Institute of Fundamental Technological Research

Kidney Cooling Jacket (KCJ) preserves the kidney graft, wrapped in the jacket, against the too fast time of temperature rise during the operation of connecting a cooled transplant to the patient’s bloodstream. The efficiency of KCJ depends on the stationarity of the fluid flow and its spatial uniformity. In this paper, the fluid velocity field inside the three different KCJ prototypes has been measured using the 20 MHz ultrasonic Doppler flowmeter. The simplified 2D geometrical model of the prototypes has been presented using COMSOL-Multiphysics to simulate the fluid flow assuming the laminar flow model. By comparing the numerical results with experimental data, the simplified 2D model is shown to be accurate enough to predict the flow distribution of the internal fluid velocity field within the KCJ. The discrepancy between the average velocity measured using the 20 MHz Doppler and numerical results was mainly related to the sensitivity of the velocity measurements to a change of the direction of the local fluid flow stream. Flux direction and average velocity were additionally confirmed by using ommercial colour Doppler imaging scanner. The current approach showed nearly 90% agreement of the experimental results and numerical simulations. It was important for justifying the use of numerical modelling in designing the baffles distribution (internal walls in the flow space) for obtaining the
most spatially uniform field of flow velocity.

multi-canal system; fluid flow prediction; cooling jacket; flow Doppler measurement

A 22 year-old woman with no family history of breast cancer developed a painful breast tumor in the inner lower quadrant of the left breast. After surgical consultation, ultrasound examination was advised. On ultrasound,the mass demonstrated malignant features such as non-parallel orientation, hypoechogenicity, spiculated margins, posterior shadowing, peripheral vessels on color Doppler and increased stiffness in the tissue surrounding the tumor. Before biopsy, mammography was performed. The mass had higher density than fibroglandular tissue, margins were ill-defined (spiculated) and had no microcalcification. BIRADS 5 category was pre-assigned. Core biopsy revealed granular cell tumor (GCT). The patient is undergoing regular follow-up. Granular cell tumor is rare and generally benign, however, it typically demonstrates malignant features clinically and on obtained diagnostic images. This article highlights the variety of imaging features accompanying benign breast tumors.

Breast Cancer,Breast Ultrasound,Granular Cell Tumor

We studied sonochemical reactions resulting from ultrasonic treatment of potassium hexacyanoferrate(II) in aqueous solutions using a custom-built apparatus working at 536 kHz. We concluded that primary reactions are completely dominated by oxidation of Fe(II) to Fe(III) and did not find any evidences for degradation of cyanide. At the highest concentration used in the present study (0.1 M) we detected formation of pentacyanoaquaferrate(II) complex, which is most probably formed in reactions between hexacyanoferrate(III) anions and hydrogen atoms or hydrated electrons formed in sonochemical processes. We also determined that hydroxyl radicals formation rate in our system, (8.7 ± 1.5)∙10^-8 M∙s^-1, is relatively high compared to other reported experiments. We attribute this to focusing of the ultrasonic wave in the sample vessel. Finally, we suggest that oxidation rate of hexacyanoferrate(II) anions can be a convenient benchmark of efficiency of sonochemical reactors.

sonochemistry,sonooxidation,sonoreactor,advanced oxidation processes,waste-water treatment

The article presents a new normalization of flow-mediated dilation (FMD) in the radial artery, taking into account the parameter BSSR being equal to the ratio of the basal shear rate (BS) measured before the cuff inflation and post occlusive shear rate (SR). The in vivo usefulness of the new normalization algorithm wasevaluated in two groups of patients. In group I, comprising 15 healthy volunteers, the normalized FMD/SR was(3.19 ± 1.4)*10^-4, while in group II, comprising 13 patients with stable coronary artery disease (CAD), it was(1.02 ± 0.76)*10^-4. We calculated almost 50% larger difference between the average values after normalizing FMD/BSSR. Specifically, the FMD/BSSR was equal to 28 ± 9.40 in group I and 6.01 ± 3.74 in group II. The prediction of CAD patients based on FMD/SR values had a sensitivity of 83.3% and a specificity of 84.6%, whereas the prediction of CAD patients based on the FMD/BSSR values revealed 100% sensitivity and specificity. These results confirm the usefulness of the novel normalization algorithm of the FMD in differentiation of normal patients from those with stable CAD.

flow-mediated vasodilation, radial artery, shear rate, pulsed Doppler, ultrasonography, coronary artery disease

In the article we describe the new, high frequency, 20 MHz scanning/Doppler probe designed to measure the flow mediated dilation (FMD) and shear rate (SR) close to the radial artery wall. We compare two US scanning systems, standard vascular modality working below 12 MHz and high frequency 20 MHz system designed for FMD and SR measurements. Axial resolutions of both systems were compared by imaging of two closely spaced food plastic foils immersed in water and by measuring systolic/diastolic diameter changes in the radial artery. The sensitivities of Doppler modalities were also determined. The diagnostic potential of a high frequency system in measurements of FMD and SR was studied in vivo, in two groups of subjects, 12 healthy volunteers and 14 patients with stable coronary artery disease (CAD). Over three times better axial resolution was demonstrated for a high frequency system. Also, the sensitivity of the external single transducer 20 MHz pulse Doppler proved to be over 20 dB better (in terms of a signal-to-noise ratio) than the pulse Doppler incorporated into the linear array. Statistically significant differences in FMD and FMD/SR values for healthy volunteers and CAD patients were confirmed, p-values < 0:05. The areas under Receiver Operating Characteristic (ROC) curves for FMD and FMD/SR for the prediction CAD had the values of 0.99 and 0.97, respectively. These results justify the usefulness of the designed high-frequency scanning system to determine the FMD and SR in the radial artery as predictors of coronary arterial disease.

low mediated dilation, shear rate, axial resolution, elevation resolution, pulsed Doppler, ultrasonic imaging

Acoustical Driving Forces (ADF), induced by propagating waves in a homogeneous and inhomogeneous lossy fluid (suspension), are determined and compared depending on the concentration of suspended particles. Using integral equations of the scattering theory, the single particle (inclusion) ADF was calculated as the integral of the flux of the momentum density tensor components over the heterogeneity surface. The possibility of negative ADF was indicated. Originally derived, the total ADF acting on inclusions only, stochastically distributed in ambient fluid, was determined as a function of its concentration. The formula for the relative increase in ADF, resulting from increased concentration was derived. Numerical ADF calculations are presented. In experiments the streaming velocities in a blood-mimicking starch suspension (2 μm radius) in water and Bracco BR14 contrast agent (SF6 gas capsules, 1 μm radius) were measured as the function of different inclusions concentration. The source of the streaming and ADF was a plane 2 mm diameter 20 MHz ultrasonic transducer. Velocity was estimated from the averaged Doppler spectrum obtained from originally developed pulsed Doppler flowmeter. Numerical calculations of the theoretically derived formula showed very good agreement with the experimental results.

streaming suspension, scattering, acoustical driving force, Doppler measurements, contrast agents

Objective: Neoadjuvant chemotherapy was initially used in locally advanced breast cancer, and currently it is recommended for patients with Stage 3 and with early-stage disease with human epidermal growth factor receptors positive or triple-negative breast cancer. Ultrasound imaging in combination with a quantitative ultrasound method is a novel diagnostic approach. Aim of study: The aim of this study was to analyze the variability of the integrated backscatter coefficient, and to evaluate their use to predict the effectiveness of treatment and compare to ultrasound examination results. Material and method: Ten patients (mean age 52.9) with 13 breast tumors (mean dimension 41 mm) were selected for neoadjuvant chemotherapy. Ultrasound was performed before the treatment and one week after each course of neoadjuvant chemotherapy. The dimensions were assessed adopting the RECIST criteria. Tissue responses were classified as pathological response into the following categories: not responded to the treatment (G1, cell reduction by ≤9%) and responded to the treatment partially: G2, G3, G4, cell reduction by 10–29% (G2), 30–90% (G3), >90% (G4), respectively, and completely. Results: In B-mode examination partial response was observed in 9/13 cases (completely, G1, G3, G4), and stable disease was demonstrated in 3/13 cases (completely, G1, G4). Complete response was found in 1/13 cases. As for backscatter coefficient, 10/13 tumors (completely, and G2, G3, and G4) were characterized by an increased mean value of 153%. Three tumors 3/13 (G1) displayed a decreased mean value of 31%. Conclusion: The variability of backscatter coefficient, could be associated with alterations in the structure of the tumor tissue during neoadjuvant chemotherapy. There were unequivocal differences between responded and non-responded patients. The backscatter coefficient analysis correlated better with the results of histopathological verification than with the B-mode RECIST criteria.

integrated backscatter coefficient (IBSCs), neoadjuvant chemotherapy (NAC), breast cancer, ultrasound

A high-frequency scanning system consisting of a 20-MHz linear array transducer combined with a 20-MHz pulsed Dopplerprobe was introduced to evaluate the degree of radial artery flow-mediated dilation (FMD [%]) in two groups of patients after5 min of controlled forearm ischemia followed by reactive hyperemia. In group I, comprising 27 healthy volunteers, FMD (mean ± standard deviation) was 15.26 ± 4.90% (95% confidence interval [CI]: 13.32%–17.20%); in group II, comprising 17 patients with chronic coronary artery disease, FMD was significantly less at 4.53 ± 4.11% (95% CI: 2.42%–6.64%). Specifically, the ratio FMD/SR (mean ± standard deviation),wasequalto5.36×10−4±4.64×10−4 (95%CI:3.54×10−4 to7.18×10−4)ingroupIand1.38×10−4±0.89×10−4 (95% CI: 0.70 × 10−4 to 2.06 × 10−4) in group II. Statistically significant differences between the two groups were confirmed by a Wilcoxon–Mann–Whitney test for both FMD and FMD/SR (p < 0.01). Areas under receiver operating characteristic curves for FMD and FMD/SR were greater than 0.9. The results confirm the usefulness of the proposed measurements of radial artery FMD and SR in differentiation of normal patients from those with chronic coronary artery disease. (E-mail: anowicki@ippt.gov.pl) © 2018 World Federation for Ultrasound in Medicine & Biology. All rights reserved.

