Ultrasound Reflection Research Articles

Sound-speed image reconstruction in sparse-aperture 3-D ultrasound transmission tomography

The paper is focused on sound-speed image reconstruction in 3-D ultrasound transmission tomography. Along with ultrasound reflectivity and the attenuation coefficient, sound speed is an important parameter which is related to the type and pathological state of the imaged tissue. This is important in the intended application, breast cancer diagnosis. In contrast to 2-D ultrasound transmission tomography systems, a 3-D system can provide an isotropic spatial resolution in the x-, y-, and z-directions in reconstructed 3-D images of ultrasound parameters. Several challenges must, however, be addressed for 3-D systems-namely, a sparse transducer distribution, low signal-to-noise ratio, and higher computational complexity. These issues are addressed in terms of sound-speed image reconstruction, using edge-preserving regularized algebraic reconstruction in combination with synthetic aperture focusing. The critical points of the implementation are also discussed, because they are crucial to enable a complete 3-D image reconstruction. The methods were tested on a synthetic data set and on data sets measured with the Karlsruhe 3-D ultrasound computer tomography (USCT) I prototype using phantoms. The sound-speed estimates in the reconstructed volumes agreed with the reference values. The breast-phantom outlines and the lesion-mimicking objects were also detectable in the resulting sound-speed volumes.

Unleashing the power of echocardiography: can we get closer to maximally exploiting all embedded information from the image?

Ultrasonic imaging has become a widespread clinical tool in almost all medical specialties. While the current generation of equipment provides excellent image quality, the principle of imaging is still very simple: send out an ultrasound pulse, receive the reflections from different tissues, and display the amplitude of the reflected signal on a monitor. In case of echocardiography, this provides high-quality scans of the beating heart, enabling the visual interpretation of morphology and contraction. But what else can we do? Obviously, cardiac ultrasound can also assess (blood and tissue) velocity information using Doppler techniques, but what other information, besides visualization of structures (thus also enabling geometrical measurement), is contained in the image and could be exploited to obtain complementary information? Recently, there is a lot of attention in analysing the typical speckle patterns present in all ultrasound images, by tracking their displacement over time in order to quantify overall tissue motion and segmental deformation. The clinically available tools that use this approach have shown to provide regional and global deformation assessment, which contains a wealth of information on cardiac mechanics and remodelling.1 But besides visualization of structures (mainly based on highly reflective boundaries) and tracking speckle patterns for motion/deformation, the power of the reflected ultrasound, from a specific site, should contain complementary information, since the intensity of the signal is determined by the structure and acoustical properties of the tissue that is reflecting it. In the past decades, several authors have attempted to use ultrasound reflectivity for characterizing different tissue types and tissue remodelling and damage in cardiovascular diseases.2 While several analysis methodologies have been proposed and assessed, some even embedded in clinical echocardiographic systems, they have proven to be difficult to use and interpret and have not found a place in clinical practice. Why would this be? To …

Abstract 17367: Echogenic Liposomes for Clot Imaging and Combined Delivery of Thrombolytic/neuroprotective Agents with Ultrasound-Facilitated Drug Release for Stroke Treatment

Background: Currently, the only FDA-approved therapy for acute ischemic stroke is the administration of recombinant tissue plasminogen activator (tPA). However, the therapeutic application of tPA requires optimization. Combining thrombolytic treatment with administration of neuroprotective agents is a promising strategy under development. We have previously developed tPA-loaded echogenic liposomes (tPA-ELIP) as an improved thrombolytic formulation. We hypothesized that tPA-ELIP can co-encapsulate another agent for combined treatment with the potential for ultrasound-controlled drug release. MATERIALS AND METHODS: Calcein, a small (MW < 1 kDa) molecular fluorophore, was used as a prototypic hydrophilic drug. Calcein-tPA-ELIP, comprising the fluorophore, protein thrombolytic, phospholipids and cholesterol, were prepared by a lipid drying-rehydration-lyophilization method. Clots were incubated with calcein-tPA-ELIP for 2 minutes in vitro. Transvascular ultrasound imaging was performed before and after the incubation to demonstrate tPA-fibrin binding. Color Doppler ultrasound was applied for 30 seconds to trigger the release of calcein from targeted calcein-tPA ELIP. The fluorescent intensity of calcein in solution was measured before and after ultrasound application. RESULTS: Fifteen percent of calcein was entrapped in tPA-ELIP with retention of ultrasound reflectivity. Transvascular B-mode ultrasound imaging demonstrated specific highlighting of clots by tPA-ELIP. The release of calcein from calcein-tPA-ELIP was triggered by application of Doppler ultrasound. CONCLUSIONS: We have demonstrated co-encapsulation of a hydrophilic drug surrogate and a protein thrombolytic agent into ELIP with targeted clot highlighting and in situ ultrasound-triggered drug release. Co-encapsulation of drugs in tPA-ELIP has potential for thrombus-targeted combination thrombolysis and neuroprotective treatment for stroke.

