1、 Origin and Basic Principles of Technology
OCT (Optical Coherence Tomography) optical coherence tomography technology was first proposed by Chinese American scientists David Huang and others at the Massachusetts Institute of Technology in 1991.
The basic principle is to use a weakly coherent light interferometer to detect the backscattered or scattered signals of incident weakly coherent light at different depth layers of biological tissue. By scanning, two-dimensional or three-dimensional structural images of biological tissue can be obtained.
2、 Technological development and evolution
Time Domain Optical Coherence Tomography (TDOCT)
Characteristics: As the first generation technology of OCT, TDOCT adopts a time/space point by point scanning mechanism, which limits the imaging speed.
Principle: Use a single point detector to record the time-domain signal of low coherence interference from broadband light sources (such as superluminescent diodes). Interference signals can only be generated when the optical paths of the reference arm and the sample arm are perfectly matched. By scanning with the reference arm, the longitudinal information inside the sample can be obtained point by point.
Application: Due to its sensitivity not decreasing with depth, TDOCT is still used in situations that require a larger range, such as the anterior segment and coronary arteries.
2. Fourier Domain Optical Coherence Tomography (FDOCT)
Features: FDOCT adopts a Fourier domain parallel detection mechanism, which greatly improves imaging speed and is considered the second-generation technology of OCT.
Classification: There are roughly two implementation methods for FDOCT based on the different acquisition methods of interferometric spectral signals: Spectral Domain OCT (SDOCT) and Sweep Frequency OCT (SSOCT).
3. Spectral Domain Optical Coherence Tomography (SDOCT):
Principle: Using a linear array camera to simultaneously record low coherence interferometric spectral signals from a broadband light source, parallel acquisition of longitudinal information inside the sample is achieved through Fourier transform.
Advantages: No need for mechanical scanning of reference arms, imaging speed mainly depends on the exposure frequency of the camera, which can generally reach tens or even hundreds of kHz.
Application: It has become the mainstream technology for clinical ophthalmic applications.
4. Scanning frequency optical coherence tomography (SSOCT) technology:
Principle: Use a point detector to record the low coherence interference spectrum signal of a broadband swept frequency light source in a time-sharing manner, and achieve parallel acquisition of longitudinal information inside the sample through Fourier transform.
Advantage: The imaging speed is mainly determined by the scanning frequency of the light source. Thanks to the development of high-speed scanning frequency light source technology, this OCT technology can achieve a maximum longitudinal line scanning speed of several MHz, and has good development prospects.
3、 Technology Expansion and Application
Depth of focus extension: To solve the problem of OCT technology being difficult to analyze cellular and below scale structures and limited contrast, researchers have proposed various depth of focus extension strategies, such as using Bessel beams, conical lenses, GRIN fibers, and other technologies to achieve depth of focus extension.
Multimodal imaging: The combination of OCT technology with other imaging techniques such as Doppler technology, spectroscopy technology, polarization technology, etc., can obtain three-dimensional spatially resolved physiological functional information of biological tissues.
Application areas: OCT technology has been widely used in ophthalmology (such as retinal and choroidal imaging), dermatology, dentistry, endoscopy, and other fields, and has shown great potential in imaging of biological tissues such as coronary arteries, digestive tract, respiratory tract, cerebral cortex, cancer, and detection of certain material properties.
4、 Future Development Trends
With the continuous advancement and innovation of technology, OCT technology will continue to develop in areas such as higher resolution, faster imaging speed, and wider application range. For example, by further optimizing the performance of core components such as light sources, detectors, interferometers, etc., the overall performance and stability of OCT systems can be improved; By integrating and innovating with other imaging technologies, we aim to expand the application areas and depth of OCT technology; By introducing intelligent and automated technologies, the operational convenience and diagnostic accuracy of OCT technology can be improved.
In summary, OCT optical coherence tomography technology has undergone significant technological evolution and extensive application expansion since its development. With the continuous advancement and innovation of technology, it will continue to play an important role in the future and drive the development of related fields.