Array Transducer Research Articles

Comparison of transrectal and transabdominal transducers for use in fast localized abdominal sonography of horses presenting with colic.

Abdominal ultrasonography is valuable in the diagnosis of equine colic. Fast localized abdominal sonography of horses (FLASH) enables practitioners with limited experience to perform ultrasonography in emergency settings. However, many practitioners only possess rectal format linear array transducers (RFLT). The hypotheses are: (a) A low frequency curvilinear transducer (LFCT) and RFLT will detect free abdominal fluid and abnormal small intestinal loops with similar frequency during FLASH, and (b) there will be a difference between the transducers for detection of gastric abnormalities and nephrosplenic entrapment. The objective is to compare transcutaneous abdominal ultrasonographic detection of abnormalities in horses presenting with colic using a LFCT and RFLT. Twenty-four horses requiring FLASH for investigation of colic were enrolled. Horses that were too painful to undergo transcutaneous abdominal ultrasonographic examination were excluded. A single investigator performed FLASH on all horses using a RFLT, while one of three other clinicians simultaneously performed FLASH using a LFCT. Comparison of abnormal findings between the two transducers was performed using Chi square, Fisher's exact or Wilcoxon tests. The incidence of identification of abnormal findings was similar between the two transducers for all comparisons except the visibility of the left kidney and stomach (kidney LFCT 81.25% vs. RFLT 22.92%, stomach LFCT 87.5% vs. RFLT 62.5%). While there are limitations to using a RFLT to identify nephrosplenic entrapment of the colon and detection of the stomach, it reliably detects other common abnormalities, including peritoneal effusion, lesions of the small intestine, and changes to the wall of the large colon and cecum.

3-D Contrast-Enhanced Fusion Ultrasound for Accurate Volume Assessment of Vessel Lumen and Plaque in Carotid Artery Disease as Compared With Computed Tomography Angiography

ObjectiveThree-dimensional contrast-enhanced fusion ultrasound (3D-CEFUS) of atherosclerotic carotid arteries provides spatial visualisation of the vessel lumen, creating a lumenography. As in 3D computed tomography angiography (3D-CTA), 3D-CEFUS outlines the contrast-filled lumen. Plaque and vessel contours are distinguished in 3D-CEFUS, allowing plaque volume quantification as a valid estimate of carotid plaque burden. 3D-CEFUS is unproven in inter-modality studies, vindicating the assessment of 3D-CEFUS applicability and comparing 3D-CEFUS and 3D-CTA lumenography as a proof-of-concept study. MethodsUsing an ultrasound system with magnetic tracking, a linear array transducer, and SonoVue contrast agent generated 3D-CEFUS acquisitions by spatial stitching of serial 2D images. From 3D-CEFUS and 3D-CTA imaging, the atherosclerotic carotid arteries were reconstructed with lumenography in an offline software programme for lumen and plaque volume quantification. Bland-Altman analysis was used for inter-image-modality agreement. ResultsThe study included 39 carotid arteries. Mean lumen and plaque volume in 3D-CEFUS were 0.63 cm3 (SD 0.26) and 0.62 cm3 (SD 0.26), respectively. Lumen volume differences between 3D-CEFUS and 3D-CTA were non-significant, with mean difference of 0.01 cm3 (SD 0.02, p = .26) and limits of agreement range (LoA-range) of ±0.11 cm3. Mean plaque volume difference was -0.12 cm3 (SD 0.19, p = .006) with LoA-range of ±0.39 cm3. ConclusionStrong agreement in lumenography between 3D-CEFUS and 3D-CTA was found. The inter-image-modality difference in plaque volumes was substantial due to challenging vessel wall definition in 3D-CTA. 3D-CEFUS is viable in quantifying carotid plaque volume burden and can potentially monitor plaque development over time.

Performance investigation and element optimization of 2D array transducer using Bat Algorithm

Performance investigation and element optimization of 2D array transducer using Bat Algorithm

Ultrasound-Guided Mechanical High-Intensity Focused Ultrasound (Histotripsy) Through an Acoustically Permeable Polyolefin-Based Cranioplasty Device.

