Search Results (27)

Background/Objectives: As a result of metabolic changes and the disruption of tissue architecture and microcirculation, the regenerative potential of the liver decreases with violations at both micro and macro levels. The development of intraoperative approaches for assessing its regenerative potential is important for reducing the risk of the occurrence of post-resection liver failure. In this study, we used multimodal optical coherence tomography (MM OCT), a combination of three optical coherence tomography modalities—OCT–angiography (OCTA), attenuation coefficient mapping, and OCT–elastography (OCE) to provide real-time three-dimensional and label-free assessment of changes in microcirculation, and in the structure and stiffness of the liver during regeneration. Methods: In our study, the regeneration of a healthy liver was induced by 70% partial hepatectomy. Monitoring of changes was carried out on the 0 (normal liver), 3rd and 7th day of regeneration using modalities of MM OCT. OCT offers the benefits of higher resolution and specificity compared with other clinical imaging modalities, and can be used, even intraoperatively. Results: By the 3rd day of liver regeneration, a decreased density of all observable vessels, together with increased values of the liver tissue’s attenuation coefficient and stiffness, was revealed compared to their initial state. However, by the 7th day, the studied parameters tended to return to their normal values, except that the density of large-caliber vessels continued to increase further. Histological and biochemical blood analysis methods were used to verify the MM OCT data. Conclusions: Such data are a first step towards further investigation of liver regeneration in pathology, and, taken in perspective, this should serve as a basis for predictive intraoperative assessment of the regenerative potential of the liver in a clinical setting. Full article

Nanofibrous dressing materials with an antitumor function can potentially inhibit recurrence of melanoma following the surgical excision of skin tumors. In this study, hydrolyzed polyacrylonitrile (hPAN) nanofibers biofunctionalized with L-carnosine (CAR) and loaded with bio (CAR)-synthesized zinc oxide (ZnO) nanoparticles, ZnO/CAR-hPAN (hereafter called ZCPAN), were employed to develop an antimelanoma wound dressing. Inspired by the formulation of the commercial wound healing Zn-CAR complex, i.e., polaprezinc (PLZ), for the first time, we benefitted from the synergy of zinc and CAR to create an antimelanoma nanofibrous wound dressing. According to scanning electron microscopy (SEM) images, ultrafine ZnO nanoparticles were homogenously distributed throughout the nanofibrous dressing. The ZCPAN nanofiber mat showed a significantly higher toughness (18.7 MJ.m⁻³ vs. 1.4 MJ.m⁻³) and an enhanced elongation at break (stretchability) compared to the neat PAN nanofiber mat (12% vs. 9.5%). Additionally, optical coherence elastography (OCE) measurements indicated that the ZCPAN nanofibrous dressing was as stiff as 50.57 ± 8.17 kPa which is notably larger than that of the PAN nanofibrous dressing, i.e., 24.49 ± 6.83 kPa. The optimum mechanical performance of the ZCPAN nanofibers originates from physicochemical interaction of CAR ligands, hPAN nanofibers, and ZnO nanoparticles through hydrogen bonding, electrostatic bonding, and esterification, as verified using ATR-FTIR. An in vitro cell viability assay using human skin melanoma cells implied that the cells are notably killed in the presence of the ZCPAN nanofibers compared to the PAN nanofibers. Thanks to ROS generating ZnO nanoparticles, this behavior originates from the high reactive oxygen species (ROS)-induced oxidative damage of melanoma cells, as verified through a CellROX assay. In this regard, an apoptotic cell response to the ZCPAN nanofibers was recorded through an apoptosis assay. Taken together, the ZCPAN nanofibers induce an antimelanoma effect through oxidative stress and thus are a high potential wound dressing material to suppress melanoma regrowth after surgical excision of skin tumors. Full article

Corneal biomechanical properties are closely related to the cornea’s physiological and pathological conditions, primarily determined by the stromal layer. However, little is known about the influence of corneal cell interaction on the viscoelasticity of the stromal extracellular matrix (ECM). In this study, collagen-based hydrogels incorporated with keratocytes were reconstructed as corneal stromal models. Air-pulse optical coherence elastography (OCE) was used to characterize the viscoelastic properties of the corneal models. Plate compression, ramp–hold relaxation testing was performed on the initial corneal models. The findings demonstrated that the elastic modulus increased 5.27, 2.65 and 1.42 kPa, and viscosity increased 0.22, 0.06 and 0.09 Pa·s in the stromal models with initial collagen concentrations of 3, 5, and 7 mg/mL over 7 days. The elastic modulus and viscosity exhibited high correlation coefficients between air-pulse OCE and ramp–hold relaxation testing, with 92.25% and 98.67%, respectively. This study enhances the understanding of the influence of cell–matrix interactions on the corneal viscoelastic properties and validates air-pulse OCE as an accurate method for the mechanical characterization of tissue-engineered materials. Full article

