Abstract. We demonstrate the capability of full-range complex ͑FRC͒ spectral domain optical coherence tomography ͑SD-OCT͒ to image the anterior eye segment from the cornea to the posterior surface of the lens. With an adapted spectrometer design, we developed a SD-OCT system with an extended normal ͑single half-space͒ depth range of 7 mm ͑in air͒. This OCT-intrinsic depth range was doubled with a FRC technique. We demonstrate the performance of our OCT system by imaging the whole anterior segment of a healthy human eye in vivo. Optical coherence tomography ͑OCT͒ is an imaging modality that enables high-resolution cross-sectional imaging of biological tissues and translucent materials.1,2 Spectral domain ͑SD͒ OCT is a high-speed and high-sensitivity variant of OCT that largely replaced the older time domain variant in the recent years.In SD-OCT, the depth-resolved information can be reconstructed by Fourier transform of the cross spectral density measured with a spectrometer located in the detection arm of an interferometer.3,4 However, SD-OCT suffers from two drawbacks that restrict its measurement range.First, the Fourier transform of the real-valued crossspectral density is symmetrical about the zero path difference. Therefore, one cannot distinguish between positive and negative optical path differences with respect to the reference mirror. This effect particularly concerns imaging of objects with larger depth extensions, such as the anterior eye segment, where measurement ranges of the order of 10 mm are needed. In order to suppress the mirror images, the so-called fullrange complex ͑FRC͒ technique was introduced.5 In addition to the amplitude of the spectral interferogram, its phase is measured to reconstruct the full complex spectral interferogram-the analytic function. Inverse Fourier transformation of the analytic function directly yields the true object structures without any mirror terms. Several FRC approaches were developed that differ in the way of generating the / 2 phase-shifted quadrature function of the spectral interferometric signal.6-8 An elegant method uses the phase modulation that is introduced by off-pivot-point illumination of the galvanometer scanner mirror.9-11 A second drawback of SD-OCT is the spectrometer-intrinsic depth range, which is limited by its spectral resolution. Until now, the depth range of standard SD-OCT systems is ϳ3 mm, which can be doubled by applying FRC methods. However, this axial measurement range is not sufficient to cover the entire anterior eye segment.In this letter, we demonstrate an SD-OCT system with a modified spectrometer design combined with a FRC measurement range doubling that achieves an imaging depth of 14 mm, sufficient to cover the human anterior eye segment from the cornea to the posterior surface of the lens. Figure 1 shows a schematic diagram of our system. A superluminescent diode ͑Superlum, Moscow͒ with a center wavelength of 835 nm and a bandwidth ͑FWHM͒ of 18 nm was used as the light source. The round trip coherence length was 17 m. The col...
BackgroundComprehensive description of ketamine’s molecular binding profile becomes increasingly pressing as use in real-life patient cohorts widens. Animal studies attribute a significant role in the substance’s antidepressant effects to the serotonergic system. The serotonin transporter is a highly relevant target in this context, because it is central to depressive pathophysiology and treatment. This is, to our knowledge, the first study investigating ketamine’s serotonin transporter binding in vivo in humans.MethodsTwelve healthy subjects were assessed twice using [11C]DASB positron emission tomography. A total of 0.50 mg/kg bodyweight ketamine was administered once i.v. prior to the second positron emission tomography scan. Ketamine plasma levels were determined during positron emission tomography. Serotonin transporter nondisplaceable binding potential was computed using a reference region model, and occupancy was calculated for 4 serotonin transporter-rich regions (caudate, putamen, thalamus, midbrain) and a whole-brain region of interest.ResultsAfter administration of the routine antidepressant dose, ketamine showed <10% occupancy of the serotonin transporter, which is within the test-retest variability of [11C]DASB. A positive correlation between ketamine plasma levels and occupancy was shown.ConclusionsMeasurable occupancy of the serotonin transporter was not detectable after administration of an antidepressant dose of ketamine. This might suggest that ketamine binding of the serotonin transporter is unlikely to be a primary antidepressant mechanism at routine antidepressant doses, as substances that facilitate antidepressant effects via serotonin transporter binding (e.g., selective serotonin reuptake inhibitors) show 70% to 80% occupancy. Administration of high-dose ketamine is widening. Based on the positive relationship we find between ketamine plasma levels and occupancy, there is a need for investigation of ketamine’s serotonin transporter binding at higher doses.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.