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The in vivo application of cytolytic peptides for cancer therapeutics is hampered by toxicity, nonspecificity, and degradation. We previously developed a specific strategy to synthesize a nanoscale delivery vehicle for cytolytic peptides by incorporating the nonspecific amphipathic cytolytic peptide melittin into the outer lipid monolayer of a perfluorocarbon nanoparticle. Here, we have demonstrated that the favorable pharmacokinetics of this nanocarrier allows accumulation of melittin in murine tumors in vivo and a dramatic reduction in tumor growth without any apparent signs of toxicity. Furthermore, direct assays demonstrated that molecularly targeted nanocarriers selectively delivered melittin to multiple tumor targets, including endothelial and cancer cells, through a hemifusion mechanism. In cells, this hemifusion and transfer process did not disrupt the surface membrane but did trigger apoptosis and in animals caused regression of precancerous dysplastic lesions. Collectively, these data suggest that the ability to restrain the wide-spectrum lytic potential of a potent cytolytic peptide in a nanovehicle, combined with the flexibility of passive or active molecular targeting, represents an innovative molecular design for chemotherapy with broad-spectrum cytolytic peptides for the treatment of cancer at multiple stages., Introduction Host defense peptides are a class of small amphipathic peptides (10-50 aa) found in most eukaryotic cells that serve diverse functions in humans and other species stemming from their [...]

The capability of energy and entropy metrics of radio-frequency ultrasonic backscatter is validated and quantified for differentiation among normal, dystrophic and steroid-treated muscle in the mdx model. Results suggest the delineation of both treated and untreated-mdx biceps from normal controls.

Characterization of backscatter from tumor tissue targeted with a nanoparticle-based ultrasound contrast agent in vivo analogs of thermodynamic quantities is described. Results reveal that the thermodynamic analog is capable of detecting differences in backscattered signals that are not apparent with the B-mode approach.

Characterization of digital signals using analogs of thermodynamic quantities, the topological entropy, Shannon entropy, thermodynamic energy, partition function, specific heat at constant volume was described. The results of applying thermodynamic quantities to a problem from nondestructive materials evaluation, detection of foreign objects embedded near the surface of thin graphite laminates using backscattered waveforms obtained by C-scanning the laminates were reported.

It is proposed that a ligand-targeted, lipid-encapsulated, liquid perfluorodichlorooctane ultrasonic contrast system system with a small nominal particle size be approximated as a simple, thin layer, acoustic transmission line. This model is evaluated, and the ultrasonic reflectivity of different perfluorocarbon formulations with varying acoustic impedances that target either nitrocellulose membranes or plasma thrombi in vitro are compared.

Transplantable kidneys are in very limited supply. Accurate viability assessment prior to transplantation could minimize organ discard. Rapid and accurate evaluation of intra-operative donor kidney biopsies is essential for determining which kidneys are eligible for transplantation. The criterion for accepting or rejecting donor kidneys relies heavily on pathologist determination of the percent of glomeruli (determined from a frozen section) that are normal and sclerotic. This percentage is a critical measurement that correlates with transplant outcome. Inter- and intra-observer variability in donor biopsy evaluation is, however, significant. An automated method for determination of percent global glomerulosclerosis could prove useful in decreasing evaluation variability, increasing throughput, and easing the burden on pathologists. Here, we describe the development of a deep learning model that identifies and classifies non-sclerosed and sclerosed glomeruli in whole-slide images of donor kidney frozen section biopsies. This model extends a convolutional neural network (CNN) pre-trained on a large database of digital images. The extended model, when trained on just 48 whole slide images, exhibits slide-level evaluation performance on par with expert renal pathologists. Encouragingly, the model’s performance is robust to slide preparation artifacts associated with frozen section preparation. The model substantially outperforms a model trained on image patches of isolated glomeruli, in terms of both accuracy and speed. The methodology overcomes the technical challenge of applying a pretrained CNN bottleneck model to whole-slide image classification. The traditional patch-based approach, while exhibiting deceptively good performance classifying isolated patches, does not translate successfully to whole-slide image segmentation in this setting. As the first model reported that identifies and classifies normal and sclerotic glomeruli in frozen kidney sections, and thus the first model reported in the literature relevant to kidney transplantation, it may become an essential part of donor kidney biopsy evaluation in the clinical setting. [ABSTRACT FROM AUTHOR]

