Medical Ultrasound Scanners Research Articles

Interaction between maintenance variables of medical ultrasound scanners through multifactor dimensionality reduction

ABSTRACT Background Proper maintenance of electro-medical devices is crucial for the quality of care to patients and the economic performance of healthcare organizations. This research aims to identify the interaction between Ultrasound scanners (US) maintenance variables as a function of maintenance indicators: US in service or decommissioned, excessive number of failures, and failure rate. Knowing those interactions, specific maintenance measures will be developed to improve the reliability of the US. Research design and methods Multifactor Dimensionality Reduction (MDR) method was eployed to analyze data from 222 US and their four-year maintenance history. Models were developed based on the variables with the greatest influence on maintenance indicators, where US were classified according to the associated risk. Results US with more than one major failure or at least one major component replacement had up to 496.4% more failures than the average. Failure rate increased by up to 188.7% over the average for those US with more than three moderate failures, three replacements, or both. Conclusions This study identifies and quantifies the causes of risk to establish a specific maintenance plan for US. It helps to better understand the degradation of US to optimize their operation and maintenance.

Assessment of the potential of radiography and ultrasonography to record flow dynamics in cohesive sediments (mud)

The possible use of both radiography and ultrasonography to visualise flow dynamics in cohesive sediments, also known as fluid mud, has been assessed. Ultimately, these techniques are intended to enable the application of Particle Image Velocimetry (PIV) in experimental fluid dynamics using such fluid mud. This research takes into account the specific requirements arising from this objective. Those requirements are primarily penetration depth, adequate frame rate and the preference not to seed with tracer particles. The evaluation of both techniques is elaborated in detail based the properties of mud originating from the Port of Zeebrugge (Belgium). The assessment of radiography starts with a chemical element analysis of the fluid mud, the results of which are used to determine the attenuation for high-energy electromagnetic radiation. Using various research software, the maximum thickness of the mud layer could be determined as a function of the maximum recordable flow velocities for different radiation sources. However, for the flow velocities expected in nautical research experiments, these thicknesses proved insufficient. Supplemented by the results of a particle size distribution analysis, it is found that high frequency ultrasound radiation will scatter in mud. In case of a great number of scatterers, the scattered ultrasound waves will interact, eventually resulting in speckle images, which are ideally suited for tracking. These findings were confirmed in a test setup with a standard medical ultrasound scanner. The penetration depth of ultrasonography with standard medical equipment is also limited. However, since ultrasonography is based on reflection, this is less of an issue compared to radiography, for which full penetration of the mud layer is required. Ultrasonography is therefore suggested as the preferred technique for the intended application.

Beamforming Algorithm Architectures for Medical Ultrasound

Medical ultrasound scanners are amongst the most sophisticated signal processing machines in use today. The Beamformer is the brain of whole signal processing system of the scanner [1]. Beamforming allows message transmission or reception to be directed or spatially selective. It is used in receiving beamforming to concentrate the noise signals obtained in the region of concern as reflections from various tissue structures. This paper reviews the various receive beamformer architectures implemented in FPGA/ASIC for ultrasound imaging. Most of the receive beamformers are implemented using the standard technique Delay and Sum. Beamforming in ultrasound instruments for medical imaging has traditionally been implemented using analog delay lines. The concept of dynamic focusing in near field has resulted more complex analog delay structures and were replaced by digital structures. By the availability of high-speed analog to digital converters, and VLSI Technology improvements have now made real time implementation of digital beamformers feasible. The current innovations involve hybrid beamformers utilizing the pros of both analog and digital structures. This paper discusses the evolution of beamforming architectures from analog to digital environment and the current beamformer designs. The changes in beamformer designs in order to be compatible to high frequency probes and yield improved imaging performance, resource optimization, etc. are discussed.

Nucleus-Targeted, Echogenic Polymersomes for Delivering a Cancer Stemness Inhibitor to Pancreatic Cancer Cells.

