Needle Transducer Research Articles

Development of an arrayed ultrasonic sensor using surface plasmon resonance (SPR)

Surface plasmon resonance (SPR) ultrasonic sensors are non-resonant and expected to show flat frequency response over a wide frequency range. Then, the sensors seem suitable for the detection of photoacoustic waves. We have developed a simple glass prism SPR sensor with thin Ag layer (deposited by an electron beam evaporator) and checked the frequency response as a function of Ag area diameter. The diameter of 1 mm was sufficient to obtain better frequency response than that of the calibrated needle transducer in the range of 2.5 to 7.0 MHz. By covering a very thin Au film on the Ag layer, we succeeded in longer working time (>6 months) of the sensor. An array-type SPR sensor (5 × 5, diameter of each sensor 1 mm) has also been fabricated to evaluate pressure distribution of ultrasonic waves. The response of each sensor was similar, telling the high reproducibility of the sensor fabrication.

Modeling ultrasonic wave fields scattered by flaws using a quasi-Monte Carlo method: Theoretical method and experimental verification

The modeling and visualization of wave fields scattered by flaws can be helpful in terms of guiding the testing and evaluation of flaws using an ultrasonic nondestructive method. In this work, the ultrasonic scattering of wave fields from flaws with different shapes is modeled using a quasi-Monte Carlo (QMC) method and measured through experiments for verification. The incident wave fields generated by a transducer can be modeled using the Rayleigh integral expression and calculated using the QMC method. When the size of the flaw is much larger than the wavelength, the incident wave over the lit portion of flaw can be treated as the source for the scattering of wave fields, and these wave fields can also be modeled using the proposed QMC method. In this paper, water is treated as the material and an embedded solid component is considered as the flaw. Numerical examples and results are presented for flaws with different shapes and sizes, and the properties of these scattering wave fields are analyzed and discussed. Experiments are performed to measure the scattering wave fields using a needle transducer, and it is shown that the results agree with the simulations, thus verifying the proposed modeling method. The work presented here can assist in understanding the wave-flaw interaction and can help in optimizing ultrasonic nondestructive testing.

Design and Micro-Fabrication of Focused High-Frequency Needle Transducers for Medical Imaging.

In this study, we report an advanced fabrication technique to develop a miniature focused needle transducer. Two different types of high-frequency (100 MHz) transducers were fabricated using the lead magnesium niobate-lead titanate (PMN-0.3PT) and lithium niobate (LiNbO3) single crystals. In order to enhance the transducer’s performance, a unique mass–spring matching layer technique was adopted, in which gold and parylene play the roles of the mass layer and spring layer, respectively. The PMN-0.3PT transducer had a 103 MHz center frequency with a −6 dB bandwidth of 52%, and a signal-to-noise ratio (SNR) of 42 dB. The center frequency, −6 dB bandwidth, and SNR of the LiNbO3 transducer were 105 MHz, 66%, and 44 dB, respectively. In order to compare and evaluate the transducers’ performances, an ultrasonic biomicroscopy (UBM) imaging on the fish eye was performed. The results showed that the LiNbO3 transducer had a better contrast resolution compared to the PMN-0.3PT transducer. The fabricated transducer showed an excellent performance with high-resolution corneal epithelium imaging of the experimental fish eye. These interesting findings are useful for the future biomedical implementation of the fabricated transducers in the field of high-resolution ultrasound imaging and diagnosis purpose.

Role of Handedness in Conducting an Ultrasound-Guided Procedure: A Comparative Study

Objective: Sonography is widely used by clinicians to provide imaging assistance in guiding invasive procedures. Many sonography users tend to prefer their dominant hand to operate the needle and their nondominant hand on the ultrasound transducer. The aim was this study was to determine whether the dominant hand guiding the needle achieves a faster time to target during ultrasound-guided procedures compared with the nondominant hand. Materials and Methods: Forty novice sonography users, medical students, were randomized to participate in the study. Twenty medical students used a Sonosite® ultrasound equipment system and the other 20 used a Mindray® ultrasound equipment system. Following a video education training session, an informed consent was obtained from each participant. In each equipment group, participants were randomly allocated to either a right-handed needle and a left-handed transducer preference or a left-handed needle and right-handed transducer preference group. A total of ten participants were in each group. A timer was started when the ultrasound transducer came in contact with the phantom model and stopped when the needle reached the target. This simulated task was repeated ten times by the participants. The hand arrangement for the needle and transducer was then switched and the task repeated another ten times by each participant. Results: Handedness was observed over multiple attempts and “time to target” was recorded for groups with both hand preferences and varied ultrasound equipment systems. The most significant finding was that the difference in time was statistically significant between the groups, when comparing the first and fifth procedural attempts. Conclusion: In this novice group of users, despite training for ultrasound-guided procedures using phantom models, irrespective of the ultrasound equipment system, or hand preference, there was no difference in the time to target.