We propose a nonlinear stress–strain law to describe nonlinear elastic properties of biological tissues using an analogy with the derivation of nonlinear constitutive laws for cracked rocks. The derivation of such a constitutive equation has been stimulated by the recently developed experimental technique—quasistatic Compression Optical Coherence Elastography (C-OCE). C-OCE enables obtaining nonlinear stress–strain dependences relating the applied uniaxial compressive stress and the axial component of the resultant strain in the tissue. To adequately describe nonlinear stress–strain dependences obtained with C-OCE for various tissues, the central idea is that, by analogy with geophysics, nonlinear elastic response of tissues is mostly determined by the histologically confirmed presence of interstitial gaps/pores resembling cracks in rocks. For the latter, the nonlinear elastic response is mostly determined by elastic properties of narrow cracks that are highly compliant and can easily be closed by applied compressing stress. The smaller the aspect ratio of such a gap/crack, the smaller the stress required to close it. Upon reaching sufficiently high compressive stress, almost all such gaps become closed, so that with further increase in the compressive stress, the elastic response of the tissue becomes nearly linear and is determined by the Young’s modulus of the host tissue. The form of such a nonlinear dependence is determined by the distribution of the cracks/gaps over closing pressures; for describing this process, an analogy with geophysics is also used. After presenting the derivation of the proposed nonlinear law, we demonstrate that it enables surprisingly good fitting of experimental stress–strain curves obtained with C-OCE for a broad range of various tissues. Unlike empirical fitting, each of the fitting parameters in the proposed law has a clear physical meaning. The linear and nonlinear elastic parameters extracted using this law have already demonstrated high diagnostic value, e.g., for differentiating various types of cancerous and noncancerous tissues. Full article

Objectives: The most important phase in the endometrial pathologies diagnostics is the histological examination of tissue biopsies obtained under visual hysteroscopic control. However, the unclear visual diagnostics characteristics of subtle focal endometrial pathologies often lead to selection errors regarding suspicious endometrial lesions and to a subsequent false pathological diagnosis/underestimation of precancer or early-stage cancer. Methods: In this study, we investigate the potential of Multimodal Optical Coherence Tomography (MM OCT) to verify suspicious endometrial lesion regions before biopsy collection. We study the polarization (by cross-polarization OCT, CP OCT) and elastic (by compression OCT-elastography, C-OCE) properties of ex vivo endometrial tissue samples in normal conditions (proliferative and secretory phases to the menstrual cycle, atrophic endometrium) with endometrial hyperplasia (non-atypical and endometrial intraepithelial neoplasia) and endometrial cancer subtypes (low-grade, high-grade, clear cell and serous). Results: To the best of our knowledge, this is the first quantitative assessment of relevant OCT parameters (depth-resolved attenuation coefficient in co-[Att(co) values] and cross-[(Att(cross) values] polarizations and Young’s elastic modulus [stiffness values]) for the selection of the most objective criteria to identify the clinically significant endometrial pathologies: endometrial intraepithelial neoplasia and endometrial cancer. The study demonstrates the possibility of detecting endometrial pathologies and establishing optimal threshold values of MM OCT criteria for the identification of endometrial cancer using CP OCT (by Att(co) values = 3.69 mm⁻¹, Sensitivity (Se) = 86.1%, Specificity (Sp) = 92.6%; by Att(cross) values = 2.27 mm⁻¹, Se = 86.8%, Sp = 87.0%) and C-OCE (by stiffness values = 122 kPa, Se = 93.2%, Sp = 91.1%). The study also differentiates endometrial intraepithelial neoplasia from non-atypical endometrial hyperplasia and normal endometrium using C-OCE (by stiffness values = 95 kPa, Se = 87.2%, Sp = 90.1%). Conclusions: The results are indicative of the efficacy and potential of clinical implementation of in vivo hysteroscopic-like MM OCT in the diagnosis of endometrial pathologies. Full article

