of 300 Hz and 44 Hz, respectively. Both the realizations use angle-weighted combination of the neighboring overlapping sub-volumes to avoid artifacts due to sharp intensity changes introduced by parallel beamforming. In simulation, the image quality in terms of the width of the point spread function (PSF), lateral shift invariance and mean clutter level for volumes produced by μBF25 and μBF169 are similar to the idealized beamforming using a conventional single-line acquisition with a fully-sampled matrix transducer (FS4k, 4225 transmit events). For completeness, we also investigated a 9 transmit-scheme (3 × 3) that allows even higher frame rates but found worse B-mode image quality with our probe. The simulations were experimentally verified by acquiring the μBF datasets from the prototype using a Verasonics V1 research ultrasound system. For both μBF169 and μBF25, the experimental PSFs were similar to the simulated PSFs, but in the experimental PSFs, the clutter level was ∼10 dB higher. Results indicate that the proposed multiline 3D beamforming techniques with the prototype matrix transducer are promising candidates for real-time pediatric 3D TEE.

@en

Most techniques that are used to reconstruct images from raw ultrasound signals are based on pre-defined geometrical processing. This type of image reconstruction typically has a low computational complexity and allows for real-time visualization. Since these techniques do not account for situation-specific parameters such as transducer characteristics and medium in-homogeneities, they cannot make proper use of the information that is contained in the raw ultrasound signals. In this paper, we explore the possibility of reconstructing images that best explain the measured ultrasound signals given the full ultrasound propagation model including all parameters. We build this model by measuring the spatiotemporal impulse response of the imaging transducer and, using the angular spectrum approach, estimate the ultrasound signal as it would originate from each individual image pixel position. An iterative search for the pixel combination that best explains the recorded signals provides the final image. We discuss the details of this model, provide experimental proof that this reconstruction allows for improved image quality, and extend our ideas to other imaging schemes such as compressive imaging.@en

This paper presents a power-and area-efficient front-end application-specific integrated circuit (ASIC) that is directly integrated with an array of 32 × 32 piezoelectric transducer elements to enable next-generation miniature ultrasound probes for real-time 3-D transesophageal echocardiography. The 6.1 × 6.1 mm² ASIC, implemented in a low-voltage 0.18-μm CMOS process, effectively reduces the number of receive (RX) cables required in the probe's narrow shaft by ninefold with the aid of 96 delay-and-sum beamformers, each of which locally combines the signals received by a sub-array of 3 × 3 elements. These beamformers are based on pipeline-operated analog sample-and-hold stages and employ a mismatch-scrambling technique to prevent the ripple signal associated with the mismatch between these stages from limiting the dynamic range. In addition, an ultralow-power low-noise amplifier architecture is proposed to increase the power efficiency of the RX circuitry. The ASIC has a compact element matched layout and consumes only 0.27 mW/channel while receiving, which is lower than the state-of-the-art circuit. Its functionality has been successfully demonstrated in 3-D imaging experiments.

@en

Three-dimensional ultrasound is a powerful imaging technique, but it requires thousands of sensors and complex hardware. Very recently, the discovery of compressive sensing has shown that the signal structure can be exploited to reduce the burden posed by traditional sensing requirements. In this spirit, we have designed a simple ultrasound imaging device that can perform three-dimensional imaging using just a single ultrasound sensor. Our device makes a compressed measurement of the spatial ultrasound field using a plastic aperture mask placed in front of the ultrasound sensor. The aperture mask ensures that every pixel in the image is uniquely identifiable in the compressed measurement. We demonstrate that this device can successfully image two structured objects placed in water. The need for just one sensor instead of thousands paves the way for cheaper, faster, simpler, and smaller sensing devices and possible new clinical applications.@en

The diastolic functioning of the left ventricle is correlated to the stiffness of the myocardium. Shear wave (SW) elastography can be used for non-invasive stiffness measurements. These waves can have external sources such as an acoustic push, natural sources such as valve closure, or diffuse sources like breathing and flow noise. SW propagation velocities in diffuse wave fields can be analyzed after a spatio-temporal correlation technique. This technique has been applied to bulk SW [Brum et al, IEEE UFFC 2015; Parker et al, Phys Med Biol 2017] and surface waves [Sabra et al, Am Inst Phys 2007; Brum et al, JASA 2008]. However, since the myocardium is relatively thin, Lamb wave phenomena including dispersion could be expected. In this study we tested the applicability of the diffuse wave technique in a PVA thin plate phantom, and compared it to direct SW measurements and a mechanically measured shear modulus.