Ultrasonic elastography to assess biomechanical properties of the optic nerve head and peripapillary sclera of the eye

PurposeTo quantitatively investigate both optic nerve head (ONH) and peripapillary sclera (PPS) biomechanical properties of porcine eyes through an ultrasonic elastography imaging system in response to both increasing and decreasing intraocular pressure (IOP). MethodsThe Young’s modulus of the ONH and PPS were assessed using our high resolution ultrasonic imaging system which utilized a mechanical shaker to induce shear waves and an off-axis aligned 40 MHz needle transducer to track micron-level displacement along the direction of wave propagation. In this study, imaging on a total of 8 ex vivo porcine eyes preloaded with IOPs from 6 mmHg to 30 mmHg was performed. To have a better understanding of the effect of varying IOP on biomechanics, both increasing and decreasing IOPs were investigated. ResultsThe increase of the Young’s modulus of ONH (92.4 ± 13.9 kPa at 6 mmHg to 224.7 ± 71.1 kPa at 30 mmHg) and PPS (176.8 ± 14.3 kPa at 6 mmHg to 573.5 ± 64.4 kPa at 30 mmHg) following IOP elevation could be observed in the reconstructed Young’s modulus of the shear wave elasticity (SWE) imaging while the B-mode structural images remained almost unchanged. In addition, for the same IOP level, both ONH and PPS have a tendency to be stiffer with decreasing IOP as compared to increasing IOP. ConclusionsOur results demonstrate the feasibility of using our ultrasonic elastography system to investigate the stiffness mapping of posterior eye with high resolution in both increasing and decreasing IOPs, making this technique potentially useful for glaucoma.

A Soft Housing Needle Ultrasonic Transducer for Focal Stimulation to Small Animal Brain.

Conventional acoustic brain stimulators that transmit low frequency (< 1MHz) bursts in a pulse repetition frequency with large-sized transducers are barely compatible with small animal models because of broad beam width, possible stimulation of auditory pathways, and blocking of field-of-view for in vivo imaging of brain hemodynamics and neuronal activities. A miniaturized ultrasound stimulator with higher stimulation frequencies will enhance spatial specificity and enable simultaneous eliciting and monitoring brain activities. Moreover, the use of non-periodic pulse sequences may reduce unintended stimulations on auditory cortex, which might be caused by transmitting periodic bursting patterns. A platform for ultrasound brain stimulations for small animal models, including a soft housing 10MHz needle transducer with a beam size of 680μm, random transmission sequences, and optical imaging systems, was developed. The platform can deliver focal stimulations to the visual and barrel cortex of mice and monitor subsequent brain activities. The stimulated sites in both the visual and primary somatosensory cortices (S1) showed approximately two to three times higher neuronal calcium signal levels than those in peripheral regions. Activities in the auditory cortex were elicited by periodic sequence stimulation, while it was reduced by 67 and 35% for barrel and visual cortex stimulation with the random sequence, respectively.

Catheter-mounted dual-frequency ultrasound transducers for intravascular contrast-enhanced superharmonic imaging

Vulnerable atherosclerotic plaques are a source of morbidity and mortality and are hypothesized to be correlated with abnormal development of microvasculature in arterial walls. Thus, there is an interest in assessing microvascularity for the plaque diagnosis. However, conventional catheter-delivered, high-frequency (>20 MHz) intravascular ultrasound imaging is unable to resolve vasa vasorum microvessels. We present here the development of a custom dual-frequency transducer-tipped catheter for contrast-enhanced superharmonic imaging of plaque-associated microvasculature. We exploit our previous design of the miniaturized dual-element, stacked-type needle transducer. A 4/22 MHz dual-frequency transducer with a lateral dimension of 800 μm is assembled with a 70 cm-long drive shaft inside a 4 Fr-catheter. We designed a 4 MHz-transmitter element to generate moderate amplitude (>1 MPa peak-negative-pressure) pulses for bubble excitation. A confocally aligned 22 MHz-receiver element is designed to detect contrast generated superharmonics (>10 MHz) with substantial tissue rejection. We tested the catheter in a tissue-mimicking phantom simulating an arterial lumen with surrounding microvasculature. The in vitro imaging data were acquired through a rotational pull-back (2 mm) imaging procedure with microbubble infusion. The resulting superharmonic images display a clearly defined microvessel with an approximated contrast-to-tissue ratio of 12 dB and an axial resolution of 300 μm.Vulnerable atherosclerotic plaques are a source of morbidity and mortality and are hypothesized to be correlated with abnormal development of microvasculature in arterial walls. Thus, there is an interest in assessing microvascularity for the plaque diagnosis. However, conventional catheter-delivered, high-frequency (>20 MHz) intravascular ultrasound imaging is unable to resolve vasa vasorum microvessels. We present here the development of a custom dual-frequency transducer-tipped catheter for contrast-enhanced superharmonic imaging of plaque-associated microvasculature. We exploit our previous design of the miniaturized dual-element, stacked-type needle transducer. A 4/22 MHz dual-frequency transducer with a lateral dimension of 800 μm is assembled with a 70 cm-long drive shaft inside a 4 Fr-catheter. We designed a 4 MHz-transmitter element to generate moderate amplitude (>1 MPa peak-negative-pressure) pulses for bubble excitation. A confocally aligned 22 MHz-receiver element is designed to detect contra...

