Can optical technology really help gastrointestinal diagnosis?

Both imaging technology and endoscope technology show what people can't see directly to doctors through X-ray, ultrasonic or optical fiber technology, so that doctors no longer need to guess melons through their stomachs. The accuracy of diagnosis is incomparable with traditional medical history and physical examination. The improvement of the diagnosis level of gastrointestinal diseases in modern medicine is inseparable from the progress of optical technology.

One of the main ways to improve the diagnostic level of endoscope by optical technology is to improve the resolution. Anyone familiar with photography knows what resolution means to a camera, and resolution is also very important to an endoscope. Digital pictures with the same content can be printed larger at high resolution and smaller at low resolution. Therefore, the picture resolution of the wedding photography shop should be very high, so that the printed poster will be clear. If it is taken by an ordinary card machine, a mosaic will appear when printed to the size of a poster. If you don't know anything about photography, you must have downloaded the movie from the internet, right? There is always a difference between tens of gigabytes of high-definition movies and so-called standard-definition movies on video websites, right? In fact, endoscopic diagnosis is more like a movie, because endoscopic diagnosis is obtained in real-time dynamic observation, and the stored images are just video screenshots, which are more used for writing articles or giving speeches at meetings.

The higher the resolution of the endoscope, the more details can be displayed. What is the use of details in the diagnosis of gastrointestinal diseases? It's so useful. Friends who have paid attention to the previous articles on the diagnosis of early gastric cancer should already know that an important significance of gastroscopy is to find asymptomatic early gastric cancer. However, the area of early gastric cancer is smaller than that of late gastric cancer, and its surface is basically parallel to the surrounding normal mucosa, which is neither obvious uplift nor obvious depression. But if you look closely, you will find that this place is not the same as its surrounding environment. What is the difference? It's a small pit in the stomach. From the gastroscope, the gastric mucosa is very smooth, but when it is enlarged, or the resolution is high enough, it will be found that it is not smooth at all, and there are many regularly arranged concave holes or protruding cobblestone-like structures, which are normal gastric pits. However, the fovea of early gastric cancer became irregular or even disappeared completely because of the invasion of cancer cells. If you use an old gastroscope with low resolution, you may not find such a subtle change. The new high-resolution gastroscope, plus a large display screen, shows the pit in the stomach. Such changes are naturally easier to find. The first time I used a high-definition endoscope, it was like watching the return of the king who was depressed in high definition for the first time, and I found that every animal warrior was wearing a disgusting scarf around his neck. I watched it many times on ordinary DVD before and didn't pay attention.

Magnifying endoscope is developed on the basis of high resolution endoscope. But some of them are equipped with high-resolution endoscopes, but most of them are not. The high-resolution endoscope is auto-focusing, keeping the image clear with the distance between the target and the lens. If you want to see clearer details, you have to get closer, but if you get too close, you can't achieve autofocus, so you need to fix a focal length. When the magnifying endoscope is very close, it will start another fixed focal length, which cannot be adjusted automatically, so it is often necessary to add a transparent cap to keep the mucosa at a fixed distance from the lens when it is pressed against the gastric mucosa.

The method to improve the resolution mainly depends on the improvement of the lens. With the rapid increase of pixel value of digital camera, the pixel value of endoscope head is also increasing. From the initial hundreds of thousands to millions of pixels today. But there is another way to improve the resolution of the endoscope, and that is the light source. To observe the inside of the human body, you must provide enough light sources, otherwise it will be dark, let alone diagnose the disease, and you can't even get in. The light source of the endoscope is white light obtained by mixing red, green and blue light sources with appropriate intensity, and the absorption rate and reflectivity of each layer of gastric mucosa are different, thus forming an image. Human mucosal tissue is essentially colorless, and it is colored because there is heme in the blood. Among these three colors, red light has the longest wavelength and the strongest penetration, while blue light has the shortest wavelength and the weakest penetration. The shorter the wavelength, the smaller the pixel point and the more pixels in unit area, that is, the higher the resolution. Based on this principle, Olympus took the lead in inventing narrow-band imaging technology. When the endoscope is injected with light source, it can switch from white light to monochromatic blue light, that is, the bandwidth of the spectrum is limited in a very narrow range. This reduces the brightness, but improves the resolution.