Recently, a biocompatible, polyolefin-based cranioplasty device was developed to allow ultrasound (US) transmission into the intracranial space with minimal distortion. In this study, we investigated the in vitro feasibility of applying US-guided histotripsy procedures across the prosthesis. Pressure waveforms and beam profiles were collected for single- and multi-element histotripsy transducers. Then, high-speed optical images of the bubble cloud with and without the prosthesis were collected in water and tissue-mimicking agarose gel phantoms. Finally, red blood cell (RBC) tissue phantom and excised brain tissue experiments were completed to test the ablative efficacy across the prosthesis. Single element tests revealed increased pressure loss with increasing transducer frequency and increasing transducer-to-prosthesis angle. Array transducer measurements at 1 MHz showed average pressure losses of >50% across the prosthesis. Aberration correction recovered up to 18% of the pressure lost, and high-speed optical imaging in water, agarose gels, and RBC phantoms demonstrated that histotripsy bubble clouds could be generated across the prosthesis at pulse repetition frequencies of 50-500 Hz. Histologic analysis revealed a complete breakdown of brain tissue treated across the prosthesis. Conclusion & Significance: Overall, the results of this study demonstrate that the cranial prosthesis may be used as an acoustic window through which intracranial histotripsy can be applied under US guidance without the need for large transcranial array transducers.

A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

High-Frequency, 2-mm-Diameter Forward-Viewing 2-D Array for 3-D Intracoronary Blood Flow Imaging.

Coronary artery disease (CAD) is one of the leading causes of death globally. Currently, diagnosis and intervention in CAD are typically performed via minimally invasive cardiac catheterization procedures. Using current diagnostic technology, such as angiography and fractional flow reserve (FFR), interventional cardiologists must decide which patients require intervention and which can be deferred; 10% of patients with stable CAD are incorrectly deferred using current diagnostic best practices. By developing a forward-viewing intravascular ultrasound (FV-IVUS) 2-D array capable of simultaneously evaluating morphology, hemodynamics, and plaque composition, physicians would be better able to stratify risk of major adverse cardiac events in patients with intermediate stenosis. For this application, a forward-viewing, 16-MHz 2-D array transducer was designed and fabricated. A 2-mm-diameter aperture consisting of 140 elements, with element dimensions of 98×98×70 μ m ( w×h×t ) and a nominal interelement spacing of 120 μ m, was designed for this application based on simulations. The acoustic stack for this array was developed with a designed center frequency of 16 MHz. A novel via-less interconnect was developed to enable electrical connections to fan-out from a 140-element 2-D array with 120- μ m interelement spacing. The fabricated array transducer had 96/140 functioning elements operating at a center frequency of 16 MHz with a -6-dB fractional bandwidth of 62% ± 7 %. Single-element SNR was 23 ± 3 dB, and the measured electrical crosstalk was - 33 ± 3 dB. In imaging experiments, the measured lateral resolution was 0.231 mm and the measured axial resolution was 0.244 mm at a depth of 5 mm. Finally, the transducer was used to perform 3-D B-mode imaging of a 3-mm-diameter spring and 3-D B-mode and power Doppler imaging of a tissue-mimicking phantom.

An Underwater Anti-Misalignment UPT System Based on Array Transducers

An Underwater Anti-Misalignment UPT System Based on Array Transducers

A Pre-Voiding Alarm System Using Wearable Ultrasound and Machine Learning Algorithms for Children With Nocturnal Enuresis.

