Research Ultrasound System Research Articles

Kidney stone twinkling power in elevated oxygen, carbon dioxide, and nitrogen environments

Clinically, ∼66% of kidney stones exhibit the Doppler ultrasound twinkling artifact. Previous studies show breathing pure oxygen at elevated pressures increases twinkling compared to ambient air. Here, we investigate how different gases influence twinkling on ex vivo and in vivo human kidney stones. 38 kidney stones were imaged with a research ultrasound system and ATL L7-4 transducer in elevated oxygen, carbon dioxide, and nitrogen environments. In vivo stones were imaged with the same ultrasound system and ATL C5-2 transducer in 25 human subjects before and after breathing pure oxygen for 15 min. IQ data were processed by calculating the average Doppler power, or twinkling, for a region of interest containing the stone. In the lab, increasing oxygen by 55%, carbon dioxide by 100%, and nitrogen by 17% increased twinkling power an average of 70 ± 28%, 137 ± 53%, and 79 ± 31%, respectively. In human subjects, breathing oxygen increased twinkling power an average of 27 ± 58%, with seven subjects showing a strong increase (>30%); stone composition and patient age influenced twinkling in patients breathing oxygen. These results suggest that varying ambient gases may be leveraged to increase the consistency of twinkling and improve kidney stone detection with ultrasound. [Work supported by the PSU Center for Biodevices.]

Developing a focused ultrasound treatment for tendinopathies in a large animal model

Current treatments for tendinopathies produce mixed success rates, with 0-84% of patients showing improvement. Our prior work in rats suggests mild microdamage induced by focused ultrasound (fUS) may perform better than traditional treatments for tendinopathies, like dry needling. Here, we work to scale our work in rats to larger animal models and develop treatment monitoring. Ex vivo bovine digital flexor tendons were obtained and injected with collagenase to induce chronic tendinopathy. One day later, tendons were treated with focused ultrasound at 1.1–3.68 MHz, with 1–10ms pulses at pressures up to p + = 127 MPa/p− = 35 MPa repeated at 0.2–1 Hz for up to 20 min. Treatments were monitored with passive cavitation detection (PCD; Sonic Concepts Y-107) and Philips/ATL L7-4 controlled by the Verasonics research ultrasound system in passive cavitation imaging (PCI) mode. Samples were collected for histological analysis. Preliminary results suggest that lower pulse repetition frequencies produce mild mechanical microdamage with no evidence of thermal necrosis. PCI and PCD results show no consistent trends to indicate the intended mechanical microdamage bioeffect has been achieved. Work is continuing to determine the treatment parameters that produce the intended bioeffects in the smallest time and to develop a means to monitor treatment progress. [Work supported by NIHR01EB032860.]

The effect of elevated oxygen on kidney stone twinkling in vivo and ex vivo

The Doppler ultrasound twinkling artifact is a rapid color shift observed in ∼66% of kidney stones. Breathing oxygen at elevated pressures was shown to enhance twinkling on kidney stones in human subjects. Here, in humans and in ex vivo stones, we investigate the effects of elevated oxygen at ambient pressure. Recruited subjects with confirmed stones were scanned with a research ultrasound system and Philips/ATL C5-2 transducer while breathing ambient air for 2 min. Then, subjects were masked with 100% oxygen for 15 min and scanned again for the last 2 min. Similarly, ex vivo stones were imaged before and after bubbling oxygen into water. Average Doppler power was calculated for in vivo and ex vivo stones. In human subjects, Doppler power increased by 30% when subjects breathed pure oxygen compared to ambient air. Similarly, on ex vivo stones, an average increase in Doppler power of 98% was observed in elevated oxygen conditions; twinkling also became visible on stones that otherwise did not twinkle at elevated oxygen (50% more oxygen than control). These results suggest that elevated oxygen at ambient pressure may improve the consistency of twinkling to detect kidney stones. [Work supported by the PSU Center for Biodevices Seed Grant.]

