Optical coherence tomography (OCT) has several advantages over other imaging modalities, such as angiography and ultrasound, due to its inherently high in vivo resolution, which allows for the identification of morphological tissue structures. Optical coherence elastography (OCE) benefits from the superior spatial resolution of OCT and has promising applications, including cancer diagnosis and the detailed characterization of arterial wall biomechanics, both of which are based on the elastic properties of the tissue under investigation. We present OCE principles based on techniques associated with static and dynamic tissue excitation, and their corresponding elastogram image-reconstruction algorithms are reviewed. OCE techniques, including the development of intravascular- or catheter-based OCE, are in their early stages of development but show great promise for surgical oncology or intravascular cardiology applications.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-16/issue-4/043001/Optical-coherence-elastography-current-status-and-future-applications/10.1117/1.3560294.pdf

Optical coherence elastography: current status and future applications.

/pdf/topical-amphotericin-b-in-ultradeformable-liposomes-2kl7dp0x2x.pdf

Topical amphotericin B in ultradeformable liposomes: Formulation, skin penetration study, antifungal and antileishmanial activity in vitro

In this study, for the first time, the transverse vibrational model of a viscous-fluid-conveying single-walled carbon nanotube (SWCNT) embedded in biological soft tissue is developed. Nonlocal Euler–Bernoulli beam theory has been used to investigate fluid-induced vibration of the SWCNT while visco-elastic behaviour of the surrounding tissue is simulated by the Kelvin–Voigt model. The results indicate that the resonant frequencies and the critical flow velocity at which structural instability of nanotubes emerges are significantly dependent on the properties of the medium around the nanotube, the boundary conditions, the viscosity of the fluid and the nonlocal parameter. Detailed results are demonstrated for the dependence of damping and elastic properties of the medium on the resonant frequencies and the critical flow velocity. Three standard boundary conditions, namely clamped–clamped, clamped–pinned and pinned–pinned, are applied to study the effect of the supported end conditions. Furthermore, it is found that the visco-elastic foundation causes an obvious reduction in the critical velocity in comparison with the elastic foundation, in particular for a compliant medium, pinned–pinned boundary condition, high viscosity of the fluid and small values of the nonlocal coefficient.

/pdf/vibration-and-instability-of-a-viscous-fluid-conveying-1avxekd15i.pdf

Vibration and instability of a viscous-fluid-conveying single-walled carbon nanotube embedded in a visco-elastic medium

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Physical principles of medical ultrasonics

The human body has long provided pharmaceutical science with biomaterials of interesting applications. Bile salts (BSs) are biomaterials reminiscent of traditional surfactants with peculiar structure and self-assembled topologies. In the pharmaceutical field, BSs were employed on the basis of two different concepts. The first concept exploited BSs’ metabolic and homeostatic functions in disease modulation, whereas the second one utilized BSs’ potential to modify drug-delivery characteristics, which recently involved nanotechnology. This review is the first to gather major pharmaceutical applications of BSs from endogenous organotropism up to integration into nanomedicine, with a greater focus on the latter domain. Endogenous applications highlighted the role of BS in modulating hypercholesterolemia and cancer therapy in view of enterohepatic circulation. In addition, recent BS-integrated nanomedicines have been surveyed, chiefly size-tunable cholate nanoparticles, BS-lecithin mixed micelles, bilosomes, probilosomes, and surface-engineered bilosomes. A greater emphasis has been laid on nanosystems for vaccine and cancer therapy. The comparative advantages of BS-integrated nanomedicines over conventional nanocarriers have been noted. Paradoxical effects, current pitfalls, future perspectives, and opinions have also been outlined.

/pdf/multifaceted-applications-of-bile-salts-in-pharmacy-an-2r1d3d043v.pdf

Multifaceted applications of bile salts in pharmacy: an emphasis on nanomedicine.

