Browsing by Author "Bisht, Sapna R."

Ultrasound phantoms mimic the acoustic and mechanical properties of native tissues. Polyvinyl alcohol (PVA) phantoms are used extensively as models for validating ultrasound elastography approaches. However, the viscous properties of PVA phantoms have not been investigated adequately. Glycerol is a viscous liquid that has been reported to increase the speed of sound of phantoms. This study aims to assess the acoustic and viscoelastic properties of PVA phantoms and PVA mixed with glycerol at varying concentrations. The phantoms were fabricated with 10% w/v PVA in water with varying concentrations of glycerol (10%, 15% and 20% v/v) and 2% w/v silicon carbide particles as acoustic scatterers. The phantoms were subjected to either one, two, or three 24-h freeze–thaw cycles. The longitudinal sound speeds of all PVA phantoms were measured, and ranged from 1529 to 1660 m/s. Attenuation spectroscopy was performed in the range of 5 to 20 MHz. The measured attenuation followed a power-law relationship with frequency, wherein the power-law fit constants and exponents ranged from 0.02 to 0.1 dB/cm/MHzⁿ and from 1.6 to 1.9, respectively. These results were in agreement with previous reports for soft tissues. Viscoelasticity of PVA phantoms was assessed using rheometry. The estimated values of shear modulus and viscosity using the Kelvin–Voigt and Kelvin–Voigt fractional derivative models were within the range of previously-reported tissue-mimicking phantoms and soft tissues. The number of freeze-thaw cycles were shown to alter the viscosity of PVA phantoms, even in the absence of glycerol. Scanning electron microscopy images of PVA phantoms without glycerol showed a porous hydrogel network, in contrast to those of PVA-glycerol phantoms with non-porous structure. Phantoms fabricated in this study possess tunable acoustic and viscoelastic properties within the range reported for healthy and diseased soft tissues. This study demonstrates that PVA phantoms can be manufactured with glycerol for applications in ultrasound elastography.

Oral cancer causes over 350 000 deaths annually worldwide. Although most cases are in Asia, the incidence of oral cancer is rising across the world. Despite recent advances in screening methods, oral cancer remains a significant cause of mortality and morbidity. The 5-year survival rate (50%-60%) has not improved over the past several decades. Early detection and accurate diagnosis of the disease can improve the survival rate and patients' quality of life. This article provides a topical review of current and emerging techniques for screening and diagnosing oral cancer. Currently available technologies have only been moderately useful towards identifying oral cancer early, motivating the development of novel approaches to address this goal. In this article, we provide an overview of adjunctive screening aids, including biofluid (saliva and serum) diagnostics, vital staining, brush biopsy, chemiluminescence, and tissue autofluorescence. Furthermore, we discuss diagnostic imaging modalities, such as computed tomography, magnetic resonance imaging, positron emission tomography, ultrasound (including traditional B-mode imaging, color Doppler, and elastography), photoacoustics imaging, and optical coherence tomography, and artificial intelligence-based methods, which are either being used clinically or are under development for oral cancer staging. The physical and biological basis underpinning each technique are discussed, along with their advantages and limitations in the technological and clinical context. The review concludes with a discussion of the future perspectives in this rapidly evolving field.

Vaporizable double emulsions, characterized by a central aqueous core, have demonstrated effectiveness in encapsulating hydrophilic drugs. This study aims to investigate the potential of incorporating an additional oil-layer in the double emulsions to encapsulate hydrophobic drugs. Vaporizable multi-layered emulsions were produced in three steps using perfluoropentane (PFP), phosphate-buffered saline (PBS), and sunflower oil. Curcumin, a natural anti-inflammatory drug, was dispersed in the oil phase. Krytox, polyglycerol polyricinoleate, and bovine serum albumin (BSA) were used as surfactants. PFP was sonicated in PBS (1:6) for 1 minute to create emulsion-1. Subsequently, emulsion-1 (1:4) was homogenized in oil to make emulsion-2. Emulsion-2 was homogenized in BSA (1:4) to yield emulsion-3 at 8000 rpm for 30 seconds. The vaporization pressure threshold was determined using 2 MHz focused ultrasound with a single-element transducer (f/# of 1.27, 0.5% duty cycle). B-mode imaging was conducted using a Verasonics Vantage 128 system with an L11-5v array to determine the droplet vaporization threshold, which was found to be 6.7 MPa. Curcumin-loading (0.87±0.1 mg) was significantly higher in the multi-layered emulsions than in single-layered BSA-shelled microbubbles (0.019±0.004 mg) (p<0.00001), indicating that multi-layered emulsions exhibit higher drug loading capacity.

Contrast-enhanced imaging has grown significantly in the past two decades. Technology has evolved from imaging based on linear principles to elaborate pulsing and microbubble-specific detection strategies. This review provides a broad overview of the research published on these topics, emphasizing the progress made, current challenges, and future research considerations. We cover the physical and conceptual underpinnings of imaging based on ultrasound contrast agents, focused on pulsing and detection strategies. The techniques proposed are categorized according to the underlying fundamental physical and signal processing principles. We revisit methods that were previously only of academic interest and may now be clinically feasible with advances in computation and hardware. We discuss unmet challenges and opportunities originating from developments in other sub-fields of ultrasound imaging to enable wider clinical adoption of contrast-enhanced ultrasound.

