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OCT Systems Comparison

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OCT Selection Guide




  • Select from our OCT Family

OCT Systems Comparison

Thorlabs offers a wide variety of Optical Coherence Tomography (OCT) imaging systems. We recognize each imaging application has their specific needs. With the growing number of OCT systems available, it can be challenging to decide which system best meets your needs. Below we have put together a Selection Guide that outlines a few key technical specifications of each of our systems as well as some tips on how to choose the best OCT system for your application.

Choosing an OCT System

 

Thorlabs currently offers OCT systems that operate with a center wavelength of either 930 nm or 1300 nm. The center wavelength contributes to the actual imaging depth and resolution of the system. Shorter wavelength OCT systems, such as our 930 nm system, are ideal for higher resolution imaging compared to systems with a center wavelength of 1300 nm. For imaging samples that have higher optical scattering properties, such as tissue, the longer wavelength systems are recommended. The longer center wavelength is not affected by scattering, and therefore, the light is able to penetrate deeper into the sample and return for detection.

The spectral bandwidth of the OCT light source is indirectly proportional to the axial (depth) resolution of the imaging system. Therefore, broadband light sources are used to provide high axial resolution.


A single depth profile (Intensity vs Depth) is called an A-Scan. A B-Scan, or two-dimensional cross-sectional image, is created by laterally scanning the OCT beam and collecting sequential Ascans. The speed with which a B-scan is collected depends on the A-Scan or Line rate.

For Spectral-Domain OCT systems, the A-Scan rate is determined by the speed of the camera in the detection spectrometer. For Swept-Source OCT systems, the A-Scan rate is determined by the sweep speed of the swept laser source. There is a tradeoff between A-Scan rate and the sensitivity of an OCT system: higher A-Scan rate results in lower sensitivity.


The sensitivity of an OCT system describes the largest permissible signal attenuation within a sample that can still be distinguished from the noise. In practice, higher sensitivity OCT systems are capable of providing higher contrast images. Since the sensitivity of an OCT system can be increased by increasing the integration time, there is usually a tradeoff between A-scan rate and sensitivity.


The length (L) and width (W) of the FOV is limited by the scan lens properties. All of our OCT systems have a 10 mm x 10 mm (L x W) FOV. The maximum depth (D) attainable is set by the design of the OCT system. The graphic below shows variation in depth among all of our OCT systems. However, the actual imaging depth will typically depend on the optical properties of the sample. Our standard OCT systems are designed to provide an optimized balance between imaging depth and axial resolution. For applications requiring greater depth or higher resolution, we offer custom configurations.

Resolution

In OCT, the axial (depth) and lateral resolutions are dependent on different factors. The axial resolution of the OCT system is proportionally dependent on the center wavelength of the source and inversely proportional to the source bandwidth. In practice, the axial resolution is also improved by the index of refraction of the sample. For example, the axial resolution of the CALLISTO OCT system is 7 μm in air or 5.2 μm in water-rich samples such as tissue (n=1.35).

As with general microscopy principles, the lateral resolution is dependent on the focusing objective in the imaging probe. All of Thorlabs' OCT systems come with our specially designed OCT scan lens which provides telecentric scans across the entire field of view.

Cross-Section of a Human Finger



OCT Cross-Sectional Image of a Human Finger.
Layers of Skin: E-Epidermis; D-Dermis; BV-Blood Vessels.
Image Size: 4.9 mm x 2.6 mm. Image Taken with TELESTO OCT System.

 

Optical Coherence Tomography Tutorial

Optical Coherence Tomography (OCT) is a noninvasive optical imaging modality that provides real-time, 1D depth, 2D cross-sectional, and 3D volumetric images with micron-level resolution and millimeters of imaging depth. OCT images consist of structural information from a sample based on light backscattered from different layers of material within the sample. It can provide real-time imaging and is capable of being enhanced using birefringence contrast or functional blood flow imaging with optional extensions to the technology.