Objective Despite significant advances in intravascular stent technology, safe prevention of stent thrombosis over prolonged periods after initial deployment persists as a medical need to decrease device failure. The objective of this project was to assess the potential of perfluorocarbon nanoparticles (NP) conjugated with the direct thrombin inhibitor D-phenylalanyl-L-prolyl-L-arginyl chloromethylketone (PPACK-NP) to inhibit stent thrombosis. Methods In a static model of stent thrombosis, 3 × 3-mm pieces of stainless steel coronary stents were cut and adsorbed with thrombin to create a procoagulant surface that would facilitate thrombus development. After treatment with PPACK-NP or control NP, stents were exposed to platelet-poor plasma (PPP) or platelet-rich plasma (PRP) for set time points up to 60 minutes. Measurements of final clot weight in grams were used for assessing the effect of NP treatment on limiting thrombosis. Additionally, groups of stents were exposed to flowing plasma containing various treatments (saline, free PPACK, control NP, and PPACK-NP) and generated thrombi were stained and imaged to investigate the treatment effects of PPACK-NP under flow conditions. Results The static model of stent thrombosis used in this study indicated a significant reduction in thrombus deposition with PPACK-NP treatment (0.00067 ± 0.00026 g; n = 3) compared with control NP (0.0098 ± 0.0015 g; n = 3; P = .026) in PPP. Exposure to PRP demonstrated similar effects with PPACK-NP treatment (0.00033 ± 0.00012 g; n = 3) vs control NP treatment (0.0045 ± 0.00012 g; n = 3; P = .000017). In additional studies, stents were exposed to both PRP pretreated with vorapaxar and PPACK-NP, which illustrated adjunctive benefit to oral platelet inhibitors for prevention of stent thrombosis. Additionally, an in vitro model of stent thrombosis under flow conditions established that PPACK-NP treatment inhibited thrombus deposition on stents significantly. Conclusions This study demonstrates that antithrombin perfluorocarbon NPs exert marked focal antithrombin activity to prevent intravascular stent thrombosis and occlusion. [ABSTRACT FROM AUTHOR]

Virtually all modern imaging devices collect electromagnetic or acoustic waves and use the energy carried by these waves to determine pixel values to create what is basically an "energy" picture. However, waves also carry "information", as quantified by some form of entropy, and this may also be used to produce an "information" image. Numerous published studies have demonstrated the advantages of entropy, or "information imaging", over conventional methods. The most sensitive information measure appears to be the joint entropy of the collected wave and a reference signal. The sensitivity of repeated experimental observations of a slowly-changing quantity may be defined as the mean variation (i.e., observed change) divided by mean variance (i.e., noise). Wiener integration permits computation of the required mean values and variances as solutions to the heat equation, permitting estimation of their relative magnitudes. There always exists a reference, such that joint entropy has larger variation and smaller variance than the corresponding quantities for signal energy, matching observations of several studies. Moreover, a general prescription for finding an "optimal" reference for the joint entropy emerges, which also has been validated in several studies. [ABSTRACT FROM AUTHOR]

Duchenne muscular dystrophy in boys progresses rapidly to severe impairment of muscle function and death in the second or third decade of life. Current supportive therapy with corticosteroids results in a modest increase in strength as a consequence of a general reduction in inflammation, albeit with potential untoward long-term side effects and ultimate failure of the agent to maintain strength. Here, we demonstrate that alternative approaches that rescue defective autophagy in tndx mice, a model of Duchenne muscular dystrophy, with the use of rapamycin-loaded nanoparticles induce a reproducible increase in both skeletal muscle strength and cardiac contractile performance that is not achievable with conventional oral rapamycin, even in pharmacological doses. This increase in physical performance occurs in both young and adult mice, and, surprisingly, even in aged wild-type mice, which sets the stage for consideration of systemic therapies to facilitate improved cell function by autophagic disposal of toxic byproducts of cell death and regeneration. [ABSTRACT FROM AUTHOR]

