🧬 biology

Quantitative method for evaluating nonstandard tissue absorption characteristics using synergetic near-infrared laser thermography and analytical modeling tools

This paper presents a novel synergetic method combining near-infrared laser thermography and analytical modeling to accurately evaluate the absorption characteristics of nonstandard internal tissues, such as porcine tongue mucosa, demonstrating results comparable to conventional spectrophotometry.

Original authors: Xin Tan, Sandhya Vasudevan, Ilyas Saytashev, Devashish Shrivastava, Ilko Ilev

Published 2026-06-25

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Xin Tan, Sandhya Vasudevan, Ilyas Saytashev, Devashish Shrivastava, Ilko Ilev

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

The Big Picture: A Missing Safety Manual

Imagine you have a very powerful flashlight (a laser) that doctors use to treat or diagnose problems inside the body. We have a very detailed "safety manual" for shining this light on your skin and your eyes. We know exactly how long you can look at it or how close you can hold it before it gets too hot and causes a burn.

However, there is no safety manual for the inside of the body—places like the tongue, the brain, or the kidneys. The authors call these "nonstandard tissues." Because we don't have a manual for these places, doctors often have to guess, using the rules for skin or eyes, which might be too strict or just plain wrong.

The goal of this paper is to create a new, smart way to figure out exactly how much heat these internal tissues absorb when hit by a laser, so we can eventually write a better safety manual for them.

The Problem: We Can't See Inside the "Black Box"

To know if a laser is safe, we need to know how much energy the tissue "eats" (absorbs) and turns into heat.

The Old Way: Usually, scientists take a piece of tissue, slice it very thin, and shine light through it in a lab machine (a spectrophotometer) to measure absorption. It's like trying to figure out how much water a sponge holds by squeezing it dry and weighing the water.
The Issue: This is hard to do for internal tissues because they are messy, wet, and hard to slice perfectly without damaging them. Plus, we don't have a big database of these numbers for internal organs.

The New Solution: The "Cooking & Guessing" Game

The authors invented a new method that combines real-life cooking with computer guessing. They call this a "synergetic" method, which is just a fancy way of saying the two parts work better together than apart.

Here is how their experiment worked, using the analogy of cooking a steak:

The Setup (The Pan): They used fresh pig tongues (because pig tongues are very similar to human tongues). They kept the tongue warm in a bath of salty water to mimic the body's temperature.
The Heat Source (The Burner): They shined a specific type of near-infrared laser (980 nm) onto the tongue for 90 seconds. They tried different power settings, from a gentle simmer (250 mW) to a high flame (1 Watt).
The Thermometer (The Infrared Camera): Instead of sticking a probe into the meat, they used a high-tech infrared camera to watch the surface of the tongue. They watched how fast the surface got hot and how the heat spread out, like watching a heat map on a cooking show.
The Computer Chef (The Simulation): At the same time, they ran a computer simulation (using software called COMSOL). They told the computer: "Here is the laser power, here is the tissue size, and here is the heat we saw. Now, guess the 'absorption coefficient' (how hungry the tissue is for laser energy) that would make the computer produce the exact same heat map we saw in real life."

The "Aha!" Moment: The Two Methods Agree

To make sure their new "Cooking & Guessing" method was actually working, they did a double-check:

Method A (The New Way): They used the laser and the computer to guess the absorption number.
Method B (The Old Way): They took the same tissue and measured it with the traditional slicing machine (spectrophotometer).

The Result: The numbers were almost identical!

The old machine said the tissue absorbed 71.57 units of energy.
The new laser-computer method said 72.75 units.
The difference was only 1.6%.

Think of it like two different chefs tasting a soup. One tastes it directly (the old machine), and the other tastes the steam rising from the pot and guesses the salt level (the new method). If both chefs say the soup is "perfectly salty," you know the guessing method is accurate.

Why This Matters (According to the Paper)

The paper claims that this new method is a "proof-of-concept." This means they have successfully shown that:

You can figure out how much heat internal tissues absorb without having to slice them up and dry them out.
You can use a laser, a camera, and a computer to get a very accurate number for how "hungry" the tissue is for laser energy.
This gives scientists a new, independent tool to study safety for internal organs where we currently have no data.

In short: They built a new way to measure how hot internal body parts get from lasers by watching the surface heat and letting a computer do the math. It works just as well as the old, difficult way of slicing up the tissue, but it's faster and doesn't require destroying the sample. This is a crucial first step toward creating safety rules for laser treatments inside the body.

