Dual Source CT (DSCT) is a CT device that acquires images of the human body simultaneously through two X-ray bulb systems and two detector systems.
Basic introduction Chinese name ：dual-source CT Foreign name ：dual-source computer tomography Specialty ：Medical Imaging Technology Background, CT technology development history, DSCT development background, structure, working principle, set, radiation dose, conclusion and outlook, Background Since the British engineer Hounsfield developed the first CT machine in 1972, the medical imaging technology has become more and more popular. Since the development of the first CT machine by British engineer Hounsfield in 1972, there has been one technological revolution after another in the field of medical imaging. Prior to 2004, the development of CT technology was mainly a change in the way the bulb and detector moved and the coverage of the radiation beam. It was not until Siemens launched the world's first dual-source CT (dua-l source computer tomography (DSCT)) in 2005 that CT imaging technology was further developed and CT cardiovascular imaging was able to be compared with digital subtraction angiography (digital CT), which is a new technology that can be used for cardiovascular imaging. The introduction of the world's first dual source computer tomography (DSCT) enabled further development of CT imaging technology, allowing CT cardiovascular imaging to be comparable to digital subtraction angiography (DSA) and greatly reducing the chance of false positives in conventional CT cardiovascular imaging. In 2006, Peking Union Medical College Hospital (PUMC) introduced China's first dual-source CT, which is currently used for cardiovascular examination, computer-aided detection of lung nodules, chest pain triad examination, body perfusion imaging and colon simulation endoscopy, in addition to some routine examinations, all of which have yielded good results. The research work carried out mainly utilizes its unique dual-energy imaging technology, including the identification of the composition and nature of stones in the body, CT reconstruction imaging of tendons and ligaments, and early diagnosis of acute pulmonary embolism. History of CT Technology The development of CT technology has been recognized as having undergone five major technological changes according to the shape of the X-ray beam and the scanning modality: single-beam translational-rotational modality; narrow sector beam-translational-rotational modality; wide sector beam-rotational-modality; wide sector beam static-rotational modality; and electron-beam CT. The 1980s were dominated by the race for scanning speed, during which the advent of carbon brush and slip ring technology led to the birth of the spiral CT, which rapidly replaced the single cross-sectional CT. Between the 1990s and the beginning of the 21st century, the development of CT technology was again characterized by an effort to increase the longitudinal coverage, with the emergence of the 4/16/32/40-slice CT machine. It was not until 2004 that Siemens introduced the world's first 64-slice spiral CT machine (SOMATOM Sensation 64). Since then, many experts thought that CT machines had reached their limits, given the many mechanical constraints. However, the following year, Siemens introduced the world's first DSCT system (SOMATOM De finition) at the Radiology Society of North America (RSNA), which completely broke the traditional concept of CT technology and triggered a new revolution in the history of CT. Background of DSCT Development CT has been used for clinical examination since its birth, especially after the emergence of spiral CT, which has been widely used for the examination and diagnosis of various parts of the human body. However, for moving organs such as the lungs, gastrointestinal tract, aorta, and especially the heart, an examination must be completed within a limited time, and the patient must not breathe during the scanning period as much as possible. Otherwise, blurred images and jagged artifacts may occur, or in severe cases, no diagnostic image is obtained and the examination cannot be completed. In addition, spatial resolution is an important parameter that also affects the correctness of the diagnosis. In view of the above technical limitations, Siemens set aside the traditional technical concepts and integrated two 64-layer image data acquisition systems in the rack on the basis of the proven SOMATOM Sensation 64 technology and Straton zero-megabyte metal dome, so that the entire rack can obtain a high-quality image after completing a 90b rotation. One rotation of the rack is 0.33 s, but the image acquisition can be completed after completing the 90b rotation, so its time resolution reaches 83 ms, realizing the acquisition and reconstruction of single-sector data, overcoming the many drawbacks of the "multisector reconstruction technology", greatly improving the image quality and diagnostic correctness, which is the world-famous device. Figure 1 Siemens dual-source CT structure Structure The basic structure of the DSCT machine includes two host electrical cabinets (1 main and 1 auxiliary), rack, examination bed, water-cooling system, imagecontro l system, image reconstructionsystem (IRS), and image age reconstructionsystem (IRS). imagecontro l system (ICS), image reconstructionsystem (IRS) and image post-processing system. The core part is mainly 2 sets of data acquisition systems which are both independent of each other and interconnected. There are two independent high voltage generators A and B, two Straton zero-megabit metal spheres A and B, two sets of ultra-high-speed rare-earth ceramic detectors A and B, and two sets of corresponding data acquisition devices A and B. In addition to the two sets of detectors, which are subject to the same conditions as the rack, the data acquisition system is also connected to the data acquisition system. The two sets of detectors are identical except that they have