Flow-mediated vasodilation, Radial artery, Shear rate, Reactive hyperemia, Endothelium, Pulsed doppler, Ultrasonography

A technique using pulsed High Intensity Focused Ultrasound (HIFU) to destroy deep-seated solid tumors is a promising noninvasive therapeutic approach. A main purpose of this study was to design and test a HIFU transducer suitable for preclinical studies of efficacy of tested, anti-cancer drugs, activated by HIFU beams, in the treatment of a variety of solid tumors implanted to various organs of small animals at the depth of the order of 1–2 cm under the skin. To allow focusing of the beam, generated by such transducer, within treated tissue at different depths, a spherical, 2-MHz, 29-mm diameter annular phased array transducer was designed and built. To prove its potential for preclinical studies on small animals, multiple thermal lesions were induced in a pork loin ex vivo by heating beams of the same: 6 W, or 12 W, or 18 W acoustic power and 25 mm, 30 mm, and 35 mm focal lengths. Time delay for each annulus was controlled electronically to provide beam focusing within tissue at the depths of 10 mm, 15 mm, and 20 mm. The exposure time required to induce local necrosis was determined at different depths using thermocouples. Location and extent of thermal lesions determined from numerical simulations were compared with those measured using ultrasound and magnetic resonance imaging techniques and verified by a digital caliper after cutting the tested tissue samples. Quantitative analysis of the results showed that the location and extent of necrotic lesions on the magnetic resonance images are consistent with those predicted numerically and measured by caliper. The edges of lesions were clearly outlined although on ultrasound images they were fuzzy. This allows to conclude that the use of the transducer designed offers an effective noninvasive tool not only to induce local necrotic lesions within treated tissue without damaging the surrounding tissue structures but also to test various chemotherapeutics activated by the HIFU beams in preclinical studies on small animals.

spherical annular phased array transducer, pulsed HIFU beam, electronically adjustable focal length, local tissue heating, thermal ablation, necrotic lesion

The purpose of this work was to determine the influence of standing waves and possible multiple reflections under the conditions often encountered in examining the effects of ultrasound exposure on the cell cultures in vitro. More specifically, the goal was to quantitatively ascertain the influence of ultrasound exposure under free field (FF) and standing waves (SW) and multiple reflections (MR) conditions (SWMR) on the biological endpoint (50% cell necrosis). Such information would help in designing the experiments, in which the geometry of the container with biological tissue may prevent FF conditions to be established and in which the ultrasound generated temperature elevation is undesirable. This goal was accomplished by performing systematic, side-by-side experiments in vitro with C6 rat glioma cancer cells using 12 well and 96 well plates. It was determined that to obtain 50% of cell viability using the 12 well plates, the spatial average, temporal average (ISATA) intensities of 0.32 W/cm2 and 5.89 W/cm2 were needed under SWMR and FF conditions, respectively. For 96 well plates the results were 0.80 W/cm2 and 2.86 W/cm2 respectively. The corresponding, hydrophone measured pRMS maximum pressure amplitude values, were 0.71 MPa, 0.75 MPa, 0.75 MPa and 0.73 MPa, respectively. These results suggest that pRMS pressure amplitude was independent of the measurement set-up geometry and hence could be used to predict the cells' mortality threshold under any in vitro experimental conditions or even as a starting point for (pre-clinical) in vivo tests. The described procedure of the hydrophone measurements of the pRMS maximum pressure amplitude at the k/2 distance (here 0.75 mm) from the cell's level at the bottom of the dish or plate provides the guideline allowing the difference between the FF and SWMR conditions to be determined in any experimental setup. The outcome of the measurements also indicates that SWMR exposure might be useful at any ultrasound assisted therapy experiments as it permits to reduce thermal effects. Although the results presented are valid for the experimental conditions used in this study they can be generalized. The analysis developed provides methodology facilitating independent laboratories to determine their specific ultrasound exposure parameters for a given biological end-point under standing waves and multiple reflections conditions. The analysis also permits verification of the outcome of the experiments mimicking pre- and clinical environment between different, unaffiliated teams of researchers.

Standing wave, Ultrasound pressure, Ultrasound intensity, C6 glioma, Anticancer therapy, Sonodynamic therapy, Ultrasound bio-effects

Streaming velocity depends on intensity and absorption of ultrasound in the media. In some cases, such as ultrasound scattered on blood cells at high frequencies, or the presence of ultrasound contrast agents, scattering affects the streaming speed. The velocities of acoustic streaming in a blood-mimicking starch suspension in water and Bracco BR14 contrast agent were measured. The source of the streaming was a plane 20MHz ultrasonic transducer. Velocity was estimated from the averaged Doppler spectrum. The single particle driving force was calculated as the integral of the momentum density tensor components. For different starch concentrations, the streaming velocity increased from 8.9 to 12.5mm/s. This corresponds to a constant 14% velocity increase for a 1 g/l increase in starch concentration. For BR14, the streaming velocity remained constant at 7.2mm/s and was independent of the microbubbles concentration. The velocity was less than in reference, within 0.5mm/s measurement error. Theoretical calculations showed a 16% increase in streaming velocity for 1 g/l starch concentration rise, very similar to the experimental results. The theory has also shown the ability to reduce the streaming velocity by low-density scatterers, as was experimentally proved using the BR14 contrast agent.

ultrasound, radiation force, starch, contrast agent, blood, thrombolysis

In therapeutic applications of High Intensity Focused Ultrasound (HIFU) the guidance of the HIFU beam and especially its focal plane is of crucial importance. This guidance is needed to appropriately target the focal plane and hence the whole focal volume inside the tumor tissue prior to thermo-ablative treatment and beginning of tissue necrosis. This is currently done using Magnetic Resonance Imaging that is relatively expensive. In this study an ultrasound method, which calculates the variations of speed of sound in the locally heated tissue volume by analyzing the phase shifts of echo-signals received by an ultrasound scanner from this very volume is presented. To improve spatial resolution of B-mode imaging and minimize the uncertainty of temperature estimation the acoustic signals were transmitted and received by 8 MHz linear phased array employing Synthetic Transmit Aperture (STA) technique. Initially, the validity of the algorithm developed was verified experimentally in a tissue-mimicking phantom heated from 20.6 to 48.6°C. Subsequently, the method was tested using a pork loin sample heated locally by a 2 MHz pulsed HIFU beam with focal intensity ISATA of 129 W/cm2. The temperature calibration of 2D maps of changes in the sound velocity induced by heating was performed by comparison of the algorithm-determined changes in the sound velocity with the temperatures measured by thermocouples located in the heated tissue volume. The method developed enabled ultrasound temperature imaging of the heated tissue volume from the very inception of heating with the contrast-to-noise ratio of 3.5–12 dB in the temperature range 21–56°C. Concurrently performed, conventional B-mode imaging revealed CNR close to zero dB until the temperature reached 50°C causing necrosis. The data presented suggest that the proposed method could offer an alternative to MRI-guided temperature imaging for prediction of the location and extent of the thermal lesion prior to applying the final HIFU treatment.

Ultrasonic temperature imaging, HIFU, Echo phase shift, Velocity image contrast

Sonodynamic therapy (SDT) is a promising technique based on the ability of certain substances, called sonosensitizers, to sensitize cancer cells to non-thermal effects of low-energy ultrasound waves, allowing their destruction. Sonosensitization is thought to induce cell death by direct physical effects such as cavitation and acoustical streaming as well as by complementary chemical reactions generating oxygen free radicals. One of the promising sonosensitizers is 5-aminolevulinic acid (ALA) which upon selective uptake by cancer cells is metabolized and accumulated as protoporphyrin IX. The objective of the study was to describe ALA-mediated sonodynamic effects in vitro on a rat RG2 glioma cell line. Glioma cells, seeded at the bottom of 96-well plates and incubated with ALA (10 μg/ml) for 6 h, were exposed to the sinusoidal US pulses with a resonance frequency of 1 MHz, 1000 μs duration, 0.4 duty-cycle, and average acoustic power varying from 2 W to 6 W. Ultrasound waves were generated by a flat circular piezoelectric transducer with a diameter of 25 mm. Cell viability was determined by MTT assay. Structural cellular changes were visualized with a fluorescence microscope. Signs of cytotoxicity such as a decrease in cell viability, chromatin condensation and apoptosis were found. ALA-mediated SDT evokes cytotoxic effects of low intensity US on rat RG2 glioma cells in vitro. This cell line is indicated for further preclinical assessment of SDT in in vivo conditions.