가속열화 된 CSPE 상태감시법 유효성 평가

The accelerated thermal aging of CSPE(chloro sulfonate polyethylene) of test cables were carried out for the period equal to 10, 20 and 30 years in air at 100℃, respectively. The CSPE cables(TAIHAN electric wire Co. Ltd) which installed in nuclear power plant for three years were used as starting materials. Condition monitering methods of the accelerated thermal aging of CSPE cables were estimated through indenter modulus and OIT(oxidation induction time) of IEC 62582, and those were newly estimated through volume electrical resistivity, ultrasound reflection time, density, FE-SEM(field emission scanning electron microscopy), XPS(x-ray photoelectron spectroscopy), EDS(energy dispersive spectroscopy), and WD-XRF(wavelength dispersive x-ray fluorescence). A new condition monitoring methods of the accelerated thermal aging of CSPE cables were generally coincident with trend of indenter modulus expect EDS, XPS and XRF. A volume electrical resistivity among new condition monitoring methods of the accelerated thermal aging of CSPE cables is excellent. It is considered that life-time of CSPE cable can be predicted through volume electrical resistivity, if CSPE jacket was aged for period such as more than 20 years.

Pulmonary Doppler signals: a potentially new diagnostic tool

To overcome the limitations due to ultrasound attenuation by the air in the lungs, in order to study the pulmonary system using an advanced signal processing technology. Pulsed spectral Doppler signals were obtained over the chest wall using a signal processing and algorithm package (transthoracic parametric Doppler, TPD, EchoSense Ltd, Haifa, Israel) in conjunction with a non-imaging Doppler device (Viasys Healthcare, Madison, WI, USA) coupled with an electrocardiogram. The signals picked up by a transducer positioned at various locations over the chest wall, were treated for noise, analysed parametrically and displayed in terms of both velocity and power originating from moving ultrasound reflectors. Clear reproducible lung Doppler signals (LDS) were recorded. Up to five bidirectional triangular waves with peak velocities of 20-40 cm/s, that survived the 40 dB/cm attenuation of the lung, were recorded during each cardiac cycle. The first signal coincides with early ventricular systole, the second with late systole, the third and fourth with diastole, and the last with atrial contraction. LDS originate from different elements and phases of cardiac activity that generate mechanical waves which propagate throughout the lung and are thus expressed in pulsatile changes in ultrasound reflections. While such signals could originate either from pulsatile blood flow or reflections from movement of the blood vessel--alveolar air interface, the experimental evidence points towards the tissue--air interface movements due to vessel expansion as the origin. The LDS can potentially be an important tool for diagnosing and characterizing cardio-pulmonary physiological states and diseases.

