Linear Phased Array Transducer Research Articles

Electronic Focus Steering Capabilities of a Diagnostic-Type Linear Ultrasound Array Designed for High Power Therapy and Its Visualization

The focus steering capabilities of a 1 MHz linear phased array transducer (64 rectangular elements, 14.8 × 51.2 mm aperture) intended for drug delivery applications in abdominal organs were assessed and compared with its design-stage computer model. Acoustic fields generated by the transducer and predicted by the models of an ideal array with uniformly vibrating elements and either a plane or a cylindrically focused surface were simulated using the Rayleigh integral and angular spectrum methods. The boundary conditions for the transducer were reconstructed from acoustic holography measurements performed for selected focusing configurations of the array and also synthesized from holography data measured for each of its individual elements. It was shown that the transducer field with electronic focus steering can be accurately synthesized based on the holography data of its elements, which significantly simplified acoustic field characterization. Variability of the power and directivity patterns of the array elements were analyzed. A twofold smaller range of electronic steering in the transverse direction for the transducer compared to its computer model is discussed.

Femoral neck phantom imaging using time-domain topological energy method.

Ultrasonic bone imaging is a complex task, primarily because of the low energy contained in the signals reflected from the internal bone structures. In this study, the reconstruction of a bone-mimicking phantom echographic image using time-domain topological energy (TDTE) is proposed. A TDTE image results from a combination of forward and adjoint fields. The first is a solution of a numerical model that reproduces the setup of the experimental data acquisition to the best extent possible. The second has similar characteristics, but the source term is the time-reversed residue between the forward field and signals obtained from the experiment. The acquisition-reconstruction system used a linear phased-array transducer with a 5 MHz center frequency to acquire the signals and was coupled with a k-wave toolbox to implement the numerical models and perform the image reconstruction. The results showed good agreement between the geometry of the real phantom and the ultrasonic images. However, thickness evaluation errors were observed, which may be due to incorrect assumptions about the velocity models throughout the medium, a priori assumed to be known. Thus, this method has shown promising results and should be applied to the real femoral neck as a long-term objective.

Rapid rotational magneto-acousto-electrical tomography with filtered back-projection algorithm based on plane waves

Magneto-acousto-electrical tomography (MAET) is designed to produce conductivity images with high spatial resolution for a conducting object. In a previous study, for an irregular conductor, transverse scanning and rotational methods with a focus transducer were combined to collect complete electrical information. This kind of method, however, is time-consuming because of the transverse scanning procedure. In this study, we proposed a novel imaging method based on plane ultrasound waves and a new aspect of projection in rotational MAET. In the proposed method, we achieved the projection in each rotation angle by using plane waves rather than mechanical scanning of the focus waves along the transverse direction. Thus, the imaging time was significantly saved. To verify the proposed method, we derived a measurement formula containing a lateral integration, which built the relationship between the measurement formula and the projection under each rotation angle. Next, we constructed two different numerical models to compute magneto-acousto-electrical signals by using a finite element method and reconstructed the corresponding conductivity parameter images based on a filtered back-projection algorithm. Then, simulated signals under different signal-to-ratios (6, 20, 40, and 60 dB) were generated to test the performance of the proposed algorithm. To improve the image quality, we further analysed the influence of the filters and the frequency scaling factors embedded in the filtered back-projection algorithm. Moreover, we computed the L2 norm of the error in case of different frequency scaling factors and measurement noises. Finally, we conducted a phantom experiment with a 64-element linear phased array transducer (center frequency of 2.7 MHz) and reconstructed the conductivity parameter images of the circular phantom with an elliptical hole. The experimental results demonstrated the feasibility and time-efficiency of the proposed rapid rotational MAET.

Optimizing linear phased array transducers for non-destructive evaluation of thin layers

AbstractIn this work, a numerical method is proposed in order to achieve design optimisation of phased array (PA) probes for the special application of defects detection in thin films. This approach relies on an extended Fourier-based model that was adapted to predict the two-dimensional ultrasonic displacement field taking place in a thin plate under individual excitation of PA probe elements which have arbitrary orientation with respect to the examined part surface. Excitation is applied through a fluid couplant and is operated at scheduled delays that are managed to enable emission of constructive pulses. This gives the possibility to steer sound waves towards a direction and to focalize the beam in a selected point. An optimisation algorithm based on the concept of pattern search that does not require evaluation of a gradient was used to find the best match in the multidimensional analysis space of possibilities including the elements orientation angles, the elements lengths, the inter-elements distances and work frequency. Optimisation was performed with the objective to maximize the displacement amplitude at the focal point while minimizing simultaneously the effect of beam side lobes. The results obtained by this approach reveal that focalisation can be achieved with enhanced features in comparison with previous algorithms assuming linear elements that are parallel to the surface of the plate.

