Infrared thermography for noninvasive real-time monitoring of HIFU ablation

Infrared imaging for spatiotemporal temperature measurements was explored in this study for non-contact monitoring of temperature increases generated by HIFU ablation. Using ex vivo cardiac tissue specimens, we investigated the correlations between the occurrence of events during HIFU ablation (e.g., lesion formation, cavity formation) and the 2D spatiotemporal temperature of the tissue surface measured during HIFU ablation from an infrared camera. An increase in the rate of temperature rise was observed when lesions formed at or slightly beneath the tissue surface. Spatial shifts in the maximum temperature location away from the HIFU focus were often observed with continuing HIFU exposure after lesion formation, suggesting tissue dehydration and cavitationformation during ablation with excessive heating

Ultrasound Imaging Techniques for Spatiotemporal Characterization of Composition, Microstructure, and Mechanical Properties in Tissue Engineering

Ultrasound techniques are increasingly being used to quantitatively characterize both native and engineered tissues. This review provides an overview and selected examples of the main techniques used in these applications. Grayscale imaging has been used to characterize extracellular matrix deposition, and quantitative ultrasound imaging based on the integrated backscatter coefficient has been applied to estimating cell concentrations and matrix morphology in tissue engineering. Spectral analysis has been employed to characterize the concentration and spatial distribution of mineral particles in a construct, as well as to monitor mineral deposition by cells over time. Ultrasound techniques have also been used to measure the mechanical properties of native and engineered tissues. Conventional ultrasound elasticity imaging and acoustic radiation force imaging have been applied to detect regions of altered stiffness within tissues. Sonorheometry and monitoring of steady-state excitation and recovery have been used to characterize viscoelastic properties of tissue using a single transducer to both deform and image the sample. Dual-mode ultrasound elastography uses separate ultrasound transducers to produce a more potent deformation force to microscale characterization of viscoelasticity of hydrogel constructs. These ultrasound-based techniques have high potential to impact the field of tissue engineering as they are further developed and their range of applications expands.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140238/1/ten.teb.2015.0453.pd

Integrinâ Targeted Cyclic Forces Accelerate Neural Tubeâ Like Rosette Formation from Human Embryonic Stem Cells

Mechanical forces play important roles in human embryonic stem cell (hESC) differentiation. To investigate the impact of dynamic mechanical forces on neural induction of hESCs, this study employs acoustic tweezing cytometry (ATC) to apply cyclic forces/strains to hESCs by actuating integrinâ bound microbubbles using ultrasound pulses. Accelerated neural induction of hESCs is demonstrated as the result of combined action of ATC and neural induction medium (NIM). Specifically, application of ATC for 30 min followed by culture in NIM upregulates neuroecdoderm markers Pax6 and Sox1 as early as 6 h after ATC, and induces neural tubeâ like rosette formation at 48 h after ATC. In contrast, no changes are observed in hESCs cultured in NIM without ATC treatment. In the absence of NIM, ATC application decreases Oct4, but does not increase Pax6 and Sox1 expression, nor does it induce neural rossette formation. The effects of ATC are abolished by inhibition of FAK, myosin activity, and RhoA/ROCK signaling. Taken together, the results reveal a synergistic action of ATC and NIM as an integrated mechanobiology mechanism that requires both integrinâ targeted cyclic forces and chemical factors for accelerated neural induction of hESCs.Acoustic tweezing cytometry (ATC) applies integrinâ targeted cyclic forces/strains to human embryonic stem cells (hESCs). Dependent on FAK, myosin activity, and RhoA/ROCK signaling, synergistic action of ATC for 30 min and neural induction medium greatly accelerates neural induction of hESCs, resulting in upregulated neuroecdoderm markers Pax6 and Sox1 by 6 h and neural tubeâ like rosette formation at 48 h.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151881/1/adbi201900064_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151881/2/adbi201900064.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151881/3/adbi201900064-sup-0001-SuppMat.pd

High-frequency ultrasound M-mode monitoring of HIFU ablation in cardiac tissue

Effective real-time HIFU lesion detection is important for expanded use of HIFU in interventional electrophysiology (e.g., epicardial ablation of cardiac arrhythmia). The goal of this study was to investigate rapid, high-frequency M-mode ultrasound imaging for monitoring spatiotemporal changes in tissue during HIFU application. The HIFU application (4.33 MHz, 1000 Hz PRF, 50% duty cycle, 1 s exposure, 6100 W/cm2) was perpendicularly applied to porcine cardiac tissue with a high-frequency imaging system (Visualsonics Vevo 770, 55 MHz, 4.5 mm focal distance) confocally aligned. Radiofrequency (RF) M-mode data (1 kHz PRF, 4 s × 7 mm) was acquired before, during, and after HIFU treatment. Gross lesions were compared with M-mode data to correlate lesion and cavity formation. Integrated backscatter, echo-decorrelation parameters, and their cumulative extrema over time were analyzed for automatically identifying lesion width and bubble formation. Cumulative maximum integrated backscatter showed the best results for identifying the final lesion width, and a criterion based on line-to-line decorrelation was proposed for identification of transient bubble activity

