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Structural abnormalities and functional changes of renal microvascular networks play a significant pathophysiologic role in the occurrence of kidney diseases. Super-resolution ultrasound imaging has been successfully utilized to visualize the microvascular network and provide valuable diagnostic information. To prevent the burst of microbubbles, a lower mechanical index (MI) is generally used in ultrasound localization microscopy (ULM) imaging. However, high-noise levels lead to incorrect signal localizations in relatively low-MI settings and deep tissue. In this study, we implemented a block-matching threedimensional (BM3D) image-denoising method, after the application of singular value decomposition filtering, to further suppress the noise at various depths. The in vitro flow-phantom results show that the BM3D method helps the significant reduction of the error localizations, thus improving the localization accuracy. In vivo rhesus macaque experiments help conclude that the BM3D method improves the resolution more than other image-based denoising techniques, such as the nonlocal means method. The obtained clutter-filtered images with fewer incorrect localizations can enable robust ULM imaging, thus helping in establishing an effective diagnostic tool.

Adaptive acoustic output selection in ultrasound imaging promises to improve adherence to the ALARA (as low as reasonably achievable) principle. Demonstrated imaging sequences have balanced image quality and safety considerations based on transducer channel lag-one coherence to select Mechanical Index (MI), a measure of acoustic output. In this study, data were collected with an adaptive output selection tool on 9 pregnant volunteers to explore factors affecting the recommended output. The placenta, fetal abdomen, and fetal heart in each volunteer were repeatedly scanned. A statistically significant difference in recommended ALARA MI was observed between target structures (p < 0.001). Each target's underlying channel data signal magnitude correlated with the recommended ALARA MI used for scanning, suggesting the brightness of a target affects the selected ALARA MI. These findings imply that continued observance of the ALARA principle during clinical examinations requires adaptive output selection be performed with each new target structure, or each time a transducer or acoustic window shift causes a change in the target brightness

Ultrasound (US) and cavitation agents such as microbubbles (MBs) have been demonstrated to decrease the barrier function of endothelial and epithelial layers. However, in vitro experiments that study this effect are often hindered by the inability to deliver buoyant contrast agents in proximity to cell monolayers in order to adequately control the decrease in barrier function whilst insonating a sufficiently large tissue area. We have addressed this by adapting a cell culture system and fabricating a bespoke high-power miniature unfocused US transducer. The setup was used to control the drop in barrier function and to determine how varying the mechanical index (MI) and the duty cycle affected the barrier function. It was found that buffer solution alone and buffer + MBs did not decrease the transepithelial electrical resistance (TEER) of the cell monolayer. Buffer + US decreased the TEER by ~40%, with 10% TEER recovery 9 min after switching US off. Buffer + MBs + US decreased the TEER by 80%, with little or no recovery following treatment. In the presence of MBs, the barrier function was decreased by a duty cycle = [1% - 50%] and by an MI = [0.25 - 0.5], without any recovery following treatment. Detectable amounts of fluorescent dextran were delivered across the Caco-2 monolayer only by a combination of US + MBs. These results suggest that our adapted setup and custom-built miniature transducer permits control of the decrease in barrier function for further therapeutic investigations.

A software-based processing approach for contrast-enhanced ultrasound (US) imaging is presented. Termed pulse-inversion spectral convolution (PISD), the main motivation here was to further evaluate the performance of this contrast-enhanced US imaging technique using a series of experimental studies. The PISD-based contrast-enhanced US approach is founded on a class of Gaussian derivative functions (GDFs). Two types of PISD pulses (one GDF and convolution of three GDF pulses) can be used to form two new inverted pulse sequences. These pulses are then used to filter backscattered US data for isolation of the nonlinear MB signal component. An US system (Vantage 256, Verasonics Inc) with a L11-4v linear array transducer was programmed and used for PISD-based contrast-enhanced US imaging. The receive data from all channels was shaped using a wide beamforming technique. In vitro US images were collected from a flow phantom perfused with a MB contrast agent using PISD and traditional pulse-inversion US (nonlinear, NL) for comparison. Further, role of the transmit aperture size ( $\text{TX}=32$ or 64) was also evaluated using a US pulse frequency of 6.25 MHz and a low mechanical index of 0.2. Contrast enhancement was measured using a contrast-to-noise ratio (CNR). Preliminary in vivo data was acquired from the hindlimb (femoral artery) of healthy rats after receiving a bolus injection of MBs. Overall, widebeam contrast-enhanced US imaging using the larger aperture size of 64 elements yielded improved CNR values. Using this widebeam US imaging approach, both in vitro and in vivo results demonstrated that the PISD-based contrast-enhanced US technique produced images with improved contrast compared to the more traditional B-mode and NL US imaging strategies.