The emerging demand for programmable functionalizafion of existing base nanocarriers necessitates development of an efficient approach for cargo loading that avoids nanoparticle redesign for each individual application. Herein, we demonstrate in vivo a postformulation strategy for lipidic nanocarrier functionalization with the use of a linker peptide, which rapidly and stably integrates cargos into lipidic membranes of nanocarriers after simple mixing through a self-assembling process. We exemplified this strategy by generating a VCAM-l-targeted perfluorocarbon nanoparticle for in vivo targeting in atherosclerosis (ApoE-deficient) and breast cancer (STAT-1-deficient) models. In the atherosclerotic model, a 4.1-fold augmentation in binding to affected aortas was observed for targeted vs. nontargeted nanoparticles (P<0.0298). Likewise, in the breast cancer model, a 4.9-fold increase in the nanoparticle signal from tumor vasculature was observed for targeted vs. nontargeted nanoparticles (P<0.0216). In each case, the nanoparticle was registered with fluorine (19F) magnetic resonance spectroscopy of the nanoparticle perfluorocarbon core, yielding a quantitative estimate of the number of tissue-bound nanoparticles. Because other common nanocarriers With lipid coatings (e.g., liposomes, micelles, etc.) can employ this strategy, this peptide linker postformulation approach is applicable to more than half of the available nanosystems currently in clinical trials or clinical uses. [ABSTRACT FROM AUTHOR]

Previously, we reported new methods for ultrasound signal characterization using entropy, Hf; a generalized entropy, the Renyi entropy, If(r); and a limiting form of Renyi entropy suitable for real-time calculation, If,∞. All of these quantities demonstrated significantly more sensitivity to subtle changes in scattering architecture than energy-based methods in certain settings. In this study, the real-time calculable limit of the Renyi entropy, If,∞, is applied for the imaging of angiogenic murine neovasculature in a breast cancer xenograft using a targeted contrast agent. It is shown that this approach may be used to reliably detect the accumulation of targeted nanoparticles at five minutes post-injection in this in vivo model. [ABSTRACT FROM AUTHOR]

Current strategies for deploying synthetic nanocarriers involve the creation of agents that incorporate targeting ligands, imaging agents, and/or therapeutic drugs into particles as an integral part of the formulation process. Here we report the development of an amphipathic peptide linker that enables postformulation editing of payloads without the need for reformulation to achieve multiplexing capability for lipidic nanocarriers. To exemplify the flexibility of this peptide linker strategy, 3 applications were demonstrated: converting nontargeted nanoparticles into targeting vehicles; adding cargo to preformulated targeted nanoparticles for in vivo site-specific delivery; and labeling living cells for in vivo tracking. This strategy is expected to enhance the clinical application of molecular imaging and/or targeted therapeutic agents by offering extended flexibility for multiplexing targeting ligands and/or drug payloads that can be selected after base nanocarrier formulation. [ABSTRACT FROM AUTHOR]

Aortic elasticity is an important factor in hemodynamic health, and compromised aortic compliance affects not only arterial dynamics but also myocardial function. A variety of pathologic processes (e.g., diabetes, Marfan's syndrome, hypertension) can affect aortic elasticity by altering the microstructure and composition of the elastin and collagen fiber networks within the tunica media. Ultrasound tissue characterization techniques can be used to obtain direct measurements of the stiffness coefficients of aorta by measurement of the speed of sound in specific directions. In this study we sought to define the contributions of elastin and collagen to the mechanical properties of aortic media by measuring the magnitude and directional dependence of the speed of sound before and after selective isolation of either the collagen or elastin fiber matrix. Formalin-fixed porcine aortas were sectioned for insonification in the circumferential, longitudinal, or radial direction and examined using high-frequency (50 MHz) ultrasound microscopy. Isolation of the collagen or elastin fiber matrices was accomplished through treatment with NaOH or formic acid, respectively. The results suggest that elastin is the primary contributor to aortic medial stiffness in the unloaded state, and that there is relatively little anisotropy in the speed of sound or stiffness in the aortic wall. [ABSTRACT FROM AUTHOR]