Chemotherapeutic agents for treating cancers show considerable side effects, toxicity, and drug resistance. To mitigate the problems, we designed nucleus-targeted, echogenic, stimuli-responsive polymeric vesicles (polymersomes) to transport and subsequently release the encapsulated anticancer drugs within the nuclei of pancreatic cancer cells. We synthesized an alkyne-dexamethasone derivative and conjugated it to N3-polyethylene glycol (PEG)-polylactic acid (PLA) copolymer employing the Cu2+ catalyzed "Click" reaction. We prepared polymersomes from the dexamethasone-PEG-PLA conjugate along with a synthesized stimuli-responsive polymer PEG-S-S-PLA. The dexamethasone group dilates the nuclear pore complexes and transports the vesicles to the nuclei. We designed the polymersomes to release the encapsulated drugs in the presence of a high concentration of reducing agents in the nuclei of pancreatic cancer cells. We observed that the nucleus-targeted, stimuli-responsive polymersomes released 70% of encapsulated contents in the nucleus-mimicking environment in 80 min. We encapsulated the cancer stemness inhibitor BBI608 in the vesicles and observed that the BBI608 encapsulated polymersomes reduced the viability of the BxPC3 cells to 43% in three-dimensional spheroid cultures. The polymersomes were prepared following a special protocol so that they scatter ultrasound, allowing imaging by a medical ultrasound scanner. Therefore, these echogenic, targeted, stimuli-responsive, and drug-encapsulated polymersomes have the potential for trackable, targeted carrier of chemotherapeutic drugs to cancer cell nuclei.

Development of a Low-Cost Medical Ultrasound Scanner Using a Monostatic Synthetic Aperture.

In this paper, we present the design of low-cost medical ultrasound scanners aimed at the detection of maternal mortality risk factors in developing countries. Modern ultrasound scanners typically employ a high element count transducer array with multichannel transmit and receive electronics. To minimize hardware costs, we employ a single piezoelectric element, mechanically swept across the target scene, and a highly cost-engineered single channel acquisition circuit. Given this constraint, we compare the achievable image quality of a monostatic fixed focus scanner (MFFS) with a monostatic synthetic aperture scanner (MSAS) using postfocusing. Quantitative analysis of image quality was carried out using simulation and phantom experiments, which were used to compare a proof-of-concept MSAS prototype with an MFFS device currently available on the market. Finally, in vivo experiments were performed to validate the MSAS prototype in obstetric imaging. Simulations show that the achievable lateral resolution of the MSAS approach is superior at all ranges compared to the fixed focus approach. Phantom experiments verify the improved resolution of the MSAS prototype but reveal a lower signal to noise ratio. In vivo experiments show promising results using the MSAS for clinical diagnostics in prenatal care. The proposed MSAS achieves superior resolution but lower SNR compared to an MFFS approach, principally due to lower acoustic energy emitted. The production costs of the proposed MSAS could be an order of magnitude lower than any other ultrasound system on the market today, bringing affordable obstetric imaging a step closer for developing countries.

