How Optical Coherence Tomography Works & How We Save You Time & Money

Time-domain OCT, also referred to as TD-OCT, has been used since the introduction of optical coherence tomography, but has more recently been replaced by spectral-domain OCT.

It is capable of acquiring approximately 400 one-dimensional scans per second, using six different radial slices that are oriented around 30° apart. It relies on the movement of a mechanical arm to capture axial scans.

Fourier-domain optical coherence tomography (FD-OCT) is based on low-coherence interferometry. This type of interferometry utilizes the coherent properties of a light source with broad optical bandwidth to measure optical path length delays coming from a sample.

Cross-sectional images are obtained by using a coupler to split the light of the low coherence source into two different paths, which are then measured using an interferometer, which measures the optical path length differences seen between the light via a sample arm and a reference arm.

There are two types of FD-OCT systems, which utilize different light sources and detection devices: spectral-domain OCT (SD-OCT) and swept-source OCT (SS-OCT).

Spectral-domain OCT, or SD-OCT, provides more speed and efficiency than time-domain technology, performing quicker acquisition rates and greater resolution. SD-OCT, as a term, can be used to refer to Fourier domain OCT. However, SD-OCT is known as a variation of FD-OCT.

It is able to execute approximately 20,000-40,000 one-dimensional scans per second, which decreases the potential for missing a scan of any part of the eye due to blinking or other instances of patient movement.

SD-OCT devices and systems are commonly used to evaluate vitreous, retinal and choroidal pathology.

SS-OCT, short for swept-source OCT, is a newer generation of OCT, offering higher speeds, increased spectral resolution, and better signal-to-noise ratio (SNR) than SD-OCT. Because of its speed, SS-OCT can reduce motion artifacts, and in some cases avoid them entirely, especially in ophthalmic or cardiologic applications, offering better imaging capabilities than the previous generations of OCT.

Furthermore, SS-OCT provides comprehensive imaging of larger hollow organs, which enables wide-field imaging for the detection of early and subtle morphological tissue changes over a larger field of view than SD-OCT.

SS-OCT system components differ from SD-OCT in numerous ways, namely the light source, optics, and detection device. While SD-OCT utilizes a broadband, low-coherence light source, SS-OCT relies on swept-source, a type of tunable laser light source that has a tightly focused wavelength which sweeps across a narrow band of wavelengths.

In SS-OCT, the sweep is capable of labeling different time delays that are detected by interference, which are then measured by a point photodetector as the light waves return to the device, resulting in faster scanning speeds. SD-OCT elies on a spectrometer, diffraction grating, Fourier transform lenses, and a detector array instead to detect these returning wavelengths.

Issues with data transfer during OCT have been addressed through SS-OCT by employing two dual-balance digital detectors in sequence , which has enabled continuous real-time imaging.

OCT angiography, or OCT-A, another variation of OCT, provides eye care professionals with another way to treat retinal conditions and diseases. It provides noninvasive label-free visualization of microvasculature of the retina and choroid. Imaging microvasculature is critical for diagnosing retinal conditions, because they can host all-important indicators of the disease and its progression. For example, cancerous tumors often rely on vasculature to feed their growth.

OCT-A uses laser light reflectance of the surface of moving red blood cells to accurately depict vessels through different segmented areas of the eye, thus eliminating the need for intravascular dyes.

The full picture of a patient’s eye health is paramount, and OCT machines provide vital data that can give your patients the peace of mind they deserve. But, these systems can be complicated to operate.

To make operating them easier, manufacturers have developed machines that offer one-touch and auto-alignment features, providing hands-free diagnosis. By simplifying the process, automation cuts down on waste and increases overall accuracy of the results.

Additionally, imaging speed is one of the most important parameters for OCT quality and efficiency. This is because high scanning and data acquisition speeds enable the reduction of motion, such as breathing and eye movements, that can impact an OCT scan. High speeds also help with field of view, providing wide-field imaging, and can even pick up morphologic changes that are often too subtle to catch with slower systems.

Because of all this, OCT systems have been developed to provide high-speed scanning capabilities, which have been closely linked to developments in OCT light sources, such as wavelength-swept lasers. These swept sources, as they’re often referred to, provide different sweep ranges that affect the speed at which a scan can be performed, as well as the axial resolution in OCT.