Quantitative, accurate, and standardized metrics are important for reliable shear wave elastography (SWE)-based biomarkers. For over two decades, the linear-elastic material assumption has been employed in SWE modes. In recent years, viscoelasticity estimation methods have been adopted in a few clinical systems. The current study aims to systematically quantify differences in SWE estimates obtained using linear-elastic and viscoelastic material assumptions. An acousto-mechanical simulation framework of acoustic radiation force impulse-based SWE was created to elucidate the effect of material viscosity and shear modulus on SWE estimates. Shear modulus estimates exhibited errors up to 72% when a numerical viscoelastic phantom was assessed as linearly elastic. Shear modulus estimates of polyvinyl alcohol phantoms between rheometry and SWE following the Kelvin-Voigt viscoelastic model assumptions were not significantly different. However, the percentage difference in shear modulus estimates between rheometry and SWE using the linear-elastic assumption was 50.1%-62.1%. In ex vivo liver, the percentage difference in shear modulus estimates between linear-elastic and viscoelastic methods was 76.1%. These findings provide a direct and systematic quantification of the potential error introduced when viscoelastic tissues are imaged with SWE following the linear-elastic assumption. This work emphasizes the need to utilize viscoelasticity estimation methods for developing robust quantitative imaging biomarkers.

In shear wave elastography, viscoelastic properties of tissues can be estimated by fitting a rheological model to the phase velocity dispersion curve. However, there is a lack of consensus on the model that best represents tissue behavior. Model-free elastography approaches based on shear wave attenuation (SWA) and dispersion slope analysis have been reported previously. This study evaluated the ability of SWA and dispersion slope analysis to assess fluid content in situ using viscoelastic phantoms and ex vivo chicken breast. Model-free parameters were estimated in viscoelastic phantoms (with fluid percentages ranging from 72.6% to 79.9%, and pre- and post-compression by 10%) and ex vivo chicken breast samples pre- and post-hydration. Estimates of SWA were computed using the frequency-shift (FS) and the attenuation measuring shear wave elastography (AMUSE) methods. Dispersion slopes were computed from the phase velocity dispersion curves. The SWA coefficient estimates were strongly correlated with the fluid percentages in phantoms (r = 0.86 and 0.92 for FS and AMUSE methods, respectively, p < 0.001). However, no trends were observed for dispersion slope estimates (r = −0.73, p < 0.001). Thus, SWA was found to be a more sensitive parameter than the dispersion slope for differentiating phantoms with a range of in situ fluid content. Additionally, when phantoms were subjected to compression, SWA was sensitive to changes in compression-induced fluid variations in situ (p < 0.05), but dispersion slope showed no such trends (p = 0.12). The SWA estimates of ex vivo samples significantly increased post-hydration using both methods (p < 0.05), while the dispersion slope decreased. The findings of this study demonstrate that SWA is sensitive to fluid content in situ, which motivates its further development as a marker to assess pathological conditions.

Ultrasound elastography enables noninvasive characterization of the tissue mechanical properties. Phantoms are widely used in ultrasound elastography for developing, testing, and validating imaging techniques. Creating phantoms with a range of viscoelastic properties relevant to human organs and pathological conditions remains an active area of research. Poly(vinyl alcohol) (PVA) cryogel phantoms offer a long shelf life, robustness, and convenient handling and storage. The goal of this study was to develop tunable phantoms using PVA with a clinically relevant range of viscoelastic properties. We combined low- and high-viscosity PVA to tune the viscoelastic properties of the phantom. Further, phantoms were created with an ethylene glycol-based cryoprotectant to determine whether it reduces the variability in the viscoelastic properties. Scanning electron microscopy (SEM) was performed to evaluate the differences in microstructure between phantoms. The density, longitudinal sound speed, and acoustic attenuation spectra (5-20 MHz) of the phantoms were measured. The phantoms were characterized using a shear wave viscoelastography approach assuming the Kelvin-Voigt model. Microstructural differences were revealed by SEM between phantoms with and without a cryoprotectant and with different PVA mixtures. The longitudinal sound speed and attenuation power-law fit exponent of the phantoms were within the clinical range (1510-1571 m/s and 1.23-1.38, respectively). The measured shear modulus (G) ranged from 3.3 to 17.7 kPa, and the viscosity (η) ranged from 2.6 to 7.3 Pa·s. The phantoms with the cryoprotectant were more homogeneous and had lower shear modulus and viscosity (G = 2.17 ± 0.2 kPa; η = 2.0 ± 0.05 Pa·s) than those without a cryoprotectant (G = 3.93 ± 0.7 kPa; η = 2.6 ± 0.14 Pa·s). Notably, phantoms with relatively constant viscosities and varying shear moduli were achieved by this method. These findings advance the development of well-characterized viscoelastic phantoms for use in elastography.