Thorlabs has designed a broad range of OCT imaging systems that cover several wavelengths, imaging resolutions, and speeds, while having a compact footprint for easy portability. Also, to increase our ability to provide OCT imaging systems that meet each customer’s unique requirements, we have designed a highly modular technology that can be optimized for varying applications.

 

Application Examples

                 
Art Conservation Drug Coatings 3D Profiling In-vivo Small Animal Biology Tissue Birefringence Mouse Lung Retina Cone Cells

 

OCT is the optical analog of ultrasound, with the tradeoff being lower imaging depth for significantly higher resolution (see Figure 1). With up to 15 mm imaging range and better than 5 micrometers in axial resolution, OCT fills a niche between ultrasound and confocal microscopy. In addition to high resolution and greater imaging depth, the non-contract, noninvasive advantage of OCT makes it well suited for imaging samples such as biological tissue, small animals, and materials. Recent advances in OCT have led to a new class of technologies called Fourier Domain OCT, which has enabled high-speed imaging at rates greater than 700,000 lines per second.1 Fourier Domain Optical Coherence Tomography (FD-OCT) is based on low-coherence interferometry, which utilizes the coherent properties of a light source to measure optical path length delays in a sample. In OCT, to obtain cross-sectional images with micron-level resolution, and interferometer is set up to measure optical path length differences between light reflected from the sample and reference arms. There are two types of FD-OCT systems, each characterized by its light source and detection schemes: Spectral Domain OCT (SD-OCT) and Swept Source OCT (SS-OCT). In both types of systems, light is divided into sample and reference arms of an interferometer setup, as illustrated in Fig 2. SS-OCT uses coherent and narrowband light, whereas SD-OCT systems utilize broadband, low-coherence light sources. Back scattered light, attributed to variations in the index of refraction within a sample, is recoupled into the sample arm fiber and then combined with the light that has traveled a fixed optical path length along the reference arm. A resulting interferogram is measured through the detection arm of the interferometer. The frequency of the interferogram measured by the sensor is related to depth locations of the reflectors in the sample. As a result, a depth reflectivity profile (A-scan) is produced by taking a Fourier transform of the detected interferogram. 2D cross-sectional images (B-scans) are produced by scanning the OCT sample beam across the sample. As the sample arm beam is scanned across the sample, a series of A-scans are collected to create the 2D image. Similarly, when the OCT beam is scanned in a second direction, a series of 2D images are collected to produce a 3D volume data set. With FD-OCT, 2D images are collected on a time scale of milliseconds, and 3D images can be collected at rates now below 1 second.

 

Spectral Domain OCT vs. Swept Source OCT

Spectral Domain and Swept Source OCT systems are based on the same fundamental principle but incorporate different technical approaches for producing the OCT interferogram. SD-OCT systems have no moving parts and therefore have high mechanical stability and low phase noise. Availability of a broad range of line cameras has also enabled development of SD-OCT systems with varying imaging speeds and sensitivities.

SS-OCT systems utilize a frequency swept light source and photodetector to rapidly generate the same type of interferogram. Due to the rapid sweeping of the swept laser source, high peak powers at each discrete wavelength can be used to illuminate the sample to provide greater sensitivity with little risk of optical damage.

 

FD-OCT Signal Processing

In Fourier Domain OCT, the interferogram is detected as a function of optical frequency. With a fixed optical delay in the reference arm, light reflected from different sample depths produces interference patterns with the different frequency components. A Fourier transform is used to resolve different depth reflections, thereby generating a depth profile of the sample (A-scan).

 

Doppler OCT Imaging

Doppler OCT is an extension of OCT that enables imaging of particle motion within a sample. In Fourier Domain OCT (FD-OCT) systems, there are no additional hardware requirements for implementation of Doppler imaging. Doppler OCT imaging capability is embedded in the software provided with all Thorlabs’ OCT systems and is ideal for functional vascular imaging, studying embryonic cardiac dynamics, or monitoring vascular treatment response. It is also useful for general flow velocimetry used in microfluidic channel monitoring.

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