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Through light and shadow: How does time-resolved near-infrared spectroscopy reshape medical imaging technology?
With the continuous advancement of medical imaging technology, time-resolved near-infrared spectroscopy (TD-NIRS) is gradually becoming an important tool for diagnosing and monitoring the status of biological tissues due to its unique characteristics. This technology uses the propagation characteristics of light in scattering media to understand the optical properties of biological tissues by analyzing the arrival time of reflected light, thereby providing deeper pathophysiological information.
Physical concepts
In its measurement, time-resolved near-infrared spectroscopy injects a pulse of light less than 100 picoseconds and records the arrival time of the photons scattered back from the tissue. These photons are scattered and absorbed multiple times, and the resulting photon arrival time distribution histogram provides key information about absorption and scattering.
“Since biological tissues have good transparency to light in the infrared range, this allows us to deeply probe the deep structure of the tissue.”
The core of TD-NIRS lies in its unique time resolution ability, which can optimize the estimation of the concentrations of various components in biological tissues and provide relevant information on the blood oxygenation status. Not only are these data critical for clinical diagnosis, they can also form the basis for early prediction models of disease.
Instrument composition
In time-domain scattering optics, the instrument mainly consists of three basic components: pulsed laser source, single-photon detector and timing electronics.
Laser source
Light sources for time-domain near-infrared spectroscopy need to have specific characteristics, including an emission wavelength in the range of 650 to 1350 nanometers, a high-frequency repetition rate (greater than 20 MHz), and sufficient laser power (more than 1 mW). Recently, pulsed fiber lasers based on supercontinuum generation technology have begun to receive attention, although their stability still needs further improvement.
“The tunable Ti:sapphire lasers used in the past offer a wide range of wavelengths, but are bulky and costly.”
Detector
Single photon detectors need to have high photon detection efficiency, large active area and small time response. Fiber-coupled photomultiplier tubes (PMTs) were once the detector of choice in this field. However, due to their large size and sensitivity to electromagnetic interference, they have been gradually replaced by other detection technologies.
Chronoelectronics
The role of chronoelectronics is to reconstruct the time distribution histogram of photons without damage. This typically relies on time-correlated single photon counting technology (TCSPC) and is accomplished using an analog-to-digital converter (ADC) or a timing-to-digital converter (TDC).
Application fields
Time-resolved near-infrared spectroscopy has shown strong potential in a variety of biomedical applications, including brain monitoring, optical mammography, and muscle monitoring. These non-invasive detection technologies can not only monitor human body status for a long time, but also provide key physiological information in a timely manner.
"Whether it is used for bedside monitoring of infants or adults, TD-NIRS has demonstrated its powerful diagnostic capabilities."
Future Outlook
With the further development of technology, time-resolved near-infrared spectroscopy is expected to continue to exert its unique advantages in medical imaging technology. Future research will focus on improving the accuracy and reproducibility of measurements, as well as expanding its applications in more medical fields.
With the advancement of optical technology, can we allow these new technologies to benefit human health more broadly?