The effect of gas composition on the color Doppler ultrasound twinkling artifact

The twinkling artifact, or twinkling, appears when imaging kidney stones and other mineralizations with Doppler ultrasound and is caused by scattering off crevice microbubbles. Previous work found that twinkling on in vivo kidney stones increased or decreased with elevated oxygen or carbon dioxide, respectively. However, it is unclear whether these results are from biological adaptions to the changing respiratory gas and thus if in vitro mineralizations are similarly affected. Here, cholesterol, calcium phosphate, and uric acid crystals were grown in vitro and imaged in deionized water using a Vantage-128 research ultrasound system with a Philips/ATL L7-4 transducer. Five of each crystal composition were imaged for one minute at different dissolved gas concentrations. By bubbling gas through water, dissolved oxygen ranged from 2 to 20 mg/L while dissolved carbon dioxide ranged from 30 to 290 mg/L. Twinkling on cholesterol crystals increased by 70% and 140% when oxygen and carbon dioxide levels were maximized, respectively. In contrast, twinkling on calcium phosphate and uric acid was not significantly affected by either gas. These results suggest that changes in twinkling from increased gas concentrations are dependent on crystal composition and are likely affected by biological adaptations in vivo. [Work supported by NSF-CAREER-1943937 and NSF-GRFP-DGE1255832.]

The effect of crystal composition and environment on the color Doppler ultrasound twinkling artifact

Objective. Pathological mineralizations form throughout the body and can be difficult to detect using conventional imaging methods. Color Doppler ultrasound twinkling highlights ∼60% of kidney stones with a rapid color shift and is theorized to arise from crevice microbubbles as twinkling disappears on kidney stones at elevated pressures and scratched acrylic balls in ethanol. Twinkling also sometimes appears on other pathological mineralizations; however, it is unclear whether the etiology of twinkling is the same as for kidney stones. Approach. In this study, five cholesterol, calcium phosphate, and uric acid crystals were grown in vitro and imaged in Doppler mode with a research ultrasound system and L7-4 transducer in water. To evaluate the influence of pressure on twinkling, the same crystals were imaged in a high-pressure chamber. Then, the effect of surface tension on twinkling was evaluated by imaging crystals in different concentrations of surfactant (1%, 2%, 3%, 4%) and ethanol (10%, 30%, 50%, 70%), artificial urine, bovine blood, and a tissue-mimicking phantom. Main results. Results showed that all crystals twinkled in water, with cholesterol twinkling significantly more than calcium phosphate and uric acid. When the ambient pressure was increased, twinkling disappeared for all tested crystals when pressures reached 7 MPa (absolute) and reappeared when returned to ambient pressure (0.1 MPa). Similarly, twinkling across all crystals decreased with surface tension when imaged in the surfactant and ethanol (statistically significant when surface tension <22 mN m−1) and decreased in blood (surface tension = 52.7 mN m−1) but was unaffected by artificial urine (similar surface tension to water). In the tissue-mimicking phantom, twinkling increased for cholesterol and calcium phosphate crystals with no change observed in uric acid crystals. Significance. Overall, these results support the theory that bubbles are present on crystals and cause twinkling, which could be leveraged to improve twinkling for the detection of other pathological mineralizations.

The Doppler ultrasound twinkling artifact on crevices etched in silicon wafers

The twinkling artifact, or rapid color shifts, are observed when imaging kidney stones and other mineralizations. The current theory is that scattering from bubbles in micron-sized crevices causes twinkling. Our objective is to investigate the effect of ultrasound frequency and crevice size and number on twinkling of silicon wafers. Ten or 100 randomly positioned cylindrical crevices with diameters of 1, 10, or 100 μm and depths of 10 μm were dry-etched on wafers. A research ultrasound system was used to image wafers at 5, 7.8, and 18.5 MHz; IQ data were post-processed to calculate twinkling or Doppler power. Twinkling for all crevice sizes and numbers followed the trend 5 MHz&amp;gt;7.8 MHz&amp;gt;18.5 MHz. For crevice size, at 5 and 7.8 MHz, twinkling was higher for 1- or 10-μm crevices compared to 100 μm; at 18.5 MHz, twinkling was only observed on 100-μm crevices. Increasing the number of crevices increased twinkling for 1 μm crevices at 5 and 7.8 MHz and 10 μm crevices at 7.8 MHz; no differences were noted at 18.5 MHz. These results support previous work showing twinkling is frequency-dependent and suggest that even 10, 1-μm crevices are sufficient to cause twinkling. [Work supported by SURIEA, NSF CAREER-1943937.]