Clinical investigation of different types of cases of outdoor patients using ultrasonography in Rangpur Medical College Hospital, Bangladesh

Ultrasonography is an easy, noninvasive, rapid investigation advised by doctors worldwide. Hence we diagnosed different types of cases through ultrasonography at outdoor patients admitted to Department of Rangpur Medical College Hospital, Rangpur Bangladesh over a period of four months. Our objective was to investigate the prevalence of different types of cases diagnosed and evaluated by ultrasonography in a variety of physical conditions with multiple clinical scenarios. Ultrasonography were performed using GE Logiq V5 Expert ultrasound machine with linear and curved linear phased array transducers. A total 300 cases were diagnosed, where female and male cases were 204 (68%), 96 (32%) respectively. Most ultrasound examinations were abdominal, with the remainder being obstetric, pelvic, breast, and genitourinary examinations. In this study, abdominal ultrasonography represented 118 case (39.33%), Pelvic 54 (18%), KUB 57 (19%), Breast 7 (2.33%) and Obstetrics 64 (21.33%). We found general clinical prevalence of abdominal cases were Cholelithiasis 17 (5.67%), Cholecystitis 3 (1%), Fatty liver 24 (8%), Hepatic Mass 2 (0.67%), Hepatic cyst 1 (0.33%), Acute hepatitis 2 (0.67%), Acute appendicitis 6 (2%), Ascites 2 (0.67%), Hernia 3(1%), Acute pancreatitis 2 (0.67%), Choledocholithiasis 2 (0.67%), Splenomegaly 1 (0.33 %), Abscess 1 (0.33%) and normal cases were 54 (18%). In genitourinary, Stone 20 (6.67%), Cyst 7 (2.33%), RPD 11 (3.67), Cystitis 4 (1.33), Ectopic kidney 1 (0.33%), Enlarged prostate 6 (2%), Hydronephrosis 1 (0.33%), Mass lesion 2 (0.67%) and normal cases were 7 (2.33%). In Pelvic, RPC 11 (3.67%), Ovarian and adnexal cyst 11 (3.67%), Uterine Anomaly 14 (4.67%), Mass lesion 2 (0.67%), Collection 7 (2.33) and normal cases were 5 (1.67%). In Obstetrics, normal pregnancy with no or minor complications, pregnancy with severe complications and abnormal pregnancy were 31(10.33%), 30(10%) and 3(1.0%) respectively. In Breast, dilated duct 1 (0.33%), Abscess 2 (0.67%), Fibroadenoma 2 (0.67%) and normal cases were 2 (0.67%). Here, we found that Fatty liver, stone in genitourinary tract and gall stone were highly prevalent. So, health care providers need to concern and raise awareness to reduce the number of cases.
 Asian J. Med. Biol. Res. June 2020, 6(2): 294-298

Application of Dual Focused Ultrasonic Phased Array Transducer in Two Orthogonal Cross-Sections for Inspection of Multi-Layered Composite Components of the Aircraft Fuselage.

Our previous studies have shown that the application of the proposed technique of a dual focused ultrasonic beam in two orthogonal cross-sections in passive (elevation) and active (azimuth) apertures of linear ultrasonic phased array transducer (ULPAT) enhances the 3D spatial resolution in the case of the inspection of conventional defects (flat bottom holes) or measurement of thickness of multi-layered metal composites. The objective of this work is to apply the proposed technique to enhance the spatial resolution of the ULPAT in the cases of detection and sizing demonstration of internal defects possessing spatially complex geometry, and during the inspection of defective multi-layered thin composite components (e.g., GLARE) of the aircraft fuselage. The specially prepared aluminium specimen possessing an internal defect of complicated geometry (crescent-shaped) was investigated. The simulation results and experiments demonstrate the resolution enhancement, higher amplitude of the reflections (e.g., 2.5 times or +8 dB) and spatial improvement in the defect detection even in the case of the non-perpendicular incidence of ultrasonic waves to the complex geometry surface of the internal defect. During the experiments, the multi-layered GFRP-metal based composite sample GLARE 3-3/2 was investigated in the case of the single-side access to the surface of the sample. The internal artificial delamination type defect of 25 mm was detected with a higher accuracy. Compared to the limitations of conventional ULPAT, the relative error (32%) (at the −6 dB level) of lateral defect dimensions estimation was completely reduced.