High-Frequency Rapid B-Mode Ultrasound Imaging for Real-Time Monitoring of Lesion Formation and Gas Body Activity During High-Intensity Focused Ultrasound Ablation

Abstract: The goal of this study was to examine the ability of high-frame-rate, high-resolution imaging to monitor tissue necrosis and gas-body activities formed during high-intensity focused ultrasound (HIFU) application. Ex vivo porcine cardiac tissue specimens (n = 24) were treated with HIFU exposure (4.33 MHz, 77 to 130 Hz pulse repetition frequency (PRF), 25 to 50% duty cycle, 0.2 to 1 s, 2600 W/cm2). RF data from Bmode ultrasound imaging were obtained before, during, and after HIFU exposure at a frame rate ranging from 77 to 130 Hz using an ultrasound imaging system with a center frequency of 55 MHz. The time history of changes in the integrated backscatter (IBS), calibrated spectral parameters, and echo-decorrelation parameters of the RF data were assessed for lesion identification by comparison against gross sections. Temporal maximum IBS with +12 dB threshold achieved the best identification with a receiver-operating characteristic (ROC) curve area of 0.96. Frame-to-frame echo decorrelation identified and tracked transient gas-body activities. Macroscopic (millimetersized) cavities formed when the estimated initial expansion rate of gas bodies (rate of expansion in lateral-to-beam direction) crossed 0.8 mm/s. Together, these assessments provide a method for monitoring spatiotemporal evolution of lesion and gas-body activity and for predicting macroscopic cavity formation

Acoustic Tweezing Cytometry Induces Rapid Initiation of Human Embryonic Stem Cell Differentiation.

Mechanical forces play critical roles in influencing human embryonic stem cell (hESC) fate. However, it remains largely uncharacterized how local mechanical forces influence hESC behavior in vitro. Here, we used an ultrasound (US) technique, acoustic tweezing cytometry (ATC), to apply targeted cyclic subcellular forces to hESCs via integrin-bound microbubbles (MBs). We found that ATC-mediated cyclic forces applied for 30 min to hESCs near the edge of a colony induced immediate global responses throughout the colony, suggesting the importance of cell-cell connection in the mechanoresponsiveness of hESCs to ATC-applied forces. ATC application generated increased contractile force, enhanced calcium activity, as well as decreased expression of pluripotency transcription factors Oct4 and Nanog, leading to rapid initiation of hESC differentiation and characteristic epithelial-mesenchymal transition (EMT) events that depend on focal adhesion kinase (FAK) activation and cytoskeleton (CSK) tension. These results reveal a unique, rapid mechanoresponsiveness and community behavior of hESCs to integrin-targeted cyclic forces

Rapid Generation of Multiplexed Cell Cocultures Using Acoustic Droplet Ejection Followed by Aqueous Two-Phase Exclusion Patterning

The development of tools for patterning cocultures of cells is a fundamental interest among cell biologists and tissue engineers. Although a variety of systems exist for micropatterning cells, the methods used to generate cell micropatterns are often cumbersome and difficult to adapt for tissue engineering purposes. This study combines acoustic droplet ejection and aqueous two-phase system exclusion patterning to introduce a method for patterning cocultures of cells in multiplexed arrays. This new method uses focused acoustic radiation pressure to eject discrete droplets of uniform size from the surface of a dextran solution containing cells. The size of droplets is controlled by adjusting ultrasound parameters, such as pulse, duration, and amplitude. The ejected dextran droplets are captured on a cell culture substrate that is manipulated by a computer-controlled 3D positioning system according to predesigned patterns. Polyethylene glycol solution containing an additional cell type is then added to the culture dish to produce a two-phase system capable of depositing different types of cells around the initial pattern of cells. We demonstrate that our method can produce patterns of islands or lines with two or more cell types. Further, we demonstrate that patterns can be multiplexed for studies involving combinations of multiple cell types. This method offers a tool to transfer cell-containing samples in a contact-free, nozzle-less manner, avoiding sample cross-contamination. It can be used to pattern cell cocultures without complicated fabrication of culture substrates. These capabilities were used to examine the response of cancer cells to the presence of a ligand (CXCL12) secreted from surrounding cocultured cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98484/1/ten%2Etec%2E2011%2E0709.pd