Recent studies by our group have demonstrated the efficacy of perfluorocarbon liquid nanoparticles for enhancing the reflectivity of tissuelike surfaces to which they are bound. The magnitude of this enhancement depends in large part on the difference in impedances of the perfluorocarbon, the bound substrate, and the propagating medium. The impedance varies directly with temperature because both the speed of sound and the mass density of perfluorocarbon liquids are highly temperature dependent. However, there are relatively little data in the literature pertaining to the temperature dependence of the acoustic impedance of these compounds. In this study, the speed of sound and density of seven different fluorocarbon liquids were measured at specific temperatures between 20 °C and 45 °C. All of the samples demonstrated negative, linear dependencies on temperature for both speed of sound and density and, consequently, for the acoustic impedance. The slope of sound speed was greatest for perfluorohexane (-278±1.5 cm/s-°C) and lowest for perfluorodichlorooctane (-222±0.9 cm/s-°C). Of the compounds measured, perfluorohexane exhibited the lowest acoustic impedance at all temperatures, and perfluorodecalin the highest at all temperatures. Computations from a simple transmission-line model used to predict reflectivity enhancement from surface-bound nanoparticles are discussed in light of these results. © 2002 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Molecular imaging contrast agents specifically detect the biochemical 'signatures' of disease before anatomical manifestations are apparent. Sensitive and specific localization of fibrin both in vivo and in vitro has been demonstrated with the use of a ligand-directed liquid perfluorocarbon nanoparticle. Since the acoustic properties of perfluorocarbons are known to vary with temperature, it was hypothesized that temperature could be used to augment the magnitude of enhancement imparted by targeted nanoparticles. Accordingly, the acoustic backscatter of two different substrates, nitrocellulose membrane and human plasma clot, targeted by the nanoparticles was measured at temperatures ranging from 27° to 47 °C in 5 °C increments. Classic avidin-biotin interactions were utilized to couple biotinylated nanoparticles to avidin-conjugated nitrocellulose membranes. Ultrasonic contrast enhancement of the nitrocellulose membrane at 25 MHz, measured by acoustic microscopy, increased from 2.0±0.3 dB at 27 °C to 3.7±0.4 at 47 °C. In a similar experiment, antifibrin nanoparticles bound to human plasma clots also exhibited temperature-dependent ultrasonic signal enhancement ranging from 13.9±1.5 dB at 27 °C to 18.1±1.5 dB at 47 °C. The increase in ultrasonic contrast enhancement measured was well described by a simple, acoustic transmission line model with temperature-dependent impedance. These results suggest that temperature-dependent changes in acoustic backscatter may be used to further differentiate tissues targeted with site-specific nanoparticles from surrounding normal soft tissues. © 2001 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Complex molecular signaling heralds the early stages of pathologies such as angiogenesis, inflammation, unstable atherosclerotic plaques, and areas of remote thrombi. In previous studies, acoustic enhancement of blood clot morphology was demonstrated with the use of a nongaseous, fibrin-targeted acoustic nanoparticle emulsion delivered to areas of thrombosis both in vitro and in vivo. In this study, a system was designed and constructed that allows visualization of the evolution of acoustic contrast enhancement. To evaluate the system, two targets were examined: avidin-complexed nitrocellulose membrane and human plasma clots. The time evolution of enhancement was visualized in 10-min increments for 1 h. A monotonic increase was observed in ultrasonic reflection enhancement from specially treated nitrocellulose membranes for targeted emulsions containing perfluorooctylbromide (1.30±0.3 dB) and for perfluorooctane (2.64±0.5 dB) within the first 60 min of imaging. In comparison, the inherently nonechogenic plasma clots showed a substantial increase of 12.0±0.9 dB when targeted with a perfluoro-octane emulsion. This study demonstrates the concept of molecular imaging and provides the first quantifiable time-evolution report of the binding of a site-targeted ultrasonic contrast agent. Moreover, with the incorporation of specific drug treatments into the nanoparticulate contrast agent, ultrasonic molecular imaging may yield reliable detection and quantification of nascent pathologies and facilitate targeted drug therapy. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