Flow imaging using differential Golay encoded ultrasound

In our research we present a new method of differential compression of the Golay encoded ultrasound (DCGEU) in the standard beamforming mode to visualize the slow (<1cm/s) blood mimicking fluid flow in small diameter tubes. The proposed DCGEU method is based on synthesis of several subsequent B-mode frames acquired with certain time intervals (30 ms in this study) followed by the visualization of differential beamformed radio frequency (RF) echoes, which yielded the images of the scatterers moving slowly in the vessel and suppressing the static echoes outside the vessel. In order to extract small backscattered echoes from the vessel area we took an advantage of improved sensitivity of the complementary Golay coded sequences (CGCS).The validation of the proposed DCGEU method was carried out in two stages. In the first one, we compared the flow images in small tubes with a diameter of 1 mm and 2.5 mm, reconstructed from numerically simulated acoustic data for the standard transmission of short pulses and 16-bits long CGCS signals. In the second stage of the research, the experimental data were acquired in a flow phantom with silicone tubes with an internal diameter of 1.5 mm and 4.5 mm and a fluid flow velocity of 0.9 cm/s. The experiments were carried out using preprogrammed Verasonics Vantage™ research ultrasound system equipped with ALT L12-5/50 mm MHz linear array transducer with 7.8 MHz center frequency.It was evidenced both in simulations and experiments that the DCGEU provided a good flow image along the entire length of tubing with virtually angle independent detection in comparison with the conventional short pulse interrogation.

Shear Wave Elastography Implementation on a Portable Research Ultrasound System: Initial Results

Ultrasound shear wave elastography (SWE) has emerged as a promising technique that enables the quantitative estimation of soft tissue stiffness. However, its practical implementation is complicated and presents a number of engineering challenges, including high-energy burst transmission, high-frame rate data acquisition and high computational requirements to process huge datasets. Therefore, to date, SWE has only been available for high-end commercial systems or bulk and expensive research platforms. In this work, we present a low-cost, portable and fully configurable 256-channel research system that is able to implement various SWE techniques. We evaluated its transmit capabilities using various push beam patterns and developed algorithms for the reconstruction of tissue stiffness maps. Three different push beam generation methods were evaluated in both homogeneous and heterogeneous experiments using an industry-standard elastography phantom. The results showed that it is possible to implement the SWE modality using a portable and cost-optimized system without significant image quality losses.

The effect of surface tension on the color Doppler ultrasound twinkling artifact

Imaging crystalline structures with Doppler ultrasound can produce a rapid color shift, termed the twinkling artifact, that can assist in diagnosing pathological mineralizations such as kidney stones, heterotopic ossification, gout, and breast microcalcifications. Twinkling is theorized to arise from scattering off surface crevice microbubbles, which are affected by the surface tension between the bubble and surrounding medium. In this study, we evaluated the effect of surface tension on twinkling in pure crystals. Cholesterol, calcium phosphate, and uric acid crystals were grown in vitro (n = 5 each) and imaged with a Philips/ATL L7-4 transducer and Vantage-128 research ultrasound system. Crystals were imaged in water while varying surfactant concentration (0%–4%) leading to surface tensions that ranged from 45–72 mN/m. Surface tension of the solution was determined by measuring the contact angle of 0.1-mL droplet on an acrylic sheet exposed to air. As the concentration of surfactant increased, twinkling was found to decrease by ∼20% for cholesterol and calcium phosphate and ∼10% for uric acid. These results continue to support the crevice bubble theory of twinkling and suggest the importance of surface tension when evaluating minerals with the twinkling artifact. [Work supported by NSF-CAREER-1943937 and NSF-GRFP-DGE1255832.]

