Medical Ultrasound Fields Research Articles

Super-resolution reconstruction of ultrasound image using a modified diffusion model

Objective. This study aims to perform super-resolution (SR) reconstruction of ultrasound images using a modified diffusion model, designated as the diffusion model for ultrasound image super-resolution (DMUISR). SR involves converting low-resolution images to high-resolution ones, and the proposed model is designed to enhance the suitability of diffusion models for this task in the context of ultrasound imaging. Approach. DMUISR incorporates a multi-layer self-attention (MLSA) mechanism and a wavelet-transform based low-resolution image (WTLR) encoder to enhance its suitability for ultrasound image SR tasks. The model takes interpolated and magnified images as input and outputs high-quality, detailed SR images. The study utilized 1,334 ultrasound images from the public fetal head-circumference dataset (HC18) for evaluation. Main results. Experiments were conducted at 2× , 4× , and 8× magnification factors. DMUISR outperformed mainstream ultrasound SR methods (Bicubic, VDSR, DECUSR, DRCN, REDNet, SRGAN) across all scales, providing high-quality images with clear structures and rich detailed textures in both hard and soft tissue regions. DMUISR successfully accomplished multiscale SR reconstruction while suppressing over-smoothing and mode collapse problems. Quantitative results showed that DMUISR achieved the best performance in terms of learned perceptual image patch similarity, with a significant decrease of over 50% at all three magnification factors (2× , 4× , and 8× ), as well as improvements in peak signal-to-noise ratio and structural similarity index measure. Ablation experiments validated the effectiveness of the MLSA mechanism and WTLR encoder in improving DMUISR’s SR performance. Furthermore, by reducing the number of diffusion steps, the computational time of DMUISR was shortened to nearly one-tenth of its original while maintaining image quality without significant degradation. Significance. This study demonstrates that the modified diffusion model, DMUISR, provides superior performance for SR reconstruction of ultrasound images and has potential in improving imaging quality in the medical ultrasound field.

Ultra‐broadband sound absorption characteristics in underwater ultra‐thin metamaterial with three layer bubbles

AbstractThe interest of this article is to obtain the underwater broadband sound absorption characteristics by filling three layers of bubbles in Polydimethylsiloxane polymer (PDMS). In this underwater ultra‐thin metamaterial, three‐layer bubbles are arranged from small to large with the same radius center. The finite element analysis (FEA) method and transfer matrix (TM) method have good consistency in calculating the sound absorption coefficient of this metamaterial. The results reveals that sub‐wavelength metamaterial properties can be achieved below 6.4 MHz. Bubble coupling critical viscosity, waning coupling between layers, waveform transformation, and increasing scattering (reflection) waves all affect broadband sound absorption characteristics. The position and size of three bubbles are discussed, and design summary could be potentially in underwater ultrasound filter devices and medical ultrasound field.

Liver Segmentation in Ultrasound Images Using Self-Supervised Learning with Physics-inspired Augmentation and Global-Local Refinement

Shear Wave Elastography (SWE) is a non-invasive ultrasound method that evaluates changes in liver stiffness, serving as a useful biomarker for liver fibrosis. The proper placement of a region of interest (ROI) on the liver in the B-mode image is imperative for obtaining accurate and dependable results in SWE. In order to develop an automated system for liver fibrosis measurement utilizing SWE, the initial crucial phase involves the segmentation of the liver capsule. This paper presents a novel approach for liver segmentation in ultrasound images using a contrastive self-supervised learning approach. The proposed method leverages a large dataset of unannotated abdominal ultrasound images to learn the feature representations, which are then fine-tuned on the downstream task of liver segmentation. The algorithm is trained in two stages: in the first stage a SimCLR model is trained to learn the feature representations from non-labeled data, and in the second stage these representations are fine-tuned with a smaller annotated dataset of liver segmentation masks. Finally, this is followed by a refinement step using CascadePSP. The study also investigates the use of physics-inspired augmentations, such as sector angle and penetration to improve the performance of the deep learning model on ultrasound images. The proposed approach of SimCLR+ENet was compared against the state-of-the-art method U-Net. Evaluation of the average Dice similarity showed that SimCLR+ENet outperformed U-Net with a result of 90.58% compared to 89.77%. Similarly, the average Huasdorff distance evaluation demonstrated that SimCLR+ENet achieved superior performance with a value of 21.71 compared to U-Net’s 29.53. This highlights the effectiveness of the proposed approach, with performance improvements of 0.9% and 26.5% for the average Dice coefficient and average Hausdorff distance, respectively. The study provides insights into the use of physics-inspired augmentations in the medical ultrasound imaging field and highlights the potential for self-supervised learning in improving segmentation results.