The presence of molecular mutations in colorectal cancer (CRC) is a decisive factor in selecting the most effective first-line therapy. However, molecular analysis is routinely performed only in a limited number of patients with remote metastases. We propose to use tissue stiffness as a marker of the presence of molecular mutations in CRC samples. For this purpose, we applied compression optical coherence elastography (C-OCE) to calculate stiffness values in regions corresponding to specific CRC morphological patterns (n = 54). In parallel to estimating stiffness, molecular analysis from the same zones was performed to establish their relationships. As a result, a high correlation between the presence of KRAS/NRAS/BRAF driver mutations and high stiffness values was revealed regardless of CRC morphological pattern type. Further, we proposed threshold stiffness values for label-free targeted detection of molecular alterations in CRC tissues: for KRAS, NRAS, or BRAF driver mutation—above 803 kPa (sensitivity—91%; specificity—80%; diagnostic accuracy—85%), and only for KRAS driver mutation—above 850 kPa (sensitivity—90%; specificity—88%; diagnostic accuracy—89%). To conclude, C-OCE estimation of tissue stiffness can be used as a clinical diagnostic tool for preliminary screening of genetic burden in CRC tissues. Full article

The utilization of a reverberant shear-wave field in shear-wave elastography has emerged as a promising technique for achieving robust shear-wave speed (SWS) estimation. However, many types of estimators cannot accurately measure SWS within such a complicated 3D wave field. This study introduces an advanced autocorrelation estimator based on angular integration known as the angular integral autocorrelation (AIA) approach to address this issue. The AIA approach incorporates all the autocorrelation data from various angles during measurements, resulting in enhanced robustness to both noise and imperfect distributions in SWS estimation. The effectiveness of the AIA estimator for SWS estimation is first validated using a k-Wave simulation of a stiff branching tube in a uniform background. Furthermore, the AIA estimator is applied to ultrasound elastography experiments, magnetic resonance imaging (MRI) experiments, and optical coherence tomography (OCT) studies across a range of different excitation frequencies on tissues and phantoms, including in vivo scans. The results verify the capacity of the AIA approach to enhance the accuracy of SWS estimation and the signal-to-noise ratio (SNR), even within an imperfect reverberant shear-wave field. Compared to simple autocorrelation approaches, the AIA approach can also successfully visualize and define lesions while significantly improving the estimated SWS and SNR in homogeneous background materials and providing improved elastic contrast between structures within the scans. These findings demonstrate the robustness and effectiveness of the AIA approach across a wide range of applications, including ultrasound elastography, magnetic resonance elastography (MRE), and optical coherence elastography (OCE), for accurately identifying the elastic properties of biological tissues in diverse excitation scenarios. Full article

Increased stiffness of tissues has been recognised as a diagnostic feature of pathologies. Tissue stiffness characterisation usually involves the detection of tissue response from mechanical stimulation. Air-puff optical coherence elastography (OCE) can generate impulse surface acoustic waves (SAWs) on tissue surface without contact and evaluate the mechanical properties of tissue. This study endeavours to explore the optimal excitation angle for air-puff OCE, a parameter that lacks standardisation at present, by investigating the relationship between the frequency bandwidth and peak-to-peak signal-to-noise ratio (SNR) of SAWs for different excitation angles (relative to the normal surface) of air-puff on the sample, from 5° to 85°, with an interval of 5° applied on the phantom. Due to the unevenness of human hands, 20°, 45° and 70° angles were employed for human skin (10 healthy adults). The results show that a smaller excitation angle could produce higher wave frequency bandwidth; a 5° angle generated an SAW with 1747 Hz frequency bandwidth, while an 85° angle produced an SAW with 1205 Hz. Significant differences were not shown in peak-to-peak SNR comparison between 5° and 65° on the phantom, but between 65° and 85° at the excitation position, a reduction of 48.6% was observed. Furthermore, the group velocity of the SAWs was used to evaluate the bulk Young’s modulus of the human tissue. The outcomes could provide essential guidance for air-puff-based elastography studies in clinical applications and future tissue research. Full article