Second-harmonic generation in focused beam fields of phased-array transducers in a nonlinear solid with a stress-free boundary

Abstract In nonlinear acoustic harmonic generation in solids with stress-free boundaries, such a boundary is known to destructively change the second harmonic generation, and the pulse-echo method is not practically applicable. Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups. This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries. The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields. The phase difference between the two second-harmonic components after reflection from the boundary—that is, the reflected and the newly generated second harmonic—is emphasized. The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.

Numerical study of the reflected elastic waves using Rayleigh diffraction integral

In this work, the transient ultrasonic waves radiated by a linear phased array transducer in a liquid then reflected at a liquid solid interface is studied. A model based on the Rayleigh integral is used where the reflection at the plane interface is considered by using the reflection coefficients for harmonic plane waves. The transient field is obtained by an inverse Fourier transform of the harmonic field. The obtained results highlight the different components of the ultrasonic field: the direct and edge waves as well as the longitudinal head waves or leaky Rayleigh waves. The temporal representation of these waves has been analyzed and discussed by the rays’ model. Instantaneous cartographies allowed a clear description of all the waves which appear at the liquid-solid interface. The results have been compared to those obtained by using a finite element method.

Research on the Actuation Performance of 2D-Orthotropic Piezoelectric Composite Materials Linear Phased Array Transducer.

Ultrasonic linear phased array actuator for electric-acoustic conversion is the key component of the ultrasonic phased array test system. Focusing on the existing deficiency of using phased array ultrasonic testing technology into complex engineering structure, using the 2D orthotropic piezoelectric composite materials (2D-OPCM) into the research of linear phased array actuator can achieve orientable exciting. The single OPCM element and its array actuator was designed and their mechanical properties of focusing were tested by experiment. The experimental results show that 2D-OPCM ultrasound phased array actuator can achieve precise phased array focusing and deflection, which might be of great promising in the nondestructive evaluation engineering application.

Data acquisition system for MAET with magnetic field measurements

Magneto-acousto-electrical tomography (MAET) is an imaging modality to image the electrical conductivity of biological tissues. It is based on electrical current induction by using ultrasound under a static magnetic field. The aim of this study is to develop a data acquisition system for MAET based on magnetic field measurements. The static magnetic field is generated by six permanent neodymium magnets. A 16-element linear phased array (LPA) transducer is utilized to generate acoustic pressure waves inside the phantom. To measure the magnetic field intensity generated by the induced currents, contactless receiver sensors are developed using two similar disk multiple layer coils, which are Helmholtz coil sensor. Physical properties and electrical characteristics of the sensors are assessed. A two-stage cascaded amplifier is designed and utilized in the receiving system. The gain of the cascaded amplifier at 1 MHz is adjusted to be 96 dB. Experimental studies are conducted with two different phantoms, having 3 S m−1 and 58 S m−1 electrical conductivity, respectively. A-scan and B-scan images of phantoms are obtained with the LPA transducer. Comparison of the ultrasound (A-scan) and MAET signals reveals that 3 S m−1 conductive inhomogeneity can be detected with this data acquisition system. Furthermore, the front and rear interfaces of an inhomogeneity () of 58 S m−1 conductivity are detectable.

Numerical implementation of magneto-acousto-electrical tomography (MAET) using a linear phased array transducer

In this study, the performance and implementation of magneto-acousto-electrical tomography (MAET) is investigated using a linear phased array (LPA) transducer. The goal of MAET is to image the conductivity distribution in biological bodies. It uses the interaction between ultrasound and a static magnetic field to generate velocity current density distribution inside the body. The resultant voltage due to velocity current density is sensed by surface electrodes attached on the body. In this study, the theory of MAET is reviewed. A 16-element LPA transducer with 1 MHz excitation frequency is used to provide beam directivity and steerability of acoustic waves. Different two-dimensional numerical models of breast and tumour are formed to analyze the multiphysics problem coupled with acoustics and electromagnetic fields. In these models, velocity current density distributions are obtained for pulse type ultrasound excitations. The static magnetic field is assumed as 1 T. To sense the resultant voltage caused by the velocity current density, it is assumed that two electrodes are attached on the surface of the body. The performance of MAET is shown through sensitivity matrix analysis. The sensitivity matrix is obtained for two transducer positions with 13 steering angles between to with angular intervals. For the reconstruction of the images, truncated singular value decomposition method is used with different signal-to-noise ratio (SNR) values (20 dB, 40 dB, 60 dB and 80 dB). The resultant images show that the perturbation (5 mm × 5 mm) placed 35 mm depth can be detected even if the SNR is 20 dB.