Nocturnal enuresis is a bothersome condition that affects many children and their caregivers. Post-voiding systems is of little value in training a child into a correct voiding routing while existing pre-voiding systems suffer from several practical limitations, such as cumbersome hardware, assuming individual bladder shapes being universal, and being sensitive to sensor placement error. Methods: A low-voltage ultrasound system with machine learning has been developed in estimating bladder filling status. A custom-made flexible 1D transducer array has been excited by low-voltage coded pulses with a pulse compression technique for an enhanced signal-to-noise ratio. In order to minimize the negative influence of possible transducer misplacement, a multiple-position training strategy using machine learning has been adopted in this work. Three popular classification methods, KNN, SVM and sparse coding, have been utilized to classify the acquired different volumes ranging from 100 ml to 300 ml into two categories: low volume and high volume. The low-volume category requires no further action while the high-volume category triggers an alarm to alert the child and caregiver. Results: When the sensor placement is ideal, i.e., the position of the practical sensor placement is on spot with the trained position, the precision and recall of the classification using sparse coding are [Formula: see text] and [Formula: see text], respectively. Even if the transducer array is misplaced by up to 4.5 mm away from the ideal location, the proposed system is able to maintain high classification accuracy (precision [Formula: see text] and recall [Formula: see text]). Category: Early/Pre-Clinical Research Clinical and Translational Impact: The proposed ultrasound sensor system for nocturnal enuresis is of significant clinical and translational value as it addresses two major issues that limit the wide adoption of similar devices. Firstly, it offers enhanced safety as the entire system has been implemented in the lowvoltage domain. Secondly, the system features ample tolerance to sensor misplacement while maintaining high classification accuracy. These features combined provide a much more user-friendly environment for children and their caregivers than existing devices.

Investigation of Transducer Distribution in Compressive Thermoacoustic Tomography for Breast Cancer Detection

Microwave-induced thermoacoustic tomography (MITAT) is a novel noninvasive method for biomedical applications like imaging and cancer detection. Recently, compressive sensing has been applied in MITAT, denoted as compressive thermoacoustic tomography (CTAT), can greatly reduce the number of measurements while maintain the image quality. This work reports the study on the effect of distribution of transducer array on image quality in CTAT for the application of breast tumor detection. Different distributions are tested by both simulation and experimental works to compare the quality of imaging. Three breast samples made of pork fat containing tumor-mimicking phantoms are used as the object to evaluate the effect of distribution of transducer array on image quality through the experiment. The results show that the transducer array which distributed evenly on a hemisphere surface is able to achieve an excellent image reconstruction result that is better than other tested types of transducer array distribution. This work gives a faithful guidance on the distribution strategy of transducer array for CTAT in breast tumor detection and other potential applications.

A 1.11 mm2 IVUS SoC with ±50°-Range Plane Wave Transmit Beamforming at 40 MHz.

Intravascular ultrasound (IVUS) imaging catheters are significant tools for cardiovascular interventions, and their use can be expanded by realizing IVUS imaging guidewires and microcatheters. The miniaturization of these devices creates challenges in SNR due to the need for higher frequencies to provide adequate resolution. An integrated IVUS system with transmit beamforming can mitigate these limitations. This work presents the first practical highly integrated system-on-a-chip (SoC) with plane wave transmit beamforming at 40 MHz for IVUS on guidewire or microcatheters. The front-end circuitry has a 20-channel ultrasound transmitter (Tx) and receiver (Rx) array interfaced with a capacitive micromachined ultrasound transducer (CMUT) array. During each firing, all 20 Tx are excited with the same analog delay with respect to each other, which can be continuously adjusted between ~0 and 10 ns in two directions, generating a steerable plane wave in a range of ±/-50° for a phased array at 40 MHz. The unit delays are generated via a voltage-controlled delay line (VCDL), which only needs two external controls, one tuning the unit delay and the other determining the steering direction. The SoC is fabricated using a 180-nm high-voltage (HV) CMOS process and features a slender active area of 0.3 mm × 3.7 mm. The proposed SoC consumes 31.3 mW during the receiving mode. The beamformer's functionality and the SoC's overall performance were validated through acoustic characterization and imaging experiments.