In this work, the Kramers-Kronig (K-K) relations are applied to experimental data of resonant nature by limiting the interval of integration to the measurement spectrum. The data are from suspensions of encapsulated microbubbles (Albunex®) and have the characteristics of an ultrasonic notch filter. The goal is to test the consistency of this dispersion and attenuation data with the Kramers-Kronig relations in a strict manner, without any parameters from outside the experimental bandwidth entering in to the calculations. In the course of reaching the goal, the artifacts associated with the truncation of the integrals are identified and it is shown how their impacts on the results can be minimized. The problem is first approached analytically by performing the Kramers-Kronig calculations over a restricted spectral band on a specific Hilbert transform pair (Lorentzian curves). The resulting closed-form solutions illustrate the type of artifacts that can occur due to truncation and also show that accurate results can be achieved. Next, both twice-subtracted and lower-order Kramers-Kronig relations are applied directly to the attenuation and dispersion data from the encapsulated microbubbles. Only parameters from within the experimental attenuation coefficient and phase velocity data sets are used. The twice-subtracted K-K relations produced accurate estimates for both the attenuation coefficient and dispersion across all 12 data sets. Lower-order Kramers-Kronig relations also produced good results over the finite spectrum for most of the data. In 2 of the 12 cases, the twice-subtracted relations tracked the data markedly better than the lower-order predictions. These calculations demonstrate that truncation artifacts do not overwhelm the causal link between the phase velocity and the attenuation coefficient for finite bandwidth calculations. This work provides experimental evidence supporting the validity of the subtracted forms of the acoustic K-K relations between the phase velocity and attenuation coefficient. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

We describe a technique for broadband measurements of the attenuation coefficient and phase velocity of highly attenuating liquid suspensions. To validate the technique we apply it to the ultrasound contrast agent Albunex® at concentrations ranging from 0.69×106 particles/mL to 364×106 particles/mL. These longitudinal wave measurements were performed on Albunex suspensions maintained at 37 °C in a special time-domain reflectometer designed and constructed in our laboratory. The frequency-dependent attenuation coefficients and phase velocities obtained in the reflectometer are compared to broadband through-transmission measurements of these same quantities, which were also performed in our laboratory. Although comparison data between the two techniques are only available at lower concentrations, the agreement is quite good and serves to validate the methods described in this paper. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The phase velocities and attenuation coefficients for suspensions of narrowly sized polymer microspheres are reported over a broadband spectrum from 3 to 30 MHz. The six suspensions used in this work contain microspheres with respective average diameters near 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, and 100 μm. The results of these measurements are compared with theoretical expressions for the phase velocity and attenuation coefficient derived from the scattering properties of an elastic sphere in water using the weak scattering limit of the Waterman and Truell dispersion relation [J. Math. Phys. 2, 512-537 (1961)]. This single-scattering limit of the theory is found to be sufficient for predicting the ultrasonic transport properties of these suspensions to a considerable degree of accuracy. © 1999 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

