Soil is a highly scattering media that inhibits imaging of plant-microbial-mineral interactions that are essential to plant health and soil carbon sequestration. However, wavefront shaping can be used to focus light through or even deep inside highly scattering objects. In this work, we seek to overcome the fundamental challenges of imaging through soil minerals by developing a custom wavefront shaping method for a multiphoton microscope. We use the adaptive stochastic parallel gradient descent optimization algorithm combined with Hadamard basis to correct the aberration and the scattering in order to focus through the soil.
Soil is a highly scattering media that inhibits imaging of plant-microbial-mineral interactions that are essential to plant health and soil carbon sequestration. In this work, we seek to overcome the fundamental challenges of imaging through soil minerals by developing a custom wavefront sensor-less adaptive optics (AO) system for a multiphoton microscope. We are using a combined experimental and modeling approach, characterizing mineral optical characteristics with scatterometry, modeling the wavefront distortion and the image quality degradation after imaging through the soil medium, simulating the image quality improvement with AO correction, and experimentally testing our models with a stand-alone AO testbed.
Optical aberrations due to the inhomogeneous refractive index of tissue degrade the resolution and brightness of images
in deep tissue imaging. We introduce a direct wavefront sensing method using cellular structures labeled with fluorescent
proteins in tissues as guide-stars. As a non-invasive and high-speed method, it generalizes the direct wavefront sensing
method for adaptive optics microscopy. An adaptive optics confocal microscope using this method is demonstrated for
imaging of mouse brain tissue. The confocal images with and without correction are collected. The results show
increased image contrast and 3X improvement in the signal intensity for fixed mouse tissues at a depth of 70 μm. The
images of the dendrite and spines are much clearer after correction with improved contrast. The Strehl ratio is improved
from 0.29 to 0.96, a significant 3.3X improvement.
Recently, there has been a growing interest in deep tissue imaging for the study of neurons. Unfortunately, because of the
inhomogeneous refractive index of the tissue, the aberrations degrade the resolution and brightness of the final image.
In this paper, we describe an adaptive optics confocal fluorescence microscope (AOCFM) which can correct aberrations
based on direct wavefront measurements using a point source reference beacon and a Shack-Hartmann Wavefront Sensor
(SHWS). Mouse brain tissues with different thicknesses are tested. After correction, both the signal intensity and contrast
of the image are improved.
We describe a novel instrument that combines adaptive optics - Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO). Both systems share a common AO sub-system and vertical scanner to permit simultaneous acquisition of retinal images from both OCT and SLO. One of the benefits of combining OCT with SLO includes automatic co-registration between the two imaging modalities and potential for correcting lateral and transversal eye motion resulting in motion artifact-free volumetric retinal imaging. Results of using this system for eye model imaging are presented. Feasibility for clinical application is briefly discussed as well as potential further improvements of the current system.
We describe a compact MEMS-based adaptive optics (AO) optical coherence tomography (OCT)
system with improved AO performance and ease of clinical use. A typical AO system consists of a
Shack-Hartmann wavefront sensor and a deformable mirror that measures and corrects the ocular
and system aberrations. Because of limitations on current deformable mirror technologies, the
amount of real-time ocular-aberration compensation is restricted and small in previous AO-OCT
instruments. In this instrument, we incorporate an optical apparatus to correct the spectacle
aberrations of the patients such as myopia, hyperopia and astigmatism. This eliminates the tedious
process of using trial lenses in clinical imaging. Different amount of spectacle aberration
compensation was achieved by motorized stages and automated with the AO computer for ease of
clinical use. In addition, the compact AO-OCT was optimized to have minimum system aberrations
to reduce AO registration errors and improve AO performance.
