Updated on 04.02
New Technology Overcomes Reflection and Smoke Challenges in Endoscopy
When a surgeon is performing a delicate minimally invasive procedure, the image is often marred by glaring bright spots. These are strong reflections bouncing off the moist surfaces of tissues, frequently obscuring critical blood vessels or nerves. Alternatively, the “surgical smoke” generated by electrosurgical knives cutting through tissue can quickly fill the field of view, turning the entire image hazy and blurry, as if operating behind a layer of frosted glass. This not only causes significant visual fatigue for the surgeon but also directly increases the risk of the procedure.
This is a challenge that surgeons worldwide face every day. However, a research team from Zhejiang University and Zhejiang Laboratory has just published a groundbreaking development in the prestigious journal Device that promises to fundamentally change this situation: the polarization-maintaining endoscope. This technology enables doctors to “see through” reflections and smoke, improving image clarity in smoke-affected scenes by 73%.
I. Why Does the Surgical Field of View Become Blurred in Traditional Endoscopes?
The endoscopes widely used in hospitals today are known as “white-light endoscopes.” They function like miniature cameras inserted deep into the body, emitting white light and capturing color images, which makes them highly intuitive.
However, their weaknesses are equally obvious—they are vulnerable to both “reflection” and “smoke.”
Reflection (Specular Reflection):
The surface of human tissues (such as moist organs) acts like a small mirror. When illuminated by the strong light source of the endoscope, it reflects the light directly back into the lens, creating bright, high-intensity glare spots. These specular highlights completely obscure the underlying tissue details.
Smoke:
When surgeons use energy devices such as electrosurgical knives or ultrasonic scalpels to cut tissue or achieve hemostasis, they generate smoke similar to that produced by burning materials. These tiny particles remain suspended in the confined body cavity, severely scattering the imaging light. This leads to a significant reduction in image contrast and loss of fine details across the entire field of view.
To address these challenges, scientists turned to the polarization properties of light.
In simple terms, ordinary light can be understood as a group of “waves” vibrating and propagating in all directions, whereas polarized light consists of “waves” that vibrate in only one specific direction. By exploiting this property, it is theoretically possible to distinguish between the strong light directly reflected from the tissue surface (which largely preserves its polarization) and the useful signal light scattered from deeper tissues (whose polarization is disrupted). This allows the system to filter out unwanted reflections or penetrate through smoke.
However, this promising concept was severely limited by the endoscope itself.
To withstand high-temperature and high-pressure sterilization as well as the complex environment inside the body, the frontmost lens of all medical endoscopes is sealed and protected by an extremely hard sapphire glass window. The problem lies in the fact that sapphire is a birefringent crystal. When light passes through it, the light splits into two beams traveling at slightly different speeds, introducing a “delay” that disrupts the polarization direction.
This is analogous to attempting to analyze the purity of water through a specialized filter (polarization imaging technology), only to find that the water pipe (the endoscope) itself actively stirs and muddies the water. As a result, traditional endoscopes inherently interfere with polarization imaging, rendering the technology impractical for clinical use.
II. Core Technology: Applying the “Negative Times Negative Equals Positive” Principle to Equip Endoscopes with “Polarized Sunglasses”
Since the problem is caused by the sapphire window, one might ask: why not simply replace it? The answer is no. The hardness, sealing performance, and biocompatibility of sapphire are irreplaceable and represent a critical “red line” for clinical safety.
The Zhejiang University team took a different approach and came up with an ingenious solution that uses “the enemy’s spear to attack the enemy’s shield”: birefringence compensation.
The principle is not complicated: since the birefringence effect of sapphire disrupts the polarization state of light, the team placed a crystal with the opposite and equal birefringence effect — magnesium fluoride — directly behind it. Sapphire causes the light to “split” and introduces a certain delay, while magnesium fluoride “twists” it back to its original state.
Through precise calculations and simulations, the researchers identified the optimal “golden ratio” of thicknesses between sapphire and magnesium fluoride (approximately 2.29:1). When a beam of polarized light passes sequentially through this “golden pair,” its polarization state is almost perfectly preserved, as if it had never been disturbed.
Even more impressive is that this solution offers a high tolerance for manufacturing variations. Even if there is an angular deviation of up to 2 degrees or a thickness error within 0.03 mm during installation, the performance still far exceeds that of traditional endoscopes. This makes the technology highly feasible for large-scale production.
III. Actual Performance: Reflections “Disappear Instantly,” Smoke “Seen Through,” Diagnosis “Upgraded”
The polarization-maintaining endoscope (PME) prototype, developed based on this principle, demonstrated revolutionary performance in experiments:
1. Real-time and Complete Elimination of Reflections
In oral cavity imaging experiments, the new endoscope physically eliminated 100% of reflective areas in real time without requiring any time-consuming computer processing.
In contrast, even the most advanced AI image restoration algorithms currently available take approximately 2 seconds to process a single image. They can only partially reduce reflections and often generate incorrect textures through “hallucination.” The images captured directly by PME show the true appearance of tissues without any glare.
2. Penetrating Smoke with 73% Improvement in Clarity
In mouse experiments simulating surgical smoke, the ordinary endoscope image became completely blurred. By combining its unique polarization imaging algorithm, PME accurately estimates and removes the effects of smoke, significantly improving image quality (peak signal-to-noise ratio) by 73%.
Traditional “dehazing” algorithms that rely solely on color analysis suffer from severe color distortion in comparison, and their detail recovery is far inferior to the PME solution.
3. Beyond Color: Revealing Tissue “Texture”
Traditional endoscopes act as “color cameras,” capable of showing only color and morphology. In contrast, PME functions as a “polarization camera,” detecting differences in polarization information caused by variations in microscopic tissue structures (such as collagen fiber arrangement).
This introduces an entirely new capability: identifying early pathological changes before color alterations occur. For example, in some early cancerous tissues, collagen fiber arrangements have already changed while color remains unchanged. PME can highlight these differences through polarization images, providing doctors with a critical additional dimension for diagnosis.
IV. Future Outlook: Equipping Precision Surgery with a “Wise Eye”
The core breakthrough of this research lies in its ability to achieve technological innovation without compromising the fundamental safety principles of medical devices (retaining the sapphire window). Instead, through ingenious optical design, it manages to “have the best of both worlds.”
For surgeons, this means:
➤ Greater Safety: A clearer and more stable field of view enables more precise operations, significantly reducing the risk of accidental injury to blood vessels and nerves.
➤ Higher Efficiency: It reduces the time spent repeatedly wiping the lens or waiting for smoke to dissipate due to poor visibility, thereby accelerating the surgical workflow.
➤ Greater Precision: By providing pathological information beyond traditional images, it helps surgeons more accurately determine tumor margins during procedures, enabling more complete resection. At present, the team has filed patent applications based on this research achievement. With further engineering development and clinical trials, this “China-made” polarization-maintaining endoscope technology is expected to enter operating rooms within the next few years. It will become a brighter and wiser “eye” in the hands of surgeons, allowing more patients to benefit from safer and more precise minimally invasive procedures.
This work, completed by researchers including Song Jiawei, Wang Daqian, and Zhou Changjiang, not only solves a long-standing technical challenge in the field of endoscopic imaging, but also lays an important foundation for the development of intelligent surgical systems and augmented reality surgical navigation.
Paper Information:
Song et al., "A polarization-maintaining endoscope for surgical imaging," Device 3, 100871, November 21, 2025.
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