Investigating the color Doppler twinkling artifact as an early detector of cellular mineralization

Heterotopic ossification (HO) occurs when bone develops in areas where bone does not usually exist, often appearing after blast injuries or other musculoskeletal trauma. Current methods of diagnosis, such as three-phase bone scintigraphy, x-ray, or CT scans, take several weeks after the trauma before HO is visible. The color Doppler ultrasound twinkling artifact has been shown to detect the presence of kidney stones and other crystals. Twinkling could provide a more sensitive method of HO detection, which would allow for earlier diagnosis and treatment and limit HO severity. In our research, human bone marrow-derived stem cells (HBMSCs) were plated onto collagen scaffolds and cultured in osteogenic media to promote mineralization orgrowth media (controls). The cells were imaged every 3rd day from day 10 – day 25 using Phillips L7-4, L12-5, and Vermon L22-14v transducers and a Vantage-128 research ultrasound system; I/Q data were bulk saved for quantitative analysis. Samples with mineralization on 0.5% of their surface showed a 17% increase in Doppler magnitude compared to controls, suggesting that the twinkling artifact is a sensitive method for detection of mineralization in vitro. Further studies will investigate whether this method is effective in a murine model. [Work supported by DoD CDMRP PR201164.]

Externally-induced shear waves in the right ventricular free wall throughout the cardiac cycle

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1. NWO STW/Dutch Heart foundation 2. NWO Vidi TTW Background The right ventricular (RV) size and function have prognostic value, not only in right heart conditions (pulmonary hypertension, congenital heart disease), but also in left ventricular (LV) disease states. There is currently no noninvasive method for measuring the elastic properties of the RV walls. Increased RV diastolic stiffness however, as determined invasively, is linked to adverse prognosis in pulmonary arterial hypertension. In the LV, new high frame rate (HFR) echocardiography applications have been used in order to determine the propagation speed of naturally-occurring or externally-induced shear waves (SW) in the septum, which is related to myocardial stiffness. Purpose We show for the first time that SWs in the RV free wall (RVFW) can be externally induced and imaged transthoracically with ultrasound. Methods SW imaging was performed using a linear array with a programmable research ultrasound system, aimed at the parasternal long-axis view of a 5-weeks-old Yorkshire-Landrace pig (Fig. 1a). SWs were induced by a high intensity focused beam (f0 = 4.5 MHz) on the RVFW (Fig. 1a). This push beam generates a downwards force at the focus, which induces SWs that propagate left and right from the focus along the RVFW, visible on tissue Doppler images (TDI) shown in Figure 1b-c. SW propagation was imaged (f0 = 5.2 MHz) using HFR ultrasound (Fig. 1b, frame rate = 3 kHz). Three acquisitions of 1 second were performed, where 14 SWs were sequentially induced during each acquisition. ECG signal was captured simultaneously and synchronized offline. SW speeds were estimated using a custom, semi-automatic pipeline that includes TDI calculation, and SW speed estimation along a manually traced spline on the RVFW. This was repeated two times to include variability due to the manual processes. Up to four SW speed estimates were made after each push beam. SW speed estimation was repeated for all push pulses throughout the cardiac cycle, and the mean and standard deviation of the estimates were plotted (Fig. 2). Results At least 85% of the waves were tracked successfully for all acquisitions. Diastole and systole were identified using the ECG signal (Fig. 2a). The average SW speed was 0.6 ± 0.1 m/s at end-diastole (Fig. 2b). The measured speeds ranged from 0.5 ± 0.1 m/s during diastole to 1.9 ± 0.3 m/s during systole. The changes in SW speeds correspond to the expected variation in muscle stiffness during the heart cycle as the RV relaxes and contracts. Conclusions We demonstrate for the first time the induction and tracking of shear waves in the RVFW of a closed-chest pig. The possibility to noninvasively quantify RV wall stiffness opens a large field of translational research, with direct applications in pulmonary hypertension, congenital heart disease and heart failure in general. Pathological increase in stiffness should be further investigated in longitudinal case/control studies. Abstract Figure. Fig1: Induction and tracking of RV SW Abstract Figure. Fig2: SW speeds during cardiac cycle