Purpose: We investigate the vaporization of phase-change ultrasound contrast agents using photon radiation for dosimetry perspectives in radiotherapy. Methods: We studied superheated perfluorobutane nanodroplets with a crosslinked poly(vinylalcohol) shell. The nanodroplets’ physico-chemical properties, and their acoustic transition have been assessed firstly. Then, poly (vinylalcohol)-perfluorobutane nanodroplets were dispersed in poly(acrylamide) hydrogel phantoms and exposed to a photon beam. We addressed the effect of several parameters influencing the nanodroplets radiation sensitivity (energy/delivered dose/dose rate/temperature). The nanodroplets-vaporization post-photon exposure was evaluated using ultrasound imaging at a low mechanical index. Results: Poly(vinylalcohol)-perfluorobutane nanodroplets show a good colloidal stability over four weeks and remain highly stable at temperatures up to 78 ◦C. Nanodroplets acoustically-triggered phase transition leads to microbubbles with diameters

Microbubbles (MB) are widely used as contrast agents to perform contrast-enhanced ultrasound (CEUS) imaging and as acoustic amplifiers of mechanical bioeffects incited by therapeutic-level ultrasound. The distribution of MBs in the brain is not yet fully understood, thereby limiting intra-operative CEUS guidance or MB-based FUS treatments. In this paper we describe a robust platform for quantification of MB distribution in the human brain, allowing to quantitatively discriminate between tumoral and normal brain tissues and we provide new information regarding real-time cerebral MBs distribution. Intraoperative CEUS imaging was performed during surgical tumor resection using an ultrasound machine (MyLab Twice, Esaote, Italy) equipped with a multifrequency (3–11 MHz) linear array probe (LA332) and a specific low mechanical index (MI

Background Improving imaging quality is a fundamental problem in ultrasound contrast agent imaging (UCAI) research. Plane wave imaging (PWI) has been deemed as a potential method for UCAI due to its’ high frame rate and low mechanical index. High frame rate can improve the temporal resolution of UCAI. Meanwhile, low mechanical index is essential to UCAI since microbubbles can be easily broken under high mechanical index conditions. However, the clinical practice of ultrasound contrast agent plane wave imaging (UCPWI) is still limited by poor imaging quality for lack of transmit focus. The purpose of this study was to propose and validate a new post-processing method that combined with deep learning to improve the imaging quality of UCPWI. The proposed method consists of three stages: (1) first, a deep learning approach based on U-net was trained to differentiate the microbubble and tissue radio frequency (RF) signals; (2) then, to eliminate the remaining tissue RF signals, the bubble approximated wavelet transform (BAWT) combined with maximum eigenvalue threshold was employed. BAWT can enhance the UCA area brightness, and eigenvalue threshold can be set to eliminate the interference areas due to the large difference of maximum eigenvalue between UCA and tissue areas; (3) finally, the accurate microbubble imaging were obtained through eigenspace-based minimum variance (ESBMV). Results The proposed method was validated by both phantom and in vivo rabbit experiment results. Compared with UCPWI based on delay and sum (DAS), the imaging contrast-to-tissue ratio (CTR) and contrast-to-noise ratio (CNR) was improved by 21.3 dB and 10.4 dB in the phantom experiment, and the corresponding improvements were 22.3 dB and 42.8 dB in the rabbit experiment. Conclusions Our method illustrates superior imaging performance and high reproducibility, and thus is promising in improving the contrast image quality and the clinical value of UCPWI.

It is known that the microbubbles of Sonazoid are accumulated in the liver parenchyma due to the phagocytosis of Kupffer cells in the sinusoid. Because this phagocytic function decreases due to the progression of fibrosis in chronic liver disease, the deterioration of the liver function may be quantified by measuring the concentration of the accumulated Sonazoid microbubbles. In this article, a new method to quantify the concentration of microbubbles accumulated in attenuating media is proposed. This method utilizes the contrast-enhanced imaging with high mechanical index, measures the depth of the bubble destruction for each frame and analyze the shape of the destruction curve to estimate the concentration of the bubbles. A phantom experiment was performed with various concentrations of the contrast agent Sonazoid solution as well as various attenuation coefficients of the viscous media. Because of the theoretical model proposed, the estimated attenuation indexes, related to the concentration of Sonazoid microbubbles, were independent of the background attenuation of the propagating medium. The result suggest it has a potential to quantify Sonazoid concentration in the liver parenchyma more precisely against different liver attenuation conditions.

In single-cell/spheroid analyses, flow cytometry plays a key role in high-throughput measurements. Among the considerable numbers of indexes available for a target evaluation, mechanical characteristics such as a Young's modulus have been focused upon as new indexes related to physiological condition. However, a continuous mechanical indexing system has yet to be achieved due to the difficulty in flow control, which brings about a fluctuation of the force sensor probe. In this letter, we propose an automated mechanical indexing system of spheroids. By utilizing a combination of two syringe pumps, we succeeded in positioning the target spheroids without an undesirable pinching. We conducted experiments on the continuous mechanical indexing of single-cell spheroids using 26 mesenchymal stem cell spheroids. The evaluation results of positioning showed that the error in the position control was 14.1 $\mu$ m with a standard deviation of 87.7 $\mu$ m, which corresponded to a measurement error of the Young's modulus of under 2%. In addition, we succeeded in achieving a measurement throughput of 3.14 spheroids per minute, which is approximately 2 times faster than a manual operation. Finally, we demonstrated the on-chip sorting of single spheroids based on the mechanical index to show the adaptability of the proposed method toward the flow cytometry.