Where did that sound come from? Comparing the ability to localise using audification and audition

Purpose: A prototype device was developed to allow individuals to hear ultrasound reflections off environmental obstacles. Previous studies have shown that this device allows for better distance judgement than audition and allows for effective passage through the centreline of apertures. The purpose of this research was to evaluate audification as a method to localise direct sound sources as compared to audition. Method: In an anechoic environment, participants localised point-sound sources for three conditions: auditory, audified ultrasound with receivers facing laterally, and audified ultrasound with receivers facing forward. Results: Azimuth localisation was similar within a range of −35° to 35° in front of the participant among all conditions. At the periphery, −70° and 70°, audified ultrasound was more accurate than audition for novice participants. No difference was evident in user elevation accuracy for these signals among the different conditions. Conclusion: Audification of ultrasound can be effective for localising point-source sounds in the azimuth direction, but more evidence is required to evaluate accuracy in the vertical direction.Implications for RehabilitationSecondary mobility devices can be used by individuals with visual impairment to avoid obstacles above waist height.Audification allows for skill-based response enabling intuitive obstacle avoidance and localization of point sound sources.Localization of peripheral sounds was shown in this study to be better with audified ultrasound than audition.

OP23.09: Fetal aortic intima media thickness measurement by decomposing unprocessed radio frequency derived ultrasound wall reflection into two Gaussian pulses

OP23.09: Fetal aortic intima media thickness measurement by decomposing unprocessed radio frequency derived ultrasound wall reflection into two Gaussian pulses

Ultrasonic measurements of particle retention by a porous medium

Ultrasound transmission and reflection are utilized to characterize the particle retention in depth of fluid-saturated porous samples under a flow of silt solution. The effect of the concentration of particles in the fluid is investigated via measurements of “comparison coefficients” which are the ratio of the Fourier transforms of the reflected (transmitted) signals before and after the particle flow. Numerical computations of the latter coefficients using Biot–Stoll’s theory are compared to the experimental data. The frequential evolution of physical parameters such as bulk and shear moduli are sought. To this end, a gradient descent algorithm is utilized to minimize the differences between the experimental and calculated comparison coefficients. Several concentrations of suspended particles are investigated to check the validity of this inversion method and a good agreement between theory and experiments is observed.

Integrated Backscatter for the In Vivo Quantification of Supraphysiological Vitamin D3-Induced Cardiovascular Calcifications in Rats

Cardiovascular calcifications are frequently found in the aging population and are independent predictors of future cardiovascular events. Integrated backscatter (IB) of ultrasound reflectivity can easily quantify calcifications. For this purpose, 30 male Wistar rats received 25,000IU/kg/day of vitamin D(3) (group 1, n=8), 18,800IU/kg/day (group 2, n=8), or injections with the vehicle only (group 3, n=14), for 10weeks. Echocardiographic calibrated IB (cIB) was measured and calculated at baseline and after 10weeks, followed by ex vivo micro-CT and histopathology of the aortic valve, ascending aorta, and myocardium. After 10weeks, the mean cIB value of the aortic valve was significantly higher for vitamin D(3)-dosed animals compared to controls. The mean cIB value of the ascending aorta and the myocardium was also significantly higher in group 1 compared to group 3. In vivo IB results were confirmed by ex vivo micro-CT and histopathology. In conclusion, IB is a non-ionizing, feasible, and reproducible tool to quantify cardiovascular calcifications in an in vivo rat model. The integration of IB in the standard echocardiographic examination for the quantification of cardiovascular calcifications could be useful for serial evaluation of treatment efficacy and for prognosis assessment.

What's that sound? Distance determination and aperture passage from ultrasound echoes

Purpose. Individuals with visual impairment have difficulty detecting obstacles that are above waist height. A prototype device was developed to allow individuals to hear ultrasound reflections off environmental obstacles. The purpose of this research was to evaluate novices' ability to evaluate distance and pass through apertures using this device.Method. The first experiment evaluated the ability to judge the distance from a wall using the ultrasound system as compared to using auditory echolocation. The second examined time for passage, centreline accuracy and angle of rotation through different sized apertures.Results. Distance judgement was found to be better with audified ultrasound than with auditory echolocation. When passing through apertures, audified ultrasound enabled centreline precision similar to that of vision, but individuals did not rotate their shoulders while passing through suggesting that more practice is necessary to combine perceptive information with proprioceptive action.Conclusions. The ability to judge distance and navigate through an environment with obstacles using a device which audifies ultrasound was shown to be better than using auditory echolocation, but not as effective as vision. This device will allow individuals with visual impairments to better detect and avoid environmental obstacles.