Many ailments and/or malfunctions of the body have been observed to change the viscous behavior and elastic properties of biological soft tissues. The technique of elastography has evolved to image such properties. The clinical evidence gathered during studies involving elastography to identify cancerous lesions is very promising. However, the quantification of the resolution and specificity of elastography is best achieved under a controlled study using tissue-mimicking phantoms. One challenge is to reproduce viscoelastic behavior in phantoms as observed in biological tissues. In this paper, polyacrylamide gel based tissue-mimicking phantoms have been developed to experimentally study the role of viscoelastic properties in a controlled manner. To measure the Young's modulus, the phantoms were subjected to linear loading, and the stress-strain relationship is deduced therefrom. It is seen that the phantoms show hysteresis behavior. The viscoelastic properties of these phantoms were measured by subjecting the samples to cyclic loading. Normal forces during this process of loading were also measured as a measure of sample elasticity. To emulate the normal and pathological lesions, samples were prepared with varying concentration of monomer and studied. Three models, namely, Maxwell, Kelvin-Voigt (KV), and Kelvin-Voigt fractional derivative (KVFD), were chosen to fit the experimental data. Of these, the KVFD model was found to be best fitting for the experimental data obtained. Results indicate that stiffer samples exhibit large variations in the storage modulus when the precompression levels are altered.

Measurement of Viscoelastic Properties of Polyacrylamide-Based Tissue-Mimicking Phantoms for Ultrasound Elastography Applications

A photophysical study on the role of bile salt hydrophobicity in solubilizing amphotericin B aggregates

Due to the isoechoic nature of lesions and their poor contrast with neighbouring tissue, a lesion may remain undetected in ultrasound B mode imaging for cancerous tissue. Imaging of the elastic properties of tissue provides new information which is collateral to tissue pathology. This study provides quantitative analysis of improvements in tumour diagnosis when the ultrasound B mode imaging is combined with elastography. Quantification was based on the textural parameters measured from the ultrasound B mode image and strain measured from the elastogram. The ability of a parameter to discriminate between diseased cases and normal cases was evaluated using receiver operating characteristic (ROC) analysis. Polyacrylamide gel based tissue mimicking phantoms with embedded inclusions of varying stiffness were used for the analysis.

/pdf/improvement-in-diagnosis-of-breast-tumour-using-ultrasound-2fn78eeks2.pdf

Improvement in diagnosis of breast tumour using ultrasound elastography and echography: A phantom based analysis.

Many lesions remain undetected in normal ultrasound B mode imaging of cancerous tissues because of their isoechoic nature and poor contrast. Imaging of the elastic properties of tissue provides new information which is correlated with tissue pathology. A quantitative analysis of the improvement in the diagnosis of the tumor by combining the ultrasound B mode imaging and elastography is carried out. Quantification is based on the textural parameters measured from the ultrasound B mode image and strain measured from the elastogram. Polyacrylamide gel based tissue mimicking phantoms were used for the analysis.

Improved Diagnosis of Breast Tumor by Combining Ultrasound Elastography and Tissue Characterization — Phantom Based Analysis

Most biological soft tissues exhibit viscous behavior in addition to their well known elastic properties. Polyacrylamide gel based tissue mimicking phantoms have been developed. The viscoelastic properties of these phantoms were measured by subjecting the samples to cyclic loading. Samples prepared with varying concentration of monomer were considered so as to cover the normal and pathological lesions. Results obtained in the measurement are fit to three models - Maxwell, Kelvin-Voigt (KV) and Kelvin-Voigt fractional derivative (KVFD) models, in order to determine the best fitting model. KVFD model is found to be best fitting model for the experimental data obtained.

M.E. Andrews

Papers

Measurement of Viscoelastic Properties of Polyacrylamide-Based Tissue-Mimicking Phantoms for Ultrasound Elastography Applications

A photophysical study on the role of bile salt hydrophobicity in solubilizing amphotericin B aggregates

Improvement in diagnosis of breast tumour using ultrasound elastography and echography: A phantom based analysis.

Improved Diagnosis of Breast Tumor by Combining Ultrasound Elastography and Tissue Characterization — Phantom Based Analysis

Viscoelastic properties of tissue mimicking phantoms for ultrasound elastograpghy