Imaging examination, as the main means of disease examination in the new era, has greatly expanded the scope of human examination, and can carry out in-depth data collection and anatomical analysis of some diseases, further enhancing the understanding of the development of human internal organs and improving the treatment methods of many diseases. In modern medicine, image examination is an important pillar.
X-ray imaging
X-ray was discovered by Roentgen in 1895. It has three characteristics: penetrability, fluorescence effect and photographic effect, which makes X-ray first used in human medical image examination.
X-ray images are composed of images with different gray levels from black to white. Images with different gray levels reflect the anatomical and pathological state of human tissue structure, that is, natural contrast. X-ray artificial contrast refers to the artificial contrast of some tissues or organs that lack natural contrast by artificially introducing a certain amount of substances higher or lower than their density.
Commonly used X-ray imaging includes perspective and X-ray photography (plain film). The main advantage of fluoroscopy is that it can rotate the patient's position, change the observation direction, and then understand the dynamic changes of various organs. However, its shortcomings are also obvious, such as insufficient observation of organs with little difference in density and thickness, low definition, and clearer plain film imaging, which can make up for the observation of organs with little difference in density and thickness and can be used as an objective record. The advantages and disadvantages of perspective and plain film are very obvious, which can be described as complementary.
CT imaging
CT uses X-ray beam to scan a certain thickness layer of human body. X-rays passing through this layer are received by the detector, converted into visible light, converted into electrical signals through photoelectric conversion, and then converted into digital by analog-digital converter, and input into the computer for processing.
CT images belong to reconstructed images, and the X-ray absorption coefficient of each voxel can be calculated by different mathematical methods.
There are three kinds of commonly used CT, spiral CT, CTA and enhanced CT.
Spiral CT scanning is realized by slip ring technology and continuous linear motion of scanning bed on the basis of rotary scanning. The tube ball rotates and the bed moves continuously at the same time, which makes the trajectory of X-ray scanning spiral, so it is called spiral scanning.
CTA is the abbreviation of CT angiography. By injecting contrast agent, the blood flow containing contrast agent passes through the target organ, and the vascular image of the scanned organ is scanned by spiral CT volume scanning and three-dimensional reconstruction, so it is often used for cardiovascular and cerebrovascular scanning.
Enhanced CT is a scanning method after intravenous injection of water-soluble organic iodine contrast agent, which can cause lesions that are not displayed or unclear on plain scan. However, it should be noted that iodine allergy test should be carried out before injection of contrast medium, and the doctor should be informed in advance if there is iodine allergy.
MRI
Magnetic resonance imaging is magnetic resonance imaging, which is called "magnetic resonance imaging" in some hospitals, but magnetic resonance imaging itself is a tomographic imaging technology that obtains electromagnetic signals from the human body and reconstructs human information, which is different from nuclear medicine. Magnetic resonance imaging (MRI) can obtain cross-sectional images in any direction, three-dimensional volume images and even four-dimensional images with spatial-spectral distribution. However, its spatial resolution is not as high as that of CT, scanning artifacts are more than that of CT, and the scanning time of each part is relatively long.
MRA: Magnetic Resonance Angiography (MRA) refers to an imaging technique that uses the magnetic resonance imaging characteristics of blood flow to display the characteristics of blood vessels and blood flow signals.
MRS: magnetic resonance spectroscopy is an inspection method to determine the molecular composition and spatial distribution by using the chemical shift phenomenon in Mr.
MRCP: short for magnetic cholangiopancreatography. It uses the principle of heavy T2WI water imaging to display the imaging technology of biliary tract and pancreatic duct, and is often used to judge the location and etiology of obstructive jaundice.
MRI water imaging: Also known as liquid imaging, weighted T2WI of prominent water signal is obtained by long TE technology, and water-containing pipeline is developed by fat suppression technology.
PET-CT imaging
PET-CT is positron emission computed tomography (PET-CT), which combines the technologies of PET and CT. PET can provide the information of pathological function and metabolic molecules, CT can provide accurate anatomical location of pathological changes, and PET-CT can combine them to obtain all sectional images of the whole body at one time.
PET-CT is sensitive, accurate, specific and localized, which is of great value for early diagnosis of tumors and brain lesions.
PET-CT can judge and differentiate tumors at an early stage, determine the pathogenic focus and lesion range, and then grade and stage tumors, guide and determine the tumor treatment plan, so PET-CT can win valuable treatment opportunities for tumor patients.
Another important judgment value of PET-CT is the examination of brain diseases, such as epilepsy and Alzheimer's disease, which can accurately locate brain lesions. Because of the difficulty in locating the focus in the examination of brain diseases, it is quite difficult to make the treatment plan. PET-CT technology can provide accurate judgment for the determination of lesions, and then solve the problem of making subsequent treatment plans.