OBJECTIVES We evaluated the detection rates for perfusion defects in hypervascular hepatocellular carcinomas comparing the low mechanical index (MI) and high MI contrast modes during the post-vascular phase (PVP) of contrast-enhanced ultrasonography. METHODS Seventy-eight patients with 84 hypervascular hepatocellular carcinomas (mean diameter, 23.4 ± 11.2 mm) were selected for this retrospective study. All the patients underwent whole-liver scanning using conventional ultrasonography before injection of a perflubutane-based contrast agent (Sonazoid), and all the detected nodules were classified as either hypoechoic or hyperechoic nodules. Next, hypoechoic and hyperechoic nodules were evaluated using contrast-enhanced ultrasonography, and the presence of a perfusion defect was assessed for each nodule using both the low MI (0.2-0.3) and the high MI (0.7-1.2) contrast modes during the PVP (10 minutes after injection). The data were analyzed using the McNemar test. RESULTS Forty-four nodules were classified as hypoechoic nodules, and the remaining 40 nodules were classified as hyperechoic nodules using conventional ultrasonography. The detection rate for perfusion defects determined using the high MI contrast mode was higher than that determined using the low MI contrast mode in hyperechoic nodules during the PVP (low MI, 58% [23 of 40]; high MI, 90% [36 of 40]; P

Background: Preliminary studies suggest that myocardial scar can be visualised by transthoracic echocardiography (TTE) using a low mechanical index (MI). Data describing the usefulness of scar imaging by TTE to predict myocardial viability are limited. Purpose: We investigated the association between myocardial scar, as imaged by low MI TTE, and viability as assessed by low-dose dobutamine stress echocardiography (DSE). Methods: We analysed 59 patients who had rest echocardiography including low MI (0.4-0.5) scans and DSEs, performed for myocardial viability between 29/04/2015 to 16/05/2018. Median age was 64 years (interquartile range 57-71), 55 (93%) were male. Left ventricular contrast opacification SonoVue (Braco) was used according to American Society of Echocardiography (ASE) standards (n = 39). Two experienced cardiologists blindly and independently performed 16-segment scar assessment at rest. Viability by DSE was used to represent the ‘gold standard’, from which sensitivity, specificity, negative and positive predictive values of viability assessed by scar at rest were calculated. Results: 42 (71%) of studies had evidence of scar at rest identified by low MI imaging. Presence of scar at rest has a sensitivity of 42%, specificity of 92%, positive and negative predictive values of 82 and 64%, respectively (Table 1). Specificity was higher in non-contrast compared to contrast images, at 97 and 90 %, respectively. The right coronary artery territory had a lower specificity compared to left anterior descending and circumflex territories. Conclusions: Presence of scar at rest has a low sensitivity but high specificity to predict non-viability on low-dose DSE. The presence of scar at rest TTE has the potential to reduce the need for low-dose DSE as these patients are unlikely to have viable myocardium in this region.

Aim : Contrast-enhanced ultrasound (CEUS) has become a relevant imaging method for the evaluation of focal liver le- sions (FLL). The aim of this study was to evaluate the performance of CEUS for the assessment of focal nodular hyperplasia (FNH) in a large study group. Material and methods : We performed a multicentre prospective observational study, which included successive CEUS examinations from fourteen Romanian centres. CEUS examinations were performed in de novo FLL, using low mechanical index ultrasound, following an intravenous bolus of 2.4 ml SonoVue. CEUS was considered conclusive for FNH if a typical pattern was present following contrast (rapid “spoke-wheel” enhancement during the arterial phase, hyperenhanced lesion during venous phase, hyper- or isoenhanced in the late phase). In all cases a reference method was available (contrast enhanced CT or MRI or biopsy). The trial was registered in clinicaltrials.gov (Identifier NCT01329458). Results : During the 6 years study, 2062 “de novo” FLL were evaluated by CEUS. From this cohort, 94/2062 (4.5%) had a typical enhancing pattern for FNH as described in the EFSUMB guidelines. Contrast enhanced CT/MRI and biopsy diagnosed additional 15 FNH. From the 94 cases diagnosed as FNH by CEUS, in nine the final diagnosis was different (five of them adenomas). CEUS had 85% sensitivity, 99.5% specificity, 90.4% positive predictive value, 99.2% negative predictive value and 98.8% diagnostic accuracy for the diagnosis of FNH. Conclusions : CEUS is a sensitive and very specific method for the diagnosis of FNH.

High mechanical index impulses from a diagnostic transducer are utilized in myocardial perfusion imaging, but can also be utilized therapeutically in three cardiovascular applications: (a) thrombus dissolution (sonothrombolysis), (b) improving microvascular flow in ischemic territories (sonoperfusion), and (c) targeted drug and nucleic acid delivery. The targeted therapeutic effect appears to be based on acoustic cavitation of the intravascular microbubbles which results in endothelial shear and pore formation, as well as mechanical destruction of thrombi. Within the last 5 years, clinical trials have been performed in acute myocardial infarction demonstrating successful reductions in myocardial infarct size with sonothrombolysis added to current guideline-based treatment. In patients with severe peripheral arterial disease, brief improvements in calf microvascular blood flow have been observed for 1 h after 10 min of sonoperfusion therapy. Targeted ultrasound therapies are developing for prevention of microvascular obstruction in acute coronary syndromes and peripheral vascular disease.

