arXiv subjects

Daniel Palanker

Publications and source records attributed to Daniel Palanker.

5 recordsLinked to original sources

arXiv2025

Simulation of prosthetic vision with PRIMA system and enhancement of face representation

Objective. Patients implanted with the PRIMA photovoltaic subretinal prosthesis in geographic atrophy report form vision with the average acuity matching the 100um pixel size. Although this remarkable outcome enables them to read and write, they report difficulty with perceiving faces. Despite the pixelated stimulation, patients see smooth patterns rather than dots. We present a novel, non-pixelated algorithm for simulating prosthetic vision, compare its predictions to clinical outcomes, and describe computer vision and machine learning (ML) methods to improve face representation. Approach. Our simulation algorithm (ProViSim) integrates a spatial resolution filter based on sampling density limited by the pixel pitch and a contrast filter representing reduced contrast sensitivity of prosthetic vision. Patterns of Landolt C and human faces created using this simulator are compared to reports from actual PRIMA users. To recover the facial features lost in prosthetic vision due to limited resolution or contrast, we apply an ML facial landmarking model, as well as contrast-adjusting tone curves to the image prior to its projection onto the photovoltaic retinal implant. Main results. Prosthetic vision simulated using the above algorithm matches the letter acuity observed in clinical studies, as well as the patients' descriptions of perceived facial features. Applying the inversed contrast filter to images prior to projection onto the implant and accentuating the facial features using an ML facial landmarking model helps preserve the contrast in prosthetic vision, improves emotion recognition and reduces the response time. Significance. Spatial and contrast constraints of prosthetic vision limit the resolvable features and degrade natural images. ML based methods and contrast adjustments prior to image projection onto the implant mitigate some limitations and improve face representation.

cs.HC↗

arXiv2020

Real-Time Optimization of the Current Steering for Visual Prosthesis

Current steering on a multi-electrode array is commonly used to shape the electric field in the neural tissue in order to improve selectivity and efficacy of stimulation. Previously, simulations of the electric field in tissue required separate computation for each set of the stimulation parameters. Not only is this approach to modeling time-consuming and very difficult with a large number of electrodes, it is incompatible with real-time optimization of the current steering for practical applications. We present a framework for efficient computation of the electric field in the neural tissue based on superposition of the fields from a pre-calculated basis. Such linear algebraic framework enables optimization of the current steering for any targeted electric field in real time. For applications to retinal prosthetics, we demonstrate how the stimulation depth can be optimized for each patient based on the retinal thickness and separation from the array, while maximizing the lateral confinement of the electric field essential for spatial resolution.

physics.bio-ph↗

arXiv2019

Current Distribution on Capacitive Electrode-Electrolyte Interfaces

The distribution of electric current on an electrode surface in electrolyte varies with time due to charge accumulation at a capacitive interface, as well as due to electrode kinetics and concentration polarization in the medium. Initially, the potential at the electrode-electrolyte interface is uniform, resulting in a non-uniform current distribution due to the uneven ohmic drop of the potential in the medium. Over time, however, the non-uniform current density causes spatially varying rate of the charge accumulation at the interface, breaking down its equipotentiality. We developed an analytical model to describe such transition at a capacitive interface when the current is below the mass-transfer limitation, and demonstrated that the steady distribution of the current is achieved when the current density is proportional to the capacitance per unit area, which leads to linear voltage ramp at the electrode. More specific results regarding the dynamics of this transition are provided for a disk electrode, along with an experimental validation of the theoretical result. These findings are important for many electrochemical applications, and in particular, for proper design of the electro-neural interfaces.

physics.app-ph↗

arXiv2018

Full-Field Interferometric Imaging of Propagating Action Potentials

Currently, cellular action potentials are detected using either electrical recordings or exogenous fluorescent probes sensing calcium concentration or transmembrane voltage. Ca imaging has low temporal resolution, while voltage indicators are vulnerable to phototoxicity, photobleaching and heating. Here we report full-field interferometric imaging of individual action potentials by detecting the movement across the entire cell membrane. Using spike-triggered averaging of the movies synchronized to electrical recording, we demonstrate deformations of up to 3 nm (0.9 mrad) during the action potential in spiking HEK-293 cells, with a rise time of 4 ms. The time course of the optically-recorded spikes matches electrical waveforms. Since the shot noise limit of the camera (~2 mrad/pix) precludes detection of the action potential in a single frame, for all-optical spike detection, images are acquired at 50 kHz, and 50 frames are binned into 1 ms steps to achieve a sensitivity of 0.3 mrad in a single pixel. Using self-reinforcing sensitivity enhancement algorithm based on iteratively expanding the region of interest for spatial averaging, individual spikes can be detected by matching the previously extracted template of the action potential with the optical recording. This allows all-optical full-field imaging of the propagating action potentials without exogeneous labels or electrodes.

physics.bio-ph↗

arXiv2010

Multi-focal laser surgery: cutting enhancement by hydrodynamic interactions between cavitation bubbles

Transparent biological tissues can be precisely dissected with ultrafast lasers using optical breakdown in the tight focal zone. Typically, tissues are cut by sequential application of pulses, each of which produces a single cavitation bubble. We investigate the hydrodynamic interactions between simultaneous cavitation bubbles originating from multiple laser foci. Simultaneous expansion and collapse of cavitation bubbles can enhance the cutting efficiency by increasing the resulting deformations in tissue, and the associated rupture zone. An analytical model of the flow induced by the bubbles is presented and experimentally verified. The threshold strain of the material rupture is measured in a model tissue. Using the computational model and the experimental value of the threshold strain one can compute the shape of the rupture zone in tissue resulting from application of multiple bubbles. With the threshold strain of 0.7 two simultaneous bubbles produce a continuous cut when applied at the distance 1.35 times greater than that required in sequential approach. Simultaneous focusing of the laser in multiple spots along the line of intended cut can extend this ratio to 1.7. Counter-propagating jets forming during collapse of two bubbles in materials with low viscosity can further extend the cutting zone - up to a factor of 1.54.

physics.bio-ph↗