High Frequency Ultrasonic Imaging Research Articles

A Study of Mechanical Scanning High-frequency Ultrasonic Color Flow Imaging

Abstract High-frequency Ultrasonic imaging can promote high-resolution images and detailed diagnostic information, which has great clinical application prospects. However, due to the difficulty and high cost of high-frequency multi-channel ultrasound systems and multi-array element transducers, it is not conducive to popularization. Mechanical scanning high-frequency ultrasound imaging system is an alternative and low-cost method. However, current mechanical scanning systems cannot perform ultrasound flow imaging, and hemodynamic information is clinically important. Therefore, an improved high-frequency, miniaturized mechanical scanning system for color flow imaging was designed and developed. The system uses a crank linkage structure to drive a miniature transducer with a center frequency of 12 MHz for reciprocating scanning imaging within a range of 15 mm. By optimizing the clutter filter and dynamic domain flow imaging process, two methods are realized: real-time rapid ultrasound imaging and highly sensitive ultrasound flow imaging. The two optimized methods used power Doppler and color flow Doppler for flow phantom imaging, and the final measured blood flow error was less than 5%, which indicates that the mechanical scanning high-frequency ultrasonic color flow imaging system has a good application prospect.

The Application of High-frequency Ultrasonic Imaging in Identifying Fillers in the Temporal Region.

This study aimed to evaluate the ultrasonic manifestations of diversified corium fillers in the temporal region and to provide clinicians with suggestions for diagnosis and treatment. The facial ultrasound images of 116 patients, including 110 women and six men, 20-61years of age, were analyzed at the Chinese Academy Medical Sciences and Peking Union Medical College from November 2014 to November 2021. We identified 48 cases of polyacrylamide, 31 cases of fat, 27 cases of hyaluronic acid, seven cases of hydroxyapatite, two cases of silicone oil, and one case of prosthesis. Polyacrylamide mainly showed irregular flocculent hypoechoic or fine punctate hypoechoic in ultrasound; it could be aggregated as a cystic hypoechoic area or diffused in the tissue space, and the probe could be pressurized to see the echo floating or dislocation flow. Fat mainly showed lobulated hypoechoic deposition with some hyperechoic linear intervals. Hyaluronic acid mainly showed an anechoic structure with a clear boundary, uniform internal echo, and no obvious blood flow signal. If diffused in the surrounding tissues, it was mainly characterized by anechoic or low-echo areas in the stratified tissues. Hydroxyapatite mainly showed strongly hyperechoic patch areas with posterior acoustic shadowing artifacts. Silicone oil was mostly found under the epidermis, showing a high echo in the form of clouds and causing unclear displays of deep tissue. Prosthesis showed hypoechoic prosthesis structure. High-frequency ultrasound had a certain significance in the identification of the fillers of the temporal region.

Echo Signal Receiving and Data Conversion Integrated Circuits for Portable High-Frequency Ultrasonic Imaging System.

Ultrasonic imaging has become a very promising technology, and it has been widely applied in biomedicine, geology, and other fields due to its advantages of safety, nondamaging, and real time. Especially, the portable high-frequency (>20 MHz) ultrasonic imaging system (UIS) has been generally used in biomedical detection and diagnosis. In the complex actual environment, the effect of integrated circuits (ICs) on the performance of portable high-frequency UIS is obvious. In the echo signal transmission link, the analog front end (AFE) and the analog-to-digital converter (ADC) are the two most critical modules, where AFE is used to receive and preprocess the analog ultrasonic echo signals and ADC to convert the analog signals from the AFE output to digital. The structure and performance of the ICs integrated into terminal equipment and in-probe for the portable high-frequency UIS are introduced and discussed. Some typical commercial ICs are also summarized. Based on the requirements and challenges of portable high-frequency UIS, the future development directions of ICs mainly include high integration, ultralow power consumption, high speed, and high precision, which can provide valuable reference and advice for the design of AFE and ADC for portable high-frequency UIS.