We previously reported that acoustic radiation force impulse (ARFI) with concomitant administration of perfluorobutane as an ultrasound contrast agent (UCA)-induced arrhythmias at a mechanical index (MI) of 1.8 or 4.0 in a rabbit model. The present study identified the location of arrhythmias with a MI

Ultrasound-targeted microbubble destruction (UTMD) has been widely applied to enhance chemotherapy of tumors, yet few studies have focused on the metastatic potential induced by UTMD. This study aimed to explore the metastasis of VX2 tumors after treatment with UTMD and chemotherapy.Forty-four New Zealand rabbits bearing subcutaneous VX2 tumors were enrolled for the treatment of UTMD with chemotherapy. For UTMD, the tumors were insonated using two pulsing protocols of diagnostic ultrasound (DUS, VINNO and ECARE) with a mechanical index (MI) of 0.29-0.33, tone burst of 8.0 cycles, and frequencies of 3-4 MHz. A total dose of 2 ml SonoVue® was injected intermittently during 10-min UTMD exposure. The combination therapy was treated using doxorubicin (DOX, 2 mg/kg) and DUS, while the tumors treated using DOX only served as the control. Tumor size was measured using the tumor volume formula. Survival time was observed until animal death or the end of the study (120 days). Specific organs (lung, liver, kidney, and brain) were removed for metastatic evaluation.There were no statistical differences in overall metastasis classification and individual organ metastases among all groups (P 0.05). The tumor growth rate only showed inhibition on the 5th day (P 0.01). The survival time did not demonstrate any significant difference between UTMD and chemotherapy only (P 0.05).UTMD using long-pulse DUS with commercial microbubbles did not pose a risk of metastasis enhancement in DOX chemotherapy.

Ultrasound imaging presents many positive attributes, including safety, real-time imaging, universal accessibility, and cost. However, inherent difficulties in discrimination between soft tissues and tumors prompted development of stabilized microbubble contrast agents. This presents the opportunity to develop agents in which drug is entrapped in the microbubble shell. We describe preparation and characterization of theranostic poly(lactide) (PLA) and pegylated PLA (PEG-PLA) shelled microbubbles that entrap gemcitabine, a commonly used drug for pancreatic cancer (PDAC). Entrapping 6 wt% gemcitabine did not significantly affect drug activity, microbubble morphology, or ultrasound contrast activity compared with unmodified microbubbles. In vitro microbubble concentrations yielding ≥ 500nM entrapped gemcitabine were needed for complete cell death in MIA PaCa-2 PDAC drug sensitivity assays, compared with 62.5 nM free gemcitabine. In vivo administration of gemcitabine-loaded microbubbles to xenograft MIA PaCa-2 PDAC tumors in athymic mice was well tolerated and provided substantial tumoral image enhancement before and after destructive ultrasound pulses. However, no significant differences in tumor growth were observed among treatment groups, in keeping with the in vitro observation that much higher doses of gemcitabine are required to mirror free gemcitabine activity. Statement of significance The preliminary results shown here are encouraging and support further investigation into increased gemcitabine loading. Encapsulation of gemcitabine within polylactic acid (PLA) microbubbles does not damage its activity towards pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) cells. Excellent imaging and evidence of penetration into the highly desmoplastic PDAC tumors is demonstrated. Microbubble destruction was confirmed in vivo, showing that elevated mechanical index shatters the microbubbles for enhanced delivery. The potential to slow PDAC growth in vivo is shown, but higher gemcitabine concentrations are required. Current efforts are directed at increasing drug loading by inclusion of drug-carrying nanoparticles for effective in vivo treatment.

The Asian Federation of Societies for Ultrasound in Medicine and Biology aimed to provide information on techniques and indications for contrast-enhanced harmonic endoscopic ultrasound (CH-EUS), and to create statements including the level of recommendation. These statements are based on current scientific evidence reviewed by a Consensus Panel of 15 internationally renowned experts. The reliability of clinical questions was measured by agreement rates after voting. Six statements were made on techniques, including suitable contrast agents for CH-EUS, differences between contrast agents, setting of mechanical index, dual imaging and duration and phases for observation. Thirteen statements were made on indications, including pancreatic solid masses, pancreatic cancer staging, pancreatic cystic lesions and mural nodules, detection of subtle pancreatic lesions, gallbladder sludge and polyps, hepatic lesions, lymph nodes, subepithelial lesions, visceral vascular diseases, guidance of fine needle aspiration and evaluation for local therapy. These international expert consensus guidelines will assist endosonographers in conducting CH-EUS according to evidence-based information.