Development of Multi-Layer Lateral-Mode Ultrasound Needle Transducer for Brain Stimulation in Mice.

Ultrasound, a non-invasive stimulation method, has proved effective in neurostimulation. Previous studies have demonstrated that low-frequency ultrasound (less than 1 MHz) is preferable owing to better penetrability through tissue and skull. However, the large size of low-frequency transducers, which are used in ultrasound neurostimulation studies, makes it difficult to perform multiple-target neurostimulation, especially in small animals such as mice. In this paper, a proposed low-frequency ultrasound needle transducer based on the multi-layer lateral-mode coupling method with a miniature aperture of 0.6 mm × 0.6 mm and a thickness of 1.65 mm was designed and fabricated. The measured electrical impedance of the fabricated 8-layer lateral-mode PZT-5H ceramic was 50.76 Ω at a resonant frequency of 866 kHz. The -6 dB bandwidth of 8-layer lateral-mode transducer was 29% at a center frequency of 876 kHz. The maximum ultrasound peak pressure amplitude at 820 kHz reached approximately 300 kPa, 4-5 times higher than that of the single-layer thickness-mode transducer with 200 V input voltage. The ultrasound beam showed no attenuation and low shift through mouse skull. To verify the feasibility of using the needle transducer to perform multiple-target nerve stimulation in mice brains, we constructed an ultrasound stimulus system to simultaneously stimulate two areas (M2 and V1) of the mouse brain in vivo and detected the c-Fos expression by immunofluorescence to evaluate the effect of stimulation. The results showed that a high ultrasound peak pressure amplitude with this transducer configuration is useful for ultrasound neurostimulation and multiple-target stimulation in mice.

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.

Ultrasonic Microelastography to Assess Biomechanical Properties of the Cornea.

To both qualitatively and quantitatively investigate corneal biomechanical properties through an ultrasonic microelastography imaging system, which is potentially useful in the diagnosis of diseases, such as keratoconus, postrefractive keratectasia, and tracking treatment such as cross-linking surgery. Our imaging system has a dual-frequency configuration, including a 4.5MHz ring transducer to push the tissue and a confocally aligned 40MHz needle transducer to track micron-level displacement. Two-dimensional/three-dimensional acoustic radiation force impulse (ARFI) imaging and Young's modulus in the region of interest were performed on ex vivo porcine corneas that were either cross-linked using formalin solution or preloaded with intraocular pressure (IOPs) from 5 to 30mmHg. The increase of corneal stiffness and the change in cross-linked volume following formalin crosslinking could be precisely observed in the ARFI images and reflected by the reconstructed Young's modulus while the B-mode structural images remained almost unchanged. In addition, the relationship between the stiffness of the cornea and IOPs was investigated among 12 porcine corneas. The corneal stiffness is significantly different at various IOPs and has a tendency to become stiffer with increasing IOP. Our results demonstrate the principle of using ultrasonic microelastography techniques to image the biomechanical properties of the cornea. Integrating high-resolution ARFI imaging labeled with reconstructed Young's modulus and structural imaging of the cornea can potentially lead to a routinely performed imaging modality in the field of ophthalmology.

Quantitative Assessment of Thin-Layer Tissue Viscoelastic Properties Using Ultrasonic Micro-Elastography With Lamb Wave Model.