Research on Golay-coded excitation in real-time imaging of high frequency ultrasound biomicroscopy

High frequency ultrasonic imaging provides clinicians with high-resolution diagnostic images and more accurate measurement results. The technique is now widely used in ophthalmology, dermatology, and small animal imaging. However, since ultrasonic attenuation in tissue increases rapidly with increasing frequency, the depth of detection of high frequency ultrasound in tissue is limited to a few millimeters. In this paper, a novel method of using Golay-coded excitation as a replacement for conventional single-pulse excitation in high frequency ultrasound biomicroscopy was proposed, and real-time imaging was realized. While maintaining the transmission voltage and image resolution unchanged, the detection depth can be effectively improved. The ultrasonic transmission frequency is 30 MHz and the transmission voltage is ± 60 V p-p. In this study, 4-bit, 8-bit, and 16-bit coding sequences and decoding compression were used. To verify the effectiveness of the coding sequence in real-time imaging of ultrasound biomicroscopy, we designed a 10-μm diameter line target echo experiment, an ultrasound phantom experiment, and an in vitro porcine eye experiment. The experimental results show that the code/decode method of signal processing can not only maintain a resolution consistent with that of single-pulse transmission, but can also improve the detection depth and signal-to-noise ratio.

Ultrasonic monitoring of early development of lower vertebrate embryos

In this paper, the scanning acoustic microscope is used for visualization of the lower vertebrate embryos in vivo. Compared to optical methods, high frequency ultrasonic imaging has a negligible effect on a developing organism, and chemical treatment of biological object is not required due to the high contrast of acoustic images and the deep penetration of ultrasound. A technique for continuous ultrasonic observation of a living embryo that grows in the immersion cell of the acoustic microscope is proposed and developed. Using this technique, it is possible to image the internal organs of the embryo, visualize the motion of the structural elements and estimate their velocity. The loach embryo (Misgurnus fossilis) at 11-12 stages of development was studied using the experimental setup based on the 50 MHz scanning acoustic microscope. The ultrasonic images of the yolk and blastula, animation of cell division and motion in the syncytial region and estimation of the velocity of the structural elements of the embryo were obtained by the developed method.

Size Effect Study on High Frequency Transducers for Sensitivity Enhancement

In a high frequency ultrasonic imaging system, high signal-noise-ratio (SNR) is highly demanded to acquire high quality images. Transducer sensitivity enhancement is essential to increase the SNR. In this work, size effect of transducers with working frequency 12MHz and 20MHz is systematically studied to find its relationship with sensitivity. FEM (Finite Element Method) models are built to analyze the impedance and sound field characteristics for different size transducers. Pulse-echo measurement experiments are carried out to compare the performance variation induced by the size effect. Simulation results suggest that working frequency is mainly determined by the piezoelectric slice thickness, the values of admittance are dependent on the area value of transducers and the optimum width is 1.5mm-1.7mm for 12MHz transducer and 1.1mm-1.3mm for 20MHz transducer. The admittance measurement results and pulse-echo results confirm the simulation conclusion and certify that 12MHz transducer with 1.5mm width and 3.0mm length, 20MHz transducer with 1.2mm width and 3.0mm length have the highest sensitivities. Their echo peak-peak values can reach 1.248V and 1.332V, respectively. These results indicate that sensitivity can be enhanced by optimizing transducer size. Methods utilized in this work are of great significance in a broader range of transducer design cases such as IVUS system and array transducers.

Eco-Friendly Highly Sensitive Transducers Based on a New KNN-NTK-FM Lead-Free Piezoelectric Ceramic for High-Frequency Biomedical Ultrasonic Imaging Applications.

High-frequency ultrasonic imaging with improved spatial resolution has gained increasing attention in the field of biomedical imaging. Sensitivity of transducers plays a pivotal role in determining ultrasonic image quality. Conventional ultrasonic transducers are mostly made from lead-based piezoelectric materials that may be harmful to the human body and the environment. In this study, a new (K,Na)NbO3-KTiNbO5-BaZrO3-Fe2O3-MgO (KNN-NTK-FM) lead-free piezoelectric ceramic was utilized in developing eco-friendly transducers for high-frequency biomedical ultrasonic imaging applications. A needle transducer with a small active aperture size of 0.45 × 0.55 mm2 was designed and evaluated. The fabricated transducer exhibits great performance with a high center frequency (52.6 MHz), a good electromechanical coupling (keff ∼ 0.45), a large bandwidth (64.4% at -6 dB), and a very low two-way insertion loss (10.1dB). Such high sensitivity is superior to those transducers based on other lead-free piezoelectric materials and can even be comparable to the lead-based ones. Imaging performance of the KNN-NTK-FM needle transducer was analyzed by imaging a wire phantom and an agar tissue-mimicking phantom. Imaging capabilities of the transducer were further demonstrated by ex vivo imaging studies on a porcine eyeball and a rabbit aorta. The results suggest that the KNN-NTK-FM piezoceramic has many attractive properties over other lead-free piezoelectric materials in developing eco-friendly highly sensitive transducers for high-frequency biomedical ultrasonic imaging applications.