Ultrasound attenuation through soft tissues can produce an acoustic radiation force (ARF) and heating. The ARF-induced displacements and temperature evaluations can reveal tissue properties and provide insights into focused ultrasound (FUS) bio-effects. In this study, we describe an interleaving pulse sequence tested in a tissue-mimicking phantom that alternates FUS and plane-wave imaging pulses at a 1 kHz frame rate. The FUS is amplitude modulated, enabling the simultaneous evaluation of tissue-mimicking phantom displacement using harmonic motion imaging (HMI) and temperature rise using thermal strain imaging (TSI). The parameters were varied with a spatial peak temporal average acoustic intensity (I(spta)) ranging from 1.5 to 311 W.cm(−2), mechanical index (MI) from 0.43 to 4.0, and total energy (E) from 0.24 to 83 J.cm(−2). The HMI and TSI processing could estimate displacement and temperature independently for temperatures below 1.80°C and displacements up to ~117 μm (I(spta)

Theranostics 11(19), 9557-9570 (2021). doi:10.7150/thno.64767, Published by Ivyspring, Wyoming, NSW

OBJECTIVES Ultrasound users are advised to observe the ALARA (as low as reasonably achievable) principle, but studies have shown that most do not monitor acoustic output metrics. We developed an adaptive ultrasound method that could suggest acoustic output levels based on real-time image quality feedback using lag-one coherence (LOC). METHODS Lag-one coherence as a function of the mechanical index (MI) was assessed in 35 healthy volunteers in their second trimester of pregnancy. While imaging the placenta or the fetal abdomen, the system swept through 16 MI values ranging from 0.15 to 1.20. The LOC-versus-MI data were fit with a sigmoid curve, and the ALARA MI was selected as the point at which the fit reached 98% of its maximum. RESULTS In this study, the ALARA MI values were between 0.35 and 1.03, depending on the acoustic window. Compared to a default MI of 0.8, the pilot acquisitions suggested a lower ALARA MI 80% of the time. The contrast, contrast-to-noise ratio, generalized contrast-to-noise ratio, and LOC all followed sigmoidal trends with an increasing MI. The R2 of the fit was statistically significantly greater for LOC than the other metrics (P

We present a case series of three patients that underwent myocardial contrast echocardiography (MCE) in the setting of recent chest pain, as paradigmatic examples of the usefulness of contrast-echocardiography with very-low mechanical index imaging in the context of rest wall motion assessment. Moreover, we analysed the pertinent literature about the use of rest MCE in the context of chest pain of unknown origin, showing its diagnostic and prognostic impact. We think that MCE could play a key role in detecting chest pain subtended by previously unknown coronary artery disease (CAD). For example, in pts without significant electrocardiogram (ECG) modifications or in whom high sensitivity troponins show only borderline increase (still below the upper limit) or have no clearly significant delta. In such cases the more sensitive evaluation of wall motion (WM) powered by MCE could add diagnostic information, above all in pts with severe CAD but apparently normal WM at standard echocardiography.

Microbubbles (MBs) are 1 to 10 µm gas particles stabilized by an amphiphilic shell capable of responding to biomedical ultrasound with strong acoustic signals, allowing them to be commonly used in ultrasound imaging and therapy. The composition of both the shell and the core determines their stability and acoustic properties. While there has been extensive characterization of the dissolution, oscillation, cavitation, collapse and therefore, ultrasound contrast of MBs under static conditions, few reports have examined such behavior under hydrodynamic flow. In this study, we evaluate the interplay of ultrasound parameters (five different mechanical indices [MIs]), MB shell parameter (shell stiffness), type of gas (perfluorocarbon for diagnostic imaging and xenon as a therapeutic gas), and a flow parameter (flow rate) on the ultrasound signal of phospholipid-stabilized MBs flowing through a latex tube embedded in a tissue-mimicking phantom. We find that the contrast gradient (CG), a metric of the rate of decay of contrast along the length of the tube, and the contrast peak (CP), the location where the maximum contrast is reached, depend on the conditions of flow, imaging, and MB material. For instance, while the contrast near the flow inlet of the field of view is highest for a softer shell (dipalmitoylphosphatidylcholine [DPPC], C16) than for stiffer shells (distearoylphosphatidylcholine [DSPC], C18, and dibehenoylphosphatidylcholine [DBPC], C22), the contrast decay is also faster; stiffer shells provide more resistance and hence lead to slower MB dissolution/destruction. At higher flow rates, the CG is low for a fixed length of time because each MB is exposed to ultrasound for a shorter period. The CG becomes high for low flow rates, especially at high incident pressures (high MI), causing more MB destruction closer to the inlet of the field of view. Also, the CP shifts toward the inlet at low flow rates, high MIs, and low shell stiffness. We also report the first demonstration of sustained ultrasound flow imaging of a water-soluble, therapeutic gas MB (xenon). We find that an increased MB concentration is necessary for obtaining the same signal magnitude for xenon MBs. In summary, this study builds a framework depicting how multiple variables simultaneously affect the evolution of MB ultrasound contrast under flow. Depending on the MB composition, imaging conditions, transducer positioning, and image processing, building on such a framework could potentially allow for extraction of additional diagnostic information than is commonly analyzed for physiological flow.