Technical Summary: Quantitative Evaluation of Nonstandard Tissue Absorption via Synergetic Thermography and Modeling

Problem Statement
The field of laser therapeutic and diagnostic devices is expanding rapidly across various medical disciplines, yet a critical gap exists in standardized safety evaluation tools for "nonstandard tissues." While recognized safety standards (such as ANSI Z136.1-2022 and IEC 60825-1:2014) provide well-established Maximum Permissible Exposure (MPE) limits for ocular and skin tissues based on decades of research, these limits do not extend to internal tissues like mucosal, brain, kidney, or cardiovascular tissues. Consequently, device evaluations for these internal applications often rely on extrapolating skin limits or applying overly conservative ocular limits. Furthermore, the development of quantitative methods to assess photothermal laser-tissue interactions in these nonstandard tissues is hindered by a lack of comprehensive databases regarding laser parameters and, specifically, tissue optical characteristics (absorption and scattering coefficients).

Methodology
To address these gaps, the authors present a proof-of-concept study utilizing a synergetic method that integrates Near-Infrared (NIR) laser thermography with computational modeling. The study focuses on nonstandard porcine tongue mucosal tissue, selected for its anatomical and optical similarity to human oral mucosa.

Sample Preparation: Fresh ex vivo porcine tongue samples were harvested, trimmed to <15 mm thickness, and maintained in a temperature-controlled saline bath to simulate physiological conditions.
Spectrophotometric Benchmarking: As a reference, optical properties were measured using a spectrophotometer with an integrating sphere. Transmittance and reflectance spectra were acquired over 700–1000 nm. Absorption ( $\mu_a$ ) and reduced scattering ( $\mu_s'$ ) coefficients were calculated using the Inverse Adding-Doubling (IAD) algorithm.
NIR Laser Thermography: A multifunctional setup irradiated the tissue with a collimated 980 nm laser beam at powers ranging from 250 mW to 1 W for 90 seconds. A high-resolution IR thermal camera (FLIR A325sc) captured spatiotemporal surface temperature distributions.
Computational Modeling: A bioheat transfer model was implemented in COMSOL Multiphysics. The model coupled the diffusion equation with the Beer–Lambert law to simulate laser energy deposition and heat distribution. Under the specific experimental conditions (surface temperature measurement of thin tissue <500 $\mu$ m), the absorption coefficient was identified as the dominant parameter driving surface heat generation.
Synergetic Analysis: The study employed a curve-fitting metric based on the Sum of Squared Errors (SSE) to iteratively adjust the absorption coefficient in the computational model until the simulated temperature curves matched the experimental thermography data.

Key Results
The study successfully demonstrated that the synergetic method could accurately derive tissue absorption characteristics without relying solely on traditional spectrophotometry.

Spectrophotometric Data: The average absorption coefficient for porcine tongue mucosa at 980 nm was determined to be 71.57 m⁻¹ (standard deviation of 3.6 m⁻¹).
Synergetic Method Data: By fitting the COMSOL simulations to the experimental thermography data across four power levels (250 mW to 1 W), the derived average absorption coefficient was 72.75 m⁻¹ (standard deviation of 1.32 m⁻¹).
Validation: The absorption coefficient obtained via the synergetic thermography/modeling approach closely matched the spectrophotometric reference, yielding a low percentage difference of 1.6%.
Statistical Consistency: The results from the synergetic method were statistically similar within 95% confidence limits, indicating the method's robustness in evaluating absorption characteristics under varying power conditions.

Significance and Claims
The paper posits that this synergetic approach offers a novel, independent, and quantitative tool for evaluating the absorption characteristics of nonstandard tissues where standard safety limits and optical databases are absent.

Methodological Validation: The close agreement (1.6% difference) between the thermography-derived values and the conventional spectrophotometric values validates the thermography/modeling approach as an accurate alternative for determining tissue optical properties.
Safety Assessment: The study demonstrates that the tissue absorption coefficient is the primary contributor to surface heat generation under the tested conditions. Therefore, accurately determining this coefficient is critical for predicting surface temperature elevations and assessing photothermal damage thresholds.
Broader Application: The authors claim this methodology can provide critical input data for computational simulations of laser-tissue interactions. This is particularly significant for the evaluation of laser safety and performance in internal organs and nonstandard tissues where current standards are undefined, potentially aiding in the development of safer diagnostic and therapeutic laser devices.

The study concludes modestly that while it focuses on porcine tongue mucosa as a proof-of-concept, the proposed test methodology holds potential for evaluating other nonstandard tissue types lacking established laser safety limits.