Fabrication Method for Spin‐Coating ITO‐Competitive PEDOT:PSS onto PVDF Film

This paper shows a four‐order reduction of magnitude in sheet resistance for spin‐coating poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) onto polyvinylidene fluoride (PVDF) film for a final sheet resistance comparable to commercially available indium tin oxide‐ (ITO‐) coated PVDF film. The resulting PEDOT:PSS transparency is 10% less than the transparency for ITO:PVDF. This is done by the combination of four techniques from the literature including (i) varying layers, (ii) plasma etching, (iii) post‐treatment submersion in an ethylene glycol (EG) bath, and (iv) adding EG and a surfactant to the PEDOT:PSS solution. The PEDOT:PSS sheet resistance falls from over 3 megaohms/sq to between 600 and 150 ohms/sq depending on the number of layers. The one‐layer sample has a sheet resistance of 600 ohms/sq and an optical transparency of about 76%, and the five‐layer sample has a sheet resistance of 150 ohms/sq and an optical transparency of about 50%. These results reported here make PEDOT:PSS an attractive option for transparent piezoelectric micromachined ultrasonic transducer (PMUT) array applications.

Design and Fabrication of 1-D CMUT Arrays for Dual-Mode Dual-Frequency Acoustic Angiography Applications.

When microbubble contrast agents are excited at low frequencies (less than 5 MHz), they resonate and produce higher-order harmonics due to their nonlinear behavior. We propose a novel scheme with a capacitive micromachined ultrasonic transducer (CMUT) array to receive high-frequency microbubble harmonics in collapse mode and to transmit a low-frequency high-pressure pulse by releasing the CMUT plate from collapse and pull it back to collapse again in the same transmit-receive cycle. By patterning and etching the substrate to create glass spacers in the device cavity we can reliably operate the CMUT in collapse mode and receive high-frequency signals. Previously, we demonstrated a single-element CMUT with spacers operating in the described fashion. In this article, we present the design and fabrication of a dual-mode, dual-frequency 1-D CMUT array with 256 elements. We present two different insulating glass spacer designs in rectangular cells for the collapse mode. For the device with torus-shaped spacers, the 3 dB receive bandwidth is from 8 to 17 MHz, and the transmitted maximum peak-to-peak pressure from 32 elements at 4 mm focal depth was 2.12 MPa with a 1.21 MPa peak negative pressure, which corresponds to a mechanical index (MI) of 0.58 at 4.3 MHz. For the device with line-shaped spacers, the 3-dB receive bandwidth at 150 V dc bias extends from 10.9 to 19.2 MHz. By increasing the bias voltage to 180 V, the 3 dB bandwidth shifts, and extends from 11.7 to 20.4 MHz. The transmitting maximum peak-to-peak pressure with 32 elements at 4 mm was 2.06 MPa with a peak negative pressure of 1.19 MPa, which corresponds to an MI of 0.62 at 3.7 MHz.

Acoustic levitation and manipulation of columns of droplets with integrated optical detection for parallelisation of reactions.

The most common methodology for performing multiple chemical and biological reactions in parallel is to use microtitre plates with either manual or robotic dispensing of reactants and wash solutions. We envision a paradigm shift where acoustically levitated droplets serve as wells of microtitre plates and are acoustically manipulated to perform chemical and biological reactions in a non-contact fashion. This in turn requires that lines of droplets can be levitated and manipulated simultaneously so that the same operations (merge, mix, and detect) can be performed on them in parallel. However, this has not been demonstrated until this work. Because of the nature of acoustic standing waves, a single focus has more than one trap, and can allow levitation of columns of droplets at the focal point and at half a wavelength above and below that point. Using this approach, we increased the number of acoustically levitated and merged droplets to 6 compared to 2 in the state-of-the-art. We showed that droplets in a column can be moved and merged with droplets in another column simultaneously and in a controlled manner to perform repeats and/or parallelisation of chemical and biological reactions. To demonstrate our approach experimentally, we built an acoustic levitator with top and bottom surfaces made of a 16 × 16 grid of 40 kHz phased array transducers and integrated optical detection system, studied two acoustic trap generation and movement algorithms, and performed an exemplar enzyme assay. This work has made significant steps towards acoustic levitation and manipulation of large numbers of droplets to eventually significantly reduce the use of the current state-of-the-art tools, microtitre plates and robots, for performing parallelised chemical and biological reactions.

Underestimation of Flow Velocity in 2-D Super-Resolution Ultrasound Imaging.

