Chinese name: Shuang Yuan CT mbth: Shuang Yuan Computerized Tomography Major: medical imaging technology background, CT technology development history, DSCT development background, structure, working principle, application, radiation dose, conclusion and prospect. BACKGROUND Since British engineer Hounsfield successfully developed the first CT machine in 1972, there have been technological revolutions in the field of medical imaging again and again. Before 2004, the development of CT technology was mainly the change of the motion mode of tube and detector and the coverage of ray beam. Until 2005, Siemens introduced the world's first Shuang Yuan CT (DSCT), which further developed CT imaging technology. CT cardiovascular imaging is equivalent to digital subtraction angiography (DSA), which greatly reduces the false positive probability of conventional CT cardiovascular imaging. In 2006, China Peking Union Medical College Hospital took the lead in introducing the first Shuang Yuan CT in China. At present, in addition to some routine examinations, it is mainly used for cardiovascular examination, computer-aided detection of pulmonary nodules, chest pain triad examination, body perfusion imaging and colon virtual endoscopy. , and achieved good results. The research work mainly uses its unique dual-energy imaging technology, including the identification of the composition and nature of stones in vivo, CT reconstruction imaging of tendons and ligaments, early diagnosis of acute pulmonary embolism and so on. The development history of CT technology According to the different shapes and scanning modes of X-ray beams, the development of CT technology has undergone the following five technological changes: single-beam translation-rotation mode; Narrow fan beam translation rotation mode; Wide fan beam rotation mode; Wide fan beam static rotation mode; Electron beam CT. In the 1980 s, it was mainly the competition of scanning speed. During this period, the appearance of carbon brush and slip ring technology contributed to the birth of spiral CT and quickly replaced single cross-sectional CT. From 1990s to 265438+the beginning of 20th century, the development of CT technology aimed at increasing the vertical axis coverage, and 4/16 /32 /40-layer CT machines appeared one after another. Until 2004, Siemens introduced the world's first 64-slice spiral CT machine (SOMATOM Sensation 64). Since then, in view of the limitations of many mechanical manufacturing, many experts believe that CT machines have developed to the extreme. But the following year, Siemens introduced the world's first DSCT system (SOMATOM De finition) at the Radiology Annual Conference in North America (RSNA), which completely broke the traditional concept of CT technology and triggered a new revolution in CT history. Background of DSCT development CT has been widely used in clinical examination since its birth, especially after the appearance of spiral CT, which has been widely used in the examination and diagnosis of various parts of the human body. However, for the lungs, gastrointestinal tract, aorta and other moving organs, especially the heart, it is necessary to complete an examination within a limited time, and try not to let the patient breathe during the scanning process. Otherwise, image blur and jagged artifacts will appear in the light, and in severe cases, no diagnostic image can be obtained at all, and the inspection cannot be completed. In addition, spatial resolution is also an important parameter, which also affects the correct rate of diagnosis. In view of the above technical limitations, Siemens abandoned the traditional technical concept, and integrated two sets of 64-layer image data acquisition systems into the frame on the basis of the mature SOMATOM Sensation 64 technology and stratton zero-megabit metal tube, so that the whole frame could obtain high-quality images after 90b rotation. For 0, gantry rotation 1 cycle. 33 s, but it only needs to rotate 90b to complete the image acquisition, so its time resolution reaches 83 ms, which realizes the acquisition and reconstruction of single sector data, overcomes many disadvantages brought by "multi-sector reconstruction technology", greatly improves the image quality and improves the diagnostic accuracy. This device is the DSCT that attracts the world's attention. Figure 1 German Siemens Shuang Yuan CT structure DSCT machine basically consists of two main electrical cabinets (1 main and 1 auxiliary), a rack, a patient table, a water cooling system, an image control system and an ICS), an image reconstruction system (IRS) and an image post-processing system. The core part is mainly two independent and interrelated data acquisition systems. It is mainly composed of two independent high voltage generators A and B, two stratton zero megohm metal bulbs A and B, two groups of ultra-high speed rare earth ceramic detectors A and B, and two sets of corresponding data collectors A and B. Except for the limitation of available effective space in the rack, the two groups of detectors have different effective detection fields (FOV), other similar components are the same. There are two high-voltage generators, each with a maximum power of 80 kilowatts. When two DSCT acquisition systems work at the same time, the maximum power can reach 160kW, which is much higher than that of a common 64-slice CT machine. There are two X-ray tubes in total. Tube A and tube B are stratton zero mega metal tubes with Siemens patented technology, with maximum voltage 140kV, maximum power of 80 kW and maximum current of 666 mA, including X-ray tube assembly, deflection electronic system and cooling device. The rotor part is directly driven by the engine and is rotationally symmetrical to a great extent. The cathode is equipped with optional independent emission system and deflection electron system, which realizes the flying focusing technology in Z axis direction, and the focusing level is 0. 6 *0.6 and 0. 8 * 0.9. The cooling system is an independent mechanical component, which is different from the X-ray tube component and connected by flexible tubing. The anode target surface is in direct contact with circulating oil to realize direct cooling of the anode, and the heat capacity of the anode is as high as 6. 5 MHU/ min (4. 8 MJ/min), it can be called "zero megabyte tube". Users don't have to worry about the heat capacity of the light bulb at all, and can realize high-power and wide-range continuous scanning, and even complete the whole body scanning of the patient at one time on the premise of ensuring the spatial resolution. Two groups of ultra-high speed rare earth ceramic detectors, each group consists of 40 rows of detectors, of which 32 rows of detectors have a collimation width of 0. 6 mm in the middle, 4 rows of detectors, collimation width 1. 