Development of a 16-Channel Broadband Piezoelectric Micro Ultrasonic Transducer Array Probe for Pipeline Butt-Welded Defect Detection.

Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average −6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.

Visualization of medical ultrasound field using optical techniques

Visualization of medical ultrasound field using optical techniques

A Few Words From the Editor: On the Flourishing Use of Ultrasound in Brain Imaging and Therapy

Looking back at the history of medical ultrasonics, the 1950s has been a pivotal era of William and Francis Fry and their pioneering attempts to perform neurosurgeries using confocal four ultrasound transducer system. The Fry brothers demonstrated the feasibility of applying high-intensity (“intense”) focused ultrasound to treat patients suffering from Parkinson’s disease. The outcome of their experiments also indicated the critical need to develop tools to provide image guidance and subsequently spurred the development of brightness-mode (B-mode) ultrasound imaging that is widely used in today’s clinical practice. In the light of these seminal contributions, it is fair to say that early developments of ultrasound applications for the brain represent a major turning point in the medical ultrasound field that is now ubiquitous in both diagnostic and therapeutic applications.

Handheld Ultrasound Video High-Quality Reconstruction Using a Low-Rank Representation Multipathway Generative Adversarial Network.

Recently, the use of portable equipment has attracted much attention in the medical ultrasound field. Handheld ultrasound devices have great potential for improving the convenience of diagnosis, but noise-induced artifacts and low resolution limit their application. To enhance the video quality of handheld ultrasound devices, we propose a low-rank representation multipathway generative adversarial network (LRR MPGAN) with a cascade training strategy. This method can directly generate sequential, high-quality ultrasound video with clear tissue structures and details. In the cascade training process, the network is first trained with plane wave (PW) single-/multiangle video pairs to capture dynamic information and then fine-tuned with handheld/high-end image pairs to extract high-quality single-frame information. In the proposed GAN structure, a multipathway generator is applied to implement the cascade training strategy, which can simultaneously extract dynamic information and synthesize multiframe features. The LRR decomposition channel approach guarantees the fine reconstruction of both global features and local details. In addition, a novel ultrasound loss is added to the conventional mean square error (MSE) loss to acquire ultrasound-specific perceptual features. A comprehensive evaluation is conducted in the experiments, and the results confirm that the proposed method can effectively reconstruct high-quality ultrasound videos for handheld devices. With the aid of the proposed method, handheld ultrasound devices can be used to obtain convincing and convenient diagnoses.

Ultrafast Plane Wave Imaging With Line-Scan-Quality Using an Ultrasound-Transfer Generative Adversarial Network.

In the medical ultrasound field, ultrafast imaging has recently become a hot topic. However, the diagnostic reliability of ultrafast high-frame rate plane-wave (PW) imaging is reduced by its low-quality images. The medical ultrasound equipment on the market usually adopts the line-scanning mode, which can obtain high-quality images at a very low frame rate. In addition, many proven data-driven ultrasound image processing methods are trained by line-scan images. Since the gray-level distributions of line-scan images and PW images are very different, these gray-level distribution-sensitive methods cannot be generalized to ultrafast ultrasound imaging, which limits further applications. Hence, we propose an ultrasound-transfer generative adversarial network to improve the quality of PW images and extend the existing image processing methods to ultrafast ultrasound imaging by reconstructing PW images into line-scan images. This network adopts a residual dense generator with a self-attention system that fully uses the hierarchical features and generates details from all the relevant physiological information. A projection discriminator and spectral normalization are introduced to increase the discernibility and to maintain a balance between the generator and the discriminator. Moreover, we reorganize the transmit sequence of the transducer array to eliminate the negative influence of human movements and facilitate the convergence of the proposed model. The experimental results are evaluated with five metrics, which confirm the feasibility of the proposed method to obtain a line-scan-quality image with a very high frame rate. This technology could significantly popularize ultrafast medical ultrasound imaging.

Investigation of the repeatability and reproducibility of hydrophone measurements of medical ultrasound fields

Accurate measurements of acoustic pressure are required for characterisation of ultrasonic transducers and for experimental validation of models of ultrasound propagation. Errors in measured pressure can arise from a variety of sources, including variations in the properties of the source and measurement equipment, calibration uncertainty, and processing of measured data. In this study, the repeatability of measurements made with four probe and membrane hydrophones was examined. The pressures measured by these hydrophones in three different ultrasound fields, with both linear and nonlinear, pulsed and steady state driving conditions, were compared to assess the reproducibility of measurements. The coefficient of variation of the focal peak positive pressure was less than 2% for all hydrophones across five repeated measurements. When comparing hydrophones, pressures measured in a spherically focused 1.1 MHz field were within 7% for all except 1 case, and within 10% for a broadband 5 MHz pulse from a diagnostic linear array. Larger differences of up to 55% were observed between measurements of a tightly focused 3.3 MHz field, which were reduced for some hydrophones by the application of spatial averaging corrections. Overall, the major source of these differences was spatial averaging and uncertainty in the complex frequency response of the hydrophones.