Viscoelasticity of the soft tissue is an important mechanical factor for disease diagnosis, biomaterials testing and fabrication. Here, we present a real-time and high-resolution viscoelastic response-optical coherence elastography (VisR-OCE) method based on acoustic radiation force (ARF) excitation and optical coherence tomography (OCT) imaging. The relationship between displacements induced by two sequential ARF loading—unloading and the relaxation time constant of the soft tissue—is established for the Kelvin-Voigt material. Through numerical simulation, the optimal experimental parameters are determined, and the influences of material parameters are evaluated. Virtual experimental results show that there is less than 4% fluctuation in the relaxation time constant values obtained when various Young’s modulus and Poisson’s ratios were given for simulation. The accuracy of the VisR-OCE method was validated by comparing with the tensile test. The relaxation time constant of phantoms measured by VisR-OCE differs from the tensile test result by about 3%. The proposed VisR-OCE method may provide an effective tool for quick and nondestructive viscosity testing of biological tissues. Full article

Assessing corneal biomechanics in vivo has long been a challenge in the field of ophthalmology. Despite recent advances in optical coherence tomography (OCT)-based elastography (OCE) methods, controversy remains regarding the effect of intraocular pressure (IOP) on mechanical wave propagation speed in the cornea. This could be attributed to the complexity of corneal biomechanics and the difficulties associated with conducting in vivo corneal shear-wave OCE measurements. We constructed a simplified artificial eye model with a silicone cornea and controllable IOPs and performed surface wave OCE measurements in radial directions (54–324°) of the silicone cornea at different IOP levels (10–40 mmHg). The results demonstrated increases in wave propagation speeds (mean ± STD) from 6.55 ± 0.09 m/s (10 mmHg) to 9.82 ± 0.19 m/s (40 mmHg), leading to an estimate of Young’s modulus, which increased from 145.23 ± 4.43 kPa to 326.44 ± 13.30 kPa. Our implementation of an artificial eye model highlighted that the impact of IOP on Young’s modulus (ΔE = 165.59 kPa, IOP: 10–40 mmHg) was more significant than the effect of stretching of the silicone cornea (ΔE = 15.79 kPa, relative elongation: 0.98–6.49%). Our study sheds light on the potential advantages of using an artificial eye model to represent the response of the human cornea during OCE measurement and provides valuable insights into the impact of IOP on wave-based OCE measurement for future in vivo corneal biomechanics studies. Full article

Robust methods to compute tissue displacements in optical coherence elastography (OCE) data are paramount, as they play a significant role in the accuracy of tissue elastic properties estimation. In this study, the accuracy of different phase estimators was evaluated on simulated OCE data, where the displacements can be accurately set, and on real data. Displacement ($∆d$) estimates were computed from (i) the original interferogram data ${(\Delta \phi }^{ori})$ and two phase-invariant mathematical manipulations of the interferogram: (ii) its first-order derivative (${\Delta \phi }^d$) and (iii) its integral (${\Delta \phi }^{int}$). We observed a dependence of the phase difference estimation accuracy on the initial depth location of the scatterer and the magnitude of the tissue displacement. However, by combining the three phase-difference estimates (${\Delta d}^{av})$, the error in phase difference estimation could be minimized. By using ${\Delta d}^{av}$, the median root-mean-square error associated with displacement prediction in simulated OCE data was reduced by 85% and 70% in data with and without noise, respectively, in relation to the traditional estimate. Furthermore, a modest improvement in the minimum detectable displacement in real OCE data was also observed, particularly in data with low signal-to-noise ratios. The feasibility of using ${\Delta d}^{av}$ to estimate agarose phantoms’ Young’s modulus is illustrated. Full article

The mechanical properties and structure alteration (e.g., layer morphology and thickness) of the oesophagus wall can reflect its pathological conditions. Hence, quantitative measurement of the above-mentioned properties can play a significant role in aiding the disease diagnosis in clinical application. As a fast and non-invasive imaging modality, Optical coherence tomography (OCT) and vibrational elastography can provide high resolution (<10 µm) structural and mechanical mapping of soft tissue. This study is a preliminary study to explore the potential of OCT and VOCE to evaluate both structural and mechanical properties of the oesophagus wall. Jn total, 52 oesophageal tissue samples were acquired from seven human Thiel-embalmed cadavers and were examined by the vibrational OCE. Both the OCT structure image and quantitative elasticity of each sample layer were obtained. In the OCT structure image, the averaged thickness for each sample layer was measured and corresponded with the histological image. Lamina propria has the largest thickness of 158.14 ± 8.75 µm, submucosa is the thinnest with a thickness of 143.19 ± 10.11 µm, and the thickness of muscularis mucosa is 149.49 ± 10.85 µm. Averaged intensity of back-scattered light from each sample layer was evaluated. Intensity of lamina propria layer, muscularis mucosa layer, and submucosa layer have an average value of 79.27 ± 0.51 dB, 69.83 ± 0.56 dB, and 76.10 ± 0.55 dB, respectively. The quantitative elasticity of each sample layer was evaluated in OCE. Elasticity of the lamina propria layer, muscularis mucosa layer, and submucosa layer were estimated as 115.64 ± 8.80 kPa, 60.28 ± 5.27 kPa, and 205.25 ± 19.03 kPa, respectively. The quantitative elasticity results obtained by vibrational OCE corresponded with the collagen distribution trend in each sample layer. This study demonstrates the ability of OCT and vibrational OCE in the characterisation and quantitative evaluation of human cadaver oesophagus wall-structure properties and mechanical properties. The feasibility of applying OCT and vibrational OCE in clinical diagnosis of oesophageal disease is also discussed. Full article