Acoustic Actuation of Integrin‐Bound Microbubbles for Mechanical Phenotyping during Differentiation and Morphogenesis of Human Embryonic Stem Cells

Early human embryogenesis is a dynamic developmental process, involving continuous and concomitant changes in gene expression, structural reorganization, and cellular mechanics. However, the lack of investigation methods has limited the understanding of how cellular mechanical properties change during early human embryogenesis. In this study, ultrasound actuation of functionalized microbubbles targeted to integrin (acoustic tweezing cytometry, ATC) is employed for in situ measurement of cell stiffness during human embryonic stem cell (hESC) differentiation and morphogenesis. Cell stiffness, which is regulated by cytoskeleton structure, remains unchanged in undifferentiated hESCs, but significantly increases during neural differentiation. Further, using the recently established in vitro 3D embryogenesis models, ATC measurements reveal that cells continue to stiffen while maintaining pluripotency during epiblast cyst formation. In contrast, during amniotic cyst formation, cells first become stiffer during luminal cavity formation, but softens significantly when cells differentiate to form amniotic cysts. These results suggest that cell stiffness changes not only due to 3D spatial organization, but also with cell fate change. ATC therefore provides a versatile platform for in situ measurement of cellular mechanical property, and cell stiffness may be used as a mechanical biomarker for cell lineage diversification and cell fate specification during embryogenesis.Ultrasound actuation of functionalized microbubbles targeted to integrin (acoustic tweezing cytometry) is employed for in situ measurement of cell stiffness during human embryonic stem cell neural differentiation and morphogenesis in 3D embryogenesis model. The results suggest that cell stiffness changes not only due to 3D spatial organization, but also with cell fate change.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146940/1/smll201803137.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146940/2/smll201803137_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146940/3/smll201803137-sup-0001-S1.pd

Noninvasive, Quantitative, Spatiotemporal Characterization of Mineralization in Three-Dimensional Collagen Hydrogels Using High-Resolution Spectral Ultrasound Imaging

As tissue engineering products move toward the clinic, nondestructive methods to monitor their development and ensure quality are needed. In this study, high-resolution spectral ultrasound imaging (SUSI) was used to noninvasively characterize mineral content in collagen hydrogels. SUSI was used to generate three-dimensional (3D) grayscale (GS) images of construct morphology with submillimeter resolution. Spectral analysis of the backscattered radio frequency (RF) ultrasound signals was used to determine the midband fit (MBF) and slope of the linearized RF spectrum. These parameters are operator and instrument independent, and were used to characterize the spatial distribution of mineral in constructs supplemented with hydroxyapatite particles. GS and MBF correlated closely with mineral content, while slope was not dependent on concentration. SUSI also was used to monitor mineralization of collagen constructs by immersion in simulated body fluid (SBF) over 21 days. The construct surface was mineralized before the interior, and there was a dose-dependent effect of SBF concentration on degree of mineralization and deposited particle size. MBF density was closely correlated with the amount of calcium deposited. These data demonstrate that SUSI has utility as a noninvasive imaging method for quantitative analysis of mineralization in 3D protein constructs. Such techniques may assist the development of engineered orthopedic tissues.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98485/1/ten%2Etec%2E2012%2E0180.pd

Lymph Node Characterization in Vivo Using Endoscopic Ultrasound Spectrum Analysis With Electronic Array Echo Endoscopes

Our purpose was to demonstrate the use of radiofrequency spectral analysis to distinguish between benign and malignant lymph nodes with data obtained using electronic array echo endoscopes, as we have done previously using mechanical echo endoscopes. In a prospective study, images were obtained from eight patients with benign-appearing lymph nodes and 11 with malignant lymph nodes, as verified by fine-needle aspiration. Midband fit, slope, intercept, correlation coefficient, and root-mean-square (RMS) deviation from a linear regression of the calibrated power spectra were determined and compared between the groups. Significant differences were observable for mean midband fit, intercept, and RMS deviation (t test P \u3c 0.05). For benign (n = 16) vs. malignant (n = 12) lymph nodes, midband fit and RMS deviation provided classification with 89 % accuracy and area under receiver operating characteristic (ROC) curve of 0.95 based on linear discriminant analysis. We concluded that the mean spectral parameters of the backscattered signals from electronic array echo endoscopy can provide a noninvasive method to quantitatively discriminate between benign and malignant lymph nodes