An Ultrasonic Lens Design Based on Prefractal Structures

The improvement in focusing capabilities of a set of annular scatterers arranged in a fractal geometry is theoretically quantified in this work by means of the finite element method (FEM). Two different arrangements of rigid rings in water are used in the analysis. Thus, both a Fresnel ultrasonic lens and an arrangement of rigid rings based on Cantor prefractals are analyzed. Results show that the focusing capacity of the modified fractal lens is better than the Fresnel lens. This new lens is believed to have potential applications for ultrasonic imaging and medical ultrasound fields.

光学的手法による医用超音波音場の可視化

光学的手法による医用超音波音場の可視化

Acoustic holography as a metrological tool for characterizing medical ultrasound sources and fields.

Acoustic holography is a powerful technique for characterizing ultrasound sources and the fields they radiate, with the ability to quantify source vibrations and reduce the number of required measurements. These capabilities are increasingly appealing for meeting measurement standards in medical ultrasound; however, associated uncertainties have not been investigated systematically. Here errors associated with holographic representations of a linear, continuous-wave ultrasound field are studied. To facilitate the analysis, error metrics are defined explicitly, and a detailed description of a holography formulation based on the Rayleigh integral is provided. Errors are evaluated both for simulations of a typical therapeutic ultrasound source and for physical experiments with three different ultrasound sources. Simulated experiments explore sampling errors introduced by the use of a finite number of measurements, geometric uncertainties in the actual positions of acquired measurements, and uncertainties in the properties of the propagation medium. Results demonstrate the theoretical feasibility of keeping errors less than about 1%. Typical errors in physical experiments were somewhat larger, on the order of a few percent; comparison with simulations provides specific guidelines for improving the experimental implementation to reduce these errors. Overall, results suggest that holography can be implemented successfully as a metrological tool with small, quantifiable errors.

Characterization of medical ultrasound fields using modeling with a boundary condition obtained from measurements

Numerical modeling is becoming an important metrological tool for accurate characterization of ultrasound fields generated by medical transducers in water and in situ. While acoustic propagation equations are well established, setting a boundary condition relevant to the experiment still remains a critical problem. Two methods differing in complexity are described to address this problem. The first method comprises 3D simulations of the Westervelt equation with a boundary condition determined from acoustic holography measurements. The second, simpler method utilizes simulations based either on the KZK or Westervelt equation with an equivalent source boundary condition obtained by matching linear simulations to low-amplitude beam profiles along and transverse to the axis of the source. Calculations with both methods are compared to fiber optic hydrophone measurements of 2D phased therapeutic arrays, a 128-element diagnostic probe, and strongly focused single-element transducers. It is shown that the 3D Westervelt model with holographic boundary condition can accurately simulate the entire nonlinear ultrasound field. The simplified methods based on an equivalent source are shown to give accurate results in the focal zone of the transducers, even when shocks are present in the focal waveform. [Work supported by NIH EB7643, EB016118, DK043881, and RSF 14-12-00974.]

Comparison between computational and experimental methods for the characterization of therapeutic ultrasound fields

Analytical modeling of medical ultrasound fields has been developed by the FDA to aid in pre-clinical characterization of therapeutic ultrasound devices. In order to assess this publicly available software, called the HIFU Simulator, acoustic and thermal measurements of power, pressure/intensity and temperature distribution have been performed for comparison. Measurement and modeling issues include using hydrophones and radiation force balances at therapeutic power levels, validation of simulation models, and tissue-mimicking material (TMM) development for temperature measurements. To better understand these issues, a comparison study was undertaken between simulations and measurements of the HITU acoustic field distribution in water and TMM, and temperature rise in TMM. For the specific conditions of this study, the following results were obtained. In water, the simulated values for p + and p- were 3% lower and 10% higher, respectively, than those measured by hydrophone. In TMM, the simulated values for p + and p- were 2% and 10% higher, respectively, than those measured by hydrophone. The simulated spatial-peak temporal-average intensity values in both water and TMM were greater than those obtained by hydrophone by 3%. Simulated and measured end-of-sonication temperatures agreed to within their respective uncertainties (coefficients of variation of approximately 20% and 10%, respectively).

