Reverberant optical coherence elastography using multifocal acoustic radiation force

Anterior segment applications of optical coherence elastography in ophthalmic and vision science: a systematic review of intrinsic measurement techniques and clinical relevance

Optical coherence elastography (OCE) is a non-invasive imaging technique that measures the biomechanical properties of materials and tissues. This systematic review focuses on the applications of OCE in the anterior segment of the eye, including the cornea, iris, and crystalline lens, and its clinical relevance in diagnosing and managing ocular diseases. A systematic literature review was conducted using the PRISMA framework to identify studies published between 2014 and 2024. The review included studies that reported intrinsic biomechanical properties of anterior segment tissues measured using OCE. Databases searched included Scopus, Pub Med, and IEEE Xplore. Twenty-five studies met the inclusion criteria. The review found that OCE has been used to measure intrinsic biomechanical parameters such as Young's modulus and shear modulus in ocular tissues. OCE has been utilised to assess corneal stiffness in keratoconus, lens elasticity in presbyopia and cataract formation, and iris biomechanical changes under different lighting conditions. The studies demonstrated that OCE could detect subtle biomechanical changes associated with ocular diseases and measure treatment efficacy, such as collagen crosslinking for keratoconus management. The findings highlight the potential of OCE to enhance clinical diagnostics and patient care by providing detailed insights into the biomechanical properties of ocular tissues. However, variability in measurement techniques, the complexity of the method and reliance on animal models limit the current clinical translation of OCE. Standardised measurement protocols and further development andin vivovalidation are needed to overcome these barriers. OCE shows promise as a valuable non-invasive tool for high-resolution assessments of tissue biomechanics, which can subsequently support the diagnosis and management of ocular diseases. Future research should focus on standardising OCE methods and integrating them into clinical practice to fully realise their potential in improving patient outcomes.

Noncontact elasticity measurement of hydrogels in a culture dish using reverberant optical coherence elastography

Estimating the elasticity of hydrogel phantoms in a cell culture plane is important for understanding the cell behavior in response to various types of mechanical stimuli. Hence, a noncontact tool for measuring the elastic properties of hydrogel phantoms in such three-dimensional cell cultures is required. A well-known method to determine the mechanical properties of hydrogels is the transient wave method. However, due to the multiple reflections of waves from the boundaries, a bigger cell culture plane or multiple directional filters may be required. In this study, we utilized reverberant shear wave elastography, which is based on the autocorrelation principle, to evaluate the shear wave speed in hydrogel samples within a culture dish. Numerical simulations were performed first to confirm the validity of the reverberant elastography method. Subsequently, we used this method to measure the wave speeds in hydrogel phantoms with different concentrations. Shear rheology tests were also performed, and their results were found to be in good agreement with the measured shear wave speeds. The proposed method could be useful for measuring the elasticity of tissues in tissue engineering applications in an inexpensive and noncontact manner.

An Infrared Near-Sensor Reservoir Computing System Based on Large-Dynamic-Space Memristor with Tens of Thousands of States for Dynamic Gesture Perception

To efficiently process the massive amount of sensor data, it is demanding to develop a new paradigm. Inspired by neurobiological systems, an infrared near-senor reservoir computing (RC) system, consisting of infrared sensors and memristors based on single-crystalline LiTaO3 and LiNbO3 (LN) thin film respectively, is demonstrated. The analog memristor is used as a reservoir in the RC system to process sensor signals with spatiotemporal characteristics. LN crystal structure stacked with oxygen octahedra provides favorable conditions for reliable Mott variable-range hopping conduction, which provides the memristor with tens of thousands of reservoir states within a large dynamic range. With the characteristics, the analog sensor signals with high data fidelity can be directly fed to the memristive reservoir, and the spatiotemporal features can be separated and mapped. The system demonstrated a dynamic gesture perception task, achieving an accuracy of 99.6%, which highlights the great application potential of the memristor in signal sensor processing and will advance the application of artificial intelligence in sensor systems. Crystal ion slicing techniques are used to fabricate a single-crystalline thin film for both the memristor and sensor, which opens up the possibility of realizing monolithic integration of a memristor-based near-sensor computing system.

Multifocal acoustic radiation force-based reverberant optical coherence elastography for evaluation of ocular globe biomechanical properties

Significance

Quantifying the biomechanical properties of the whole eye globe can provide a comprehensive understanding of the interactions among interconnected ocular components during dynamic physiological processes. By doing so, clinicians and researchers can gain valuable insights into the mechanisms underlying ocular diseases, such as glaucoma, and design interventions tailored to each patient's unique needs.

Aim

The aim of this study was to evaluate the feasibility and effectiveness of a multifocal acoustic radiation force (ARF) based reverberant optical coherence elastography (RevOCE) technique for quantifying shear wave speeds in different ocular components simultaneously.

Approach

We implemented a multifocal ARF technique to generate reverberant shear wave fields, which were then detected using phase-sensitive optical coherence tomography. A 3D-printed acoustic lens array was employed to manipulate a collimated ARF beam generated by an ultrasound transducer, producing multiple focused ARF beams on mouse eye globes ex vivo. RevOCE measurements were conducted using an excitation pulse train consisting of 10 cycles at 3 kHz, followed by data processing to produce a volumetric map of the shear wave speed.

Results

The results show that the system can successfully generate reverberant shear wave fields in the eye globe, allowing for simultaneous estimation of shear wave speeds in various ocular components, including cornea, iris, lens, sclera, and retina. A comparative analysis revealed notable differences in wave speeds between different parts of the eye, for example, between the apical region of the cornea and the pupillary zone of the iris (p = 0.003 ). Moreover, the study also revealed regional variations in the biomechanical properties of ocular components as evidenced by greater wave speeds near the apex of the cornea compared to its periphery.

Conclusions

The study demonstrated the effectiveness of RevOCE based on a non-invasive multifocal ARF for assessing the biomechanical properties of the whole eyeball. The findings indicate the potential to provide a comprehensive understanding of the mechanical behavior of the whole eye, which could lead to improved diagnosis and treatment of ocular diseases.