Left ventricular high frame rate echo-particle image velocimetry: feasibility and comparison with conventional echocardiography

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Echo-Particle Image Velocimetry (echoPIV) tracks speckle patterns from ultrasound contrast agent (UCA) microbubbles injected intravenously, being less angle-sensitive than colour Doppler. One limitation of conventional echoPIV is the inability to accurately resolve high velocities, because of relatively low frame rates. In contrast, high frame rate (HFR) echoPIV enables tracking of fast flow in the left ventricle (LV). Purpose To investigate the feasibility and precision of HFR echoPIV in patients. Methods 19 heart failure patients were included. UCA was infused with a dedicated pump. HFR contrast images were acquired, in apical long axis view (ALAX, ensuring simultaneous visualization of LV inflow and outflow), using a fully-programmable research ultrasound system, with a phased array probe. In the same session, complete echocardiographic studies were obtained using a clinical ultrasound system, with a matrix array probe, including LV UCA. Non-contrast pulsed-wave (PW) Doppler were also obtained in ALAX (Figure 1) from the mitral valve tips (inflow) and the LV outflow tract (outflow). HFR echoPIV image quality and tracking were assessed offline by two independent observers. The peak velocity of the inflow and outflow were determined by the automated tracking algorithm of the HFR echoPIV, and measured by the peak modal velocity of the conventional PW. These velocities were compared using Pearson’s correlations and Bland-Altman plots. All patients gave their informed consent. The study was approved by the institutional review board. Results Conventional echo image quality was good in 12 (63%), medium in 5 (26%) and bad in 2 (11%). EchoPIV tracking was good in 12 (63%), medium in 2 (10%) and bad in 5 (26%). In the 12 patients where echoPIV tracking was good, the direction and velocity of intracavitary vortices could be visualized (Figure 1). The inflow velocity could be determined by echoPIV in 17/19 (89%), and outflow in 14/19 (74%). EchoPIV tended to underestimate the maximal velocity as determined by PW (Figure 2), with a bias of 0.19 m/s (inflow) and 0.28 m/s (outflow). This negative bias is expected as the PW is assessing maximum velocity in the interrogation kernel whereas echoPIV returns the mean velocity. The correlation of the two methods was good for the inflow (R2 = 0.77, p &amp;lt; 0.001) and moderate for the outflow (R2 = 0.54, p &amp;lt; 0.001). This may be explained by the position of the LV outflow tract deeper in the image, leading to increased attenuation, clutter and reduced lateral resolution. Conclusion HFR echoPIV has comparable feasibility to routine echocardiography, and the ability to correctly estimate intraventricular flow velocity. It can provide in one acquisition all the functional information that can be detected by routine echocardiography, PW and color Doppler, as well as contrast. It succeeds in surpassing the shortcomings of Doppler (angle dependency) and classical contrast imaging (low frame rate). Abstract Figure 1: HFR echoPIV in study patients Abstract Figure 2: study results

Abstract 14321: A Validation Study of Myocardial Elastography Against Coronary Computed Tomography Angiography in Patients With Coronary Artery Disease