Impact of left atrial fibrosis and left atrial size on the outcome of catheter ablation for atrial fibrillation

BackgroundLeft atrial (LA) dilatation is an important risk factor for recurrence of atrial fibrillation (AF) after radiofrequency catheter ablation (RFCA). However, the clinical applications to select patients eligible for RFCA...

Method For Ultrasound Perfusion Imaging

An ultrasound imaging system transmits a broad beam of ultrasound into tissues that are perfused with blood containing microbubbles. The ultrasound has an intensity that is sufficient to destroy the microbubbles in the tissues. A plurality of ultrasound imaging beams are then transmitted into the tissues over a sufficient period to allow the tissues to re-perfuse, and reflections from the transmitted imaging beams are processed to provide a perfusion image. The transmitted microbubble-destroying ultrasound may be in the form of a single beam or a plurality of beams that insonify a substantially larger area than the area insonified by the transmitted imaging beams. As a result, the microbubbles are all destroyed at substantially the same time, and the imaging ultrasound is transmitted only into regions of the tissues from which ultrasound reflections will be received.

Effective spring stiffness for a planar periodic array of collinear cracks at an interface between two dissimilar isotropic materials

Explicit analytical expressions are obtained for the longitudinal and transverse effective spring stiffnesses of a planar periodic array of collinear cracks at the interface between two dissimilar isotropic materials; they are shown to be identical in a general case of elastic dissimilarity (the well-known open interface crack model is employed for the solution). Since the interfacial spring stiffness can be experimentally determined from ultrasound reflection and transmission analysis, the proposed expressions can be useful in estimating the percentage of disbond area between two dissimilar materials, which is directly related to the residual strength of the interface. The effects of elastic dissimilarity, crack density and crack interaction on the effective spring stiffness are clearly represented in the solution. It is shown that in general the crack interaction weakly depends on material dissimilarity and, for most practical cases, the crack interaction is nearly the same as that for crack arrays between identical solids. This allows approximate factorization of the effective spring stiffness for an array of cracks between dissimilar materials in terms of an elastic dissimilarity factor and two factors obtained for cracks in a homogeneous material: the effective spring stiffness for non-interacting (independent) cracks and the crack interaction factor. In order to avoid the effect of the crack surface interpenetration zones on the effective spring stiffness, the range of the tensile to transverse load ratios is obtained under the assumption of small-scale contact conditions. Since real cracks are often slightly open (due to prior loading history and plastic deformation), it is demonstrated that for ultrasound applications the results obtained are valid for most practical cases of small interfacial cracks as long as the mid-crack opening normalized by the crack length is at least in the order of 10 −5.

Development and characterization of new nanoscaled ultrasound active lipid dispersions as contrast agents

Ultrasound contrast agents are widely used in clinical diagnosis. In recent years, the use of ultrasound contrast agents as therapeutic agents has gained a lot of attention. Of special interest are ultrasound-enhanced gene delivery in various tissues (e.g. cardiac, vascular, skeletal muscle and tumor tissue), ultrasound-enhanced protein delivery (e.g. insulin delivery) and ultrasound-enhanced delivery of small chemicals (e.g. doxorubicin, vancomycin). Commercially available ultrasound contrast agents such as SonoVue® or Optison® are ranged in a size of 2–8μm. These micronscaled agents show a good ultrasound contrast enhancement and thus they are used for diagnostic imaging. But they are not suitable for targeted drug delivery to tumor tissues or blood clots because for these applications particles smaller than 700nm are needed. In the present study, we developed new nanoscaled ultrasound contrast agents with a size between 70 and 300nm. The lipid formulations show excellent contrast intensities using diagnostic ultrasound of about 1.4MHz. The negatively charged colloidal dispersions are long-time stable under physiological conditions without loss of ultrasound reflectivity. The adjustable supramolecular organization of the carriers depends on the composition and varies from micellar to liposomal structures. The small size and the circulation stability of these systems make them promising for novel diagnostics and controlled drug release applications.

