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. When the sound of this frequency comes in contact with an object, it bounces back. Ultrasound uses a sound of frequency of more than 20 kHz. For a sound to be heard by the human ear, the frequency must be between 20 and 20,000 Hz (20 kHz). Segmentation of features is the basis for automatic depth measurements and standardized measurements to be compared with normative databases. A-scan and B-scan techniques are based on the principles of ultrasonography. 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. OCTs measure the echo time delay and the signal intensity after its reflection or back-scattering from the coronary wall structures while simultaneously operating a pull-back along the coronary artery, and thus performing a scan of the segment of interest (1). Different technical methods are introduced and compared regarding their properties like sensitivity, imaging speed and penetration depth. OCT catheters contain a single optical fiber that emits infrared light. 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. OCT scans are especially helpful for the early detection of the sight-threatening eye disease, glaucoma, which shows few symptoms until it is advanced, as well. It typically uses light in the near-infrared spectral range which has a penetration depth of several hundred microns in tissue. Also, the image quality numbers can alert you to a poor quality scan.Optical coherence tomography (OCT) is a non-invasive technique for cross-sectional tissue imaging. Images with artifacts due to microsaccades have areas that appear “blacked out,” which can be identified on the printout. Many of the recent instruments come with this feature, but some of the earlier models did not. Likewise, the problem of microsaccades is avoidable if the OCT instrument has eye tracking and can confirm that the eye was being tracked during the measurements. The only certain way to avoid this problem is to own a machine that’s designed to compensate for this. Unfortunately, even an 8-degree tilt results in a major difference in the thickness reading. The former is an issue because a patient may put his head in one position during a scan and then put his head in a slightly different position at the next visit. Some instruments correct for these concerns, but others don’t. The two most common problems here are patient head tilt and micro-saccades. This is easily detectable on the posterior pole retinal thickness map and hemisphere asymmetry analysis (right). An example of “green disease.” Left: The retinal nerve fiber layer measurement of both eyes is labeled normal, but the small red arrow points to a focal loss of RNFL inferotemporally in the left eye.
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