Introduction: Myocardial Elastography (ME) is a new quantitative strain imaging method capable of detecting ischemia due to Coronary Artery Disease (CAD). ME has been compared to nuclear perfusion imaging with good agreement. Coronary Computed Tomography Angiography (CCTA) has been shown to have superior accuracy to nuclear perfusion imaging for CAD staging. In this study, ME is compared to CCTA in CAD patients. Methods: High framerate (300 fps) echocardiography in five patients presented with chest pain or shortness of breath symptoms, or having prior history of CAD. Standard short-axis views were acquired at the mid-, basal, and apical left-ventricular (LV) levels using a research ultrasound system (Vantage, Verasonics) with a phased array (P4-2, Philips). ME radial systolic strain (ε) was imaged to evaluate wall thickening using 2D cross-correlation and gradient-based methods on the raw (RF) signals. Average ε within each perfusion territory (LAD, RCA, LCX) was then computed N=45. CCTA was performed using an AcquilionOne Scanner (Canon) with Iohexol (Omnipaque, GE) for contrast. Echocardiograms were coregistered with CCTA using anatomical landmarks. Results: Good qualitative agreement between ε (ME) and stenosis level (CCTA) was obtained (Fig. 1A). ME was sensitive in detecting moderate to severe stenosis showing reduced ε. At mild stenosis, despite a trend of ε reduction, some territories maintained mechanical functionality, possibly due to collateral engagement, demonstrating that both structural (CCTA) and functional (ME) properties are complementary in informing on myocardial viability and functionality, especially at mild stenosis. Future work will entail incorporation of FFR CT measurements as an additional functional reference measurement to validate ME strain.

Color Doppler imaging of pure crystals in hyperbaric conditions

The color Doppler ultrasound twinkling artifact is a rapid color shift that appears on some kidney stones and other pathological mineralizations during ultrasound imaging. Twinkling on kidney stones is primarily attributed to scattering from stabilized microbubbles as increasing hydrostatic pressures has been shown to decrease twinkling. However, it is unknown whether microbubbles are also present and cause twinkling on other forms of pathological mineralizations or pure crystals. In this study, 5 cholesterol and 5 calcium phosphate crystals were grown in vitro from supersaturated solutions and imaged in a custom-built, hydrostatic pressure chamber with a Philips/ATL L7-4 transducer and Vantage-128 research ultrasound system. Hydrostatic pressure was increased to a maximum of 14 MPa while saving IQ data at 1 fps for evaluation of Doppler power. On all 10 imaged crystals, twinkling was found to decrease by approximately 90% when pressures reached 4 MPa absolute. Twinkling reappeared when the pressure was returned to atmospheric levels. These results suggest that bubbles are present on pure crystals and give rise to the twinkling artifact. [Work supported by NSF CAREER 1943937 and NSF GRFP DGE1255832.]

Recondensation of nano-sized perfluorocarbon droplets after acoustic droplet vaporization for blinking ultrasound localization microscopy

Ultrasound localization microscopy (ULM) is a promising super-resolutionimaging technique based on the build-up of subwavelength localizations of gas-filled ultrasound contrast agents (UCAs) within the microvascular space. Slow flow regions can reduce localization rates and diminish the isolation of microbubble signals from tissue. This work compares the blinking contrast dynamics of nano-sized perfluorocarbon droplets to the slowly changing contrast dynamics of traditional gas-filled UCAs. A 16-MHz linear array connected to a Verasonics research ultrasound system was used to capture high-frame rate acquisitions of contrast agents flowing through an in vitro- flow phantom. Nano-sized droplets produced an on and off contrast signal due to vaporization/recondensation events which enhanced microbubble separation from tissue. This allows for higher localization rates for droplets at slow flow speeds, since a new population of bubbles was localized with each ultrasound pulse and was independent of flow speed. This could improve ULM at slow flow speeds, where UCAs require long acquisition times for adequate microbubble movement via flow to produce sufficient localization rates. Preliminary in-vivo experiments comparing UCAs to nano-sized droplets for contrast-enhanced imaging of a mouse kidney will also be discussed. [This work was supported by NIH grant R21 HD097485.]