A Simple Technique for Visualizing Ultrasound Fields Without Schlieren Optics

A simple technique designed for visualization of ultrasound fields without Schlieren optics is introduced. An optical system of direct shadowgraphy with diverging light, which consists of a point light source and a shadow screen, constituted the basic system, but the screen was replaced by focusing optics: a camera that makes a virtual screen at its focus plane. The proposed technique visualizes displacement of light deflected by ultrasound, and the use of focusing optics enables flexible settings of the virtual screen position and optical magnification. Insufficient sensitivity of shadowgraphy was overcome by elimination of non-deflecting light using image subtraction of shadowgrams taken with and without ultrasound exposure. A 1-MHz focused transducer for ultrasound therapy and a 20-MHz miniature transducer for intravascular imaging were used for experiments, and alternate pressure change in short-pulsed ultrasound was visualized, indicating the usefulness of the proposed technique for evaluation of medical ultrasound fields.

A CMUT probe for medical ultrasonography: from microfabrication to system integration

Medical ultrasonography is a powerful and cost-effective diagnostic technique. To date, high-end medical imaging systems are able to efficiently implement real-time image formation techniques that can dramatically improve the diagnostic capabilities of ultrasound. Highly performing and thermally efficient ultrasound probes are then required to successfully enable the most advanced techniques. In this context, ultrasound transducer technology is the current limiting factor. Capacitive micromachined ultrasonic transducers (CMUTs) are micro-electro-mechanical systems (MEMS)-based devices that have been widely recognized as a valuable alternative to piezoelectric transducer technology in a variety of medical imaging applications. Wideband operation, good thermal efficiency, and low fabrication cost, especially for those applications requiring high-volume production of small-area dice, are strength factors that may justify the adoption of this MEMS technology in the medical ultrasound imaging field. This paper presents the design, development, fabrication, and characterization of a 12-MHz ultrasound probe for medical imaging, based on a CMUT array. The CMUT array is microfabricated and packed using a novel fabrication concept specifically conceived for imaging transducer arrays. The performance of the developed probe is optimized by including analog front-end reception electronics. Characterization and imaging results are used to assess the performance of CMUTs with respect to conventional piezoelectric transducers.

Evaluation of Acoustic Cavitation in Terephthalic Acid Solutions Containing Gold Nanoparticles by the Spectrofluorometry Method

Background. When a liquid is irradiated with high intensity and low-frequency ultrasound, acoustic cavitation occurs. The existence of particles in a liquid provides nucleation sites for cavitation bubbles and leads to a decrease in the ultrasonic intensity threshold needed for cavitation onset.Materials and Methods. The study was designed to measure hydroxyl radicals in terephthalic acid solutions containing gold nanoparticles in a near field of a 1 MHz sonotherapy probe. The effect of ultrasound irradiation parameters containing mode of sonication and ultrasound intensity in hydroxyl radicals production have been investigated by the spectrofluorometry method.Results. Recorded fluorescence signal in terephthalic acid solution containing gold nanoparticles was higher than the terephthalic acid solution without gold nanoparticles. Also, the results showed that any increase in intensity of the sonication would be associated with an increase in the fluorescence intensity.Conclusion. Acoustic cavitation in the presence of gold nanoparticles has been introduced as a way for improving therapeutic effects on the tumors in sonodynamic therapy. Also, the terephthalic acid dosimetry is suitable for detecting and quantifying free hydroxyl radicals as a criterion of cavitation production over a certain range of conditions in medical ultrasound fields.

Calculations of intensities for radiation force modeling with the commercial software package FOCUS.

Rapid calculations of the intensity are required for models of the radiation force generated by linear ultrasound phased arrays. To determine the computation times and numerical errors produced by two medical ultrasound simulation packages, namely, FIELD II and FOCUS, comparisons of the calculated pressures and intensities are performed using a simulated Vermon L5 phased array probe with 128 active elements. In these simulations, the array generates a fixed focus 25 mm from the array for a 5‐MHz excitation, and the pressure field is computed on a 133 × 133 × 261 rectilinear grid that is centered at the focus. Half wavelength sampling is employed in all three directions. In FIELD II, this calculation takes approximately 4 h on a 64‐bit laptop running Linux, and in FOCUS, the same calculation takes less than 4 min on the same computer. The numerical errors are also much smaller with FOCUS. Details of the simulation approaches employed for this transducer model will be presented, including selection of FIELD II and FOCUS simulation parameters and calculations of the reference pressure field for error evaluations. The impact of numerical errors on shear wave calculations will also be discussed.