Characterizing the viscoelastic properties of thin-layer tissues with micro-level thickness has long remained challenging. Recently, several micro-elastography techniques have been developed to improve the spatial resolution. However, most of these techniques have not considered the medium boundary conditions when evaluating the viscoelastic properties of thin-layer tissues such as arteries and corneas; this might lead to estimation bias or errors. This paper aims to integrate the Lamb wave model with our previously developed ultrasonic micro-elastography imaging system for obtaining accurate viscoelastic properties in thin-layer tissues. A 4.5-MHz ring transducer was used to generate an acoustic radiation force for inducing tissue displacements to produce guided wave, and the wave propagation was detected using a confocally aligned 40-MHz needle transducer. The phase velocity and attenuation were obtained from k-space by both the impulse and the harmonic methods. The measured phase velocity was fit using the Lamb wave model with the Kelvin-Voigt model. Phantom experiments were conducted using 7% and 12% gelatin and 1.5% agar phantoms with different thicknesses (2, 3, and 4 mm). Biological experiments were performed on porcine cornea and rabbit carotid artery ex vivo. Thin-layer phantoms with different thicknesses were confirmed to have the same elasticity; this was consistent with the estimates of bulk phantoms from mechanical tests and the shear wave rheological model. The trend of the measured attenuations was also confirmed with the viscosity results obtained using the Lamb wave model. Through the impulse and harmonic methods, the shear viscoelasticity values were estimated to be 8.2 kPa for $0.9~\text {Pa}{\cdot} \text {s}$ and 9.6 kPa for $0.8~\text {Pa}{\cdot} \text {s}$ in the cornea and 27.9 kPa for $0.1~\text {Pa}\cdot \text {s}$ and 26.5 kPa for $0.1~\text {Pa}\cdot \text {s}$ in the artery.

High-Performance Ultrasound Needle Transducer Based on Modified PMN-PT Ceramic With Ultrahigh Clamped Dielectric Permittivity.

A modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) polycrystalline ceramic with ultrahigh relative clamped dielectric permittivity ( ) and high piezoelectric properties ( pC/N, ) was used to fabricate high-frequency miniature ultrasound transducers. A 39-MHz high-frequency ultrasound needle transducer with a miniature aperture of 0.4 mm mm was designed and successfully characterized. The fabricated needle transducer had an electromechanical coupling factor of 0.55, large bandwidth of 80% at -6 dB, and low insertion loss of -13 dB. A wire phantom and porcine eyeball imaging study showed good imaging capability of this needle transducer. The transducer performance was found to be superior to that of other needle transducers with miniature apertures, making this modified PMN-PT ceramic-based needle transducer quite promising for minimally invasive procedures in medical applications.

Electrical impedance matching networks based on filter structures for high frequency ultrasound transducers

An electrical impedance matching (EIM) network is proposed to achieve the broad bandwidth of a high frequency ultrasound transducer and to improve the signal-to-noise ratio (SNR) of an ultrasound image. The proposed EIM network is based on a general filter structure, i.e., either low-pass filter (LPF) or high-pass filter (HPF) structure composing a capacitor and an inductor. Either filter type can be selected depending on the spectral characteristics of a transducer. The prominent advantage of the proposed method is the capability to broaden the spectrum of a transducer by means of modifying its original spectrum. The values of the electronic components are computed with the measured electrical impedances of a transducer and an imaging system. In this paper, the EIM between a custom-made 50MHz ultrasound needle transducer and a commercial pulser/receiver system was conducted to verify the characteristics and performance of the proposed method. The experimental results demonstrated that the proposed EIM network is capable of achieving the best performance of the transducer, i.e., broad bandwidth and high SNR that are desirable for the high quality of high frequency ultrasound images.

AIUM Practice Parameter for the Performance of Selected Ultrasound‐Guided Procedures

AIUM Practice Parameter for the Performance of Selected Ultrasound‐Guided Procedures

AIUM Practice Parameter for the Performance of Selected Ultrasound-Guided Procedures

AIUM Practice Parameter for the Performance of Selected Ultrasound-Guided Procedures

Dual Orientation 16-MHz Single-Element Ultrasound Needle Transducers for Image-Guided Neurosurgical Intervention.

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue through the incorporation of an ultrasound device within the type of biopsy needles commonly used as an interventional tool to provide immediate feedback to neurosurgeons during surgical procedures. To identify the most appropriate path to access a targeted tissue site, single-element transducers that look either forward or sideways have been designed and fabricated. Micromolded 1-3 piezocomposites were adopted as the active materials for feasibility tests and epoxy lenses have been applied to focus the ultrasound beam. Electrical impedance analysis, pulse-echo testing, and wire phantom scanning have been carried out, demonstrating the functionality of the needle transducers at [Formula: see text]. The capabilities of these transducers for intraoperative image guidance were demonstrated by imaging within soft-embalmed cadaveric human brain and fresh porcine brain.

Dual-element needle transducer for intravascular ultrasound imaging.

