There is a gas density shadow visible in the spinal canal. What is going on? Does anyone know the answer?

The gas density shadow in the spinal canal may be caused by trauma or other conditions. It is recommended to cooperate with orthopedic surgery for further examination and treatment.

Low-density shadow: The reason why X-rays can form an image of the human body on a screen or film is, on the one hand, based on the characteristics of X-rays, namely its penetrability, fluorescence effect and photographic effect; on the other hand, The aspect is based on the differences in density and thickness of human tissue. Due to this difference, when X-rays pass through various tissue structures of the human body, they are absorbed to different degrees, so the amount of X-rays reaching the screen or film is different. In this way, images with different black and white contrasts are formed on the screen or X-ray. For example, if bones absorb more X-rays, they will form a high-density shadow on the film, which will appear off-white. The soft tissue absorbs less and forms a low-density shadow that appears gray-black on the film. In this way, different X-rays form gray and white images on the film.

Physiology

The structure of human tissue is composed of different elements, with different densities depending on the total amount of each element in the unit volume of various tissues. The density of human tissue structures can be summarized into three categories: high-density bone tissue and calcification lesions, etc.; medium-density ones include cartilage, muscles, nerves, solid organs, connective tissue, and body fluids; low-density ones include adipose tissue and Gas present in the respiratory tract, gastrointestinal tract, sinuses and mastoid processes, etc.

Principle

When X-rays with uniform intensity penetrate tissue structures of different densities with equal thickness, they will appear due to different degrees of absorption. X-ray images with black and white (or light and dark) contrast and gradation differences are displayed on X-ray films or screens.

In the structure of the human body, the ribs of the chest have high density, absorb more X-rays, and appear as white shadows in photos; the gas contained in the lungs has low density, absorb less X-rays, and appear as dark shadows in photos. It's a low-density shadow.

When X-rays penetrate low-density tissues, less X-rays are absorbed and more X-rays remain, making the X-ray film more sensitive to light, and more metallic silver is reduced by photochemical reactions, so the X-ray film appears as a dark shadow; The fluorescent screen produces more fluorescence, so the fluorescent screen becomes brighter. High-density tissue is just the opposite

Human tissue structures and organ shapes are different, and the thickness is also inconsistent. The thick and thin parts are either clearly defined or gradually shifted. The thick part absorbs more X-rays and transmits less X-rays, while the thin part is the opposite. Therefore, the X-ray projection may have different performances. The contrast between black and white and the difference between light and dark, as well as the clear or gradual transition from black to white and from light to dark, shown on X-ray films and screens, are all related to the difference in their thickness.

When X-rays pass through the trapezoidal body, the thick part absorbs more X-rays and transmits less X-rays, which appears as a white shadow in the photo. On the contrary, the thin part appears as a black shadow. There is a clear line between white and black shadows. On the fluorescent screen, it's just the opposite. When X-rays pass through a triangular body, their absorption and imaging are similar to those of a trapezoidal body, but the black and white shadows gradually transition without clear boundaries. When X-rays pass through the tubular body, the outer part of the tubular body absorbs more X-rays and transmits less, and appears as a white shadow. The middle part appears as a black shadow, and the boundary between the white shadow and the black shadow is relatively clear. What is seen on the fluorescent screen is opposite

It can be seen that the difference in density and thickness is the basis for image contrast and is the basic condition for X-ray imaging. It should be noted that the role of density and thickness in imaging depends on which one is dominant. For example, in the chest, the ribs have high density but small thickness, while the large blood vessels of the heart have low density but large thickness. Therefore, the image of the large blood vessels of the heart is whiter than the image of the ribs. Similarly, the density of a large pleural effusion is medium, but due to its thicker thickness, its image is whiter than that of the ribs. It should be pointed out that the density of human tissue structure and the image density on X-ray films are two different concepts. The former refers to the mass of material per unit volume in human tissue, while the latter refers to the black and white of the image shown on the X-ray film. However, the density of a substance is directly proportional to its specific gravity. The density of a substance is high and its specific gravity is heavy. It absorbs a large amount of X-rays, and the image appears as a white shadow in the photo. On the contrary, the density of the substance is low, the specific gravity is small, and the amount of X-rays absorbed is small, and the image appears as a dark shadow on the photo. Therefore, although the white and black shadows in the photo are also related to the thickness of the object, they can reflect the density of the material. In terminology, high and low density are usually used to express the white and black of an image. For example, high density, medium density and low density are used to express white shadow, gray shadow and black shadow respectively, and represent the density of matter. When the density of human tissue changes, an increase or decrease in density is used to express the white and black shadows in the image.

Pathology

Pathological changes can also change the density of human tissue. For example, pulmonary tuberculosis lesions can produce moderate-density fibrous changes and high-density calcifications in originally low-density lung tissue. On chest X-rays, white shadows representing lesions appear on the background of lung shadows. Therefore, pathological changes in different tissue densities can produce corresponding pathological X-ray images. If a high-density shadow appears where there should be a low-density shadow, it indicates the possibility of a lesion. The presence of low-density shadows where there should be high-density shadows is also a symptom of disease.