Detection of cellular mineralization using the Doppler ultrasound twinkling artifact

Heterotopic ossification (HO), or the growth of bone in soft tissue where bone does not usually exist, can occur after any musculoskeletal trauma. While the exact cause of HO is unknown, it can take 2i–3 months before HO can be detected on x-ray or computed tomography (CT). The color ultrasound Doppler twinkling artifact is a rapid color shift that was discovered when imaging kidney stones. Here, our objective is to determine whether twinkling can be used to detect the earliest signs of cellular mineralization in HO. A Vantage-128 research ultrasound system with Philips/ATL L7-4, L12-5, and Vermon L22-14 transducers was used to image human bone marrow-derived stem cells (hBMSCs) cultured in osteogenic media and supersaturated solutions of calcium phosphate. Preliminary results show a 50% increase in Doppler magnitude and a 250% increase in Doppler variance in the presence of cellular mineralization or calcium phosphate crystals compared to images of cells without minerals or in non-crystalline solutions. The L7-4 was found to be more sensitive to twinkling from mineralization than the higher frequency transducers. The increase in Doppler magnitude and variance with cellular mineralization suggests twinkling may be a sensitive early detector of HO. [Work supported by DoD CDMRP PR201164.]

Photoacoustic tomography of fingerprint and underlying vasculature for improved biometric identification

Capitalizing on the photoacoustic effect, we developed a new fingerprint sensing system that can reveal both fingerprints and underlying vascular structures at a high spatial resolution. Our system is built on a 15 MHz linear transducer array, a research ultrasound system, and a 532-nm pulsed laser. A 3D image was obtained by scanning the linear array over the fingertip. The acquired fingerprint images strongly agreed with the images acquired from ultrasound. Additional experiments were also conducted to investigate the effect of acoustic coupling. We discovered that high-quality fingerprint and vessel images can be acquired from both wet and dry fingers using our photoacoustic system. The reduced subdermal features in dry coupling can be enhanced through post-processing. Compared to existing fingerprint scanners, the photoacoustic approach provides a higher quality 3D image of the fingerprint, as well as unique subdermal vasculature structures, making the system almost impossible to counterfeit.

A Prototype Therapy System for Boiling Histotripsy in Abdominal Targets Based on a 256-Element Spiral Array.

Boiling histotripsy (BH) uses millisecond-long ultrasound (US) pulses with high-amplitude shocks to mechanically fractionate tissue with potential for real-time lesion monitoring by US imaging. For BH treatments of abdominal organs, a high-power multielement phased array system capable of electronic focus steering and aberration correction for body wall inhomogeneities is needed. In this work, a preclinical BH system was built comprising a custom 256-element 1.5-MHz phased array (Imasonic, Besançon, France) with a central opening for mounting an imaging probe. The array was electronically matched to a Verasonics research US system with a 1.2-kW external power source. Driving electronics and software of the system were modified to provide a pulse average acoustic power of 2.2 kW sustained for 10 ms with a 1-2-Hz repetition rate for delivering BH exposures. System performance was characterized by hydrophone measurements in water combined with nonlinear wave simulations based on the Westervelt equation. Fully developed shocks of 100-MPa amplitude are formed at the focus at 275-W acoustic power. Electronic steering capabilities of the array were evaluated for shock-producing conditions to determine power compensation strategies that equalize BH exposures at multiple focal locations across the planned treatment volume. The system was used to produce continuous volumetric BH lesions in ex vivo bovine liver with 1-mm focus spacing, 10-ms pulselength, five pulses/focus, and 1% duty cycle.

Mutually orthogonal Golay complementary sequences in the simultaneous synthetic aperture method for medical ultrasound diagnostics. An experimental study

Complementary Golay coded sequences (CGCS) have several advantages over conventional short pulse transmitted signals. Specifically, CGCS allow the signal-to-noise ratio (SNR) to be increased. Moreover, due to matched filtering and compression, echoes resembling the short pulse waveform with substantially higher amplitude can be obtained. However, CGCS require two subsequent transmissions to obtain a single compressed signal. This decreases the data acquisition rate and the frame rate of ultrasound imaging by two-fold. To alleviate this problem, mutually orthogonal Golay complementary sequences (MOGCS) can be used. MOGCS allow the simultaneous transmission of two CGCS pairs to be implemented, yielding the acoustic data for two image frames in one data acquisition cycle.The main objective of this work was an experimental study of the most crucial parameters of the received acoustic signals, e.g. the signal-to-noise ratio (SNR), the side-lobes level (SLL) of the signal and the axial resolution, obtained from simultaneous transmission of two pairs of CGCS comprising a MOGCS set to demonstrate their feasibility of being used in ultrasonography. For this purpose, a simultaneous synthetic transmit aperture method (SSTA) was proposed. The SSTA is based on MOGCS transmission and simultaneous reconstruction of two image frames from a single data acquisition cycle. This doubles the image reconstruction rate in comparison with conventional CGCS signals.In this paper, the ultrasound data from a perfect reflector, commercial phantoms and in vivo measurements were analysed. Two 16-bit long CGCS pairs comprising the MOGCS set were programmed and transmitted using the Verasonics Vantage™ research ultrasound system equipped with a Philips ATL L7-4 linear array ultrasound probe. It was shown that the signal parameters and overall quality of reconstructed B-mode images did not deteriorate when using the MOGCS in comparison to the conventional CGCS and short pulse signals explored so far.

