Does human photography belong to X-ray?

Accurately speaking, it should be said that X-ray is a way of filming.

Everyone who has been to the hospital has more or less experienced or heard of X-ray, CT, MRI, B-ultrasound and so on. These are all important medical image detection methods, which play a decisive role in the diagnosis of diseases. To be sure, each technology has its own scope of application.

X-ray imaging

The principle of X-ray imaging is based on the characteristics of X-ray itself and human tissue structure. X-rays have strong penetrability and can penetrate human tissues, but there are differences in density and thickness between human tissues. Therefore, the amount of X-rays absorbed in the process of penetration is different, and the remaining X-rays use their fluorescence effect and photosensitive effect to form images with different light and dark or black and white contrast on the screen or X-ray film. In this way, doctors can identify various tissues through X-ray examination and analyze whether the shadow is normal according to its shape and depth. The density of human tissue structure can be divided into high density (such as bone, calcification, etc. ); Medium density (such as cartilage, muscle, nerve, parenchymal organs, etc. ) and low density (such as fat, gas in respiratory tract and gastrointestinal tract, etc. When X-rays penetrate low-density tissues, less X-rays are absorbed. There are a lot of residual X-rays, which make the X-rays more sensitive and thus show shadows on the X-rays. This is because the photosensitive substance on the film is the same as the photosensitive substance on the film used in our daily photography, both of which are silver bromide. If you have some photographic knowledge, you will know that the film will produce a latent image after exposure. After developing and fixing, silver ions are reduced to silver and deposited in the film, so it is black. The unexposed silver bromide will be washed away, showing the true color of transparency. Therefore, when X-rays penetrate high-density tissues, white shadows will appear on the X-rays (that is, the transparency is high and white is relatively dark). The thickness of tissues and organs will also affect the penetration of X-rays. Thick parts absorb more X-rays, while thin parts do the opposite. For example, normal lung tissue appears black on X-rays because it contains a lot of low-density gas. At the onset of pulmonary tuberculosis, there will be moderate-density fibrous changes and high-density calcification in lung tissue, and gray shadow and white shadow will appear on X-ray films, which is helpful for diagnosis. Although modern imaging techniques, such as CT and MRI, show great advantages in the diagnosis of diseases, some parts, such as gastrointestinal tract, are still mainly examined by X-ray, and musculoskeletal system and chest are mostly examined by X-ray first. The diagnosis of brain, spinal cord, liver, gallbladder and pancreas mainly depends on modern imaging, and X-ray examination has little effect. X-rays are radioactive and can produce ionization effect. Excessive exposure to x-rays can lead to radiation damage. Although there will be no impact within the allowable range, unnecessary radiation should be avoided, especially for pregnant women and children, and special attention should be paid to protection.

Computed tomography

CT uses X-ray beam to scan a layer with a certain thickness at the examination site of human body. X-rays passing through this layer are received by detectors, converted into visible light, converted into electrical signals by photoelectric converters, and then converted into digital signals by analog-to-digital converters, and input into computers for processing, thus obtaining digital reconstructed tomographic images. Its density resolution is obviously better than that of X-ray images, which expands the scope of human examination and improves the detection rate and diagnostic accuracy of lesions. As mentioned earlier, the density of different tissues in the human body is different. The degree of absorption of X-rays is the same as that in No Wind ウ カ, which is quite similar to that in X-rays. * The black shadow on CT film also indicates low absorption area, i.e. low density area, such as lung; White shadow indicates high absorption area, that is, high density area, such as bone. But the density resolution of CT is much higher than that of X-ray images, which is its outstanding advantage. It can make the soft tissue structure with small density difference and absorption coefficient close to water form contrast and image, and can clearly show the organs composed of soft tissue such as brain, spinal cord, mediastinum, lung, liver, gallbladder, pancreas and pelvic organs and their lesions. Another breakthrough of CT is to make the so-called high density and low density have the concept of quantity, and use CT value to explain density, which X-ray film can't do. In addition, CT images are cross-sectional images, usually cross-sectional. Therefore, in order to display the whole organ, multiple continuous cross-sectional images are needed, which is why there are several small images on a CT film. CT equipment is expensive, and the inspection cost is high. The examination and diagnostic value of some parts, especially the qualitative diagnosis value, is still limited, so CT examination should not be used as a routine diagnostic means except for diseases such as brain, liver, gallbladder, pancreas and spleen.

