In 2006 Heidelberg Engineering introduced SPECTRALIS-the first imaging platform that combined SD-OCT technology with a scanning laser ophthalmoscope (SLO). Image quality and imaging speed were significantly improved by SD-OCT, which is able to capture the whole depth information simultaneously. The introduction of spectral domain OCT (SD-OCT) was able to overcome the limitations of TD-OCT. Usability and the impact of the noisy images on clinical diagnosis limited adaption of this new technology. Time-domain OCT technology (TD-OCT, see subsequent section for the working principles) requires acquisition of a depth scan for every location and subsequently offers very slow imaging speed and poor image quality. This can be understood examining the technology that was initially introduced to the market. Despite the technological promise that OCT offered, in the first years only a total of ~180 units were sold until 1999. It entered the marked in 1996, only 5 years after the inception of OCT was founded. With a lack of alternative diagnostic tools for depth resolved assessment of the retina, and the distinct characteristics of OCT it is no surprise that the first commercially available OCT was an ophthalmic imaging device. Retina: confocal scanning laser ophthalmoscopy (cSLO), adaptive optics scanning (more.) Skin/cornea: reflectance confocal microscopy (RCM). The extended focus and the operation with light in the near-infrared maintain a penetration depth of a few hundred microns, covering the whole retina.Ĭomparison of resolution in axial and lateral direction between some medical imaging techniques for different body parts. Therefore it is overcoming the limitations of optical focusing due to the limited pupil size of the eye. Due to the interferometric measurement method, the axial resolution is defined by the light source, not the focusing optics. Typically OCT systems have a resolution of 20–5 μm. It combines an axial resolution that can reach that of confocal microscopy with a lateral resolution comparable to confocal scanning laser ophthalmoscopy. 3.1, the resolution of OCT is much higher than that of other medical imaging methods like ultrasound or magnetic resonance imaging (MRI). Fast scanning rates and quick signal processing allows for image visualization in real time and at video rate. Since OCT is completely noninvasive, it provides in vivo images without impacting the tissue that is imaged. Therefore it is especially valuable in organs, where traditional microscopic tissue diagnosis by means of biopsy is not available-such as the human eye. Optical coherence tomography (OCT) is a non-contact imaging technique which generates cross-sectional images of tissue with high resolution. Recent approaches to improve the resolution and the acquisition speed show the ongoing research interest in OCT. New trends show the ability of functional OCT to image flow, polarizing properties of tissue and even mechanical properties like elasticity. Segmentation of features is the basis for automatic depth measurements and standardized measurements to be compared with normative databases. Combining retinal OCT with a confocal scanning laser ophthalmoscope allows for motion tracking during acquisition and to examine the exact same position at any time again. Regardless of the technical realization, axial resolution and imaging range of an OCT system are determined by light source and detector characteristics. Different technical methods are introduced and compared regarding their properties like sensitivity, imaging speed and penetration depth. A scanning OCT beam allows for acquisition of cross-sectional images of the tissue structure. The backscattered light is measured with an interferometric set-up to reconstruct the depth profile of the sample at the selected location. It typically uses light in the near-infrared spectral range which has a penetration depth of several hundred microns in tissue. Optical coherence tomography (OCT) is a non-invasive technique for cross-sectional tissue imaging.
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