Velocity estimation in ultrasound imaging is a technique to measure the speed and direction of blood flow. The flow velocity in small blood vessels, i.e., arterioles, venules, and capillaries, can be estimated using super-resolution ultrasound imaging (SRUS). However, the vessel width in SRUS is relatively small compared with the full-width-half-maximum of the ultrasound beam in the elevation direction (FWHMy), which directly impacts the velocity estimation. By taking into consideration the small vessel widths in SRUS, it is hypothesized that the velocity is underestimated in 2-D super-resolution ultrasound imaging when the vessel diameter is smaller than the FWHMy. A theoretical model is introduced to show that the velocity of a 3-D parabolic velocity profile is underestimated by up to 33% in 2-D SRUS, if the width of the vessel is smaller than the FWHMy. This model was tested using Field II simulations and 3-D printed micro-flow hydrogel phantom measurements. A Verasonics Vantage 256™ scanner and a GE L8-18i-D linear array transducer with FWHMy of approximately 770 μm at the elevation focus were used in the simulations and measurements. Simulations of different parabolic velocity profiles showed that the velocity underestimation was 36.8%±1.5% (mean±standard deviation). The measurements showed that the velocity was underestimated by 30%±6.9%. Moreover, the results of vessel diameters, ranging from 0.125×FWHMy to 3×FWHMy, indicate that velocities are estimated according to the theoretical model. The theoretical model can, therefore, be used for the compensation of velocity estimates under these circumstances.

Super-Resolution Ultrasound Imaging for Analysis of Microbubbles Cluster by Acoustic Vortex Tweezers.

Using acoustic vortex tweezers (AVT) to spatially accumulate microbubbles (MBs) shows promise for enhancing drug delivery efficiency and reducing off-target effects. The strong echogenicity of accumulated MBs also improves diagnostics via conventional ultrasound (US) B-mode imaging. However, the annular high-pressure distribution of AVT inhibits MBs inflow at the inlet, reducing MBs collection. The spatial resolution of US B-mode imaging further limits theranostic applications of AVT-mediated MBs accumulation. To address these challenges, we integrated an AVT waveform with volumetric super-resolution imaging (VSRI) to monitor the dynamic growth of MBs cluster during accumulation. We used a 5-MHz 2D array transducer for VSRI, employing plane wave pulses interleaved with accumulating pulses to retain MBs at a flow rate of 0.023-0.047 mL/s in a 3-mm vessel phantom. An asymmetrical AVT waveform (AVT*) was produced by modulating the pressure at the MBs inlet compared to the outlet. The effectiveness was validated in rat cerebral vessels for real-time volumetric tracking of MBs clusters. Microscopy observations showed that AVT* could quickly gather flowing MBs into cluster without repelling them at a flow rate of 0.023 mL/s. Statistical results indicated that microscopic data correlated better with VSRI than with B-mode images, suggesting VSRI suffices to detect the dynamics of AVT*-actuated MBs accumulation in real-time. Additionally, VSRI detected a significant increase in MBs cluster size over time during AVT* in the superior sagittal sinus of the rat brain. These findings demonstrate that the proposed strategy can accumulate the flowing MBs at a desired location and simultaneously observe this phenomenon.

Increasing the Maximum Detectable Flow Velocity in High-Frequency Ultrasound Vector Doppler Imaging.

High-frequency ultrasound (HFUS; >30 MHz) Doppler imaging has been widely used in the imaging of small animals and humans because of its high resolution. Vector Doppler imaging (VDI) has certain advantages for visualizing complex flow patterns independent of the Doppler angle. However, no commercial HFUS VDI system is currently available; therefore, several studies have connected an ultrasound research platform (Verasonics Vantage 256) with an HFUS array transducer for HFUS VDI. Unfortunately, the maximum frame rate of this system is only 10 kHz at an operational frequency of 40 MHz because of limitations related to data transmission hardware, thereby restricting the maximum detectable velocity of Doppler measurements. To address this drawback, in the present study, an electrocardiography (ECG)-gating-based HFUS VDI system was developed to avoid Doppler flow aliasing in data acquisition by ultrasound research platform at its maximum frame rate of 10 kHz. The developed method aligns all tilted plane waves with the ECG R-wave, which avoids the trade-off between frame rate and tilted angles number in conventional VDI. The performance of the proposed data acquisition method in HFUS VDI was verified using a steady-flow phantom, for which estimation errors were less than 10% under different flow settings. In animal studies, peak flow velocities in the carotid artery, left ventricle, and aortic arch of wild-type mice were measured (approximately 55, 655, and 765 mm/s, respectively). Also, the HFUS VDI from the mitral regurgitation mice model was obtained to present the complex flow patterns through the proposed method. In contrast to the conventional method, no Doppler aliasing occurs in the proposed method because the frame rate is sufficient. The experimental results indicate the developed HFUS VDI has the potential to become a useful tool for vector flow visualization in small animals, even under a high flow velocity.