Characterization of Center Frequency and Bandwidth of Broadband Ultrasound Reflected by the Articular Cartilage to Subchondral Bone Interface

Osteoarthritis (OA) produces degenerative changes both in articular cartilage and subchondral bone. During OA, reflection of high frequency ultrasound from the cartilage-bone interface is affected by both changes in attenuation of the cartilage layer and acoustic properties of the interface. The objective of this study was to experimentally investigate the spectral content of ultrasound reflection from the cartilage-bone interface. Specifically, we analyzed the center frequency and –6 dB bandwidth of the broadband high-frequency (40 MHz) ultrasound signal. Intact bovine articular cartilage samples with and without the underlying subchondral bone ( n = 6) were measured in vitro using a commercial high-frequency ultrasound scanner. Furthermore, the diagnostic potential of the measurement of center frequency and bandwidth for OA was studied with another series of bovine articular cartilage samples ( n = 40) after enzymatic degradations of tissue proteoglycans and collagen. Compared with the reference spectrum at the same depth from a perfect reflector, a major downshift (>51%) of the center frequency and a reduction (>42%) of the bandwidth were observed in both sample groups when analyzing the ultrasound reflection from the cartilage-bone interface. The results suggest that attenuation in the cartilage layer primarily controls the observed downshift of the center frequency and acoustic properties of the subchondral bone play only a minor role in affecting the spectrum of the cartilage-bone interface. Changes in the ultrasound bandwidth of the cartilage-bone interface signals, compared with reference signals, were found to vary more than those in the center frequency in both cartilage sample groups. Compared with pretreatment values, a significant downshift in center frequency ( p < 0.01) and a minor reduction in bandwidth of spectra from the cartilage-bone interface were recorded after chemical degradation of proteoglycans with trypsin. In contrast, center frequency and bandwidth of the echoes from the cartilage-bone interface did not change after the chemical degradation of cartilage collagen fibrils. The results suggest that proteoglycan loss, typical to OA, may be detected via the changes in the center frequency of the ultrasound reflected from the cartilage-bone interface. (E-mail: ypzheng@ieee.org, simo.saarakkala@oulu.fi)

Mathematical Model Research on Ultrasonic Breaking Up Dendrite in Preparing Semi-Solid A356

In this paper, we introduce an mathematical theory model of ultrasonic breaking up dendrite through the experiment of put ultrasonic vibration on melting A356, which is based on the condition of the effect factors of particles compelled movement on crystal integrality. It can be seen that two factors are very importment to crushing the grain through ultrasonic vibration, namely, structure conditions of the grain growth and the dynamic conditions provided by the ultrasonic. The driving force provide by the ultrasonic can be direct alternating mechanical force and the second, third and so on sound wave force caused by ultrasound wave reflection, scattering etc.. Form the model we can found that the larger the ultrasonic power and amplitude, conditions can be more easily satisfied; simlarly the higher the ultrasonic frequency, angle crossing number, grain structure defects, the longer action time to make greater fatigue, all this factors can also make the conditions more easily satisfied.

Preparation of a Micro-Porous Alginate Gel Using a Microfluidic Bubbling Device

Demand for low-energy food products has greatly increased in recent years due to the growing concerns over obesity related health problems. The aim of the work described in this short communication was to use a microfluidic T-junction device to prepare microporous calcium alginate gels by incorporating monodisperse air bubbles (177 ?m in diameter) which would both increase the volume to energy content ratio of the product and improve sample homogeneity. Homogeneous, 5mm-thick gel samples were successfully obtained and found to have a density of 365 kg/m3. The high gas content was confirmed by ultrasound reflectivity measurements. The mean pore diameter, determined by optical and SEM measurements, was 131?m with a standard deviation of 57?m.