Scanning laser ophthalmoscopes with adaptive optics (AOSLO) have been shown previously to provide a noninvasive,
cellular-scale view of the living human retina. However, the clinical utility of these systems has been
limited by the available deformable mirror technology. In this paper, we demonstrate that the use of dual
deformable mirrors can effectively compensate large aberrations in the human retina, making the AOSLO system a
viable, non-invasive, high-resolution imaging tool for clinical diagnostics. We used a bimorph deformable mirror to
correct low-order aberrations with relatively large amplitudes. The bimorph mirror is manufactured by Aoptix, Inc.
with 37 elements and 18 &mgr;m stroke in a 10 mm aperture. We used a MEMS deformable mirror to correct high-order
aberrations with lower amplitudes. The MEMS mirror is manufactured by Boston Micromachine, Inc with 144
elements and 1.5 &mgr;m stroke in a 3 mm aperture. We have achieved near diffraction-limited retina images using the
dual deformable mirrors to correct large aberrations up to ±3D of defocus and ±3D of cylindrical aberrations with
test subjects. This increases the range of spectacle corrections by the AO systems by a factor of 10, which is crucial
for use in the clinical environment. This ability for large phase compensation can eliminate accurate refractive error
fitting for the patients, which greatly improves the system ease of use and efficiency in the clinical environment.
Two deformable mirrors (2DM) were used in an adaptive optics - optical coherence tomography (AO-OCT) system to
image in vivo microscopic retinal structures of healthy and diseased retinas. As a result, multiple morphological
structures not previously seen in vivo have been visualized. Among those presented are three-dimensional
representations of the fovea and optic nerve head (ONH), revealing cellular structures and micro-vasculature. Drusen in
macular degeneration and photoreceptor dystrophies are also presented. Different methods for displaying volumetric
AO-OCT data to facilitate visualization of certain morphological details are compared.
Ultrahigh axial resolution in adaptive optics - optical coherence tomography (AO-OCT) is fundamentally limited by the
intrinsic chromatic aberrations of the human eye. Variation in refractive index of the ocular media with wavelength
causes the spectral content of broadband light sources to focus at different depths in the retina for light entering the eye
and at the imaging detector for light exiting. This effect has not been previously reported for ultrahigh-resolution OCT
(without AO) likely because the effect is masked by the relatively long depth of focus dictated by the small pupils used
in these systems. With AO, the pupil size is much larger and depth of focus substantially narrower. As such the
chromatic aberrations of the eye can counteract the lateral resolution benefit of AO when used with broadband light
sources. To more fully tap the potential of AO-OCT, compensation of the eye's chromatic and monochromatic
aberrations must occur concurrently. One solution is to insert an achromatizing lens in front of the eye whose chromatic
aberrations are equal but opposite in sign to that of the eye. In this paper we evaluate the efficacy of a novel design that
uses a custom achromatizing lens placed near the fiber collimating optic. AO-OCT images are acquired on several
subjects with and without the achromatizing lens and in combination with two light sources of different spectral width.
The combination of the achromatizing lens and broadband light source yielded the sharpest images of the retina and the
smallest speckle.
Adaptive Optics (AO) have been increasingly combined with a variety of ophthalmic instruments over the last decade to
provide cellular-level, in-vivo images of the eye. The use of MEMS deformable mirrors in these instruments has recently
been demonstrated to reduce system size and cost while improving performance. However, currently available MEMS
mirrors lack the required range of motion for correcting large ocular aberrations, such as defocus and astigmatism.
In order to address this problem, we have developed an AO system architecture that uses two deformable mirrors, in a
woofer / tweeter arrangement, with a bimorph mirror as the woofer and a MEMS mirror as the tweeter. This setup
provides several advantages, including extended aberration correction range, due to the large stroke of the bimorph
mirror, high order aberration correction using the MEMS mirror, and additionally, the ability to 'focus' through the
retina.
This AO system architecture is currently being used in four instruments, including an Optical Coherence Tomography
(OCT) system and a retinal flood-illuminated imaging system at the UC Davis Medical Center, a Scanning Laser
Ophthalmoscope (SLO) at the Doheny Eye Institute, and an OCT system at Indiana University. The design, operation
and evaluation of this type of AO system architecture will be presented.
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