Sound fields radiated from a linear phased array based on analytical solutions of transient elastic waves

Beam characteristics of a linear phased array transducer are critical to its engineering applications as well as to its design. This paper proposes a method for the theoretical calculation of ultrasound field radiated by a linear phased array coupled to an elastic solid by a longitudinal wave couplant. In this case, the ultrasound field can be determined by superposition of the exact and analytical solutions of transient elastic waves induced by a number of discrete line sources normally acting on an elastic half-space. Based on the theoretical calculation, this work investigated the influences of several important parameters in a linear array transducer, such as wave length, array size, ratio of element width to inter-element spacing, to the ultrasound field characteristics. Interesting phenomena and useful results are obtained, which provide fast and accurate guidance for linear phased array transducer design. It also satisfies diverse and specific demands for actual engineering testing using arrayed transducers.

Development of the technique for independent dual focusing of contact type ultrasonic phased array transducer in two orthogonal planes

Due to a low lateral resolution in elevation plane, the application of linear ultrasonic phased array transducers (ULPAT) is limited. The objective is to enhance the spatial resolution by means of spatial dual focusing technique of ULPAT in two orthogonal planes – azimuth and elevation.A design of a special delay line possessing a convex cylindrical lens has been proposed. The lens enables fixed geometrical focusing of the excited beam in the elevation plane, while in the other, azimuth, plane the beam is electronically focused at an arbitrary point by the active aperture of the ULPAT. The simulation results demonstrate the extended possibilities of resolution enhancement. Experiments show that the undetectable defect is detected using the designed acoustic lens. In addition, the interfaces of the intermediate layer of metal composite were detected.

Роль неалкогольной жировой болезни печени в формировании атеросклеротического поражения сосудистой стенки у пациентов с абдоминальным ожирением

Aim of investigation. To study the vascular wall changes of common carotid artery and internal carotid arteries in patients with abdominal obesity (AO) and different forms of nonalcoholic fatty liver disease (NAFLD). Material and methods. The study involved 60 patients with AO (waist circumference ≥80 cm in women and ≥94 cm in men) and NAFLD who provided written informed consent to participate in the study. The age of the patient ranged from 18 to 59 years. Patients’ symptoms, past history, were evaluated to exclude alcoholic or drug-induced liver disease, anthropometric parameters were studied. All patients underwent a complex of laboratory and instrumental tests required by the Russian guidelines for diagnosis and treatment of NAFLD (2015). Severity of pathological changes in the liver tissue (fibrosis and steatosis) was assessed by noninvasive Steatoskrin diagnostic method (Biopredictive laboratory, France). Measurement of the intima-media complex thickness of the common carotid artery (IMT CCA) was performed by standard procedures at Voluson 730 Expert device, equipped with 7,5 MHz linear phased array transducer. The presence of early atherosclerotic markers was evaluated by local thickening of the IMT CCA over 0.86 mm in any point of the carotid artery (IMT CCA max). The data were processed by comparative and correlation analysis. Results. The relationship between the presence of NAFLD, initial manifestations of atherosclerosis and insulin resistance was established. This resulted in the rank of prognostic factors based on severity of carotid artery changes, making it possible to conclude individual atherosclerotic risk score for AD and different forms of NAFLD. Conclusion. The results of the study require more profound examination of patients with NAFLD to evaluate both liver and cardiovascular diseases risk.

Pharmaco Penile Duplex Ultrasonography in the Evaluation of Erectile Dysfunction.

The National Institute of Health defined 'erectile dysfunction' as the persistent inability to achieve and/or to maintain an erection for a satisfactory sexual performance. In last few years, the concept of erectile dysfunction has evolved from that of a disorder referred to as 'impotence' which used to be considered predominantly psychogenic to that of 'Erectile Dysfunction' (ED), a well understood physiologic result of multiple risk factors, both psychological and organic. The most common cause of organic erectile dysfunction is vasculogenic causes. Doppler evaluation of cavernosal arteries after intracavernosal injection of Papaverine is particularly useful in the evaluation of vasculogenic causes. To define the role of intracavernosal injection of Papaverine in the evaluation of vasculogenic causes of erectile dysfunction that includes arterial insufficiency and veno occlusive nature. Pharmaco Penile Duplex Ultrasonography (PPDU) was done using a linear broadband phased array transducer (7-12 MHz) on a E-Saote MyLab 60 ultrasound colour Doppler system on 73 patients over a period of three years. Informed consent was taken from all patients. Visual grading score for erection, Cavernosal Artery Diameter (CAD), PSV (Peak Systolic Velocity), EDV (End Diastolic Velocity), RI (Resistive Index), AT (Acceleration Time) and dorsal vein changes were obtained in all patients following intracavernosal injection of Papaverine. Visual grading for erectile response was E0 in one patient, E1 in 11 patients, E2 in 9 patients, E3 in 7 patients, E4 in 4 patients and E5 in 41 patients. Eighteen patients were diagnosed as having arterial insufficiency, three patients were diagnosed as having venous insufficiency and two patients showed indeterminate results. In our study, Papaverine induced PPDU proved to be highly accurate and excellent method for assessing patients with erectile dysfunction.

