Volumetric full-range magnetomotive optical coherence tomography

In vivo morphological study of obese development in mice model guided by swept-source optical coherence tomography (SSOCT)

This article shows the adequacy of the custom-built optical imaging system in the advancement investigation of obese mice. Obesity is defined as increased adipose/fatty mass resulting from a chronic imbalance between energy intake and expenditure. The in vivo investigation was performed for the tissue characterization of obese mice utilizing swept-source optical coherence tomography (SSOCT) for in situ examination and histology of delicate tissues in mice skin. It provides a noninvasive, painless visualization of the subsurface in life systems. Our SSOCT system's data is comparable to the regular invasive histology. Cross-assessment is done in various skin layers in obese mice like epidermis, papillary dermis, dermis, and fat tissue, which are likewise separated from the nonobese mice group. Histopathology results were further assessed with the obtained SSOCT results. This high precision of characterizing tissues using SSOCT helps us perform in vivo imaging and can also be used for the variable purpose of clinical practice.

Single-shot two-dimensional spectroscopic magnetomotive optical coherence elastography with graphics processing unit acceleration

Biomechanical contrast within tissues can be assessed based on the resonant frequency probed by spectroscopic magnetomotive optical coherence elastography (MM-OCE). However, to date, in vivo MM-OCE imaging has not been achieved, mainly due to the constraints on imaging speed. Previously, spatially-resolved spectroscopic contrast was achieved in a "multiple-excitation, multiple-acquisition" manner, where seconds of coil cooling time set between consecutive imaging frames lead to total acquisition times of tens of minutes. Here, we demonstrate an improved data acquisition speed by providing a single chirped force excitation prior to magnetomotion imaging with a BM-scan configuration. In addition, elastogram reconstruction was accelerated by exploiting the parallel computing capability of a graphics processing unit (GPU). The accelerated MM-OCE platform achieved data acquisition in 2.9 s and post-processing in 0.6 s for a 2048-frame BM-mode stack. In addition, the elasticity sensing functionality was validated on tissue-mimicking phantoms with high spatial resolution. For the first time, to the best of our knowledge, MM-OCE images were acquired from the skin of a living mouse, demonstrating its feasibility for in vivo imaging.

Optical elastography and tissue biomechanics

Mechanical forces play an important role in the behavior and development of biological systems and disease at all spatial scales, from cells and their constituents to tissues and organs. Such forces have a profound influence on the health, structural integrity, and normal function of cells and organs. Accurate knowledge of cell and tissue biomechanical properties is essential to map the distribution of forces and mechanical cues in biological systems. Cell and tissue biomechanical properties are also known to be important on their own as indicators of health or diseases state. Hence, optical elastography and biomechanics methods can aid in the understanding and clinical diagnosis of a wide variety of diseases. We provide a brief overview and highlight of the Optical Elastography and Tissue Biomechanics VI conference, which took place in San Francisco, February 2 and 3, 2019, as a part of Photonics West symposium.

Optical coherence elastography - OCT at work in tissue biomechanics [Invited]

Optical coherence elastography (OCE), as the use of OCT to perform elastography has come to be known, began in 1998, around ten years after the rest of the field of elastography - the use of imaging to deduce mechanical properties of tissues. After a slow start, the maturation of OCT technology in the early to mid 2000s has underpinned a recent acceleration in the field. With more than 20 papers published in 2015, and more than 25 in 2016, OCE is growing fast, but still small compared to the companion fields of cell mechanics research methods, and medical elastography. In this review, we describe the early developments in OCE, and the factors that led to the current acceleration. Much of our attention is on the key recent advances, with a strong emphasis on future prospects, which are exceptionally bright.

Magnetic and Plasmonic Contrast Agents in Optical Coherence Tomography

Optical coherence tomography (OCT) has gained widespread application for many biomedical applications, yet the traditional array of contrast agents used in incoherent imaging modalities do not provide contrast in OCT. Owing to the high biocompatibility of iron oxides and noble metals, magnetic and plasmonic nanoparticles, respectively, have been developed as OCT contrast agents to enable a range of biological and pre-clinical studies. Here we provide a review of these developments within the past decade, including an overview of the physical contrast mechanisms and classes of OCT system hardware addons needed for magnetic and plasmonic nanoparticle contrast. A comparison of the wide variety of nanoparticle systems is also presented, where the figures of merit depend strongly upon the choice of biological application.

Magnetomotive Optical Coherence Elastography for Magnetic Hyperthermia Dosimetry Based on Dynamic Tissue Biomechanics

Magnetic nanoparticles (MNPs) have been used in many diagnostic and therapeutic biomedical applications over the past few decades to enhance imaging contrast, steer drugs to targets, and treat tumors via hyperthermia. Optical coherence tomography (OCT) is an optical biomedical imaging modality that relies on the detection of backscattered light to generate high-resolution cross-sectional images of biological tissue. MNPs have been utilized as imaging contrast and perturbative mechanical agents in OCT in techniques called magnetomotive OCT (MM-OCT) and magnetomotive elastography (MM-OCE), respectively. MNPs have also been independently used for magnetic hyperthermia treatments, enabling therapeutic functions such as killing tumor cells. It is well known that the localized tissue heating during hyperthermia treatments result in a change in the biomechanical properties of the tissue. Therefore, we propose a novel dosimetric technique for hyperthermia treatment based on the viscoelasticity change detected by MM-OCE, further enabling the theranostic function of MNPs. In this paper, we first review the basic principles and applications of MM-OCT, MM-OCE, and magnetic hyperthermia, and present new preliminary results supporting the concept of MM-OCE-based hyperthermia dosimetry.

Intravascular magnetomotive optical coherence tomography of targeted early-stage atherosclerotic changes in ex vivo hyperlipidemic rabbit aortas

We report the development of an intravascular magnetomotive optical coherence tomography (IV-MM-OCT) system used with targeted protein microspheres to detect early-stage atherosclerotic fatty streaks/plaques. Magnetic microspheres (MSs) were injected in vivo in rabbits, and after 30 minutes of in vivo circulation, excised ex vivo rabbit aorta samples specimens were then imaged ex vivo with our prototype IV-MM-OCT system. The alternating magnetic field gradient was provided by a unique pair of external custom-built electromagnetic coils that modulated the targeted magnetic MSs. The results showed a statistically significant MM-OCT signal from the aorta samples specimens injected with targeted MSs.

Mechanical contrast in spectroscopic magnetomotive optical coherence elastography

The viscoelastic properties of tissues are altered during pathogenesis of numerous diseases and can therefore be a useful indicator of disease status and progression. Several elastography studies have utilized the mechanical frequency response and the resonance frequencies of tissue samples to characterize their mechanical properties. However, using the resonance frequency as a source of mechanical contrast in heterogeneous samples is complicated because it not only depends on the viscoelastic properties but also on the geometry and boundary conditions. In an elastography technique called magnetomotive optical coherence elastography (MM-OCE), the controlled movement of magnetic nanoparticles (MNPs) within the sample is used to obtain the mechanical properties. Previous demonstrations of MM-OCE have typically used point measurements in elastically homogeneous samples assuming a uniform concentration of MNPs. In this study, we evaluate the feasibility of generating MM-OCE elastograms in heterogeneous samples based on a spectroscopic approach which involves measuring the magnetomotive response at different excitation frequencies. Biological tissues and tissue-mimicking phantoms with two elastically distinct regions placed in side-by-side and bilayer configurations were used for the experiments, and finite element method simulations were used to validate the experimental results.