High-Frequency Ultrasonic Imaging with Lead-free (Na,K)(Nb,Ta)O3 Single Crystal.

Lead-free (Na,K)(Nb,Ta)O3 (KNNT) piezoelectric single crystal has been successfully grown using the top-seeded solution growth technique. The electromechanical coupling factors are very high ( k33 = 0.827, kt = 0.646), and the dielectric loss tangent is as low as 0.004. Acoustic impedance was calculated to be 26.5 MRayl. From the single crystal, a single element transducer was fabricated. The transducer achieved a 57.6% -6 dB bandwidth and 32.3 µm axial resolution at the center frequency of 45.4 MHz, which can identify the cornea of porcine eyeball with high resolution. Comparison between KNNT single crystal and lead-based single crystal was discussed. The results suggest that this single crystal transducer is an excellent candidate to replace lead-containing transducer for high-frequency ultrasonic imaging applications.

High-Frequency Ultrasonic Imaging of Growth and Development in Manufactured Engineered Oral Mucosal Tissue Surfaces

This study uses high-resolution ultrasound to examine the growth and development of engineered oral mucosal tissues manufactured under aseptic conditions. The specimens are a commercially available natural tissue scaffold, AlloDerm, and oral keratinocytes seeded onto AlloDerm to form an ex vivo-produced oral mucosal equivalent (EVPOME) suitable for intra-oral grafting. The seeded cells produce a keratinized protective upper layer that smooths out any remaining surface irregularities on the underlying AlloDerm. Two-dimensional acoustic imaging of unseeded AlloDerm and developing EVPOMEs was performed on each day of their growth and development, each tissue specimen being imaged under aseptic conditions (total time from seeding to maturation: 11 d). Ultrasonic monitoring offers us the ability to determine the constituents of the EVPOME that are responsible for changes in its mechanical behavior during the manufacturing process. Ultrasonic monitoring affords us an opportunity to non-invasively assess, in real time, tissue-engineered constructs before release for use in patient care.

(Invited) CMUT Based Microscale Integrated Ultrasound Systems for Minimally Invasive Intracardiac and Intravascular Imaging

High frequency ultrasonic imaging devices are widely used in minimally invasive catheter-based interventions especially in intravascular imaging, but there is still a need for more flexible devices with true 3-D volumetric imaging capability in front of the catheter tip. Single chip capacitive micromachined ultrasonic transducer (CMUT) arrays with on-chip CMOS electronics implementation provides great flexibility in designing array geometry and integrated front-end electronics. We have successfully implemented dual ring CMUT arrays for forward-looking intravascular ultrasound (IVUS) and intracardiac echography (ICE) imaging which provide 3-D volumetric imaging functionality. In this paper, we report on the details of the single-chip microscale imaging system and experimental results. We also discuss system improvements with initial experimental results.

High frequency ultrasonic imaging using thermal mechanical noise recorded on capacitive micromachined transducer arrays

The cross-correlation of diffuse thermal-mechanical noise recorded by two sensors yields an estimate of the ultrasonic waves propagating between them. We used this approach at high frequencies (1-30 MHz) on a capacitive micromachined ultrasonic transducer (CMUT) ring array (d = 725 μm), monolithically integrated with low noise complementary metal oxide semiconductor electronics. The thermal-mechanical noise cross-correlations between the CMUT array elements in immersion reveal both evanescent surface waves (below 10 MHz) and waves propagating primarily in the fluid (above 10 MHz). These propagating waves may allow passive imaging of scatterers closer to the array as compared to conventional pulse-echo systems, providing potentially higher resolution.

Intrinsic effect of Mn doping in PZN–12%PT single crystals

In this work we study the influence of manganese doping on the electromechanical properties of PZN–12%PT single crystal. The full electromechanical tensor of doped PZN–12%PT in the tetragonal single domain state is determined by the resonance-antiresonance method. Doping leads to a decrease in the dielectric transverse permittivity ε11T and of the shear piezoelectric coefficient d15. We show by dielectric constant ε33T measurements that the single domain state in doped crystal is stable in plates as thin as 90 μm, whereas it was unstable in plates thinner than 300 μm for the undoped crystals. This intrinsic effect is discussed by using a volume effect model based on the symmetry conforming principle of point defects. [Ren, Nature Mater. 3, 91 (2004)]. Mn doping forces the stability of PZN–12%PT single domain state, which makes the doped crystal a most suitable candidate than the pure crystal for high frequency ultrasonic medical imaging probe.

