In-vivo diffusing-wave-spectroscopy measurements of the ocular fundus

Rovati, Luigi; Cattini, Stefano; Zambelli, N.; Viola, Francesco; Staurenghi, Giovanni

doi:10.1364/oe.15.004030

Cited by 11 publications

(21 citation statements)

References 23 publications

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“…This loss of contrast deep within thick absorbing or scattering samples occurs because signaling from fluorophores located within the focal volume is overwhelmed by that from fluorophores located closer to sample surface and excited by scattered light [4]. Using photon transport mean-free-path length (L) in the retina for 750 nm light at 1.2 mm (L = 0.27 mm at 400 nm) based on previous reports of bovine retina [5,6], the estimated maximal imaging depth is 2.4 mm -more than enough to penetrate the mouse retina. Taking into account dramatically shorter mean free paths in the RPE and choroid, the theoretical maximum depth is 0.44 mm, still sufficient to image mouse retina and RPE.…”

Section: Introductionmentioning

confidence: 99%

Image registration and averaging of low laser power two-photon fluorescence images of mouse retina

Palczewska¹,

Stremplewski²,

Wojtkowski³

et al. 2016

Biomed. Opt. Express

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Two-photon fluorescence microscopy (TPM) is now being used routinely to image live cells for extended periods deep within tissues, including the retina and other structures within the eye . However, very low laser power is a requirement to obtain TPM images of the retina safely. Unfortunately, a reduction in laser power also reduces the signal-to-noise ratio of collected images, making it difficult to visualize structural details. Here, image registration and averaging methods applied to TPM images of the eye in living animals (without the need for auxiliary hardware) demonstrate the structural information obtained with laser power down to 1 mW. Image registration provided between 1.4% and 13.0% improvement in image quality compared to averaging images without registrations when using a high-fluorescence template, and between 0.2% and 12.0% when employing the average of collected images as the template. Also, a diminishing return on image quality when more images were used to obtain the averaged image is shown. This work provides a foundation for obtaining informative TPM images with laser powers of 1 mW, compared to previous levels for imaging mice ranging between 6.3 mW [Palczewska G., Nat Med.20, 785 (2014) Sharma R., Biomed. Opt. Express4, 1285 (2013)].

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Section: Introductionmentioning

confidence: 99%

Image registration and averaging of low laser power two-photon fluorescence images of mouse retina

Palczewska¹,

Stremplewski²,

Wojtkowski³

et al. 2016

Biomed. Opt. Express

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“…The superficiality of ocular tissues confers some advantage to focusing. The mean free path of transport (the mean distance between photon scatterings) at 633 nm for the retina, the retinal pigment epithelium and the choroid are reported to be 1 mm, 10 μm and 86 μm, respectively (Hammer et al 1995; Rovati et al 2007). Because the retinal mean free path of transport exceeds retinal thickness (about 0.25 mm in humans), OCT, which relies on ballistic photons, can image the retina with great success.…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Photoacoustic Imaging of Ocular Tissues

Silverman

Kong

Chen

et al. 2010

Ultrasound in Medicine & Biology

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Optical coherence tomography (OCT) and ultrasound (US) are methods widely used for diagnostic imaging of the eye. These techniques detect discontinuities in optical refractive index and acoustic impedance respectively. Because these both relate to variations in tissue density or composition, OCT and US images share a qualitatively similar appearance. In photoacoustic imaging (PAI), short light pulses are directed at tissues, pressure is generated due to a rapid energy deposition in the tissue volume, and thermoelastic expansion results in generation of broadband US. PAI thus depicts optical absorption, which is independent of the tissue characteristics imaged by OCT or US. Our aim was to demonstrate the application of PAI in ocular tissues and to do so with lateral resolution comparable to OCT. We developed two PAI assemblies, both of which used single-element US transducers and lasers sharing a common focus. The first assembly had optical and 35-MHz US axes offset by a 30° angle. The second assembly consisted of a 20-MHz ring transducer with a coaxial optics. The laser emitted 5-ns pulses at either 532-nm or 1064-nm, with spot sizes at the focus of 35-μm for the angled probe and 20-μm for the coaxial probe. We compared lateral resolution by scanning 12.5-μm diameter wire targets with pulse/echo US and PAI at each wavelength. We then imaged the anterior segment in whole ex vivo pig eyes and the choroid and ciliary body region in sectioned eyes. PAI data obtained at 1064 nm in the near infrared had higher penetration but reduced signal amplitude compared to that obtained using the 532-nm green wavelength. Images were obtained of the iris, choroid and ciliary processes. The zonules and anterior cornea and lens surfaces were seen at 532 nm. Because the laser spot size was significantly smaller than the US beamwidth at the focus, PAI images had superior resolution than those obtained using conventional US.

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“…Also, the technique of diffusing‐wave spectroscopy (DWS) appears as a promising solution (Maret & Wolf 1987; Pine et al. 1990; Rovati et al. 2007).…”

Section: Discussionmentioning

confidence: 99%

Analysis of diabetic vitreopathy with dynamic light scattering spectroscopy – problems and solutions related to photon correlation

Fankhauser

2012

Acta Ophthalmologica

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. Purpose: To explore the molecular alterations of the vitreous by dynamic light scattering (DLS) spectroscopy (quasi‐elastic light scattering spectroscopy, photon‐correlation spectroscopy) in normals and in patients afflicted with various degrees of non‐proliferative and with proliferative diabetic retinopathy. Methods: Dynamic light scattering spectroscopy was employed to analyze the vitreous of normals and of patients with diabetes non‐invasively to estimate both the sizes and diffusion coefficients of mobile macromolecules and/or microparticles. Results: Abnormal molecular behaviour of vitreous molecules was observed in patients with diabetes afflicted with various degrees of diabetic vitreo‐retinopathy. In the non‐proliferative (background) retinopathy, both the diameters of the microparticles increase and the diffusion constants decrease significantly and progressively as the diabetic disease progresses. In the proliferative phase, a significant trend in the direction of smaller particles and greater diffusion constants is evident. These behaviours could also be interpreted as an increase in the viscosity of the intermolecular substance in the first case and as a decrease in the second. Conclusions: The vitreous in normals and even more so in diabetics with diabetic vitreo‐retinopathy is optically a highly non‐isotropic, multidispersive structure, making an optical analysis difficult. Advanced, but available models and technology, however, permits a major step forward in the optical analysis of the normal and the diseased vitreous.

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In-vivo diffusing-wave-spectroscopy measurements of the ocular fundus

Cited by 11 publications

References 23 publications

Image registration and averaging of low laser power two-photon fluorescence images of mouse retina

Image registration and averaging of low laser power two-photon fluorescence images of mouse retina

High-Resolution Photoacoustic Imaging of Ocular Tissues

Analysis of diabetic vitreopathy with dynamic light scattering spectroscopy – problems and solutions related to photon correlation

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