Mesenchymal stem cells are mechano-sensitive cells with the potential to restore the function of damaged tissues. Low-intensity ultrasound has been increasingly considered as a bioactive therapeutic apparatus. Optimizing transplantation conditions is a critical aim for radiation-induced skin tissue injury. Therefore, the therapeutic function of adipose-derived mesenchymal stem cells to ultrasound stimulus was examined based on the mechanical index (MI). Mesenchymal stem cells were isolated from the adipose tissues of mature guinea pigs. An ultrasound system (US) was constructed with a 40 kHz frequency. The radiation-induced skin injury model was produced on the abdominal skin of guinea pigs by 60 Gy of radiation. Then, they were divided to 7 groups (n = 42): control, sham, US (MI = 0.7), AdMSCs injection, US AdMSCs (AdMSCs, under US with MI = 0.2), AdMSCs + US (AdMSCs transplantation and US with MI = 0.7) and US AdMSCs + US (combining the last two groups). The homing of stem cells was verified with fluorescence imaging. The groups were followed with serial photography, ultrasound imaging, tensiometry, and histology. The thickness of the skin was analyzed. Functional changes in skin tissue were evaluated with Young’s modulus (kPa). One-way ANOVA tests were performed to analyze differences between treatment protocols (p

Introduction: Diagnostic ultrasound high mechanical index (MI) impulses are used during an ultrasound enhancing agent (UEA) infusion to improve endocardial border resolution and study myocardial perfusion. They have also been shown to cause endothelial shear, resulting in prolonged increases in ATP release and augment microvascular flow. The potential for these high MI impulses to alter cardiac output (CO) are unknown. Hypothesis: To study the impact of high MI impulses on CO Methods: Fifty one patients (mean age 63±15 years; 41% female) referred for contrast echocardiography underwent very low MI imaging with intermittent high MI impulses (1.6-1.7 Megahertz) in three different apical windows during either a Definity (Lantheus Medical) or Lumason (Bracco Diagnostics) infusion or bolus. CO was determined from Doppler measurements of left ventricular outflow tract stroke volume and heart rate. Mean contrast enhanced biplane left ventricular ejection fraction (LVEF) was 53±15%; (range 10-75%). CO from baseline without contrast (COwoC) and baseline after contrast (COwC) before high MI impulses were compared to CO after contrast and after high MI impulses (COaHMI). All CO measurements were made by an independent reviewer blinded to time of measurement (before or after high MI impulses). Results: Although heart rate did not change before and after intermittent high MI impulse administration, COaHMI increased significantly when compared to COwoC and COwC (p< 0.001 for both comparisons; Figure). In nine patients (18%), CO increased by more than 20%. In patients with LVEF < 40% COwC was 2.4±0.8 liters per minute (LPM) and COaHMI increased to 2.7± 0.8 LPM (p=0001). In patients with LVEF≥40%, COwC was 3.4±1.06 LPM while COaHMI increased to 3.8± 1.2 LPM (p=0.00001). Conclusions: Application of diagnostic guided high MI impulses during a commercially available microbubble infusion significantly increases CO irrespective of underlying left ventricular systolic function.

Introduction: Preclinical studies in ST elevation myocardial infarction (STEMI) indicate that high mechanical index impulses guided with transthoracic diagnostic ultrasound associated with intravenously administered microbubbles results in the dissolution of the thrombus (sonothrombolysis), improving coronary microcirculation and epicardial coronary recanalization rate. Hypothesis: Left atrial (LA) echocardiographic parameters are compromised in STEMI and can be accurately measured by two-dimensional echocardiography. To study the effect of sonotrombolysis on the LA pressure and volume we propose our study. Methods: A total of 100 patients were randomized, 50 for the control group and 50 for the therapy group. Echocardiographic analysis of LA pressure and volume were performed immediately before and after percutaneous coronary intervention (PCI), 72 hours, 1 month and 6 months of follow-up. LA pressure was classified in normal or elevated, depending on the grade of left ventricular diastolic disfunction (DD): normal diastolic function and DD grade 1 have normal LA pressure, and DD grades 2 and 3 have elevated LA pressure, according to the American and European guideline. LA volume was evaluated by Simpson method and indexed to the body surface area. Results: The LA pressure and volume had lower values in the therapy group after 6 months of PCI. The comparison of LA pressure between the therapy and control groups respectively was: before PCI (72% vs. 70% normal; 28% vs. 30% elevated; p=0.826), after PCI (68% vs. 65% normal; 32% vs. 35% elevated; p=0.777), 72 hours (75% vs. 62% normal; 25% vs. 38% elevated; p=0.147), 1 month (68% vs. 52% normal; 32% vs. 48% elevated; p=0.123) and 6 months (84% vs. 64% normal; 16% vs. 36% elevated; p=0.035). The comparison of LA volumes between the therapy and control groups respectively was: before PCI (19.0±6.2 vs. 22.4±9.8 ml/m 2 ; p=0.061), after PCI (22.8±7.9 vs. 24.4±12.1 ml/m 2 ; p=0.469), 72 hours (25.9±8.5 vs. 26.4±12.7 ml/m 2 ; p=0.815), 1 month (27.2±8.3 vs. 29.1±13.1 ml/m 2 ; p=0.410) and 6 months (26.7±7.5 vs. 33.1±14.9 ml/m 2 ; p=0.013). Conclusions: The use of sonothrombolysis as adjuvant therapy in STEMI patients results in better values of LA pressure and volume, demonstrating the benefit of using this new therapy.

