OCT Technology

Optical Coherence Tomography (OCT)

What Is Optical Coherence Tomography?

Optical Coherence Tomography (OCT) is a technology for non-invasive optical imaging of tissue. This cross-sectional image is also referred to as tomography.

OCT is widely adopted within eye care where it is the gold standard for in vivo imaging of the retina. The eye specialist can perform non-invasive optical biopsies using the OCT technique. This allows the doctor to see a cross-section of the retina of the eye where the sharp vision is formed. Full 3D wide-field OCT scans have the potential to become a comprehensive tool for mapping out all the layers of the eye with better results in diagnosis and treatment.

OCTLIGHT´s Caliper technology has the following features and benefits with Ophthalmic OCT

Center wavelength of 1060 nm for deeper penetration into the eye (choroid imaging)
High sweep rates for wide-field, video-rate, and high-resolution 3D imaging
Long imaging range by its inherently long coherence length of more than 50 mm
Less constraints on sample positioning and simplified design of scanning equipment
Better sweep stability enabling high-quality imaging and phase-sensitive OCT (e.g., angiography)

What Can Optical Coherence Tomography (OCT) Be Used for?

OCT is especially useful in Ophthalmic imaging since other methods such as ultrasound, x-ray, positron imaging and magnetic resonance imaging (MRI) are not convenient due to the invasive nature, high cost and large size.

There are several other areas where OCT is an active research area or commercialized. Specific to OCT is the consideration of the optical penetration which is limited by absorption and scattering. OCT provide very high resolution in the micrometer range with limited penetration depth in the millimeter range. This is strongly wavelength depended why for imaging of tissue with high water content lower wavelength is chosen, and for tissue with low water content longer wavelength is chosen. There are certain regions such as 1060, 1300 and 1700 nm which are optimal due to dip in the water absorption.

The imaging range further depends on the optical detector bandwidth and data acquisition (DAQ). Typically for longer imaging ranges the sampling rate and data transfer will become a limiting factor that must be considered in engineering design.

Why Should I Choose SS-OCT instead of SD-OCT?

Optical Coherence Tomography (OCT) was first introduced and commercialized in the 90’ties and from a commercialization perspective it has developed in 3 technology generation.

First generation was time-domain OCT (TD-OCT) which was slow due to need for sweeping the mechanical delay line. This makes it useful for A-scan or OCDR imaging, such as for biometers, but not for tomography where the slow acquisition rate impedes sufficient resolution to be achieved on the B-scan.

Second generation was Spectral-Domain OCT (SD-OCT) which was spurred by the development of fast and cost-efficient spectrometers enabling Fourier-Domain OCT (FD-OCT) at center wavelength in the range of around 8-900nm where silicon photodetectors have good sensitivity. For longer wavelength InGaAs photodetectors was available, but it is not until recently prompted by the adoption in fiber communication that they have begun to be competitive. In FD-OCT multiple wavelengths are detected at the same time which improves greatly the SNR and speed why FD-OCT has been commercially successful for B-scan and even C-scan imaging.

Third generation was Swept-Source (SS-OCT) based on Swept Source lasers, only requiring a single detector, that can sample much faster than CMOS high-resolution spectrometers, enabling >10x faster imaging rate opening for larger field of view and velocity information. Swept Source lasers do not have the inherent trade-off from the spectrometer that limits the linewidth and thus SS-OCT enables >10x larger imaging depth. Recently the rise of the Photonics Integrated Circuit (PIC) industry has also shown the path to further miniaturization.

More variations of Swept Sources are under development such as Fuld-Field OCT (FF-OCT), and Adaptive Optics OCT (AO). OCTLIGHT is following the vibrant research community closely to stay at the forefront of technology development and adoption.

Optical Coherence Tomography (OCT)

What Is Optical Coherence Tomography?

What Can Optical Coherence Tomography (OCT) Be Used for?

Why Should I Choose SS-OCT instead of SD-OCT?

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