Non-invasive evaluation of facial crestal bone with ultrasonography

PurposeFacial crestal bone level and dimension determine function and esthetics of dentition and dental implants. We have previously demonstrated that ultrasound can identify bony and soft tissue structures in the oral cavity. The aim of this study is to evaluate the accuracy of using ultrasound to measure facial crestal bone level and thickness.Materials and methodsA commercially available medical ultrasound scanner, paired with a 14 MHz imaging probe was used to scan dental and periodontal tissues at the mid-facial site of each tooth on 6 fresh cadavers. The alveolar crest level in relation to the cemento-enamel junction and its thickness on ultrasound images were measured and compared to those on cone-beam computed tomography (CBCT) scans and/or direct measurements on a total of 144 teeth.ResultsThe mean crestal bone level measured by means of ultrasound, CBCT and direct measures was 2.66 ± 0.86 mm, 2.51 ± 0.82 mm, and 2.71 ± 1.04 mm, respectively. The mean crestal bone thickness was 0.71 ± 0.44 mm and 0.74 ± 0.34 mm, measured by means of ultrasound and CBCT, respectively. The correlations of the ultrasound readings to the other two methods were between 0.78 and 0.88. The mean absolute differences in crestal bone height and thickness between ultrasound and CBCT were 0.09 mm (-1.20 to 1.00 mm, p = 0.06) and 0.03 mm (-0.48 to 0.54 mm, p = 0.03), respectively.ConclusionUltrasound was as accurate in determining alveolar bone level and its thickness as CBCT and direct measurements. Clinical trials will be required to further validate this non-ionizing and non-invasive method for determining facial crestal bone position and dimension.

Geometric distortion of area in medical ultrasound images

Medical ultrasound scanners are typically calibrated to a speed of sound corresponding to the soft tissue average of 1540 m s−1. In regions of different sound speed, for example, organs and tumours, the B-mode image becomes geometrically distorted from the true tissue cross-section, due to refraction and the misrepresentation of length. A ray model is developed to predict this distortion for a generalized two-dimensional object with atypical speed of sound, and verified against ultrasound images of a test object. We quantify the areal image distortion as a function of the key dependencies, including the speed of sound mismatch, the scanning format, the object size and its elongation. Our findings show that the distortion of area can be significant, even for relatively small speed of sound mismatches. For example, a 5% speed mismatch typically leads to a 10 – 20% distortion in area. These findings have implications for the accuracy of ultrasound-based evaluation of area and volume.

Scattering and reflection identification in H-scan images

Medical ultrasound imaging scanners typically display the envelope of the reflected signal on a log scale. The properties of this image and speckle patterns from collections of scatterers have a number of well-known disadvantages. One is the inability to differentiate between different scatterers that may have fundamentally different frequency-dependent scattering cross sections. This study proposes a framework for characterizing scattering behavior and visualizing the results as color coding of the B-scan image. The methodology matches a model of pulse-echo formation from typical situations to the mathematics of Gaussian weighted Hermite functions. The results show an ability to reveal some of the information otherwise hidden in the conventional envelope display, and can be generalized to more conventional bandlimited pulse functions. This new class of images is termed H-scan where ‘H’ stands for ‘Hermite’ or ‘hue’ to distinguish it from conventional B-scan format.

Microcontroller USB interfacing with MATLAB GUI for low cost medical ultrasound scanners

This paper presents an 8051 microcontroller-based control of ultrasound scanner prototype hardware from a host laptop MATLAB GUI. The hardware control of many instruments is carried out by microcontrollers. These microcontrollers are in turn controlled from a GUI residing in a computing machine that is connected over the USB interface. Conventionally such GUIs are developed using ‘C’ language or its variants. But MATLAB GUI is a better tool, when such GUI programs need to do huge image/video processing. However interfacing MATLAB with the microcontroller is a challenging task. Here, MATLAB interfacing through an intermediate MEX ‘C’ language program is presented. This paper outlines the MEX programming methods for achieving the smooth interfacing of microcontrollers with MATLAB GUI.