5-aminolevulinic acid, sonodynamic therapy, rat RG2 glioma cells, cell viability

Therapeutic and surgical applications of High Intensity Focused Ultrasound (HIFU) require monitoring of local temperature rises induced inside tissues. It is needed to appropriately target the focal plane, and hence the whole focal volume inside the tumor tissue, prior to thermo-ablative treatment, and the beginning of tissue necrosis. In this study we present an ultrasound method, which calculates the variations of the speed of sound in the locally heated tissue. Changes in velocity correspond to temperature change. The method calculates a 2D distribution of changes in the sound velocity, by estimation of the local phase shifts of RF echo-signals backscattered from the heated tissue volume (the focal volume of the HIFU beam), and received by an ultrasound scanner (23). The technique enabled temperature imaging of the heated tissue volume from the very inception of heating. The results indicated that the contrast sensitivity for imaging of relative changes in the sound speed was on the order of 0.06%; corresponding to an increase in the tissue temperature by about 2 °C.

HIFU, echo phase shift, parametric imaging, velocity/brightness CNR

Background:
There is a growing interest in the application of non-invasive clinical tools allowing one to assess the endothelial function, preceding atherosclerosis. The precision in estimating of the artery Flow Mediated Vasodilation (FMD) using standard 10-12 MHz linear array probes does not exceed 0.2 mm, far beyond that required.

Methods:
We have introduced a wide-band, high frequency 25-30 MHz, Golay encoded wobbling type imaging to measure dilation of the radial artery instead of the brachial one. 18 young volunteers, and 4 volunteers with cardiac events history, were examined. In the second approach 20 MHz linear scanning combined with 20 MHz pulsed Doppler attached to the linear array was used. The radial artery FMD was normalized using shear rate at the radial artery wall.

Results and Conclusions:
For the “healthy” group, the FMD resulting from reactive hyperemia response was over 20%; while in the “atherosclerotic” group, the FMD was at least twice as small, not exceeding 10%. The shear rate (SR) normalized FMDSR was in the range from 7.8 to 9.9 in arbitrary units, while in patients with minor cardiac history FMDSR was clearly lower, 6.8 to 7.6. The normalized FMDSR of radial artery RARR can be an alternative to the brachial FMD where the precision of measurements is lower and the diameter dilation does not exceed 7-10%.

thick film transducers, atherosclerosis, flow mediated vasodilation

The aim of this work was to use the streaming phenomena to assist clot dissolution in blood vessel. Such treatment is called sonothrombolysis. Acoustic streaming is a steady flow in a fluid driven by the acoustic wave propagating in a lossy medium. It is a non-linear effect and it depends on ultrasound intensity, and sound absorption in the media.

The source of ultrasound was a flat piezoceramic disc generating long pulses at 1 MHz frequency and 0.2 W/cm2 ITA acoustical intensity. The streaming was generated in a vessel simulating free space, and next repeated in a multi-well cell culture plate, and in the limited space inside the 8 mm diameter silicone tube positioned perpendicular to the ultrasonic beam. The tube was filled with a mixture of water, glycerol, and starch, so with acoustic properties similar to blood. The streaming velocity was recorded either by the Siemens Acuson Antares ultrasonic scanner operating in the color Doppler mode at 8.9 MHz, or by the custom built 20 MHz pulsed Doppler flowmeter.

The results obtained using both systems were very similar. The recorded streaming velocities were 3.2 cm/s, 6.1 cm/s and 0.3 cm/s, respectively. They were an order of magnitude smaller than that calculated theoretically. However, the results obtained confirm existence of streaming, even very close to the source, in the limited space. This effect will be explored in in-vitro experiments of blood clot dissolution within the tube simulating a blood vessel.

ultrasound, radiation force, blood, thrombolysis

A tissue thermal conductivity (Ks) is an important parameter which knowledge is essential whenever thermal fields induced in selected organs are predicted. The main objective of this study was to develop an alternative ultrasonic method for determining Ks of tissues in vitro suitable for living tissues. First, the method involves measuring of temperature-time T(t) rises induced in a tested tissue sample by a pulsed focused ultrasound with measured acoustic properties using thermocouples located on the acoustic beam axis. Measurements were performed for 20-cycle tone bursts with a 2 MHz frequency, 0.2 duty-cycle and 3 different initial pressures corresponding to average acoustic powers equal to 0.7 W, 1.4 W and 2.1 W generated from a circular focused transducer with a diameter of 15 mm and f-number of 1.7 in a two-layer system of media: water/beef liver. Measurement results allowed to determine position of maximum heating located inside the beef liver. It was found that this position is at the same axial distance from the source as the maximum peak-peak pressure calculated for each nonlinear beam produced in the two-layer system of media. Then, the method involves modeling of T(t) at the point of maximum heating and fitting it to the experimental data by adjusting Ks. The averaged value of Ks determined by the proposed method was found to be 0.5±0.02 W/(m·°C) being in good agreement with values determined by other methods. The proposed method is suitable for determining Ks of some animal tissues in vivo (for example a rat liver).

Acoustics, Sound pressure, Beef, Thermal conductivity, Thermocouples, Nonlinear systems, Sound waves, Bioacoustics

In order to have consistent and repeatable effects of sonodynamic therapy (SDT) on various cancer cells or tissue lesions we should be able to control a delivered ultrasound energy and thermal effects induced. The objective of this study was to investigate viability of rat C6 glioma cells in vitro depending on the intensity of ultrasound in the region of cells and to determine the exposure time inducing temperature rise above 43°C, which is known to be toxic for cells. For measurements a planar piezoelectric transducer with a diameter of 20 mm and a resonance frequency of 1.06 MHz was used. The transducer generated tone bursts with 94 μs duration, 0.4 duty-cycle and initial intensity ISATA (spatial averaged, temporal averaged) varied from 0.33 W/cm2 to 8 W/cm2 (average acoustic power varied from 1 W to 24 W). The rat C6 glioma cells were cultured on a bottom of wells in 12-well plates, incubated for 24 h and then exposed to ultrasound with measured acoustic properties, inducing or causing no thermal effects leading to cell death. Cell viability rate was determined by MTT assay (a standard colorimetric assay for assessing cell viability) as the ratio of the optical densities of the group treated by ultrasound to the control group. Structural cellular changes and apoptosis estimation were observed under a microscope. Quantitative analysis of the obtained results allowed to determine the maximal exposure time that does not lead to the thermal effects above 43°C in the region of cells for each initial intensity of the tone bursts used as well as the threshold intensity causing cell death after 3 min exposure to ultrasound due to thermal effects. The averaged threshold intensity was found to be about 5.7 W/cm2.

Cancer cells, Photo-sensitizers, Sonodynamic therapy, Thermal effects, Ultrasonic beam properties

Therapeutic and surgical applications of focused ultrasound require monitoring of local temperature rises induced inside tissues. From an economic and practical point of view ultrasonic imaging techniques seem to be the most suitable for the temperature control. This paper presents an implementation of the ultrasonic echoes displacement estimation technique for monitoring of local temperature rise in tissue during its heating by focused ultrasound The results of the estimation were compared to the temperature measured with thermocouple. The obtained results enable to evaluate the temperature fields induced in tissues by pulsed focused ultrasonic beams using non-invasive imaging ultrasound technique

HIFU, therapeutic ultrasound, ultrasonic imaging, echo strain estimation

Sonodynamic therapy is the ultrasound dependent enhancement of the cytotoxic activities of certain drugs called sonosensitizers. The study of therapeutic efficacy of ultrasound is always preceded by in-vitro tests. In this work, two in-vitro sonication procedures were compared. One with the transducer positioned bellow the cell colony, radiating upward, with standing wave reflected from the water-air surface, the second, in the free field conditions. Efficiency of the cancer cells necrosis caused by ultrasound was compared with acoustical field intensity ISPTA measured by a hydrophone. The standing wave conditions effectively increased the intensity of the ultrasonic wave at the level of cells. To achieve 50% of cell viability, the intensity ISATA, decreased from 5.8 W/cm2 to 0.3 W/cm2. In summary, sonication in the standing wave conditions can effectively and reproducibly destroy cells by ensuring the sterility and without the risk of overheating.