2 mm on both sides. One main detector group with a radian of about 60b corresponds to the light bulb A, while the other auxiliary detector group with a radian of about 32b corresponds to the light bulb B. Due to the limited space in the rack, the horizontal lengths of the two detectors are different, so the scanning coverage is also different. DSCT has a large gantry aperture of 78 cm and a scanning range of 200 cm, which expands the scope of clinical application. Like multi-spiral CT, the moving part of the gantry adopts carbon brush and low-voltage slip ring technology, but unlike them, the rotating part adopts electromagnetic direct drive technology. Working principle Two sets of X-ray generators and two sets of detector systems are installed on the same plane at a certain angle for synchronous scanning. Two sets of X-ray tubes can emit rays with the same voltage or different voltages, thus realizing data integration or separation. Different data sets have different resolution for the same organs and tissues. Through two sets of data with different energy, we can separate the tissue structure that ordinary CT can't separate or display. Namely energy imaging. If the two sets of data are scanned with the same voltage and current, the two sets of data can be integrated and the tissue structure of the same part can be obtained quickly, which breaks through the speed limit of ordinary CT. DSCT has two working modes, namely single source mode and Shuang Yuan mode, which can be set through the console. In the single source mode, the main data acquisition and reconstruction system A works, and the data acquisition and reconstruction system B closes. At this time, it is the same as the ordinary 64-slice CT machine, that is, the X-ray emitted by the tube A is received by the detector A after being attenuated by the examinee, and then the corresponding image processing and reconstruction are carried out to generate the CT image of the corresponding part. For 1 scan (i.e. 1 acquisition cycle), the tube and detector group must rotate at least 180b to obtain enough data and reconstruct the image, and a maximum of 64-slice images can be obtained. Single source mode is often used for routine plain scan and enhanced scan of positioning images, head and neck, chest, abdomen and limbs. In Shuang Yuan mode, two sets of data acquisition and reconstruction systems work at the same time, and two sets of ray tubes and detectors are combined together to independently emit and receive rays and independently complete image processing. In image reconstruction, two sets of independent images and 1 fused images can be reconstructed from the data obtained by two sets of acquisition systems. The 1 acquisition period of the former is the same as that of the single source mode, that is, the tube and detector group must rotate at least 65430. In the following 1 acquisition cycle, only the tube and the detector group need to be rotated by 90b. After corresponding mathematical operation and combination, the two sets of data obtained by the two sets of data acquisition systems can be rotated by 180b under a single source, but the time resolution is improved by 1 times, which is mainly used for examining the heart with extremely high time resolution. The application of traditional spiral CT only has a set of X-ray generator and a set of detector system, which will be inadequate when scanning high-speed moving objects (such as coronary arteries). Usually, engineers improve the ability of CT to capture moving objects by accelerating the rotation speed of CT, but limited by the industrial level and the huge centrifugal force generated by CT rotation, the fastest CT at present can only rotate once in 0.27 seconds. Shuang Yuan CT system Figure 2 Shuang Yuan CT imaging image uses two radiation sources and two detector systems at the same time, which can acquire images of the heart and coronary artery synchronized with ECG with a time resolution of 83 ms ... This system can image the heart of patients with high heart rate, arrhythmia or even arrhythmia without controlling the heart rate. At the same time, the two radiation sources can output X-rays with different energies. Dual-energy exposure technology obviously improves the tissue resolution of CT. DSCT is not much different from ordinary CT in structure, but it has incomparable advantages in some aspects of clinical application analysis. The biggest advantage of cardiac imaging DSCT is cardiac imaging. Dual energy imaging means imaging at two different energies. The basis is that different components of tissue show different CT values under different X-ray energy irradiation, and then through image fusion and reconstruction technology, CT images that can reflect the chemical components of tissue, that is, tissue characteristic images, can be obtained. Ordinary scanning For ordinary inspection, DSCT only uses data acquisition system A, and data acquisition system B is closed, which is equivalent to an ordinary 64-slice CT machine. The radiation problem of radiation dose CT has long been widely concerned. Although the existing CT equipment generally controls the radiation dose within the safe dose range, we still hope that the radiation dose during CT examination can be as low as possible. Although Shuang Yuan CT system uses two X-ray tube systems and two detector groups, the radiation dose of cardiac scanning is only 50% of that of conventional CT. Because of its high time resolution, the acquisition of cardiac images can be completed in one heartbeat, thus making the large-dose scanning method using multi-sector reconstruction a thing of the past. In addition, Shuang Yuan CT adopts adaptive dose control according to ECG to minimize the radiation dose during rapid heart movement. The comprehensive application of these technologies has improved the speed and efficiency of image acquisition by 1 times. Even compared with the single-energy scanner with the highest energy effect, the radiation dose of Shuang Yuan ct at normal heart rate will be reduced by at least 50%. Conclusion and prospect DSct is a brand-new equipment based on Siemens' mature 64-slice CT technology, which has made a higher breakthrough in scanning speed, time resolution and spatial resolution. Its overall superior performance mainly depends on Huste Raton zero trillion metal tube, electromagnetic direct drive technology, silent scanning technology, special scattering line correction and reconstruction technology, special radiation dose control technology, especially the application of adaptive ECG control dose control technology. It has incomparable advantages in coronary artery imaging and dual-energy imaging, but its clinical practical value needs a lot of clinical verification because there are many problems to be solved urgently. But on the whole, DSCT is a new revolution in CT technology, which has opened a new era in CT history.