In brief

PAGE 18 Researchers in Korea have proposed a method to significantly reduce the computation complexity of a phase rotation beamforming technique commonly used in medical ultrasound scanners. They demonstrate that it can be implemented on smartphone hardware and that the technique doesn't sacrifice image quality, either analytically or experimentally. PAGE 29 Optical cloaking of arbitrary cross-section cylindrical structures using scattering cancellation is presented in work from Iran. The approach uses nano-strips of silver in a dielectric host as a cloaking shell around the object and the work explores the effect of the nano-strip parameters on the cloaking efficiency. The computational complexity of the technique is improved sufficiently to run in realtime on a smartphone without compromising quality PAGE 51 A compact Ka-band full bandwidth 3-dB waveguide hybrid has been designed by researchers in China. With high directivity over the full bandwidth of the WR-28 standard waveguide. The hybrid can also be used as a two-way power divider and can be made with excellent repeatability at low-cost. Optical cloaking of cylindrical objects of arbitrary cross-section PAGE 12 Researchers in China present a surface diagnosis approach for large reflector radio astronomy antennas with active surface control systems. Based on microwave holographic techniques, it allows far field patterns to be measured in focus by actively adjusting the primary surface. The 3-dB waveguide hybrid can be fabricated at low-cost with excellent repeatability PAGE 36 A robust, portable stereoscopic system for rapid identification of hidden objects using only a small number of X-ray projections has been demonstrated in work from the US. The system uses a single fixed sensor and obtains different angles using a motion-controlled single X-ray source. With a known system geometry, a series of depth planes can be computed to allow rapid object identification and realtime operation. The approach applies techniques from microwave holography to large reflector radio astronomy antennas The single source, single sensor, portable X-ray system allows rapid identification of hidden objects

Computationally efficient architecture for ultrasound phase rotation beamforming

A commonly used phase rotation beamforming (PRBF) technique in medical ultrasound scanners requires four multipliers to realise phase rotation (PR) in addition to two lowpass filters for quadrature demodulation for each channel. A new scheme is presented to reduce the computational complexity of PRBF without sacrificing image quality that uses only 16 PRs located behind inter-channel adders, regardless of the number of channels, each of which is dedicated for one of 16 quantised PR values using a step size of 2π/16.

Low-Echo Sphere Phantoms and Methods for Assessing Imaging Performance of Medical Ultrasound Scanners

Tissue-mimicking phantoms and software for quantifying the ability of human observers to detect small low-echo spheres as a function of depth have been developed. Detectability is related to the imager's ability to delineate the boundary of a 3-D object such as a spiculated tumor. The phantoms accommodate a broad range of transducer shapes and sizes. Three phantoms are described: one with 2-mm-diameter spheres (for higher frequencies), one with 3.2-mm-diameter spheres (for lower frequencies) and one with 4-mm-diameter spheres (for lower frequencies). The spheres are randomly distributed in each phantom. The attenuation coefficients of spheres and surroundings are nearly identical; thus, compromising shadowing or enhancement distal to spheres does not occur. Reproducibility results are given for pairs of independent data sets involving eight different combinations of scanner, transducer and console settings. The following comparison results are also reported: (i) only the selected frequency differs; (ii) transducers and scan parameters are nearly the same but manufacturers differ; (iii) ordinary B-scanning, spatial compounding and tissue harmonic imaging are addressed. The phantoms and software promise to be valuable tools for scanning system and setup comparisons and for acceptance testing.

Acoustic characterization and contrast imaging of microbubbles encapsulated by polymeric shells coated or filled with magnetic nanoparticles

The combination of superparamagnetic iron oxide nanoparticles with polymeric air-filled microbubbles is used to produce two types of multimodal contrast agents to enhance medical ultrasound and magnetic resonance imaging. The nanoparticles are either covalently linked to the shell or physically entrapped into the shell. In this paper, the characterization of the acoustic properties (backscattered power, fracturing pressure, attenuation and dispersion of the ultrasonic wave) and ultrasound imaging of the two types of magnetic microbubbles are presented. In vitro B-mode images are generated using a medical ultrasound scanner by applying a nonconventional signal processing technique that is suitable to detect polymeric bubbles and based on the combination of multipulse excitation and chirp coding. Even if both types of microbubbles can be considered to be effective ultrasound contrast agents, the different structure of the shell loaded with nanoparticles has a pronounced effect on the echogenicity and the detection sensitivity of the imaging technique. The best results are obtained using microbubbles that are externally coated with nanoparticles. A backscattered power of 20 dB was achieved at lower concentration, and an increment of 8 dB in the contrast-to-tissue ratio was observed with respect to the more rigid microbubbles with particles entrapped into the shell.