A broadband ultrasonic measurement system has been utilized to characterize the concentration and frequency dependence of in vitro suspensions of Albunex® microspheres at concentrations ranging from 1.7×105 to 2.1×107 microspheres/mL and over a bandwidth of 1-16 MHz. The apparent backscattered power (not compensated for effects due to attenuation) was shown to increase with dose for lower concentrations of microspheres, but then to decrease rapidly with increasing concentration where attenuation effects become significant. Measurements of signal loss demonstrated that the attenuation grew exponentially with increasing concentration, so that a doubling of the number of microspheres led to a doubling of the value of the attenuation coefficient measured in dB/cm. This relationship was demonstrated over the entire system bandwidth. Compensation of the apparent backscattered power for the attenuation yielded the backscatter transfer function. This quantity was shown to be linearly proportional to concentration, so that a doubling of the number of microspheres led to a 3-dB increase in the backscatter transfer function. A broadband data reduction technique was used to further reduce the data to backscatter coefficient, an absolute parameter describing the intrinsic scattering efficiency of the Albunex® microsphere suspensions. The backscatter coefficient was shown to be linearly proportional to microsphere concentration at all concentrations investigated and over all the usable bandwidth. This suggests that, with appropriate compensation for attenuation and equipment parameters, perfusion or flow quantification techniques which assume a linear dependence of backscatter with contrast agent concentration should be applicable. The backscatter coefficient exhibits a rapid rise with frequency below 3 MHz, and appears to approach a frequency independent limit above 3 MHz. The relationships of the attenuation coefficient and backscatter transfer function to concentration were generally consistent with predictions from a simple scattering model. These relationships appear to be valid within the usable bandwidth of our measurement system for all concentrations investigated. © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The phase velocities in suspensions of Albunex®, an ultrasound contrast agent, are determined using the technique of broadband phase spectroscopy. In these suspensions, phase velocities were measured as a function of Albunex concentration in Isoton II (buffered saline). The dispersion over the measurement bandwidth (1-15 MHz) grew with increasing Albunex concentration, exhibiting a 221-m/s change (17% increase) in phase velocity between 1.0 and 3.8 MHz at the highest concentration reported (32 μL Albunex/8 mL Isoton). The dispersion behavior of the Albunex suspensions is described using a model of encapsulated gas bubbles. The influence of the dispersion in Albunex on broadband pulses is discussed, as well as the potential impact this dispersion may have on the formation of ultrasonic images of the heart. © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Broadband normalized signal loss of commercially available Albunex®, an ultrasonic contrast agent, was measured in vitro at concentrations approaching those which may be found in vivo for clinical doses. The measurements were made using a novel specimen chamber, careful material handling procedures, and a broadband square wave pulser system. Results were obtained over the full bandwidth of the experimental system (1 to 20 MHz) at concentrations up to 1.9×106 microspheres/mL. Further results were obtained over a partial bandwidth of the experimental system at concentrations up to 1.5×107 microspheres/mL. The frequency-dependent signal loss exhibited a peak for all concentrations investigated. In the meaningful bandwidth of the system, the signal loss (expressed in dB) was directly proportional to microsphere concentration. The experimental results for normalized signal loss were compared with predictions from a linear single-scattering model for encapsulated bubbles. The experimental data was used to estimate values for the two adjustable parameters in the model: microsphere shell elasticity (4200±1000 dyn/cm) and friction (0.0054±0.0015 dyn s/cm). © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Tissue characterization would be facilitated by improved methods of calibration with which to make absolute measurements of the backscatter and attenuation of tissue or contrast agents. In this paper, the use of polystyrene microspheres is examined as a potential broadband in vitro calibration tool by employing an experimental system designed to characterize ultrasonic contrast agents. The frequency-dependent attenuation coefficient and backscatter coefficient were measured for a series of microsphere size distributions with a broadband ultrasound system using a custom-built specimen chamber and a novel suspension mixing technique. The measurements were used in a broadband reduction method to yield the backscatter coefficient. The range of ka spanned in this study is from ka=0.5 to ka=12. The broadband nature of the pulses permitted simultaneous measurement of different regimes of scattering of the microspheres (specifically, the transition region from Rayleigh to short-wavelength asymptotic scattering). Experimental results were compared with corresponding theoretical predictions for the attenuation and backscatter of solid elastic spheres in liquid and yielded good quantitative agreement. Discussion of some possible applications of this technique to the fields of tissue characterization and contrast is presented. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

© 2002 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Labeling stem/progenitor cells for non-invasive imaging and tracking typically requires long exposure times or adjunctive methods, such as electroporation or transfection agents. Recently, we demonstrated that perfluorocarbon nanoparticles (PFC NP: 200 nm) provide a unique and sensitive label for cell tracking by MRI that entails 12 hours of incubation for efficient cellular labeling. To develop an approach that reduces the prolonged labeling time, stem/progenitor (CD34+CDI33+CD31+) cells derived from human umbilical cord mononuclear cells were incubated with PFC NP and exposed to clinical levels of ultrasound (US) energy with a standard medical imaging system at typical imaging frequencies (2MHz) and power levels (1.9MI). Flow eytometry revealed US application greatly improved labeling in under 1 hour versus cells not exposed to US (55±4% vs. 6±3% respectively, p<0.001), which approaches the labeling efficiency achieved in the 12 hour incubation method (71±4%). No reduction in cell viability due to the labeling procedure was observed when comparing untreated and US-exposed cells (∼90% viable). This unique approach should facilitate investigation of regenerative therapeutics by providing a safe adjunctive method to label cells for real-time tracking. Furthermore, the labeling procedures can be carried out with conventional ultrasound imaging devices available to most researchers. [ABSTRACT FROM AUTHOR]