A dual-element needle transducer for intravascular ultrasound imaging has been developed. A low-frequency element and a high-frequency element were integrated into one device to obtain images which conveyed both low- and high-frequency information from a single scan. The low-frequency element with a center frequency of 48MHz was fabricated from the single crystal form of lead magnesium niobate-lead titanate solid solution with two matching layers (MLs) and the high frequency element with a center frequency of 152MHz was fabricated from lithium niobate with one ML. The measured axial and lateral resolutions were 27 and [Formula: see text], respectively, for the low-frequency element, and 14 and [Formula: see text], respectively, for the high-frequency element. The performance of the dual-element needle transducer was validated by imaging a tissue-mimicking phantom with lesion-mimicking area, and ex vivo rabbit aortas in water and rabbit whole blood. The results suggest that a low-frequency element effectively provides depth resolved images of the whole vessel and its adjacent tissue, and a high-frequency element visualizes detailed structure near the surface of the lumen wall in the presence of blood within the lumen. The advantages of a dual-element approach for intravascular imaging are also discussed.

New KNN-based lead-free piezoelectric ceramic for high-frequency ultrasound transducer applications

Based on new KNN-based piezoelectric material 0.96(K0.48Na0.52)(Nb0.95Sb0.05)O3–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 with a giant d33 of 490, a 37-MHz high-frequency ultrasound needle transducer with the aperture size of 1 mm was successfully fabricated. The obtained transducer had a high electromechanical coupling factor kt of 0.55, a good bandwidth of 56.8 % at −6 dB, and a low insertion loss of −16 dB at the central frequency. Its excellent performance is comparable to lead-containing transducer and is superior to that of any other lead-free transducer. This promising result demonstrates that this new KNN-based lead-free piezoelectric ceramic is a good candidate to replace lead-based materials for high-frequency ultrasound imaging.

High-resolution harmonic motion imaging (HR-HMI) for tissue biomechanical property characterization.

Elastography, capable of mapping the biomechanical properties of biological tissues, serves as a useful technique for clinicians to perform disease diagnosis and determine stages of many diseases. Many acoustic radiation force (ARF) based elastography, including acoustic radiation force impulse (ARFI) imaging and harmonic motion imaging (HMI), have been developed to remotely assess the elastic properties of tissues. However, due to the lower operating frequencies of these approaches, their spatial resolutions are insufficient for revealing stiffness distribution on small scale applications, such as cancerous tumor margin detection, atherosclerotic plaque composition analysis and ophthalmologic tissue characterization. Though recently developed ARF-based optical coherence elastography (OCE) methods open a new window for the high resolution elastography, shallow imaging depths significantly limit their usefulness in clinics. The aim of this study is to develop a high-resolution HMI method to assess the tissue biomechanical properties with acceptable field of view (FOV) using a 4 MHz ring transducer for efficient excitation and a 40 MHz needle transducer for accurate detection. Under precise alignment of two confocal transducers, the high-resolution HMI system has a lateral resolution of 314 µm and an axial resolution of 147 µm with an effective FOV of 2 mm in depth. The performance of this high resolution imaging system was validated on the agar-based tissue mimicking phantoms with different stiffness distributions. These data demonstrated the imaging system's improved resolution and sensitivity on differentiating materials with varying stiffness. In addition, ex vivo imaging of a human atherosclerosis coronary artery demonstrated the capability of high resolution HMI in identifying layer-specific structures and characterizing atherosclerotic plaques based on their stiffness differences. All together high resolution HMI appears to be a promising ultrasound-only technology for characterizing tissue biomechanical properties at the microstructural level to improve the image-based diseases diagnosis in multiple clinical applications.

Implementation of a rotational ultrasound biomicroscopy system equipped with a high-frequency angled needle transducer--ex vivo ultrasound imaging of porcine ocular posterior tissues.

The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled needle transducer is designed and implemented in order to minimize the space required. It was applied to ex vivo ultrasound imaging of porcine posterior ocular tissues through a minimal incision hole of 1 mm in diameter. The retina and sclera for the one eye were visualized in the relative rotating angle range of 270° ∼ 330° and at a distance range of 6 ∼ 7 mm, whereas the tissues of the other eye were observed in relative angle range of 160° ∼ 220° and at a distance range of 7.5 ∼ 9 mm. The layer between retina and sclera seemed to be bent because the distance between the transducer tip and the layer was varied while the transducer was rotated. Certin features of the rotation system such as the optimal scanning angle, step angle and data length need to be improved for ensure higher accuracy and precision. Moreover, the focal length should be considered for the image quality. This implementation represents the first report of a rotational scanning UBM system.