ultrasound, sonodynamic therapy, cancer cells, necrosis

Many therapeutic applications of pulsed focused ultrasound are based on heating of detected lesions which may be localized in tissues at different depths under the skin. In order to concentrate the acoustic energy inside tissues at desired depths a new approach using a planar multi-element annular array transducer with an electronically adjusted time-delay of excitation of its elements, was proposed. The 7-elements annular array transducer with 2.4 MHz center operating frequency and 20 mm outer diameter was produced. All its elements (central disc and 6 rings) had the same radiating area. The main purpose of this study was to investigate thermal fields induced in bovine liver in vitro by pulsed focused ultrasonic beams with various acoustic properties and electronically steered focal plane generated from the annular array transducer used. The measurements were performed for the radiating beams with the 20 mm focal depth. In order to maximize nonlinear effects introducing the important local temperature rise, the measurements have been performed in two-layer media comprising of a water layer, whose thickness was specific for the transducer used and equal to 13 mm, and the second layer of a bovine liver with a thickness of 20 mm. The thickness of the water layer was determined numerically as the axial distance where the amplitude of the second harmonics started to increase rapidly. The measurements of the temperature rise versus time were performed using a thermocouple placed inside the liver at the focus of the beam. The temperature rise induced in the bovine liver in vitro by beams with the average acoustic power of 1W, 2W, and 3W and duty cycle of 1/5, 1/15 and 1/30, respectively, have been measured. For each beam used the exposure time needed for the local tissue heating to the temperature of 43◦C (used in therapies based on ultrasonic enhancement of drug delivery or in therapies involving stimulation of immune system by enhancement of the heat shock proteins expression) and to the temperature of 56◦C (used in HIFU therapies) was determined. Two sets of measurements were done for each beam considered. First, the thermocouple measurement of the temperature rise was done and next, the real-time monitoring of dynamics of growth of the necrosis area by using ultrasonic imaging technique, while the sample was exposed to the same acoustic beam. It was found that the necrosis area becomes visible in the ultrasonic image only for beams with the average acoustic power of 3 W, although after cutting the sample the thermally ablated area was visible with the naked eye even for the beams with lower acoustic power. The quantitative analysis of the obtained results allowed to determine the exposure time needed to get the necrosis area visible in the ultrasonic image.

annular array transducer, pulsed focused nonlinear ultrasound, electronically moved focus, tissue heating, biological effects, tissue necrosis

The use of therapeutic ultrasound continues to grow. A focused ultrasonic wave can increase the tissue temperature locally for the non-invasive cancer treatment or other medical applications. The authors have designed a seven-element annular array transducer operating at 2.4 MHz. Each element was excited by sine burst supplied by a linear amplifier and FPGA control circuits. The acoustic field, generated by a transducer was initially numerically simulated in a computer and next compared to water tank hydrophone measurements performed at 20, 40 and 60 mm focal depth. The results showed good agreement of the measurements with theory and the possibility to focus the ultrasound in the preselected area. The total acoustic power radiated by the annular array was equal to 2.4W.

ultrasonic therapy, annular array transducer, ultrasonic field

A clinically applicable method for noninvasive measurement of hematocrit based on 20 MHz multigate Doppler ultrasound was developed. The ultrasound attenuation coefficient in blood is obtained by measuring the power of the signal coming from gates at different depths. A robust averaging method is introduced, which provides stable and repeatable results by using the echo signals from all depths inside the vessel. In vitro measurements have been done on porcine blood with hematocrit ranging from 3.0% to 65.0%. Steady and pulsatile flow conditions have been simulated using a peristaltic pump. The attenuation coefficient indicated the linear relation to hematocrit. The resulting correlation coefficient was R=0.999 for the continuous blood flow and R=0.992 for pulsatile flow. In vivo measurements have been performed in the brachial artery in 43 patients with hematocrit in the range of 32.0% to 49.3%. The mean absolute error has been 3.24% with a standard deviation of 3.72%.

blood, hematocrit, Doppler, ultrasonic attenuation

The gas filled polymer spheres are used either as an ultrasonic contrast agents or controlled drug delivery microcapsules. The power spectrum of the ultrasonic backscattered signal was calculated from the resonance scattering theory for the gas bubbles surrounded by elastic shield. The size distribution of the measured microspheres was included in the calculations. In experiment, the backscattered power spectrum of measured sample was recorded by Siemens Antares ultrasonic scanner. Radio frequency (RF) data was recorded for 2.5 – 6.7 MHz transmitted ultrasonic frequencies. The backscattered spectra were calculated by Matlab software and subtracted from the transmitter spectrum, recorded as an echo from the perfect reflector. The particle size in measured sample was 12 μm mean ± 8 μm sd. The resonance frequency, measured under the microscope, was 0.60 MHz for 45 μm diameter microsphere which corresponds to 2.25 MHz for 12 μm sphere. The sample volume was 10cm³ and the mean quantity of scatterers was 6·103/cm³. In conclusion, measured spectra matched those calculated from theory. The use of ultrasonic scanner with RF data output and the high sensitivity, wide bandwidth ultrasonic transducer allows to measure backscattered signal from the very small quantity of resonance scatterers with satisfactory results at 40 dB signal to noise ratio.

ultrasound, ultrasonic contrast agents, microcapsules, resonance frequency

This study investigates a new composing method of double transmission of short coded sequences based on well-known Golay complementary codes, which allow to obtain the higher signal-to-noise ratio (SNR) and increase penetration depth. The proposed method can potentially find application in small parts ultrasonography and play important role in examination of superficial structures, e.g. in dermatology, ophthalmology, etc., where using longer coded sequences leads to increase of a dead zone and single pulse transmission of short sequences does not assure sufficient SNR. This paper discusses the comparison of results obtained during the examination of four different lengths pairs of Golay coded sequences excited at 3.7 MHz: the single 64-bits pair of Golay sequences and combined sequences consisting of two 8-, 16-, and 32-bits Golay codes separated in time. The experimental results have shown that using the double pulse transmission allows to suppress considerably the noise level, the SNR increases by 5.7 dB in comparison with the single pulse transmission of Golay sequences of the same length. The results of this work indicate that double pulse transmission enhances SNR while maintaining the dead zone short.

Golay complementary sequences, double pulse transmission, dead zone

Two 3.7 MHz focused ultrasonic transducers were built. One without backing and the second loaded on back. The primary application of the first transducer is Doppler blood flow measuring ultrasonic devices, the second is most useful for the B-mode imaging devices. The electrical and acoustical properties were tested and finally the results of the different Golay code excitations were compared. Efficiency of the not backed transducer was 4.1 dB higher. The not backed transducer performed maximum sensitivity for 8 bit two periods per bit code excitation. The backed transducer achieved maximum axial resolution for 16 bit one period per bit excitation.

ultrasonic transducers, imaging, backing, coded excitation, Golay codes

An influence effect of fractional bandwidth of ultrasound imaging transducer on the gain of compressed echo signal being the complementary Golay sequences (CGS) with different spectral widths is studied in this paper. Also, a new composing transmission method of CGS is discussed together with compression technique applied in order to increase the signal-to-noise ratio (SNR) and penetration.
The CGS with two different bit lengths, one-cycle and two-cycles are investigated. Two transducers with fractional bandwidth of 25% and 80% at centre frequency 6 MHz are used. The experimental results are presented, clearly proofing that increasing of the code length leads to compressed echo amplitude enhancement. The smaller the bandwidth is the larger is this effect; the pulse-echo sensitivity of the echo amplitude increases by 1.88 for 25% fractional bandwidth and 1.47 for 80% while preserving time resolution. The presented results of double transmission of short codes show the penetration and SNR improvement while maintaining dead zone.

ultrasound, transducer, bandwidth, Golay code

We present a new method that uses nonlinear properties of tissue to improve contrast-to-noise ratio.
In our novel method, the acoustic source is activated with two tone-bursts (2.2 and 4.4 MHz), with specially designed polarization of the individual tone-burst. This new approach is called multitone nonlinear coding (MNC) because the choice of polarization of both tones (and their amplitudes), allowing optimization of the receiving properties, depends on the nonlinear properties of tissue. The calculations were done for two tone-bursts propagating in the tissue-like glossy medium with absorption of 7 Np/m · MHz. The method was experimentally verified by scanning the incident pulses propagating in soft tissue and by scanning the thread phantom immersed in water. The concept of the virtual fields was introduced to explain abilities and properties of pulse inversion and MNC and to compare the two methods. Comparison of the spatial field distribution obtained using MNC with the conventional harmonic imaging approach, in which the second harmonic is used to reconstruct the image, is presented. It was shown that, for the same peak pressure amplitude, the resulting mechanical index was about 40% lower for MNC, lateral resolution was 10% to 30% better and, what seems to be the most encouraging, the signal gain was up to eight times higher than pulse inversion.

