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The secret journey of light: Why can time-domain diffuse optics reveal the deep mysteries of biological tissues?
In the scientific community, exploring the mysteries of life has always been one of the greatest challenges for scientists. With the advent of time domain diffuse optics, the direction of this field has changed. This technology not only helps us understand the structure of biological tissues, but is also a key tool for future medical diagnosis. This article will explore the principles, instruments and equipment of this technology and its applications in biomedicine.
Principles of Time Domain Diffusion Optics
Time-domain diffuse optics, also known as time-resolved functional near-infrared spectroscopy, is a technique that focuses on the propagation of light in diffuse media. By emitting narrow light pulses, these light pulses will be scattered and absorbed multiple times after entering biological tissue. The arrival times of the detected photons can be recorded and converted into a histogram of the photon flight time distribution, which reveals the behavior of light in the tissue.
This technology will separate different biological tissue features and can independently extract the effects of absorption and scattering.
In diffuse media, the main phenomena affecting the motion of photons include absorption and scattering. Absorption is caused by the presence of various pigments in biological tissues, while scattering is caused by structural differences in the medium. These two factors together determine the time and intensity of the photons arriving at the detector. Therefore, by analyzing the flight time distribution, the concentration of various components in the tissue can be obtained, such as the oxygenated and deoxygenated state of hemoglobin.
Composition of instruments and equipment
Time domain diffusion optical instruments mainly consist of three key parts: pulsed laser source, single photon detector and time electronics. The performance of these components directly affects the accuracy and sensitivity of the overall system.
Pulsed laser source
The pulsed laser source used in time domain diffuse optics requires certain characteristics. Its emission wavelength should be between 650 and 1350 nanometers and ideally have a narrow half-width. In addition, the laser source needs to have a high repetition rate and sufficient laser power to ensure a good signal-to-noise ratio. With the advancement of technology, the previous adjustable-release lithium-chromium-sapphire lasers have gradually been replaced by pulsed fiber lasers.
Single Photon Detector
Detectors suitable for time domain diffusion optics require not only high efficiency and large effective area, but also good temporal response and low noise background. Traditional photomultiplier tubes are no longer the only option. The emergence of single-photon avalanche diodes and silicon photomultipliers (SiPMs) has provided more options in this field.
Time Electronics
The goal of chronotronics is to losslessly reconstruct the histogram of photon flight times. Using time-correlated single photon counting, a process that involves marking the arrival times of photons, data is collected to generate a histogram. Current electronics systems rely primarily on a combination of a time-to-digital converter (TDC) or a time-to-analog converter (TAC) and an analog-to-digital converter (ADC).
Value in biomedical applications
Time-domain diffusion optics has great potential for application in biomedicine. It can continuously and non-invasively monitor the optical properties of tissues, becoming an important tool for long-term diagnosis. This technology has been successfully applied to brain monitoring, optical mammography, and muscle monitoring, showing its potential as a clinical diagnostic.
As the academic community conducts in-depth research on this technology, we will be able to reveal more of the deep mysteries of biological tissues in the future.
The Secret Journey of Light continues to push the boundaries of medicine through the combination of technology and science. Looking to the future, we can't help but ask, how will this technology change our understanding of life?