Ultrasound Image Intensity Nonuniformity Correction by Combining Intensity and Spatial Information

Medical ultrasonic B-scans often suffer from intensity inhomogeneities that originates from the nonuniform attenuation properties of the sonic beam within the body. In order to correct signal attenuation in the tissue, time gain compensation (TGC) is routinely used in medical ultrasound scanners. However, TGC assumes a uniform attenuation coefficient for all body tissues. Since this assumption is evidently inaccurate, over-amplification or under-amplification sometimes appear. This is a major problem for intensity-based, automatic segmentation of video-intensity images because conventional threshold-based or intensity-statistic-based approaches do not work well in the presence of such image distortions. The main contribution of this paper is that additional spatial image features are incorporated to improve inhomogeneity correction and to make it more dynamic besides most commonly used intensity features, so that local intensity variations can be corrected more efficiently. The degraded image is corrected by the inverse of the image degradation model. The image degradation process is described by a linear model, consisting of a multiplicative and an additive component which are modeled by a combination of smoothly varying basis functions. Spatial information about intensity nonuniformity is obtained using cubic spline smoothing and entropy minimizing. Gray-level histogram information of the image corrupted by intensity inhomogeneity is exploited from a signal processing perspective. We explain how this model can be related to the ultrasonic physics of image formation to justify our approach. Experiments are presented on synthetic images and real US data to evaluate quantitatively the accuracy of the method.

Use of thick piezoelectric elements to expand the bandwidth of medical ultrasonic ultrasound scanners

The possibility of using various nonresonant-excitatory piezoelements to extend the frequency bandwidth acoustical transducers used in medical ultrasound devices is considered. Preferences of unevenly-polarized and surface-excitatory thick piezoelements as broadband aperiodic transducers of ultrasonic fluctuations is presented.

Implementation of a versatile research data acquisition system using a commercially available medical ultrasound scanner

This paper describes the design and implementation of a versatile, open-architecture research data acquisition system using a commercially available medical ultrasound scanner. The open architecture will allow researchers and clinicians to rapidly develop applications and move them relatively easy to the clinic. The system consists of a standard PC equipped with a camera link and an ultrasound scanner equipped with a research interface. The ultrasound scanner is an easy-to-use imaging device that is capable of generating high-quality images. In addition to supporting the acquisition of multiple data types, such as B-mode, M-mode, pulsed Doppler, and color flow imaging, the machine provides users with full control over imaging parameters such as transmit level, excitation waveform, beam angle, and focal depth. Beamformed RF data can be acquired from regions of interest throughout the image plane and stored to a file with a simple button press. For clinical trials and investigational purposes, when an identical image plane is desired for both an experimental and a reference data set, interleaved data can be captured. This form of data acquisition allows switching between multiple setups while maintaining identical transducer, scanner, region of interest, and recording time. Data acquisition is controlled through a graphical user interface running on the PC. This program implements an interface for third-party software to interact with the application. A software development toolkit is developed to give researchers and clinicians the ability to utilize third-party software for data analysis and flexible manipulation of control parameters. Because of the advantages of speed of acquisition and clinical benefit, research projects have successfully used the system to test and implement their customized solutions for different applications. Three examples of system use are presented in this paper: evaluation of synthetic aperture sequential beamformation, transverse oscillation for blood velocity estimation, and acquisition of spectral velocity data for evaluating aortic aneurysms.