harmonic imaging, ultrasonography, nonlinear propagation

In contrast to previously published papers [A. Nowicki, Z. Klimonda, M. Lewandowski, J. Litniewski, P.A. Lewin, I. Trots, Comparison of sound fields generated by different coded excitations – Experimental results, Ultrasonics 44 (1) (2006) 121–129; J. Litniewski, A. Nowicki, Z. Klimonda, M. Lewandowski, Sound fields for coded excitations in water and tissue: experimental approach, Ultrasound Med. Biol. 33 (4) (2007) 601–607], which examined the factors influencing the spatial resolution of coded complementary Golay sequences (CGS), this paper investigates the effect of ultrasound imaging transducer’s fractional bandwidth on the gain of the compressed echo signal for different spectral widths of the CGS. Two different bit lengths were considered, specifically one and two cycles. Three transducers having fractional bandwidth of 25%, 58% and 80% and operating at frequencies 6, 4.4 and 6 MHz, respectively were examined (one of the 6 MHz sources was focused and made of composite material). The experimental results have shown that by increasing the code length, i.e. decreasing the bandwidth, the compressed echo amplitude could be enhanced. The smaller the bandwidth was the larger was the gain; the pulse-echo sensitivity of the echo amplitude increased by 1.88, 1.62 and 1.47, for 25%, 58% and 80% bandwidths, respectively. These results indicate that two cycles bit length excitation is more suitable for use with bandwidth limited commercially available imaging transducers. Further, the time resolution is retained for transducers with two cycles excitation providing the fractional bandwidth is lower than approximately 90%. The results of this work also show that adjusting the code length allows signal-to-noise-ratio (SNR) to be enhanced while using limited (less that 80%) bandwidth imaging transducers. Also, for such bandwidth limited transducers two cycles excitation would not decrease the time resolution, obtained with ‘‘conventional’’ spike excitation. Hence, CGS excitation could be successfully implemented with the existing, relatively narrow band imaging transducers without the need to use usually more expensive wideband, composite ones.

ultrasound imaging, transducer bandwidth, complementary Golay sequences

The maximization of penetration depth with concurrent retaining or enhancement of image resolution constitutes one of the time invariant challenges in ultrasound imaging. To solve this problem a pulse compression technique employing long coded sequences is now under intensive investigation and in fact some of the corresponding techniques were already implemented in commercial scanning machines. This paper investigates the influence of the effective bandwidth of the transducer on the behaviour of the encoding/compression technique and its potential influence on the axial resolution. We have investigated two different bits lengths – one and two periods – in the Golay sequences resulting in substantial difference of the bandwidth of the transmitted sequences. Three transducers with different fractional bandwidths were used in the experiments: 6 MHz focused transducer with 25% fractional bandwidth, 4.4 MHz flat transducer with 58% fractional bandwidth and 6 MHz flat, composite transducer with 80% fractional bandwidth. The experimental results are clearly showing that the elongation of the Golay single bit length (two cycles in our case) compensates for the limited transducer bandwidth. For 25% bandwidth peak-to-peak echo increased by 1.89 times; for 58% bandwidth peak-to-peak echo amplitude increased by 1.62 times, and for 80% bandwidth peak-to-peak echo increased by 1.47 times.

ultrasound imaging, transducer bandwidth, Golay complementary sequences

This study concerns the development and investigation of a new composing method of short coded sequences and their transmission based on well-known Golay complementary codes and applied compression technique allowing to increase the signal-to-noise ratio (SNR) and penetration. This new method can potentially play important role in examination of superficial structures, e.g. dermatology, ophthalmology, etc. This paper reports the results of examination of the two pairs 3.5 MHz coded sequences of the same duration: the single 32-bits pair Golay sequences and combined sequences consisting of two 16-bits Golay codes separated in time. The results clearly demonstrate the potential of the combined coded transmission obtaining the SNR = 22.6 dB that is 2.6 dB higher than for the traditional Golay sequences and it is in case when coded length is two times shorter. For obtaining the same SNR using traditional method the code length should be at least 64 bits long, resulting in the increased dead zone up to 1.4 cm.

Golay complementary sequences, double transmission, dead zone

Objective:
The goal of this work was to develop a clinically applicable method for non-invasive acoustic determination of hematocrit in vivo.

Methods:
The value of hematocrit (HCT) was determined initially in vitro from the pulse-echo measurements of acoustic attenuation. The testing was carried out using a laboratory setup with ultrasound transducer operating at 20 MHz and employing human blood samples at the temperature of 37C. The attenuation coefficient measurements in blood in vitro and in vivo were implemented using multi-gated (128-gates), 20 MHz pulse Doppler flow meter. The Doppler signal was recorded in the brachial artery. Both in vitro and in vivo HCT data were compared with those obtained using widely accepted, conventional centrifuge method.

Results:
The attenuation coefficient in vitro was determined from the measurements of 168 samples with hematocrit varying between 23.9 and 51.6%. Those experiments indicated that the coefficient increased linearly with hematocrit. The HCT value was obtained from the 20 MHz data using regression analysis. The attenuation (() was determined as a 42.14 + 1.02*HCT (Np/m). The corresponding standard deviation (SD), and the correlation coefficient were calculated as SD = 2.4 Np/m, and R = 0.9, (p<0.001), respectively The absolute accuracy of in vivo measurements in the brachial artery was determined to be within 5% HCT.

Conclusions:
The method proposed appears to be promising for in vivo determination of hematocrit as 5% error is adequate to monitor changes in patients in shock or during dialysis. It was found that the multigate system largely simplified the placement of an ultrasonic probing beam in the center of the blood vessel. Current work focuses on enhancing the method’s applicability to arbitrary selected vessels and reducing the HCT measurement error to well below 5%.

hematocrit, blood, Doppler, power Doppler, multigate Doppler

An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation, the solution of the Navier-Stokes equation for the axial components of the streaming velocity. The theoretical model was verified experimentally using a 32 MHz pulsed Doppler unit. The experimental acoustical fields were produced by three different 4 mm diameter flat and focused transducers driven by the transmitter generating the average acoustic power within the range from 1 microW to 6 mW. The streaming velocity was measured along the ultrasonic beam from 0 to 2 cm. Streaming was induced in a solution of water and corn starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water, changed from 0.3 to 40 grams of starch in 1 l of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2 to 40 mm/s. Both, the theoretical solutions for plane and focused waves and the experimental results were in good agreement. The streaming velocity field was also visualised using the particle image velocimetry (PIV) and two different evaluation methods. The first based on the FFT-based cross-correlation analysis between small sections for each pair of images and the second employing the algorithm of searching for local displacements between several images.

The pressure gradient along the ultrasonic beam results in medium streaming. Following Nyborg's analysis of the Navier-Stokes equation, Wu and Du developed an approximate solution for the streaming velocity generated by flat and weakly focused transducers. We have modified their solution of the Poisson equation by directly deriving the Dirichlet boundary conditions to be applied for this type of equation. Our numerical results (for the linear case) were about one half smaller for flat and weakly focused Gaussian beam transducers compared to the results by Wu and Du. The theoretical calculations were verified using a purpose-designed 32-MHz pulsed Doppler unit. The applied average acoustic power was changed from 1 μW to 6 mW, the burst width was 0.5 μs and the pulse repetition frequency was 32 kHz. The experiments were done on 4-mm-diameter flat and focused (focal distance = 8 and 12 mm) transducers. The streaming was measured along the ultrasonic beam from 0–20 mm; at all positions, the maximum Doppler frequency was estimated from the recorded spectra. Streaming was induced in a solution of water and corn starch. The experimental results showed that, for a given acoustic power, the streaming velocity was independent of the starch density in water changed from 0.3–40 g of starch in 1 l of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2–40 mm/s. Both the theoretical solutions for plane and focused waves and the experimental results were in good agreement.

Ultrasound, Streaming, Nonlinear ultrasound effects, Doppler

Examination of the carotid artery stenosis is very important in the diag-nosis of cerebrovascular diseases. New possibilities in the diagnosis of stenotic lesions are provided by ultrasonic Doppler angiography. The aim of this paper is to present a Doppler imaging system developed by the authors for the exami¬nation of blood flowing in carotid arteries. The system is based upon a 5 MHz bi-directional c.tv. Doppler flowmeter with a separate output for anterograde and retrograde flows. A special bank of filters converts signals into various levels of the gray-scale display which correspond to the value of the blood flow velocity. The ultrasonic probe is held by the scanning arm. The position of the probe on the skin of the patient is electronically sensed by the position-sensing circuity which causes the bright spot on the image display to move according to the position of the probe. The Doppler image from the artery is stored in a digital memory system. The clinical results obtained by means of this system showed good agreement with X-ray arteriography for obstructions occluding more than 50 per cent of the arterial diameter.

Precise quantitative analysis of the sonothrombolysis process is required to minimise the amount of thrombolytic drug dangerous for the patient, because it can cause internal hemorrhage. Verification of the effects of other drugs or other procedures for the elimination of thrombi, for example ultrasound contrast microbubbles, also requires quantitative research. For microscopic examination of the thrombolysis process, the Rexolite parallel plate flow chamber has been used. The internal dimensions of the chamber were 11x1x20 mm. In order to eliminate the standing wave, the incident wave was perpendicular to the reflected one. The narrowband chirp driven transducer suppressed the surface waves in Rexolite. The clot dissolution was processed at 40 kHz – 6 MHz ultrasound frequencies and 2 W/cm2 spatial averaged, temporal averaged intensities. The thrombus was obtained from a 5 μl drop of blood placed directly inside a flow chamber. The flow chamber was filled with the cell culture medium Dulbecco's modified Eagle's medium. The flow in the chamber was forced by a peristaltic pump at a speed of 3.8 ml/min. The Actilyse tissue plasminogen activator at a concentration of 10 μg/ml was added. The similarity of the thrombolysis process obtained from 5 μl of blood with a similar volume fragment cut from a larger thrombus was experimentally verified. Thrombus volume was estimated from microscopic photographs by calculating its surface area and its optical transparency. At 2 W/cm2 ultrasound intensity, took the thrombus 4, 8, 9 and 12 minutes to completely dissolve for the centre ultrasound frequencies of 40.9, 149, 209 kHz and 1.02 MHz, respectively. For higher frequencies, the thrombus only reduced its volume by 82%, 69% and 27% for the frequencies 2.10, 3.34 and 6.63 MHz, respectively. Sonication for 20 - 60 minutes did not cause further dissolution of thrombi.

ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

Neoadjuvant chemotherapy (NAC) is used in breast cancer patients to reduce tumor size, decrease the risk of local recurrence, and diminish the likelihood of metastases, all of which reduce patient mortality. Assessment of the response to NAC at an early stage of treatment allows therapy to be personalized. The quantitative ultrasound method is a novel diagnostic approach with great potential to improve outcomes for breast cancer patients. The aim of this study was to analyze the variability of the integrated backscatter coefficient (IBSC) in the context of the assessment of changes in tumor tissue structure resulting from chemotherapy, and to evaluate use of IBSC to predict the effectiveness of treatment. Ultrasound data (B-mode images and raw ultrasonic radio frequency signals RF) were collected from cancerous tumors from patients intended to NAC before starting treatment and a week after each chemotherapy dose. Data were processed to generate IBSC maps and to determine IBSC mean values. The assessment of tumors using IBSC, in comparison with histopathological verification, showed that IBSC changes can be associated with changes which tumor structure changes during NAC. IBSC analysis correlated better with the results of histopathological verification than B-mode imaging.

Under the influence of pathological changes, the blood coagulates inside the blood vessel, creating a thrombus. The thrombus dissolution process is called thrombolysis. The aim of the study is to evaluate the thrombolysis process by the interaction of the thrombolitic drug and ultrasound. The clot dissolution process was analyzed in a specially designed, transparent for ultrasound parallel plate flow chamber. Inside, a freshly coagulated human blood sample was exposed to ultrasound. A liquid containing the tissue plasminogen activator drug in a concentration of 10 μg/ml passed around the sample. The liquid flow was forced by a peristaltic pump. The source of ultrasound was a 1 MHz flat ultrasonic transducer with a 25 mm diameter. The transducer radiated a 1000 periods burst, repeated every 2500 periods and space averaged time averaged intensities of 0.2-1.6 W/cm2. The efficacy of thrombus dissolution was observed by means of a designed parallel plate flow chamber and the time of thrombus complete dissolution was measured. The best result for the 1 MHz frequency and space averaged time averaged intensity of 1.6 W/cm2 was recorded, where the thrombus was dissolved within 5.5 minutes.

ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

Parallel plate flow chambers are widely used for cell research in conditions of constant or pulsatile liquid flow. They are also used to analyze the formation of thrombi. The authors designed a flow chamber that is transparent to ultrasound, thus enabling the microscopic observation of the thrombus dissolution process by interaction of drug, microbubbles and ultrasound in real time, in-vitro. Sonothrombolysis was performed at 1 MHz and 3.3 MHz ultrasound frequencies, at space-averaged and time-averaged intensities ISATA of 0.2 – 1.6 W/cm2. 1 mm thick slices of the human blood clots were exposed to ultrasound in the presence of the Actilyse tissue plasminogen activator at a concentration of 10 μg/ml flowing around the sample. Next, the effect of SonoVue microbubbles at a concentration of 5x105/ml on the dissolution of the thrombus was investigated. Thrombus size changes were observed under a 4x magnification microscope and were recorded as a function of time. The best result was achieved for the Actilyse tissue plasminogen activator at the 1 MHz and 1.6 W/cm2 ISATA, the thrombus was sonolysed within 5.5 minutes. The noticeable effect of the SonoVue microbubbles on the thrombolysis process appeared at 3.3 MHz, the thrombus was sonolysed in 12 min at ISATA = 1.6 W/cm2.

ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

The article attempts to select an ultrasound system to assess of endothelium dysfunction-dependent flow mediated dilation (FMD) and shear rate (SR) in radial artery after several minutes of hyperaemia. Methods: We compare the effective axial resolution and Doppler sensitivity of the standard US working below 12 MHz and high frequency (close to 20 MHz) scanning systems measuring the vessel diameter and blood flow measurements in radial arteries. FMD and FMD and SR were measured in Control group of 14 healthy volunteers, and in 13 with stable coronary artery diseases (CAD). Results: In a laboratory experiment of imaging two closely spaced food plastic foils, over three times better axial resolution was demonstrated for the 20 MHz ultrasound system in which the resolution was close to 0.1 mm. Also the sensitivity of the external single 20 MHz pulse Doppler transducer proved to be over 20 dB better (in terms of signalto-noise ratio) than the pulse Doppler incorporated into the L14-5 linear array. FMD in Control group was in the range of 8÷16% with mean±sd equal to 12.13 ± 2.34%; in CAD group FMD was in the range of 0.1÷7 % with mean±sd equal to 3.01±2.18% which was significantly less. FMD/SR was equal to 3.08 ± 1.34 × 10–4 in Control group and 1.01 ± 0.76 × 10–4 in CAD group with ranges equal to 1.66 ÷ 7.8× 10–4 and 0.4 ÷ 2.4× 10–4, respectively. Conclusions: Increasing scanning and Doppler mode frequency to 20 MHz improved the precision of FMD and SR measurements. Statistically significant differences between the two groups were confirmed by statistical tests for FMD and FMD/SR with p-values < 0.05. The results obtained suggest the usefulness of the proposed ultrasonic system for measurements of FMD and SR in the radial artery to differentiate normal subjects from those with CAD.

radial artery, shear rate, reactive hyperaemia, endothelium, pulsed Doppler

Streaming velocity mainly depends on the intensity and absorption of ultrasound in the media. For high frequencies exceeding 20 MHz the speed of streaming in blood is also affected by scattering effects on the blood cells and contrast agent microbubbles. According to theoretical calculations, 12.2 % increase in streaming velocity for 1 g/l starch concentration rise should be expected. The theory has also shown the reduction of the streaming velocity by low-density scatterers, estimated decrease was -9.7 % for BR14 contrast agent. The experimental measurements of streaming velocities were done in blood mimicking fluid and Bracco BR14 microbubbles dissolved in water. The streaming was generated by a plane 20 MHz ultrasonic transducer driven by a pulsed Doppler flowmeter. For starch concentration changing from 0.01g/l (reference fluid) up to 1g/l the streaming velocity increased by 13%, very close to the theoretical prediction. For BR14, the measured velocity was 9% less than in reference fluid and remained independent on the microbubbles concentration.

streaming, radiation force, starch, contrast agent, blood

A novel high-frequency scanning system, with a 20-MHz linear array transducer combined with 20-MHz pulsed Doppler, was introduced to evaluate the degree of radial artery flow-mediated dilation (FMD) and shear rate (SR)-normalized FMD (FMD/SR) after 5 min of reactive hyperaemia. In group I, comprising 27 healthy volunteers, FMD was 15 ± 4.8%, and in group II, comprising 17 patients with coronary artery disease, FMD was significantly smaller, being equal to 4.6 ± 4%. FMD/SR was equal to 5.365 ± 4.835·10-4 in group I and 1.3 ± 0.89·10-4 in group II. Statistically significant differences between the two groups were confirmed by Wilcoxon-Mann-Whitney test for FMD and FMD/SR (p-values < 0.01). AUCs of ROC curves for FMD and FMD/SR were greater than 0.9. The results confirm the usefulness of the proposed measurements of radial artery FMD and SR in differentiation of normal subjects from those with atherosclerotic lesions.

flow mediated vasodilation, radial artery, shear rate, reactive hyporaemia, endothelium, pulsed Doppler, ultrasonography.

Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. There are commercially available ultrasound scanners to estimate Brachial Artery Reactive Response BARR by measuring the flow-mediated vasodilatation (FMD) of the brachial artery using 10–12 MHz linear array probes; however the precision in estimating of artery dilation does not exceeds 0.2 mm, far beyond the required one. We have introduced a high frequency scanning schemes; 25–35 MHz encoded (Golay) wobbling type imaging with- out Doppler (uScan developed in our lab, thick film wide bandwidth transducer, 50 microns axial resolution). In the second approach we have used 20 MHz linear scanning with 20 MHz pulsed Doppler attached to the linear array. Instead of brachial artery we have examined the radial artery where Radial Artery Reactive Response RARR was measured. The radial artery FMD were normalized using AUC of shear rate at the radial artery wall. The precision of the radial artery diameter measurements is over two times better using 20 MHz US instead of 7.5 MHz used for brachial artery FMD. The measured initial internal radial artery diameter was in range of 1.59–2.35 mm, the maximum diameter 2.01–2.60 mm was observed 40 to 55 seconds after releasing the cuff. In a limited number (14) of examined young, healthy patients the FMDSR were in the range from 7.8
to 9.9 in arbitrary units. In older patients with minor cardiac history the normalized FMDSR was clearly lower, 6.8 to 7.6.

thick film transducers, atherosclerosis, flow mediated vasodilation.

Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. There are commercially available ultrasound scanners to measure flow-mediated vasodilatation (FMD) of the brachial artery using 10-12 MHz linear array probes, however the attainable precision in estimating the changes in artery dilation does not exceeds 0.2 mm, far beyond the required one. We have introduced a high frequency scanning schemes 25-35MHz encoded (Golay) wobbling type imaging without Doppler (uScan developed in our lab, thick film wide bandwidth transducer, 50 microns axial resolution) and 20 MHz ultrasound (Ultrasonix) with 20 MHz pulsed Doppler attached to the linear array. The FMD results were normalized using AUC of shear rate at the radial artery wall.

thick-film transducers, flow-mediated vasolidation, radial artery, shear rate

The long term goal of this research is to develop the system enabling the imaging and quantitative measure of ultrasonic attenuation in tissue. It may support the diagnosis by accurate discrimination of the lesions from normal tissue at the early stage of the disease. The attenuation is estimated from the stochastic ultrasonic backscatter and time/spatial averaging is necessary to achieve reasonable accuracy. However the averaging worsens the spatial resolution. Two techniques of ultrasonic imaging, the Synthetic Aperture Focusing technique (SAFT) and Spatial Compounding (SC), were applied and compared with respect to the quality of attenuation estimation. The ultrasonic RF data were collected from a tissue mimicking phantom using ultrasonic scanner (Ultrasonix SonixTOUCH). Both acquired echoes-sets were processed in the same way in order to calculate the downshift in a mean frequency fm of the backscatter signal and resulting spatial distribution of attenuation coefficient. Compensation for the diffraction effects was included in the data processing. The RF data obtained with use of the SAFT proved to be more suitable for attenuation estimation.

tissue attenuation imaging, synthetic aperture, spatial compounding

Terapeutyczne i chirurgiczne zastosowania ogniskowych ultradźwięków wymagają monitorowania lokalnych zmian temperatury w tkance. Najkorzystniejsze z punktu widzenia użytkowego i ekonomicznego byłoby zastosowanie do tych celów technik ultradźwiękowych.
Praca przedstawia próbę zastosowania metody estymacji przemieszczenia ech do monitorowania zmian temperatury podczas ultradźwiękowego nagrzewania tkanki in vitro. Dane uzyskane drogą pomiarów ultradźwiękowych zostały przetworzone w celu wyznaczenia mapy przemieszczeń ech i odniesione do pomiarów rozkładu temperatury przeprowadzonych za pomocą termopar. Uzyskane wyniki umożliwiają ocenę pola temperatury i pozytywnie rokują połączeniu ultradźwiękowych technik nagrzewania i szacowania lokalnej temperatury tkanki.

obrazowanie temperatury, prędkość akustyczna

Nową metodą terapii antynowotworowej glejaków jest sonoterapia polegająca na jednoczesnym podawaniu leku kumulującego się w tkankach nowotworowych i napromieniowanie falą akustyczną. Skuteczność metody została sprawdzona na komórkach glejaka C6, poddanych działaniu kwasu aminolewulinowego (ALA) i fali ultradźwiękowej 1MHz o natężeniu 0.94, 1.88 i 3.77W/cm2 przez 3 min. Jednoczesne działanie fali akustycznej i ALA było skuteczniejsze (pozostało 15%-13% żywych komórek) niż samej fali akustycznej (41%-27%) dla natężeń 0.94 i 1.88W/cm2. Natężenie 3.77W/cm2 było wystarczające do zniszczenia większości komórek niezależnie od obecności ALA. Podczas eksperymentu zaobserwowano powstawanie fali stojącej, zwiększającej natężenie 7x-10x. Otrzymane wyniki wskazują na przydatność nowej techniki sonodynamicznej do terapii nowotworów.

ultradźwięki, sonoterapia, terapia antynowotworowa, glejaki

Therapeutic and surgical applications of focused ultrasound require monitoring of local temperature rises induced inside tissues. From an economic and practical point of view ultrasonic imaging techniques seem to be the best for a temperature control. In this work an attempt to apply the method of the ultrasonic echoes displacement estimation for monitoring local temperature rises in tissues during their heating by focused ultrasound is presented. The estimated temperature rise was compared with this measured by a thermocouple. The obtained results enable to evaluate the temperature fields induced in tissues by pulsed focused ultrasonic beams using non-invasive imaging ultrasound technique.

HIFU, therapeutic ultrasound, ultrasonic imaging, echo strain estimation

Many therapeutic applications of focused ultrasound are based on heating of a detected lesion which may be located inside tissues at different depths under a skin. In order to raise the tumor temperature the focal spot of the ultrasonic beam is guided to it. The focusing of acoustic energy in tissues at the desired depth can be achieved using single-element circular concave piezoelectric transducers with the selected diameters and radii of curvature. This solution is inefficient because it requires as many transducers as there are depths at which tumors are localized. In order to solve this problem a new approach, allowing to concentrate the acoustic energy at different depths inside tissues using a planar multi-element phased annular array with electronically steered focus, was proposed in this work. The main purpose of this study was to investigate the thermal fields induced in bovine liver in vitro by the pulsed focused ultrasound beam with various acoustic properties generated from the planar multi-element phased annular array with electronically steered focal spot. The array with 20 mm outer diameter and 2.4 MHz centre frequency has 7 elements with the same radiating surface. The electronic steering of the time-delay of excitation of each array element allowed to obtain the focal spot of the beam at any distance from the transducer surface. This paper presents measurement results performed for the beam focused at 20 mm distance. In order to maximize nonlinear propagation effects being one of the reason of the local temperature rise induced in tissues by focused ultrasound the measurements have been performed in two-layer parallel media of propagation comprising of a water layer, whose thickness was specific for the transducer used and equal to 13 mm, and of a bovine liver in vitro layer with a thickness of 27 mm. It was determined numerically as the axial distance at which the second harmonics amplitude for the tone burst generated by the transducer used in water starts to increase rapidly. The measurements of temperature rise versus time were performed using a thermocouple placed inside the liver at the beam focus. The temperature rises induced in the bovine liver in vitro for beams with the average acoustic power of 1W, 2W and 3W and duty cycle of 1/5, 1/15 and 1/30 have been measured. For each beam the exposure time needed for local heating of the liver to a temperature of 43 °C (used in therapies based on ultrasonic enhancement of drug delivery or therapies involving stimulation of immune system by enhancement of the heat shock proteins expression) and to a temperature of 56 °C (used in HIFU therapies) was determined. In each sample of liver for each considered beam at first, the measurement of temperature rise (with thermocouple) was carried out, and then, exposing the sample (without thermocouple) to the same beam the real-time monitoring of dynamics of the thermo ablation area growth was performed using the ultrasonic imaging technique. The necrosis spot becomes visible in the ultrasonic image only when the beam has sufficient acoustic power. The quantitative analysis of the obtained results allowed to determine the beam acoustic power and exposure time that are sufficient to visualize necrosis spot in the ultrasonic image.

phased annular array, pulsed focused nonlinear ultrasound beams, electronically movable focus, tissue heating, biological effects, tissue necrosis

The use of the ultrasonically destructible microcapsules as local drug delivery systems continues to grow. Microbubble destruction requires correct ultrasonic frequency equal to its resonance. This frequency depends on the bubble size and polymer shell stiffness. Measurements of the ultrasonic signal, backscattered from microspheres gives practical information of the bubble resonance and nonlinearity.
In experiment, the backscattered power spectrum of measured sample was recorded by an ultrasonic scanner. Radio frequency (RF) data was recorded at 2.0 – 6.6 MHz. The mean particle diameter in the measured sample was 21 μm. The resonance frequency, measured under the microscope, was 0.60 MHz for 43 μm diameter microsphere. The sample volume was 10cm³ and the mean quantity of scatterers was 6•103/cm³.
The simulated power spectrum of the ultrasonic backscattered signal was calculated from the resonance scattering theory for the gas bubbles surrounded by elastic shell.
In conclusion, the measured spectra matched those calculated from the theory. The use of the ultrasonic scanner with RF data output and the high sensitivity, wide bandwidth ultrasonic transducer allows to measure the backscattered signal from the very small quantity of resonance scatterers with satisfactory results at 40 dB signal to noise ratio.

ultrasound, microcapsules, controlled drug delivery, backscattering

This paper investigates the effect of ultrasound imaging transducer’s fractional bandwidth on the gain of the compressed echo signal for different spectral widths of the complementary Golay sequences (CGS). Two different bit lengths were investigated, specifically one and two cycles. Three transducers having fractional bandwidth of 25%, 58% and 80% and operating at frequencies 6 MHz, 4.4 MHz and 6 MHz, respectively were examined (one of the 6 MHz sources was made of composite material). The experimental results have shown that by increasing the code length, i.e. decreasing the bandwidth, the compressed echo amplitude could be enhanced. The smaller the bandwidth was the larger was the gain; the pulse-echo sensitivity of the echo amplitude increased by 1.88, 1.62 and 1.47, for 25%, 58% and 80% bandwidths, respectively. These results indicate that two cycles bit length excitation is more suitable for use with bandwidth limited commercially available imaging transducers. Further, the time resolution is retained for transducers with two cycles excitation providing the fractional bandwidth is lower than approximately 90%. The results of this work indicate that adjusting the code length allows signal-to-noise-ratio (SNR) to be enhanced while using limited (less that 80%) bandwidth imaging transducers. Also, for such transducers two cycles excitation would not decrease the time resolution, obtained with ’conventional’ spike excitation. These results also indicate that CGS excitation could be successfully implemented with the existing, relatively narrow band imaging transducers without the need to use usually more expensive wide-band, composite ones.

ultrasound imaging, coded transmission, transducer badnwidth, Golay codes

Tissue Harmonic Imaging (THI) was introduced in 1997 [1] and is today routinely used in diagnostic ultrasound. The benefits of harmonic imaging in many clinical situations have been proved. However, it has to be stressed that it is away from optimal because only half of the available transducer bandwidth is used for image formation - lower half for transmission and upper half during reception.