Ultrasonic imaging

Ultrasonic wave refers to the sound wave whose vibration frequency is more than 20000 times per second and exceeds the upper limit of hearing threshold. Ultrasonic examination is the information generated by the interaction between the physical characteristics of ultrasonic waves and the acoustic characteristics of human organs and tissues, which is received and amplified to form graphs, curves or other data, thus diagnosing diseases. Human body structure is a complex medium, and various organs and tissues, including pathological tissues, have their specific acoustic impedance and attenuation characteristics. After ultrasound is injected into human body, it passes through organs and tissues with different acoustic impedance and attenuation characteristics from surface to deep, resulting in different reflections and attenuation. After the ultrasonic equipment receives the echo, according to the intensity of the echo, different light spots are displayed on the screen in turn, and the ultrasonic image can be displayed. When incident ultrasound encounters a small or large moving interface, its scattered and reflected echo will change its frequency, that is, frequency shift. This is the so-called ultrasonic Doppler effect. This characteristic can be used to observe the blood perfusion of heart, liver and kidney in real time. What we often see in the hospital is B-ultrasound, which is B-ultrasound. In fact, there are many kinds of ultrasonic equipment. B-mode ultrasonic instrument reflects echo changes with different light spots, forming a two-dimensional ultrasonic image of the section; A-type ultrasonic instrument reflects the echo with changing amplitude, which is an early product; M-mode is to obtain the echo of the moving interface through single sound beam sampling, and finally get the "distance-time" curve, such as the curve of heart valve and the curve of heart wall activity, which is the M-mode group acoustic heart field. All the above three are impulse feedback.

Acoustic mode. There is also a frequency shift echo mode, which uses Doppler effect to detect and analyze the heart and blood flow. It includes frequency shift oscillogram and color Doppler blood flow imaging, and it is a new detection technology developed in recent years. In clinic, pulse echo B-mode ultrasound is widely used, and it is mostly the core component of new advanced ultrasound equipment. Echocardiography is also a common clinical examination. In fact, it also includes many kinds, such as M-mode echocardiography and two-dimensional echocardiography (showing the spatial position and continuous relationship of heart structure). ), spectrum Doppler echocardiography and color Doppler echocardiography (showing the direction, speed and state of blood flow in cardiovascular system). Ultrasound examination has no enucleation, no pain and no ionizing radiation. It is the first choice for many internal organs and soft tissue organs, especially for the diagnosis of localized lesions of liver, kidney and other substantive organs, as well as the diagnosis of gallbladder micro-protuberance lesions and stones. It is also widely used in early pregnancy diagnosis, physical examination and cancer screening. However, due to the physical characteristics of ultrasound, its examination of bones, lungs and intestines is limited. There are many artifacts in ultrasound imaging, and the image quality is easily disturbed by gas and subcutaneous fat. Therefore, when doing gynecological or pelvic examination, you must hold your urine to fill your bladder and avoid gas interference. In addition, its display range is small, and the image integrity is not as good as CT and Mr.

MRI

Nuclear magnetic resonance, also known as magnetic resonance, is a nuclear physical phenomenon. Magnetic resonance imaging (MRI) is an imaging technique that uses the signal generated by pronucleus resonance in a strong magnetic field to reconstruct images. Magnetic resonance imaging involves many factors, more complex technology and more professional content. We'll just make a brief introduction. MR is to put the patient in a strong external magnetic field, emit radio waves, then turn off the radio waves instantly, receive the patient's magnetic resonance signal, and then reconstruct the image with the magnetic resonance signal.

We already know that the density difference of different tissues is the basis of CT imaging, and there are CT values to represent the density. However, magnetic resonance imaging has many parameters, such as T 1, T2 and spin proton density. T 1 is the longitudinal relaxation time and T2 is the transverse relaxation time. We don't need to know much about their specific contents, as long as we know that T 1, T2 and proton density are different in different organizational structures. For example, the T 1 value of normal liver is 140-70, and that of liver cancer is 300-450; Another example is that the T 1 value of the normal brain is 600, and the T2 value is 100. The normal cerebellum T 1 value is 585, and the T2 value is 90. Using this difference, we can obtain images of various normal or pathological tissues at the selected level. Like CT, MR images are black-and-white images with different gray levels, but CT only reflects tissue density, while MR images can reflect T 1, T2 or proton density. On T 1 image, fat is white shadow; Gray scale of brain and muscle images; The images of bones and air are dark. It should be noted that due to the different reflection times of T 1 and T2, the gray levels of the same organization on T 1 and T2 images may be different, or even the opposite. For example, cerebrospinal fluid appears black (low signal) on t 1 image, but white (high signal) on T2 image. The signal intensity of different pathological tissues is also different. For example, edema appears as a black shadow on the t 1 image, but as a white shadow on the T2 image. Calcified lesions were dark on T 1 and T2 images.

The anatomical structure displayed by MR is vivid, which can clearly show the diseased tissue and normal tissue. It has high contrast resolution of soft tissue and no interference of bone artifacts. It can be used for blood flow imaging without contrast agent. Its multi-parameter imaging is convenient for comparison and can obtain multi-directional imaging, which is difficult for ordinary CT. Magnetic resonance diagnosis has been widely used in clinic, especially in nervous system. However, it is not without its shortcomings, such as insensitivity to calcification, showing that bones and gastrointestinal tract have certain limitations and are interfered by MRI artifacts, motion artifacts and metal foreign body artifacts. MR equipment is expensive, the inspection cost is high, and the inspection time is long. In addition, patients with artificial metal materials such as pacemakers or aneurysm clips are forbidden to undergo MR examination. In addition, the patient has to stay still for a long time in the relatively closed scanning hole, which may bring discomfort.