A Fast Method to Calculate the Spatial Impulse Response for 1-D Linear Ultrasonic Phased Array Transducers.

A method is developed to accurately determine the spatial impulse response at the specifically discretized observation points in the radiated field of 1-D linear ultrasonic phased array transducers with great efficiency. In contrast, the previously adopted solutions only optimize the calculation procedure for a single rectangular transducer and required approximation considerations or nonlinear calculation. In this research, an algorithm that follows an alternative approach to expedite the calculation of the spatial impulse response of a rectangular linear array is presented. The key assumption for this algorithm is that the transducer apertures are identical and linearly distributed on an infinite rigid plane baffled with the same pitch. Two points in the observation field, which have the same position relative to two transducer apertures, share the same spatial impulse response that contributed from corresponding transducer, respectively. The observation field is discretized specifically to meet the relationship of equality. The analytical expressions of the proposed algorithm, based on the specific selection of the observation points, are derived to remove redundant calculations. In order to measure the proposed methodology, the simulation results obtained from the proposed method and the classical summation method are compared. The outcomes demonstrate that the proposed strategy can speed up the calculation procedure since it accelerates the speed-up ratio which relies upon the number of discrete points and the number of the array transducers. This development will be valuable in the development of advanced and faster linear ultrasonic phased array systems.

Reflection at a liquid–solid interface of a transient ultrasonic field radiated by a linear phased array transducer

In order to put in evidence the specular reflection and the non-specular reflection in the transient case, we have used a model for the study of the transient ultrasonic waves radiated by a linear phased array transducer in a liquid and reflected by a solid plane interface. This method is an extension of the angular spectrum method to the transient case where the reflection at the plane interface is taken into account by using the reflection coefficient for harmonic plane waves.The results obtained highlighted the different components of the ultrasonic field: the direct and edge waves as well as the longitudinal head waves or leaky Rayleigh waves. The transient representation of these waves have been carefully analyzed and discussed by the rays model. Instantaneous cartographies allowed a clear description of all the waves which appear at the liquid–solid interface.The obtained results have been compared to those obtained with a finite element method package.

Design and optimization of an OPFC ultrasonic linear phased array transducer

In contrast to piezoceramics, orthotropic piezoelectric fibre composites (OPFC) which can be used as actuator/sensor elements in damage detection show clear advantages because of their high sensitivity along the fibre direction and directivity. The focusing acoustic field distribution of the OPFC phased array transducer is analyzed by the finite element method together with directivity analysis in metallic materials. The optimal array parameters such as spacing, width and number of elements are obtained by studying the total displacement changes as various parameters change at the focus point. The feasibility of an OPFC ultrasonic phased array transducer for damage detection is validated.

Estimation of scatterer size and acoustic concentration in sound field produced by linear phased array transducer

Although there have been several quantitative ultrasound studies on the methods of estimation of scatterer size and acoustic concentration based on the analysis of RF signals for tissue characterization, some problems, e.g., narrow frequency bandwidths and complex sound fields, have limited the clinical applications of such methods. In this report, two types of ultrasound transducer are investigated for the estimation of the scatterer size and acoustic concentration in two glass bead phantoms of different weight concentrations of 0.25 and 2.50% and those in an excised pig liver. The diameters of the glass beads ranged from 5 to 63 µm with an average of 50 µm. The first transducer is a single element and the other is a linear phased array. A comparison of the estimations obtained using both transducers gives an insight into how these methods could be applied clinically. Results obtained using the two transducers were significantly different. One of the possible explanations is that beamforming could significantly affect the backscatter coefficient estimation, which was not taken into account.

Parameter Optimization of Linear Phased Array Transducer for Defect Detection

An optimization design method was proposed for linear phased array ultrasonic imaging testing. In the method, main lobe width and the amplitude ratio of side lobe to main lobe were served as optimization objectives to judge the test- ing precision of phased array beam directivity. The combination of element of width and inter-element space was served as optimize parameter for the optimization objectives. The combination of optimal parameters for phased array transducer was finally achieved and applied to phased array B-mode imaging ultrasonic testing on a flat bottom hole in standard test block. The results show that the method can not only obtained the optimal parameters for linear array of phased array transducer, but also improve the accuracy of the location and size for defect detection.