Ultrasonic imaging, Image resolution, Polarization, Absorption, Image coding, Pulse inverters, Dynamic range, Nonlinear equations, Boundary conditions, Propagation losses

An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation. The theoretical calculations were verified using a purpose-designed 32 MHz pulsed Doppler unit. The applied average acoustic power was changed from 1 /spl mu/W to 6 mW. The experiments were done on 4 mm diameter flat and focused transducers. The streaming velocity was measured along the ultrasonic beam from O to 20 mm. Streaming was induced in a solution of water and corn starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water changed from 0.3 grams to 40 grams of starch in 1 litre of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2 to 40 mm/s. Theoretical solutions for both plane and focused waves agreed with experimental results.

Acoustic beams, Poisson equations, Acoustic transducers, Ultrasonic transducers, Differential equations, Ultrasonic variables measurement, Acoustic waves, Impedance, Navier-Stokes equations, Boundary conditions

Acoustical Driving Forces (ADF), induced by propagating waves in a homogeneous and inhomogeneous lossy fluid (suspension), are determined and compared depending on the concentration of suspended particles. Using integral equations of the scattering theory, the single particle (inclusion) ADF was calculated as the integral of the flux of the momentum density tensor components over the heterogeneity surface. The possibility of negative ADF was indicated. Originally derived, the total ADF acting on inclusions only, stochastically distributed in ambient fluid, was determined as a function of its concentration. The formula for the relative increase in ADF, resulting from increased concentration was derived. Numerical ADF calculations are presented. In experiments the streaming velocities in a blood-mimicking starch suspension (2 mu m radius) in water and Bracco BR14 contrast agent (SF6 gas capsules, 1 mu m radius) were measured as the function of different inclusions concentration. The source of the streaming and ADF was a plane 2 mm diameter 20 MHz ultrasonic transducer. Velocity was estimated from the averaged Doppler spectrum obtained from originally developed pulsed Doppler flowmeter. Numerical calculations of the theoretically derived formula showed very good agreement with the experimental results.

Tissue mimicking materials for ultrasound research, phantoms, should be acousticaly similar to the tissues. Such requirements are filled by the AGO (agar-oil) phantoms. Here, they have been used in experiment of heating internal region of samples by the high intensity ultrasound (HIFU) transducer. During heating the RF (radio frequency) ultrasound signals have been collected. It is demonstrated that the temperature changes in AGO phantoms can be described by the special properties of the backscattered RF signals, namely the shape parameter of the Nakagami distribution and SNR (signal to noise ratio) of signal envelopes random distribution. Reveal of qualitative relationships between the temperature increase/decrease measured by thermocouples and the statistical parameters changes are the main result of the paper.

soft tissue phantom, absorption of acoustic energy, temperature marker, signal-to-noise ratio, Nakagami distribution

Ultradźwięki są stosowane w medycynie zarówno w diagnostyce - ultrasonografii jak i w terapii. Działanie terapeutyczne sprowadza się do efektów termicznych, uśmiercania komórek przez apoptozę oraz efektów sonomechanicznych. Terapie in-vivo są poprzedzane testami in-vitro komórek umieszczonych na szalce Petriego. W tej pracy zostaną przedstawione dwa efekty oddziaływania fali akustycznej na komórki: wspomaganie rozpuszczania skrzepliny oraz apoptoza komórek nowotworowych.
Do badań przygotowano zbiornik wypełniony odgazowaną wodą destylowaną z termostatem i mieszadłem elektromagnetycznym. W zbiorniku umieszczono płaski przetwornik ultradźwiękowy, promieniujący do góry, w kierunku zanurzonej w wodzie szalki Petriego ze skrzepliną lub komórkami.
W pierwszej części oddziaływano falą ultradźwiękową o częstotliwości 1.0 MHz i natężeniu Isata = 0.2 W/cm2 na skrzeplinę uzyskaną z kropli krwi 30 min po pobraniu. Skrzeplinę umieszczono w roztworze soli fizjologicznej z dodatkiem leku rozpuszczającego skrzeplinę tPA typu Actilyse 50 w stężeniu 10μg/ml i nadźwiękawiano przez 20 min. Eksperyment powtórzono z kolejnymi skrzeplinami stosując same ultradźwięki oraz sam lek Actilyse. Współdziałanie leku i fali ultradźwiękowej w ciągu 20 min spowodowało całkowite rozpuszczenie skrzepliny. W pozostałych przypadkach skrzeplina pozostała zmniejszając swoją objętość o 10-20%.
W drugiej części badano wpływ fali ultradźwiękowej 1.0 MHz na komórki nowotworowe szczurzego glejaka C6. Komórki wysiano na dnie szalki i hodowano w pożywce DMEM w temperaturze 37ºC. Następnie do pożywki dodano 1mM kwasu 5-aminolewulinowego ALA. Po 24h inkubacji, komórki poddano działaniu ultradźwięków o natężeniu Isata = 0.4, 0.8 oraz 1.2 W/cm2 przez 3 min. Po kolejnych 24h, żywotność komórek zbadano spektrofotometrem po dodaniu do pożywki odczynnika MTT assay. Badania powtórzono dla komórek bez ALA oraz bez ultradźwięków. Dla natężenia Isata = 1.2 W/cm2, żywotność komórek wynosiła 39% dla współdziałania ALA i ultradźwięków, 78% dla ALA oraz 99% dla ultradźwięków.
Przygotowane przez autorów stanowisko pomiarowe umożliwia prowadzenie badań in-vitro nad terapeutycznym oddziaływaniu ultradźwięków na komórki. Uzyskano pozytywne rezultaty w wykorzystaniu ultradźwięków zarówno do rozpuszczania skrzeplin – sonotrombolizy jak i uśmiercania komórek nowotworowych – terapii sonodynamicznej. Stosowano ultradźwięki małej mocy, niepowodujące zniszczenia komórek przez przegrzanie lub kawitację.

ultradźwięki terapeutyczne, sonotromboliza, tromboliza, leczenie nowotworów

To target a focal spot of an ultrasound beam on a tumor located deep inside tissues during thermo-ablative treatment by HIFU technique, beams with different focal distances are required. To be able to control a depth of local thermal fields induced in tissues by a single beam, both, the planar and concave 7-element annular phased array transducers with a 2 MHz frequency and 29 mm diameter generating beams with electronically controlled focal length were designed and produced. The radius of curvature (ROC) for the concave transducer was equal to 60 mm. Elements of each transducer had the same area to provide uniform pressure distribution on the radiating surface due to the same impedance and were excited by pulses with time delays providing the beam focusing in water at three different depths (25 mm, 30 mm, and 35 mm). To select sets of time delays for each focal depth the measurements of pressure waveforms on the axis of each beam generated in water were performed using a needle hydrophone. For these measurements 10-cycle tone bursts with 1 kHz PRF were used. In order to induce local thermo-ablative necrosis inside a tissue at three different depths (10mm, 15mm, and 20mm) a two-layer media of propagation comprising of 15-mm layer of water and 25-mm layer of pork loin was used. To heat the pork loin locally 20-cycle tone bursts with 0.2 duty-cycle and average acoustic power varied between12W and 18W (initial intensity ISATA varied between 2W/cm2 and 3W/cm2) was applied. In order to determine the exposure time required to induce necrosis (rise in temperature to 56 °C) inside the pork loin sample at the selected depth the thermocouples placed on the acoustic beam axis were used. After exposure to focused ultrasound three necrotic lesions were observed after cutting the tested tissue sample along the axes of the beams used. The obtained results proved the feasibility of controlling the depth of local tissue necrosis using pulsed focused ultrasound beams with electronically movable focal spot generated by the annular phased array transducer designed.

annular phased array transducer, pulsed High Intensity Focused Ultrasound, electronically movable focus, local tissue heating, thermal ablation, tissue necrosis