In this study, 3-D non-linear ultrasound simulations and experimental measurements were used to estimate the range of in situ pressures that can occur during transcutaneous abdominal imaging and to identify the sources of error when estimating in situ peak rarefaction pressures (PRPs) using linear derating, as specified by the mechanical index (MI) guideline. Using simulations, it was found that, for a large transmit aperture (F/1.5), MI consistently over-estimated in situ PRP by 20%–48% primarily owing to phase aberration. For a medium transmit aperture (F/3), the MI accurately estimated the in situ PRP to within 8%. For a small transmit aperture (F/5), MI consistently underestimated the in situ PRP by 32%–50%, with peak locations occurring 1–2 cm before the focal depth, often within the body wall itself. The large variability across body wall samples and focal configurations demonstrates the limitations of the simplified linear derating scheme. The results suggest that patient-specific in situ PRP estimation would allow for increases in transmit pressures, particularly for tightly focused beams, to improve diagnostic image quality while ensuring patient safety.

The quality of contrast-enhanced ultrasound (CEUS) imaging performed with high-frequency convex and linear transducers is often suboptimal. A common solution to improving the microbubble signal is by increasing the volume of the ultrasound contrast agent being administered. An alternative technique to improve the signal from the contrast agent is to adjust the mechanical index (MI). This study aimed to compare the manufacturer's default MI to an optimal MI (as determined by the best contrast-to-tissue ratio) for improving the CEUS image quality using linear and convex transducers. This study found that in most cases, the default CEUS MI setting by the manufacturer is often suboptimal, and increasing the MI is necessary to improve the contrast-to-tissue ratio and image quality. The MI can be modified by the clinician during the study to improve the quality of the clinical CEUS examination.

This paper reports underestimation of peak compressional pressure (p(c)), peak rarefactional pressure (p(r)), and pulse intensity integral (pii) due to hydrophone spatial averaging of acoustic radiation force impulse (ARFI) beams generated by clinical linear and phased arrays. Although a method exists for correcting for hydrophone spatial averaging for circularly-symmetric beams, there is presently no analogous method for rectangularly-symmetric beams generated by linear and phased arrays. Consequently, pressure parameters (p(c), p(r), and pii) from clinical arrays are often not corrected for spatial averaging. This can lead to errors in Mechanical Index (MI) and Thermal Index (TI), which are derived from pressure measurements and are displayed in real-time during clinical ultrasound scans. ARFI beams were generated using three clinical linear array transducers. Output pressure waveforms for all three transducers were measured using five hydrophones with geometrical sensitive element sizes (d(g)) ranging from 85 to 1000 μm. Spatial averaging errors were found to increase with hydrophone sensitive element size. For example, if d(g) = 500 μm (typical membrane hydrophone), frequency = 2.25 MHz and F/# = 1.5, then average errors are approximately −20% (p(c)), −10% (p(r)), and −25% (pii). Therefore, due to hydrophone spatial averaging, typical membrane hydrophones can exhibit significant underestimation of ARFI pressure measurements, which likely compromises exposure safety indexes.

This paper reports underestimation of peak compressional pressure (pc), peak rarefactional pressure (pr), and pulse intensity integral (pii) due to hydrophone spatial averaging of pulsed Doppler beams generated by clinical linear and phased arrays. Although a method exists for correcting for hydrophone spatial averaging for circularly-symmetric beams, there is presently no analogous method for rectangularly-symmetric beams generated by linear and phased arrays. Consequently, pressure parameters (pc, pr and pii) from clinical arrays are often not corrected for spatial averaging. This can lead to errors in Mechanical Index (MI) and Thermal Index (TI), which are derived from pressure measurements and are displayed in realtime during clinical ultrasound scans. Pulsed Doppler beams were generated using three clinical linear array transducers. Output pressure waveforms for all three transducers were measured using five hydrophones with geometrical sensitive element sizes (d g ) ranging from 85 to 1000 µm. Spatial averaging errors were found to increase with hydrophone sensitive element size. For example, if d g = 500 µm (typical membrane hydrophone), frequency = 6 MHz and F /# = 2, then average errors are approximately -40% (pc), -20% (pr), and -50% (pii). Therefore, due to hydrophone spatial averaging, typical membrane hydrophones can exhibit significant underestimation of Doppler pressure measurements, which likely compromises exposure safety indexes.