Comparison of pre-mortem 2D-3D ultrasound examination to post-mortem micro-CT of carotid arteries - first experiences.

<p>A prerequisite for the treatment of carotid atherosclerosis is the accurate measurement of the stenosis, that is most commonly evaluated by duplex ultrasonography. In this study, we aimed to verify the reliability of 2D and 3D ultrasonography, comparing the data to results of post-mortem micro-CT examination.</p>. <p>Neurological patients with any life-threatening, presumably fatal neurological disease were enrolled. Ultrasound examinations were performed with a Philips Epiq 5G machine, using a VL13-5 broadband linear volume array transducer. Plaque length, diameter and vessel area reduction (stenosis) were calculated using the 2D images. Finally, the stenosis was reassessed using automatized, 3D application as well. After the death of the patient, autopsy was performed, during which the previously examined carotid artery was removed. The samples were examined with micro-CT. Similar to the ultrasound examination, plaque length, diameter and vessel area reduction (stenosis) were determined.</p>. <p>Ten vessels of seven patients were eligible for complex comparison. Plaque diameter and length measured by CT did not correlate with the ultrasound data. CT-measured axial plaque and vessel areas showed no correlation with ultrasound results either. While determining the strength of correlation between stenoses measured by the different modalities, significant correlation was found between the results measured by ultrasound (2D) and CT (Pearson r: 0.902, P&lt;0.001).</p>. <p>Three-dimensional ultrasound analysis is a spectacular method for examining carotid plaques, as it can assist in a more detailed evaluation of the plaque morphology and composition, thereby identifying plaques with a particularly high risk of stroke. Micro-CT is an excellent tool for the exact determination of calcified plaque areas, but ultrasound images are not suitable yet for such a precise examination due to acoustic shadowing and artifacts.</p>.

Three-Dimensional Magneto-Acousto-Electrical Computed Tomography (3D MAE-CT): A Preliminary Study Using Ultrasound Linear Array Transducer.

Magneto-acousto-electrical tomography (MAET) is a hybrid imaging method that combines the high spatial resolution of ultrasonography with the high contrast of electrical impedance tomography (EIT). While most previous studies on MAET have focused on two-dimensional imaging, our recent research proposed a novel three-dimensional (3D) MAET method using B-mode and translational scanning. This method has been the first to reconstruct a 3D volume image of conductivity interfaces. However, this method has its limitations in mapping irregular shapes of conductivity. To address this challenge, we propose a 3D magneto-acousto-electrical computed tomography (3D MAE-CT) method utilizing an ultrasound linear array transducer in this work. Both phantom and in vitro experiments were conducted to validate our proposed method. The results from the phantom experiments demonstrate that our method can map the 3D volume conductivity with high spatial resolution. The oblique angles extracted from the 3D image closely match practical value, with the relative error ranging between -2.80% and 4.07%. Furthermore, the in vitro experiment successfully obtained a 3D image of a chicken heart, marking the first MAET 3D conductivity image of a tissue sample to date.

Development of a Sound Directional Device Based on Ultrasound Modulation and Transducer Array Optimization

Development of a Sound Directional Device Based on Ultrasound Modulation and Transducer Array Optimization

Design and Optimization of Flexible and Stretchable Ultrasonic Transducer Array for Arterial Blood Pressure Monitoring

Design and Optimization of Flexible and Stretchable Ultrasonic Transducer Array for Arterial Blood Pressure Monitoring