Despite the rapidly growing popularity of laser vision correction (LVC) in the correction of myopia, its quantitative evaluation has not been thoroughly investigated. In this paper, an acoustic radiation force–optical coherence elastography (ARF-OCE) system was proposed to evaluate LVC by measuring the residual stromal bed (RSB) elasticity, because it is directly relevant to the RSB thickness that is critical to maintaining normal corneal function. As expected, the Young’s modulus of the RSB was calculated, then its relationship with the RSB thickness was determined. More significantly, a specific thickness was revealed in which the Young’s modulus changed dramatically, which may imply that there is a high risk of complication caused by over-cutting of the cornea. To the best of our knowledge, this is the first ARF-OCE imaging of the RSB, which may help to determine the safe RSB thickness and thus may help us to quantitatively assess LVC surgery. Full article

In this work, we use the method of optical coherence elastography (OCE) to enable quantitative, spatially resolved visualization of diffusion-associated deformations in the areas of maximum concentration gradients during diffusion of hyperosmotic substances in cartilaginous tissue and polyacrylamide gels. At high concentration gradients, alternating sign, near-surface deformations in porous moisture-saturated materials are observed in the first minutes of diffusion. For cartilage, the kinetics of osmotic deformations visualized by OCE, as well as the optical transmittance variations caused by the diffusion, were comparatively analyzed for several substances that are often used as optical clearing agents, i.e., glycerol, polypropylene, PEG-400 and iohexol, for which the effective diffusion coefficients were found to be 7.4 ± 1.8, 5.0 ± 0.8, 4.4 ± 0.8 and 4.6 ± 0.9 × 10⁻⁶ cm²/s, respectively. For the osmotically induced shrinkage amplitude, the influence of the organic alcohol concentration appears to be more significant than the influence of its molecular weight. The rate and amplitude of osmotically induced shrinkage and dilatation in polyacrylamide gels is found to clearly depend on the degree of their crosslinking. The obtained results show that observation of osmotic strains with the developed OCE technique can be applied for structural characterization of a wide range of porous materials, including biopolymers. In addition, it may be promising for revealing alterations in the diffusivity/permeability of biological tissues that are potentially associated with various diseases. Full article

The purpose of this study is to quantitatively evaluate the differences in corneal biomechanics after SMILE and FLEx surgery using an acoustic radiation force optical coherence elastography system (ARF-OCE) and to analyze the effect of the corneal cap on the integrity of corneal biomechanical properties. A custom ring array ultrasound transducer is used to excite corneal tissue to produce Lamb waves. Depth-resolved elastic modulus images of the in vivo cornea after refractive surgery were obtained based on the phase velocity of the Lamb wave. After refractive surgery, the average elastic modulus of the corneal flap decreased (71.7 ± 24.6 kPa), while the elastic modulus of the corneal cap increased (219.5 ± 54.9 kPa). The average elastic modulus of residual stromal bed (RSB) was increased after surgery, and the value after FLEx (305.8 ± 48.5 kPa) was significantly higher than that of SMILE (221.3 ± 43.2 kPa). Compared with FLEx, SMILE preserved most of the anterior stroma with less change in corneal biomechanics, which indicated that SMILE has an advantage in preserving the integrity of the corneal biomechanical properties. Therefore, the biomechanical properties of the cornea obtained by the ARF-OCE system may be one of the essential indicators for evaluating the safety of refractive surgery. Full article