Current localization-based super-resolution ultrasound imaging requires a low concentration of flowing microbubbles to visualize microvasculature beyond the diffraction limit and acquisition is slow. Recent studies have shown that Acoustic Wave Sparsely Activated Localization Microscopy (AWSALM) using phase change nanodroplets can generate fast or even real-time super-resolution imaging. However, the optimal experimental conditions to activate the droplets for generating the super-resolution images are still unknown, especially the activation ultrasound amplitude or mechanical index (MI). The aim of this study is to investigate the effect of the activation MI on the repeated activation of decafluorobutane nanodroplets in vivo . Noninvasive ultrasound data acquisition on a rabbit kidney using the AWSALM pulse sequence was repeated for different activation MIs. It was found that the droplet activation was not observed in the rabbit kidney at an MI of 1.1. The activation of droplet started at an activation MI of 1.3. The contrast of activated droplet signals is maximized at an MI of 1.5 and decreased when the activation MI was increased above 1.5. Such understanding of the effects of activation MI could help improve droplet-base fast super-resolution imaging.

Lonidamine (LND) has been widely explored due to its ability to target metabolic glycolysis and mitochondrial respiration in tumors [4]. However, clinical translation has stalled due to poor bioavailability after oral administration. In this study, we explored three incubation time points of loading oxygen-filled microbubbles with LND (SE61O2-LND) for radiotherapy sensitization by modifying our published methods for creating surfactant-shelled oxygen microbubbles (SE61 O2). Acoustic enhancement and stability were quantified in vitro in a continuously insonated sample holder using a 5 MHz single element transducer which generated a peak positive pressure of 0.69 MPa and a peak negative pressure of 0.25 MP at a PRF of 100 Hz and in a pulsatile flow phantom insonated at a single point using a C1-6 transducer on a GE Logiq E9 system (GE Healthcare) operating at 4.0 MHz at a mechanical index of 0.12. Flow cytometry was performed to analyze the total bubble count for each incubation time point. Lonidamine encapsulation was determined using liquid chromatography-mass spectrometry (LC-MS), the loading approach consisted of incubating the LND and TPGS at 37°C at 0, 24, and 48 hours. Bubbles incubated for 24 hours had an average encapsulation of 2.64 ± 0.32 µg LND/ mL MB, and those incubated for 48 hours had an average of 2.97 ± 0.36 µg LND/ mL MB, while non-incubated micelles had an average of 1.51 ± 0.05 µg LND/ mL MB, both TPGS micelle methods that were incubated showed a statistically significant improvement p < 0.001 compared to non-incubated. This work demonstrates the feasibility of fabricating lonidamine-loaded microbubbles and an improved approach for increasing drug encapsulation. The microbubbles retained their acoustic properties, and by incubating the lonidamine with the TPGS to form micelles, drug loading was increased.

Contrast-enhanced ultrasound (CEUS) is being used increasingly frequently for paediatric diagnostic examinations. Although most applications involve ‘off label’ use of stabilised microbubble contrast agents, it is generally assumed that CEUS is a safe technique, presenting less risk than contrast-enhanced X-rays, and a similar risk to magnetic resonance imaging. Although some biological effects (notably microvascular damage) have been seen in pre-clinical models with exposures using high mechanical index (MI), if an MI of 0.4 or lower is used then the microbubbles remain intact and these effects are not seen. The review of clinical exposures reveals only minor, transient effects that are rapidly resolved. These adverse effects are similar to those seen in adults. The conclusion is that CEUS is a safe and acceptable technique for use in paediatrics.

Non-ablative ultrasound (US)-based techniques to improve targeted tropism of systemically infused cell therapies, particularly mesenchymal stromal cell (MSC), have gained attention in recent years. Mechanotransduction following targeted US sonications have been shown to modulate tissue microenvironments by upregulating cytokines, chemokines, and trophic factors in addition to vascular cell adhesion molecules (CAM) that are necessary to promote tropism of MSC. While numerous US treatment parameters have demonstrated increased MSC homing, it remains unclear how the different mechanical US forces [i.e., acoustic radiation forces (ARF) or cavitation forces] influence tissue microenvironments. This study sonicated murine muscle tissue with pulsed focused ultrasound (pFUS) at 0.5 or 1.15 MHz each over a range of US intensities. Following sonication, tissue was assayed for the prostaglandins (PG) PGH2 and PGE2 as indicators of microenvironmental changes that would support MSC tropism. PGH2 and PGE2 levels were correlated to physical pFUS parameters and acoustic emissions measured by hydrophone. While ARF (pFUS with absence of cavitation signatures) was sufficient to increase PGH2 and PGE2, non-linear curve fitting revealed a frequency-independent relationship between prostaglandin production and mechanical index (MI), which accounts for increased cavitation probabilities of lower frequencies. The prostaglandin data suggested molecular changes in muscle would be particularly sensitive to cavitation. Therefore, low-intensity pulsed ultrasound (LIPUS) at 1 MHz was administered with low ARF (MI = 0.2) in combination with intravenous (IV) infusions of microbubble (MB) contrast agents. This combination upregulated prostaglandins and CAM without ultrasound-mediated microbubble destruction and ultimately promoted tropism of IV-infused MSC. This study revealed that accentuating non-destructive MB cavitation by US using parameters similar to diagnostic US contrast imaging increased MSC homing. Such approaches are particularly attractive to overcome clinical translation barriers of many still-experimental US parameters used in previous stem cell tropism studies.