@en

Real-time 3D ultrasonic imaging requires a matrix of transducer elements with a number of elements that readily exceeds the number of channels of a conventional imaging system. This paper presents an ASIC, realized in a
high-voltage 0.18 μm BCDMOS process, that interfaces a piezo-electric transducer array of 24 × 40 elements, directly integrated on top of the ASIC, to an imaging system using only 24 transmit and receive channels by means of a reconfigurable switch matrix and row-level low-noise amplifiers. Each element is associated with a compact bootstrapped high-voltage transmit/receive switch and programmable logic that enables a variety of imaging modes to be realized. The ASIC has been successfully used in a 3D imaging experiment.@en

Echocardiography is a portable, safe, and low-cost imaging technique for accurate assessment of the heart. In transesophageal echocardiography (TEE) the esophagus is utilized as the imaging window to examine the cardiac anatomy and function. In conventional TEE probes, a one-dimensional (1D) ultrasound array is employed to obtain two-dimensional (2D) cross-sectional images of the heart. Since cardiac morphology, leakage of valves and function of the outflow tracts are all three-dimensional (3D) phenomena, it is beneficial to interpret them from 3D images. Therefore, there is high clinical demand for matrix TEE probes that are capable of providing real-time volumetric images [1]. Several matrix arrays (Philips X7-2t, Siemens V5M TEE, General Electric 6VTD) have been developed for this purpose, however all of them are large in size (~10 cm3) and uncomfortable to use on non-anesthetized patients [2]. We aim to develop a matrix TEE probe with a small head volume (<1 cm3), which is suitable for long term monitoring of cardiac system on adults and in babies. We have developed a prototype of a small matrix TEE probe, which consists of a piezoelectric matrix transducer directly mounted on an Application Specific Integrated Circuit (ASIC). The ASIC performs the task of micro-beamforming, signal amplification and efficient data reduction. The piezoelectric matrix array consist of a 32×32 PZT elements with a pitch of 150 μm × 150 μm. The transmit aperture consists of 8×8 elements at the centre of the array, which are directly wired out to the ultrasound system. The remaining 864 elements are used in receive and are organized in 96 sub-arrays of 3×3 elements to reduce the cable count with a factor of 9. The signals from the individual elements in a sub-array are combined to a single output signal using a micro-beamformer on the ASIC. The micro-beamformer allows pre-steering of 0◦, ±17◦, and ±37◦ angles in both lateral and elevation directions. By recording datasets for different pre-steering angles, and by processing and combining them, a large volume image can be constructed. Acoustic performance of the prototype is evaluated in a water tank. The transmit transfer function of a single element is measured by applying a 20 cycle sinusoidal voltage, sweeping from 3 to 8 MHz with steps of 50 kHz. The output pressure is recorded by a calibrated hydrophone. It is found that the transducer has a central frequency of 5 MHz, a bandwidth of 40% and a transmit efficiency of 6.4 kPa/V (at 51 mm). To characterize the micro-beamforming function, three delay angles of 0◦, 17◦ and 37◦ were programmed. While transmitting with a well-defined external source, the output voltage from a sub-group was recorded from -50◦ to +50◦ degrees. We observe that the theoretical values of the beam profile agree well with the measurement results, especially with regard to the position of the grating lobes and side lobes. @en

We present a method for estimating the one-way electro-mechanical impulse response or transfer function of self-reciprocal ultrasound transducers. The one-way impulse response is needed for forward field simulations, or for pulseecho simulations and excitation code design when the oneway impulse response per array element is different. Using a flat plate reflector that is positioned parallel to the transducer surface, the resulting pulse-echo signal is measured. Since the transducer is self-reciprocal, the transmit and receive impulse responses are equivalent. Consequently, the measured signal is the autoconvolution of the one-way impulse response. We propose a new de-autoconvolution algorithm to obtain the one-way impulse response from such a signal. The proposed measurement procedure is especially time-efficient for large arrays, and does not rely on hydrophones or additional transducers. Experimental results are shown to demonstrate the effectiveness of the proposed method.@en