Quantitative Evaluation of Spontaneously and Surgically Repaired Rabbit Articular Cartilage Using Intra-Articular Ultrasound Method in situ

During the last decade, a major effort has been devoted to developing surgical methods for repairing localized articular cartilage lesions. Despite some promising results no ultimate breakthrough in surgical cartilage repair has been achieved. Improvements in repair techniques would benefit from more sensitive and quantitative methods for long-term follow-up of cartilage healing. In this study, the potential of a new ultrasound technique for detecting the compositional and structural changes in articular cartilage after surgery, using recombinant human type II collagen gel and spontaneous repair was, investigated. Rabbit knee joints containing intact ( n = 13) and surgically ( n = 8) or spontaneously ( n = 5) repaired tissue were imaged in situ at 6 months after the operation using a clinical intravascular high-frequency (40 MHz) ultrasound device. Based on the ultrasound raw data, ultrasound reflection coefficient ( R), integrated ultrasound reflection coefficient ( IRC), apparent integrated backscattering coefficient ( AIB) and ultrasound roughness index ( URI) were determined for each sample. URI was significantly higher in both repair groups than in intact cartilage ( p < 0.05). The reflection parameters ( R and IRC) were significantly lower in surgically repaired cartilage ( p < 0.05) than in intact cartilage. Furthermore, AIB was significantly higher in surgically repaired cartilage than in intact tissue ( p < 0.05). To conclude, the integrity of the rabbit articular cartilage repair could be quantitatively evaluated with the nondestructive ultrasound approach. In addition, clinically valuable qualitative information on the changes in cartilage integration, structure and composition could be extracted from the ultrasound images. In the present study, the structure and properties of repaired tissue were inferior to native tissue at 6 months after the operation. The applied ultrasound device and probes are FDA approved and, thus, applicable for the quantitative in vivo evaluation of human articular cartilage. (E-mail: tviren@hytti.uku.fi)

2-D finite difference time domain model of ultrasound reflection from normal and osteoarthritic human articular cartilage surface

Quantitative high-frequency ultrasonic evaluation of articular cartilage has shown a potential for the diagnosis of osteoarthritis, where the roughness of the surface, collagen and proteoglycan contents, and the density and mechanical properties of cartilage change concurrently. Experimentally, these factors are difficult to investigate individually and thus a numerical model is needed. The present study is the first one to use finite difference time domain modeling of pulse-echo measurements of articular cartilage. Ultrasound reflection from the surface was investigated with varying surface roughness, material parameters (Young's modulus, density, longitudinal, and transversal velocities) and inclination of the samples. The 2-D simulation results were compared with the results from experimental measurements of the same samples in an identical geometry. Both the roughness and the material parameters contributed significantly to the ultrasound reflection. The angular dependence of the ultrasound reflection was strong for a smooth cartilage surface but disappeared for the samples with a rougher surface. These results support the findings of previous experimental studies and indicate that ultrasound detects changes in the cartilage that are characteristic of osteoarthritis. In the present study there are differences between the results of the simulations and the experimental measurements. However, the systematic patterns in the experimental behavior are correctly reproduced by the model. In the future, our goal is to develop more realistic acoustic models incorporating inhomogeneity and anisotropy of the cartilage.

Ultrasound B‐scan image simulation, segmentation, and analysis of the equine tendon

The hypothesis is that an imaging technique based on decompression and segmentation of B-scan images with morphological operators can provide a measurement of the integrity of equine tendons. Two complementary approaches were used: (i) Simulation of B-scan images to better understand the relationship between image properties and their underlying biological structural contents and (ii) extraction and quantification from B-scan images of tendon structures identified in step (i) to diagnose the status of the superficial digital flexor tendon (SDFT) by using the proposed imaging technique. The simulation results revealed that the interfascicular spaces surrounding fiber fascicle bundles were the source of ultrasound reflection and scattering. By extracting these fascicle bundles with the proposed imaging technique, quantitative results from clinical B-scan images of eight normal and five injured SDFTs revealed significant differences in fiber bundle number and areas: mean values were 50 (+/- 11) and 1.33(+/- 0.36) mm2 for the normal SDFT data set. Different values were observed for injured SDFTs where the intact mean fiber bundle number decreased to 40 (+/- 7) (p = 0.016); inversely, mean fiber bundle areas increased to 1.83 (+/- 0.25) mm2 (p = 0.008), which indicate disruption of the thinnest interfascicular spaces and of their corresponding fiber fascicle bundles where lesions occurred. To conclude, this technique may provide a tool for the rapid assessment and characterization of tendon structures to enable clinical identification of the integrity of the SDFT.