But the significance of narrow-band imaging is not limited to this, which involves another aspect of optics, namely contrast. What is contrast? What's the point? For example, the following two pictures, each picture has a hundred points. If I ask you how many red and blue there are in the first picture, it may be difficult to answer at the moment, so I have to count them carefully. But if it is the second picture, we can easily know that there are 50 reds and 50 blues. This is because after the points are sorted and arranged neatly, the chaotic arrangement becomes layered and the interference between them is eliminated. Using white light can get an image that is consistent with the natural state, but because of the different light penetration of various colors, the light and dark information are mixed together, which may cover up some details. After the spectrum of the incident light source narrows, the light can only reach the shallow layer, so that the details of the shallow layer can be displayed more clearly without deep interference. The change of gastric concavity is in the superficial layer.

After entering 2 1 century, endoscopic technology used laser as the incident light source for the first time. In fact, this is nothing new, but a microscope commonly used in the laboratory, called laser focusing microscope, has been miniaturized and integrated with endoscope. Why use a laser? We must first know the characteristics of laser. First, compared with ordinary light, laser can reach the projection site more accurately with little divergence. Secondly, the frequency of the laser spectrum is more single, the color of the laser excited at one time is purer, and smaller pixels can be obtained. According to the first feature, the observed mucosal tissue can be scanned layer by layer, and the scanning thickness can reach only a few microns. What's the point of doing this? The significance is the same as pathological examination. Because human tissues are opaque, we can only see the surface in blocks. It is necessary to analyze the interior, cut it into thin slices, and transform the three-dimensional tissue into a two-dimensional image for observation. And depending on the second characteristic, the resolution can be improved to a higher height. Magnifying endoscope can only be magnified to more than 1000 times, and mosaic will appear, while focusing microscope endoscope can be magnified to 500 to1000 times at most, which has reached or even exceeded the magnification of ordinary microscope inspection. Not to mention the pit of the stomach, even cells and microvessels can be clearly displayed. The existing high-speed scanning probe focusing microscope endoscope can even display the dynamic video of red blood cells rolling in microvessels. This kind of situation has only been seen in science and education films before. Although the clinical function of focusing microscope is still in doubt, it is undoubtedly the ultimate display of current optical technology in endoscopy.

If the technology of lens and light source provides ammunition for the diagnosis of stomach diseases, then modern optical fiber transmission technology is the tool to launch these ammunition. As I said before, the gastrointestinal tract is dark, and if you want to see it clearly, you must have a light source. Before the optical fiber technology, the ingested light and the reflected light can only travel straight, so the endoscope can only be straight. Doing gastroscopy is like swallowing a sword in a Jianghu performance, which makes the patient's head lean back painfully, which is not safe. Colonoscopy? Don't even think about it. With the application of optical fiber technology, light can spread along curved mirror without loss, and hose endoscope can become a reality. In addition, there are digestive endoscopy, bronchoscopy, cystoscopy and so on. Also benefit from fiber optic technology.

Of course, optical technology is only used as a tool. The diagnosis of diseases must rely on the subjective judgment of doctors. For example, the changes of surface microstructure, whether it is gastric pit or colonic recess, are regular from normal, inflammatory, precancerous lesions to canceration. These laws are summarized through the long-term observation of professionals on the basis of understanding pathology, and then learned and mastered by endoscopists all over the world through academic conferences, training and publishing papers, and verified in practice. When people find that these laws are really feasible, they become words in textbooks and guides. If it is not feasible, no matter how big the blow, how many senior officials support it and win the national award, it will still be abandoned by most clinicians.

(Author: lw56 102, editor-in-chief of Healthy China People's Network, author of popular science)