Retinal laser photocoagulation represents a widely used treatment for retinal pathologies such as diabetic chorioretinopathy or diabetic edema. For effective treatment, an appropriate choice of the treatment energy dose is crucial to prevent excessive tissue damage caused by over-irradiation of the retina. In this manuscript we investigate simultaneous and time-resolved optical coherence tomography for its applicability to provide feedback to the ophthalmologist about the introduced retinal damage during laser photocoagulation. Time-resolved and volumetric optical coherence tomography data of 96 lesions on ex-vivo porcine samples, set with a 577 nm laser prototype and irradiance of between 300 and 8800 W=cm2 were analyzed. Time-resolved scans were compared to volumetric scans of the lesion and correlated with ophthalmoscopic visibility. Lastly, image parameters extracted from optical coherence tomography Mscans, suitable for lesion classification were identified. Results presented in this work support the hypothesis that simultaneous optical coherence tomography provides valuable information about the extent of retinal tissue damage and may be used to guide retinal laser photocoagulation in the future.
Retinal laser photocoagulation is an established and successful treatment for a variety of retinal diseases. While being a valuable treatment modality, laser photocoagulation shows the drawback of employing high energy lasers which are capable of physically destroying the neural retina. For reliable therapy, it is therefore crucial to closely monitor the therapy effects caused in the retinal tissue. A depth resolved representation of optical tissue properties as provided by optical coherence tomography may provide valuable information about the treatment effects in the retinal layers if recorded simultaneously to laser coagulation. Therefore, in this work, the use of ultra-high resolution optical coherence tomography to represent tissue changes caused by conventional and selective retinal photocoagulation is investigated. Laser lesions were placed on porcine retina ex-vivo using a 577 nm laser as well as a pulsed laser at 527 nm built for selective treatment of the retinal pigment epithelium. Applied energies were varied to generate lesions best representing the span from under- to overtreatment. The lesions were examined using a custom-designed optical coherence tomography system with an axial resolution of 1.78 μm and 70 kHz Ascan rate. Optical coherence tomography scans included volume scans before and after irradiation, as well as time lapse scans (Mscan) of the lesions. Results show OCT lesion visibility thresholds to be below the thresholds of ophthalmoscopic inspection. With the ultra-high resolution OCT, 42% - 44% of ophthalmoscopically invisible lesions could be detected and lesions that were under- or overexposed could be distinguished using the OCT data.
We present a multi-channel spectrometer that allows simultaneous acquisition of up to eight channels in order to perform
parallel optical coherence tomography or low coherence interferometry. The rigid and compact design is employed in
polarization sensitive optical coherence tomography measurements. Furthermore it is employed in distances and wedgeangle
measurements between two glass slides. The spectrometer operates at a central wavelength of 835 nm and at a
spectral bandwidth of 45 nm. This facilitates an axial resolution of 7.7 μm. The key feature is the simultaneous acquisition
of up to eight channels, at a maximum frame rate of 6.5 kHz. The sensitivity is 91 dB at an integration time of 11 μs and
an optical power of 0.7 mW at each of the sample arms. We obtained polarization sensitive OCT images of technical and
biological samples and investigated the system inherent phase stability to multipoint low coherence interferometry
measurements.
In this manuscript, we present the design and realization of a Fourier-Domain Spectroscopic-OCT system with a
simple spectrometer, based on off-the-shelf parts and a low-cost, state-of-the-art broadband S-LED light source
with three spectrally shifted S-LED modules. Depth resolved spectral absorption measurements in the wavelength
range from 750 nm to 850 nm are demonstrated using an expansion of OCT called spectroscopic OCT
(SOCT). The realized setup was tested and evaluated towards its ability to measure physical parameters such
as blood oxygen saturation quantitatively in vivo. Different sample configurations including multilayer setups
and scattering layers were used. Additionally, we present the theoretical model and experimental verification of
interferences between autocorrelation terms and the signal carrying crosscorrelation terms, strongly affecting the
absorption measurements. A simple background subtraction, minimizing the artifacts caused by the interferences
of autocorrelation and crosscorrelation terms is presented and verified.
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