TU-D-210A-04: Development of High Frequency Ultrasound Transducers for Medical Imaging

Ultrasonic imaging is one of the most important and still growing diagnostic tools today. Ultrasonic imaging is more appealing as a clinical imaging modality compared to such imaging modalities as magnetic resonance imaging(MRI), nuclear imaging, and x‐ray computed tomography(CT) in that it is more cost‐effective, non‐invasive, capable of real‐time operation, and portable while providing images of comparable quality and resolution. State‐of‐the‐art ultrasonic scanners offer real‐time gray scale images of anatomical detail with millimeter spatial resolution superimposed on which is a map of Doppler blood flow information displayed in color. Clinical applications of these devices are still expanding and the operating frequencies of these devices seem to inch higher and higher. High frequency (HF) ultrasound (>20 MHz) yields improved spatial resolution at the expense of a shallower depth of penetration. There are a number of clinical problems that may benefit from high frequency ultrasonic imaging. Intravascular imaging with probes mounted on catheter tips at frequencies higher than 20 MHz with the highest frequency being 60 MHz has been used to characterize atherosclerotic plaque and to guide stent placement and angioplastic procedures. The medical efficacy of ultrasonic imaging of anterior segments of the eye at frequencies higher than 50 MHz in diagnosing glaucoma and ocular tumors and in assisting refractive surgery has been demonstrated. Applications in dermatology for defining tumor involvement and for monitoring treatment, in vascular surgery for characterizing atherosclerotic plaques, and in small animal imaging are also being investigated. To further expand the role of HF ultrasound, probe performance must be improved since current HF ultrasound imaging devices, dubbed “ultrasound biomicroscopes” or “UBMs” by a number of investigators use mechanically scanned single element transducers. Compared to electronic scanning with linear arrays, mechanical scanning of a single element transducer has three major drawbacks: poorer resolution, slower frame rate, and motion of the probe. Single element transducers can only produce beams with a fixed focus which means the spatial resolution of the device is best only within the depth of focus, i.e., in a very tight zone and degrades rapidly beyond the focal point. Mechanical motion of the transducer limits the frame rate, is unreliable, and may cause discomfort and, at worst, hazard to the patient. My presentation will introduce several HF ultrasound transducers currently being developed by the NIH Transducer Resource Center at the University of California. Emphasis will be placed on the construction and implementation of high frequency array transducers. Learning Objectives: 1. Familiarize audience with high frequency ultrasound transducers and their applications.

High-Frequency Ultrasonic Imaging of the Anterior Segment Using an Annular Array Transducer

Very high-frequency ultrasound (VHFU; >35 megahertz [MHz]) allows imaging of anterior segment structures of the eye with a resolution of less than 40 microm. The low focal ratio of VHFU transducers, however, results in a depth of field (DOF) of less than 1 mm. The aim was to develop a high-frequency annular array transducer for ocular imaging with improved DOF, sensitivity, and resolution compared with conventional transducers. Experimental study. Cadaver eyes, ex vivo cow eyes, in vivo rabbit eyes. A spherically curved annular array ultrasound transducer was fabricated. The array consisted of 5 concentric rings of equal area, had an overall aperture of 6 mm, and a geometric focus of 12 mm. The nominal center frequency of all array elements was 40 MHz. An experimental system was designed in which a single array element was pulsed and echo data were recorded from all elements. By sequentially pulsing each element, echo data were acquired for all 25 transmit-and-receive annuli combinations. The echo data then were focused synthetically and composite images were produced. Transducer operation was tested by scanning a test object consisting of a series of 25-microm diameter wires spaced at increasing range from the transducer. Imaging capabilities of the annular array were demonstrated in ex vivo bovine, in vivo rabbit, and human cadaver eyes. Depth of field, resolution, and sensitivity. The wire scans verified the operation of the array and demonstrated a 6.0-mm DOF, compared with the 1.0-mm DOF of a conventional single-element transducer of comparable frequency, aperture, and focal length. B-mode images of ex vivo bovine, in vivo rabbit, and cadaver eyes showed that although the single-element transducer had high sensitivity and resolution within 1 to 2 mm of its focus, the array with synthetic focusing maintained this quality over a 6-mm DOF. An annular array for high-resolution ocular imaging has been demonstrated. This technology offers improved DOF, sensitivity, and lateral resolution compared with single-element fixed focus transducers currently used for VHFU imaging of the eye.