1081: Basic Research on Safety Assessment of Medical Ultrasound - The Problems in the Estimation of Safety Indexes

New type ultrasound diagnostic equipments with new functions like color Doppler imaging, harmonic imaging, 3 dimensional imaging etc. tend to irradiate higher intensity ultrasound with high frequency. Therefore the safety became important topic in medical ultrasound field. We measured the irradiated ultrasound pulse waveform, acoustic field and -12 dB output beam dimensions. The mechanical index MI, soft-tissue thermal index TIS and cranial-bone thermal index TIC were calculated from the results. The mechanical index can be calculated from attenuated peak-rarefactional acoustic pressure Pr,α divided by the square root of acoustic working frequency fawf. And they were divided by CMI. The soft-tissue thermal index can be calculated from the output power P multiplied by acoustic working frequency. And they were divided by CTIS1. In this case, CMI is defined as 1 MPa MHz-1/2 and CTIS1 is defined as 210 mW MHz in JIS T 0601-2-37: 2005 and IEC 62359 Ed. 1.0: 2005. Harmonic components with many different frequencies are generated by propagation of ultrasound in water and tissues or nonlinear behavior of micro bubble in the ultrasound diagnosis like tissue harmonic imaging or contrast harmonic imaging methods. These frequency components are different from the transmitting frequency and the fundamental frequency. Therefore it is difficult to determine the acoustic working frequency in the measured frequency spectrum for calculation of safety indexes by conventional definition. We will report about this important problem. New type ultrasound diagnostic equipments with new functions like color Doppler imaging, harmonic imaging, 3 dimensional imaging etc. tend to irradiate higher intensity ultrasound with high frequency. Therefore the safety became important topic in medical ultrasound field. We measured the irradiated ultrasound pulse waveform, acoustic field and -12 dB output beam dimensions. The mechanical index MI, soft-tissue thermal index TIS and cranial-bone thermal index TIC were calculated from the results. The mechanical index can be calculated from attenuated peak-rarefactional acoustic pressure Pr,α divided by the square root of acoustic working frequency fawf. And they were divided by CMI. The soft-tissue thermal index can be calculated from the output power P multiplied by acoustic working frequency. And they were divided by CTIS1. In this case, CMI is defined as 1 MPa MHz-1/2 and CTIS1 is defined as 210 mW MHz in JIS T 0601-2-37: 2005 and IEC 62359 Ed. 1.0: 2005. Harmonic components with many different frequencies are generated by propagation of ultrasound in water and tissues or nonlinear behavior of micro bubble in the ultrasound diagnosis like tissue harmonic imaging or contrast harmonic imaging methods. These frequency components are different from the transmitting frequency and the fundamental frequency. Therefore it is difficult to determine the acoustic working frequency in the measured frequency spectrum for calculation of safety indexes by conventional definition. We will report about this important problem.

High intensity focused ultrasound lithotripsy with cavitating microbubbles

In the medical ultrasound field, microbubbles have recently been the subject of much interest. Controlling actively the effect of the microbubbles, a novel therapeutic method has been investigated. In this paper, our works on high intensity focused ultrasound (HIFU) lithotripsy with cavitating microbubbles are reviewed and the cavitation detection method to optimize the HIFU intensity is investigated. In the HIFU lithotripsy, collapse of the cloud cavitation is used to fragment kidney stones. Cloud cavitation is potentially the most destructive form of cavitation. When the cloud cavitation is acoustically forced into a collapse, it has the potential to concentrate a very high pressure. For the control of the cloud cavitation collapse, a novel two-frequency wave (cavitation control [C-C] waveform) is designed; a high-frequency ultrasound pulse (1-4 MHz) to create the cloud cavitation and a low-frequency trailing pulse (500 kHz) following the high-frequency pulse to force the cloud into collapse. High-speed photography showed the cavitation collapse on the stone and the shock-wave emission from the cloud. In vitro erosion tests of model and natural stones were also conducted. In the case of model stones, the erosion rate of the C-C waveform showed a distinct advantage with the combined high- and low-frequency waves over either wave alone. For the optimization of the high-frequency ultrasound intensity, the subharmonic acoustic pressure was examined. The results showed relationship between the subharmonic pressure from cavitating bubbles induced by the high-frequency ultrasound and eroded volume of the model stones. Natural stones were eroded and most of the resulting fragments were less than 1 mm in diameter. The method has the potential to provide a novel lithotripsy system with small fragments and localized cavitating bubbles on a stone.