Closed-chest measurement of diastolic and systolic shear wave speed to assess myocardial stiffness

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Research Foundation Flanders (FWO): grant 1211620N TTW – Dutch Heart Foundation partnership program "Earlier recognition of cardiovascular diseases": project number 14740 Background Echocardiographic shear wave elastography (SWE) encompasses all ultrasound techniques tracking shear wave (SW) motion in the cardiac wall, of which the propagation speed is linked to the intrinsic mechanical properties. SWs can be induced naturally, for example by valve closure, or externally by using an acoustic radiation force (ARF). Although the latter is technically more demanding, it enables instantaneous stiffness assessment throughout the entire cardiac cycle (fig. a). However, it is unknown how factors such as cardiac loading and contractility, next to intrinsic mechanical properties, affect ARF-based SW speeds. Purpose We performed transthoracic SWE measurements in pigs to study the effects of hemodynamic alterations, inotropic state and myocardial infarction (MI) on diastolic and systolic SW speeds. Methods Different cardiac conditions were considered in three pigs: (i) baseline (BL), (ii) preload decrease (PD), (iii) afterload increase (AI), (iv) preload increase (PI), (v) administration of dobutamine (DOB), (vi) BL2, (vii) MI through 60-100 min. occlusion of the LAD and (viii) 40 min. reperfusion (REP). For each condition, transthoracic high frame rate ARF-based SWE acquisitions were taken in a parasternal long-axis view with a research ultrasound system. SWs were induced in the septum at 34 Hz during 1.5 s to track SW speeds throughout the cardiac cycle (fig. a&amp;b). Systolic and diastolic SW speeds were determined from the 10% highest and lowest median values per condition, respectively. Left ventricular pressure-volume (PV) loops were recorded to estimate end-diastolic pressure (EDP), end-systolic pressure (ESP) and passive chamber stiffness (dPdV). dPdV was determined as the slope of the tangent to the fitted end-diastolic PV relationship at mean ED volume. Linear regressions and Pearson’s correlation coefficients were computed. Results Diastolic SW speed was correlated to EDP for conditions with changes in loading, and to dPdV for conditions with changes in chamber stiffness (fig. c). Both relationships were significant, with a moderate positive correlation for EDP (R = 0.48, p = 0.02) and a strong positive correlation for dPdV (R = 0.76, p &amp;lt; 0.01). Furthermore, the observed change in diastolic SW speed was smaller when altering EDP compared to dPdV (0.4 m/s vs. 1.0 m/s). For systolic SW speed, very strong positive correlations were found with ESP (R = 0.91, p &amp;lt; 0.01), and with dPdV (R = 0.81, p &amp;lt; 0.01) in fig. d. Conclusion This study shows that both diastolic and systolic SW speed are related to passive chamber stiffness. Moreover, loading also influenced systolic SW speed and, to a lesser extent, diastolic SW speed, presumably because of material nonlinearity. Systolic SW speed is linked to contractility as well. Thus, while SWs after valve closure occur at a certain moment in the cardiac cycle, the timing of ARF-based SWs can be chosen such to assess specific aspects of the cardiac (structural and functional) status. Abstract Figure.