High-frequency ultrasonic imaging: A spatio-temporal approach of rheology

We describe how high-frequency ultrasound can be used to measure and follow velocity profiles in complex fluids sheared in the Couette geometry with a 0.5–1 mm gap. The technique provides a spatial resolution of 40 μ m and velocity profiles can be recorded every second typically. Such ultrasonic velocimetry is coupled to a standard rheometer. The resulting “ultrasonic rheo-velocimeter” is tested on various complex fluids that display both inhomogeneous velocity profiles and temporal fluctuations close to a shear-induced transition: a lamellar phase, a triblock copolymer, a concentrated emulsion, and an organogel.

High Frequency Ultrasonic Imaging: System Design and Performance Optimization

High Frequency Ultrasonic Imaging: System Design and Performance Optimization

Boundary element simulation of backscattering properties for red blood with high frequency ultrasonic transducers

High frequency ultrasonic imaging (e.g. >30 MHz) from blood is difficult due to its tenuous backscattered pressure and the interference from adjacent tissues as well. To increase the sensitivity focused transducer has to be used, thus raising the complexity of interpreting the received signals. A numerical simulation of the ultrasonic scattering property from erythrocyte and rouleaux based on boundary element method was performed with experimental results based on a modified substitution method. The results (proportional relationship between backscattered pressure and frequency and the frequency limit for Rayleigh scattering) closely coincide with experimental data for erythrocyte. Rouleaux model results also show the dependence of degree of red cell aggregation on backscattering properties. The boundary element method serves as a good means to calculate the acoustic scattering from blood cells under arbitrary incident waves.

Miniature high frequency focused ultrasonic transducers for minimally invasive imaging procedures

Abstract Spherically focused, high frequency (30–50 MHz) ultrasonic imaging transducers are fabricated using poly(vinylidene) difluoride (PVDF) film and a membrane deflection technique that is compatible with CMOS microelectronics fabrication. Micromachined ultrasonic transducers with 0.75–2.00 mm-diameter apertures and f-numbers of 1.30–2.45 are fabricated and characterized. The transducers exhibit focused radiation patterns with 50 μm axial resolution and 51–92 μm lateral resolution and bandwidths of 80–110% around center frequency values. A miniature preamplifier hybrid circuit, which is designed to be mounted within the transducer housing, is fabricated and characterized to reveal a low noise level of 5.3 nV / H z . Tissue imaging capabilities of the micromachined ultrasonic transducers are demonstrated through successful imaging of human cadaveric aorta.

Clinical applications of acoustical microscopy

Very high frequency ultrasonic imaging offers an important tool for biomedical research as well as for clinical practice. Using ultrasound systems operating between 20 and 200 MHz, morphological and functional images of the skin may be obtained. For example, ultrasound may be used to assess wound healing, determine the extent of skin tumors, measure skin thickness, and visualize skin vascularization. At higher frequencies (600 to 1000 MHz), ultrasonic imaging can be used for histological studies with far greater sensitivity than optical microscopy and with a spatial resolution equivalent to optical methods. For example, ultrasound may be used to evaluate biopsy specimens more quickly and more accurately than optical microscopy. Here we report our experiences with very high frequency ultrasound as a clinical tool and, using this technology, the development of new standards by which tissue changes and disease processes may be defined.

High frequency optoacoustic arrays using etalon detection

Two-dimensional phased arrays for high frequency (>30 MHz) ultrasonic imaging are difficult to construct using conventional piezoelectric technology. A promising alternative involves optical detection of ultrasound, where the array element size is defined by the focal spot of a laser beam. Element size and spacing on the order of a few microns are easily achieved, suitable for imaging at frequencies exceeding 100 MHz. We have previously shown images made from a receive-only, two-dimensional optoacoustic array operating at 10 to 50 MHz. The main drawback of optical detection has been poor sensitivity when compared with piezoelectric detection. In this paper, we explore a different form of optical detection demonstrating improved sensitivity and offering a potentially simple method for constructing two-dimensional arrays. Results from a simple experiment using an etalon sensor confirm that the sensitivity of etalon detection is comparable with piezoelectric detection. This paper concludes with a proposal for a high frequency optoacoustic array system using an etalon.