Computationally Efficient Time-Recursive IAA-Based Blood Velocity Estimation

High-resolution spectral Doppler is an important and powerful noninvasive tool for estimation of velocities in blood vessels using medical ultrasound scanners. Such estimates are typically formed using an averaged periodogram technique, resulting in well-known limitations in the resulting spectral resolution. Recently, we have proposed techniques to instead form high-resolution data-adaptive estimates exploiting measurements along both depth and emission. The resulting estimates gives noticeably superior velocity estimates as compared to the standard technique, but suffers from a high computational complexity, making it interesting to formulate computationally efficient implementations of the estimators. In this work, by exploiting the rich structure of the iterative adaptive approach (IAA) based estimator, we examine how these estimates can be efficiently implemented in a time-recursive manner using both exact and approximate formulations of the method. The resulting algorithms are shown to reduce the necessary computational load with several orders of magnitude without noticeable loss of performance.

Blood velocity estimation using ultrasound and spectral iterative adaptive approaches

This paper proposes two novel iterative data-adaptive spectral estimation techniques for blood velocity estimation using medical ultrasound scanners. The techniques make no assumption on the sampling pattern of the emissions or the depth samples, allowing for duplex mode transmissions where B-mode images are interleaved with the Doppler emissions. Furthermore, the techniques are shown, using both simplified and more realistic Field II simulations as well as in vivo data, to outperform current state-of-the-art techniques, allowing for accurate estimation of the blood velocity spectrum using only 30% of the transmissions, thereby allowing for the examination of two separate vessel regions while retaining an adequate updating rate of the B-mode images. In addition, the proposed methods also allow for more flexible transmission patterns, as well as exhibit fewer spectral artifacts as compared to earlier techniques.

Wireless implantable passive strain sensor: design, fabrication and characterization

This work presents a new passive sensor concept for monitoring the deformation of orthopedic implants. The novel sensing principle of the WIPSS (wireless implantable passive strain sensor) is based on a hydro-mechanical amplification effect. The WIPSS is entirely made from biocompatible PMMA and consists of a microchannel attached to a reservoir, which is filled with an incompressible fluid. As the reservoir is exposed to strain, its volume changes and consequently the fill level inside the microchannel varies. The wireless detection of the microchannel's strain-dependent fill level is based on ultrasound. The WIPSS' sensing principle is proved by finite-element simulations and the reservoir's design is optimized toward maximum volume change, in order to achieve high sensitivity. A fabrication process for WIPSS sensor devices entirely made from PMMA is presented. The obtained measurement results confirmed the sensor's functionality and showed very good agreement with the obtained results of the conducted FE simulations regarding the sensor's sensitivity. A strain resolution of 1.7 ± 0.2 × 10−5 was achieved. Further, the determination of the cross-sensitivity to temperature and strains applied out of the sensing direction is presented. The response to dynamic inputs (0.1–5 Hz) has been measured and showed decreasing sensor output with increasing frequency. Test structures of the sensor device allow the application of a signal bandwidth up to 1 Hz. Therefore, the proposed sensor concept of the WIPSS presents a promising new sensor system for static in vivo strain monitoring of orthopedic implants. In combination with the developed ultrasound-based read-out method, this new sensor system offers the potential of wireless sensor read-out with medical ultrasound scanners, which are commercially available.

Novel ultrasound read-out for a wireless implantable passive strain sensor (WIPSS)

In vivo monitoring the deformation of orthopedic implants during rehabilitation helps preventing their possible failure and enables the observation of healing processes. For these reasons we propose a completely new load-monitoring concept, which consist of a passive load sensor and its associated external ultrasound-based read-out unit. The new concept allows the sensor to be built from inexpensive biocompatible or even bioresorbable polymers and the read-out will be carried out with a standard medical ultrasound scanner. The measurement principle is based on the transformation of an external force into a varying amount of fluid in a microchannel integrated into the sensor. A novel ultrasound read-out method based on an integral evaluation of C-scans of the microchannel is proposed to determine the amount of fluid in the microchannel. Furthermore, suitable reference reflectors inside the sensor will be used to calibrate the ultrasound echoes. In this paper we will present first ultrasound in vitro experiments, which shows promising results for in vivo load monitoring.