Optical coherence tomography (OCT) is a rapidly growing, advanced technology that has transformed ophthalmology practice. Thin films may be characterized non-destructively and without touch using optical methods. OCT is widely employed in the medical profession, particularly in ophthalmology. It is based on low-coherence interferometry, and a focused probe may be utilized to acquire the reflectivity profile of material along an optical axis.
There are two basic OCT approaches in particular. The first and most recent technology is known as spectral-domain optical coherence tomography (SD-OCT) or Fourier domain OCT, and it uses a broadband light source. The standard method is known as time domain optical coherence tomography (TD-OCT).
In this blog, the differences between SD-OCT and regular TD-OCT will be examined, highlighting the advantages SD-OCT has over TD-OCT. But first, let’s find out what time-domain OCT imaging is.
What is Time Domain OCT Imaging?
With the Stratus OCT, time-domain OCT imaging was accomplished by shifting the reference mirror, and the depth information of the retina is acquired as a function of time. A spectrometer is used to detect the light spectrum from the interferometer. The interference spectrum data is then Fourier converted to provide axial retina measurements. Time-domain OCT (TD-OCT) will be presented first, as spectral-domain OCT (SD-OCT) employs comparable hardware with a few modifications.
Because of their analogous principles, TD-OCT is sometimes compared to ultrasound, with OCT employing light as its medium and ultrasound using sound waves. Although spectral-domain OCT has been proven to enhance visualization of broadband light source structures, quantification of macular thickness has yet to be thoroughly validated. It remains uncertain whether spectral-domain OCT’s greater sample rate and enhanced scan resolution would lead to improved measurement reliability.
What is Spectral Domain OCT Imaging?
Spectral Domain Optical Coherence Tomography (SD-OCT) allows for high-resolution, optical cross-sectional, and en-face examination of the retina, retinal pigment epithelium (RPE), and choroid with depth-resolved segmentation. It has been used most commonly in retinal clinics and is highly valued for its ability to provide detailed imaging of retinal structures. SD-OCT has been proven to measure and quantify atrophy and has been utilized as a crucial adjunct in major clinical investigations.
With anatomic tracking features, SD-OCT enables the overlay of baseline and follow-up images, allowing for a thorough examination of the progression of dry age-related macular degeneration (AMD). As a result, longitudinal SD-OCT scanning is a sensitive approach that may identify structural changes in drusen-associated atrophy before geographic atrophy (GA) development, as determined by color fundus photography (CFP) or fundus autofluorescence (FAF).
How Broadband Light Source-based SD-OCT is Superior to TD-OCT?
The most recent kind of OCT is spectral domain OCT, which uses a broadband light source and a spectrometer to measure and preserve the reading. A low-loss spectrometer in the detector arm detects the spectrum of the interferometer’s interference pattern of light returned from the reference and sample arms. Spectral-domain OCT has quickly become vital for research, diagnosis, monitoring, and screening of illnesses affecting the macula and optic nerve head.
A desirable feature of an OCT system is high spatial resolution, which necessitates the use of a broadband light source with a wider spectral width or a very short coherence length. This is crucial because OCT is a technique that employs a broad-spectrum light source. According to this principle, a beam of light is directed into the eye’s retina. The detector captures the reflected light, which is then compared to the reference light beam to determine the echo time delay. This process allows for detailed imaging of the retina’s structure, revealing fine anatomical details with high precision.
This principle is the same for both SD-OCT, which is based on a broadband light source, and a conventional technique called TD-OCT. Compared to traditional TD-OCT, SD-OCT showed statistically significantly better reproducibility in measuring macular thickness and the RNFL sector around the papilla in most sectors.
The information is obtained from a mechanically moving reference mirror. In contrast, in spectral domain OCTs based on broadband light sources, the reference mirror is stationary. This stationary reference mirror setup in SD-OCT allows for faster data acquisition and higher resolution imaging. There was no statistically significant difference between the average overall macula or RNFL reproducibility, or the identification of glaucoma using TD-OCT and SD-OCT. Both techniques offer reliable methods for assessing retinal structures and diagnosing conditions, but SD-OCT’s advantages include improved imaging speed and resolution.
The Benefits of Using Broadband Light Source-based Spectral Domain OCT
There are various benefits connected to using a broadband light source based on SD-OCT. The following are a few of the major advantages:
- Using a broadband light source, the improved sensitivity afforded by SD-OCT can be translated into a faster OCT scan collection rate, deeper penetration, or increased sensitivity of the different functional OCT approaches.
- SD-OCT has a faster acquisition speed than TD-OCT due to the stationary reference arm. This enables SD-OCT-based Broadband Light Source to capture quality cross-sectional images of the retina.
- SD-OCT separates itself from previous TD generations by providing high-speed 2-D and 3-D imaging of weak backscattering retinal tissue with great axial resolution.
- Broadband light source-based spectral domain OCT helps in better diagnosis of retinal tissue.
- The SD-OCT’s high resolution of nearly 5-7 microns can produce subtle anomalous images that are invisible to time-domain optical coherence tomography. Thanks to this feature, today’s SD-OCT-based Broadband light source has been able to provide high accuracy in retina-level measurements.
With a better understanding of how broadband light source-based SD-OCT outperforms TD-OCT, it is clear that this technology has revolutionized the therapeutic field by providing high-resolution imaging and improved diagnostic capabilities. Its enhanced depth resolution and speed make it a critical tool in modern ophthalmology and other medical applications.
Inphenix is a US-based light source manufacturer that specializes in optical devices such as Swept-Source Lasers, Fabry Perot Lasers, Gain Chips, Distributed Feedback Lasers, and VCSELs. Their products are cutting-edge and work with a broad variety of devices, offering high performance and reliability for various applications, from telecommunications to medical imaging.
