Nizan Meitav

Point spread function estimation from projected speckle illumination

The resolution of an imaging apparatus is ideally limited by the diffraction properties of the light passing through the system aperture, but in many practical cases, inhomogeneities in the light propagating medium or imperfections in the optics degrade the image resolution. Here we introduce a powerful and practical new approach for estimating the point spread function (PSF) of an imaging system on the basis of PSF Estimation from Projected Speckle Illumination (PEPSI). PEPSI uses the fact that the speckles’ phase randomness cancels the effects of the aberrations in the illumination path, thereby providing an objective pattern for measuring the deformation of the imaging path. Using this approach, both wide-field-of-view and local-PSF estimation can be obtained by calibration-free, single-speckle-pattern projection. Finally, we demonstrate the feasibility of using PEPSI estimates for resolution improvement in iterative maximum likelihood deconvolution.

Measuring the ordering of closely packed particles

We look at irregularity and phase transitions in two-dimensional patterns. Two independent methods are provided for identifying and measuring hexagonal close packing of particles. We implemented these methods on images of melting colloidal films at different melting processes. We could easily spot various defects in the hexagonal crystal film. The feasibility of the methods is also demonstrated on human retinal images, for measuring the unit cell size and fraction of close-packed cone photoreceptors.

Improving retinal imaging by corneal refractive index matching

Imaging the retina at high resolution requires a dilated pupil, which in turn exposes more corneal irregularities. We diminish the optical errors of the cornea by refractive index matching. Lens-fitted goggles were used for corneal immersion, to reduce its aberrations, while keeping the ocular power. An additional aspheric plate reduced the residual ocular spherical aberration. A comparison of the index-matching-based retinal images with those acquired directly shows resolution improvement for subjects with normal extent of ocular aberrations. A simulation of the point spread function, obtained from an averaged ocular and corneal wavefront error, also reveals substantial improvement when using corneal index matching. The demonstrated improvement using index matching may enable further improvement of current retinal imaging techniques or relaxing requirements for active ocular aberration correction.

Realistic Modeling of Optogenetic Neuronal Excitation in Light-Scattering Brain Tissue

We introduce a realistic simulation of optogentic modulation, which includes an analytical model for the light distribution in brain tissue and a neuronal biophysical model, highlighting the importance of indirect excitation in optogenetics.

Microscopic PSF Estimation and Resolution Enhancement by Speckle Pattern Illumination

A method for estimating the PSF of an imaging system by projecting a speckle pattern onto the imaged object is presented. This provides a critical measure of the imaging performance and of the presence of aberrations.