The main structure of CT includes two major parts: the X-ray body scanning device and computer system. The former is mainly composed of the generator and bulb tube that produce the X-ray beam, and the detector that receives and detects the X-rays; the latter mainly consists of the data acquisition system, the central processing system, the tape machine, and the operating table. In addition, the CT machine should also include image monitors, multi-frame cameras and other auxiliary equipment.
The X-ray bulb tube and the detector are installed on both sides of the scanned tissue in opposite directions. When the X-ray generated by the bulb tube passes through the scanned tissue, the remaining rays through the tissue are received by the detector. The detector is highly sensitive to X-rays, it will receive the X-rays first into an analog signal, and then converted to digital signals, input into the computer's central processing system. The processed results are sent to a tape drive for storage, or are displayed on a monitor after digital/modular processing to become a CT image, which is then photographed by multiple cameras for diagnostic purposes.
Spiral CT
Spiral CT machine is currently one of the world's most advanced CT equipment, its scanning speed, high resolution, image quality is excellent. With fast spiral scanning, it can finish checking a part in about 15 seconds, and can find lesions smaller than a few millimeters, such as small liver cancer, pituitary microadenomas and small aneurysms. Its comprehensive functions, can carry out the examination of the whole body, feasible for a variety of three-dimensional imaging, such as multi-layer reconstruction, CT angiography, organ surface reconstruction and simulation of intestinal, trachea, vascular endoscopy. It can perform real-time fluoroscopic CT-guided puncture biopsy, which is fast, convenient and accurate.
Specific uses and characteristics of spiral CT (part)
1. CT angiography of the hepatic artery shows intrahepatic blood vessels and guides interventional therapy for liver cancer.
2. Cranial scanning provides clear images without artifacts. It is superior to other CT in detecting lesions in the posterior cranial recess.
3. The image clarity of chest CT scan is significantly higher than that of other CT.
4. Liver, biliary, pancreatic, splenic, and retroperitoneal CT scans are fast to examine and have good image quality.
5. Renal, pelvic and lumbar spine CT scanning, fast examination, good image quality.
6. To show the relationship between intracranial tumor and blood vessels is crucial for surgery.
7. Small hepatocellular carcinomas that cannot be detected by CT or ultrasound are revealed under the arterial enhancement scan of spiral CT.
8. Three-dimensional reconstruction of the surface of peripheral lung and adrenal tumors shows the relationship between the tumor and blood vessels, which is conducive to surgery.
The working principle of CT
The various tissues of the human body (including normal and abnormal tissues) absorb X-rays differently, and CT makes use of this characteristic to divide a selected level of the human body into many cubic pieces, which are called voxels. x-ray passes through the human body and measures the density or gray scale of each voxel, which is the basic unit of a CT image, called a pixel. They are arranged in a row-column square matrix to form the image matrix. When an X-ray bulb sends an X-ray beam in one direction through a selected layer, each pixel arranged in that direction absorbs a portion of the X-rays to some extent, causing the X-rays to attenuate. By the time the beam penetrates the tissue level (including many voxels) and is received by the detector on the opposite side, the amount of X-rays has been attenuated so much that it is the sum of the attenuation values of all the voxels in that direction. Then the X-ray bulb tube rotates at a certain angle, and then sends out an X-ray beam in another direction, then the detector on the opposite side of the X-ray attenuation of all the voxels along the direction of the second irradiation can be measured as the sum of all the voxel X-ray attenuation values; in the same way, the same method is repeated several times in different directions on the selected level of the tissue for X-ray scanning, you can obtain a number of X-ray attenuation value sums. In the above process, an equation is obtained for each scan. The total amount of X-ray attenuation in this equation is a known value, and the X-ray attenuation values of the individual voxels that form this total are unknown. After a number of scans, you can get a joint equation, after the computer can solve this joint equation, and find out the X-ray attenuation value of each pixel, and then by the digital / analog conversion, so that different attenuation values of each pixel to form the corresponding pixel of different gray scale, the pixels formed by the matrix image that is the level of different density of the organization of the black-and-white image.
Density on CT
Analyzing a CT image is a way of observing the anatomical structure on the one hand, and understanding the density changes on the other. The latter can be known by measuring the CT value, and can also be observed by comparing with the density of the surrounding tissues. The density of tumor tissues in the human body varies according to their location, metabolism, growth and accompanying conditions, and CT has a high density resolution of the tissues and is a cross-sectional scan, which improves the accuracy of tumor diagnosis.