different effective fields of detection (FOV) due to the different lateral lengths of the detectors, which are limited by the available effective space in the rack. 2 high-voltage generators, each with a maximum power of 80 kW, when the DSCT 2 sets of acquisition systems work at the same time, the maximum power can reach 160 kW, much higher than the ordinary 64-slice CT machine. Two X-ray tubes, tube A and tube B, are Siemens patented Straton zero-megabit metal tubes with a maximum voltage of 140 kV, a maximum power of 80 kW and a maximum current of 666 mA, including the X-ray tube assembly, the deflection electronics system and the cooling unit. The rotor section is directly driven by the engine and is rotationally symmetrical to a large extent. The cathode, with its selectable independent emission system, deflection electronics and flying focus technology in the Z-axis direction, has a focus rating of 0.6 * 0.6 and 0.8 * 0.9. The cooling system is a separate mechanical assembly, which, unlike the X-ray tube assembly, is connected by means of a bendable oil pipe. The anode target surface is in direct contact with the circulating oil, thus realizing direct cooling of the anode, with an anode heat capacity of up to 6.5 MHU/min (4.8 MJ/min), making it a "zero megaball tube". Users no longer need to worry about the heat capacity of the bulb, and can realize high-power, wide-range continuous scanning, and even complete the whole-body scanning of the patient in one go under the premise of ensuring spatial resolution. Two sets of ultra-high-speed rare-earth ceramic detectors, each consisting of 40 rows of detectors, 32 rows in the center with a collimated width of 0.6 mm and four rows of detectors with a collimated width of 1.2 mm on each side. One main detector group with an arc of about 60b corresponds to the bulb A, and the other auxiliary detector group with an arc of about 32b corresponds to the bulb B. The main detector group with an arc of about 60b corresponds to the bulb A, and the auxiliary detector group with an arc of about 32b corresponds to the bulb B. Due to the limited space inside the rack, the two sets of detectors have different lateral lengths and therefore different scanning fields. The DSCT has a large rack aperture of 78 cm and a scanning field of 200 cm, which extends the clinical envelope. The frame motion is based on carbon brushes and low voltage slip ring technology, as in the multi-helix CT, but unlike the multi-helix CT, the rotation is based on electromagnetic direct drive technology. Principle of operation Two X-ray generators and two detector systems are mounted in the same plane at an angle for synchronized scanning. The two sets of X-ray bulbs can emit either the same or different voltages of radiation, thus enabling the integration or separation of data. Different two sets of data on the same organ and tissue resolution is not the same, through the two sets of different energy data can be separated by ordinary CT can not be separated or show the structure of the tissue. That is, energy imaging. If the two sets of data are scanned with the same voltage and current value, the two sets of data can be integrated to quickly obtain the tissue structure of the same area, breaking the speed limit of ordinary CT. The DSCT has two modes of operation, single source mode and dual source mode, both of which can be set through the console. In single-source mode, the main data acquisition and reconstruction system A is working and the data acquisition and reconstruction system B is off. This is similar to a normal 64-slice CT machine, i.e., X-rays are emitted from the bulb A, attenuated by the subject and received by the detector A, and then processed and reconstructed accordingly to produce a CT image of the corresponding part of the body. 1 scan (i.e., 1 acquisition cycle) requires a rotation of the bulb and the detector set of at least 180b in order to obtain enough data to reconstruct an image, and a maximum of 64-slice images can be obtained. Single-source mode is often used for localization images and for some routine plain and enhanced scans of the head and neck, chest, abdomen, and extremities. In dual-source mode, two sets of data acquisition and reconstruction systems work at the same time, with two sets of bulb tubes and detectors, each emitting and receiving rays independently, and completing image processing independently. However, in image reconstruction, the data obtained by the two acquisition systems can be used to reconstruct either two separate sets of images or one fused set of images, with the former being the same as in the single-source mode for one acquisition cycle, i.e., the bulb tubes and detector sets must be rotated at least 180b, which is mainly used for bone and limb reconstruction. The former is the same as the single-source mode for one acquisition cycle, i.e., the bulb tube and detector group must rotate 180b, which is mainly used for the separation of bones and calcifications, identification of tissues and collagen components, etc.; the latter needs to rotate 90b for one acquisition cycle, and the data obtained by the two sets of data acquisition systems can realize the effect of rotating 180b in the single-source mode after corresponding mathematical operations and combinations, but the time resolution has been improved by a factor of one, which is mainly used in examinations requiring extremely high time resolution, such as the examination of the heart. It is mainly used for cardiac and other examinations that require very high time resolution. Conventional spiral CT has only one X-ray generator and one detector system, so it is not capable of scanning high-speed moving objects, such as coronary arteries. Usually, engineers speed up the rotation of the CT to improve the CT's ability to capture moving objects, but due to industrial standards and the huge centrifugal force generated by the rotation of the CT, the fastest CT can only reach 0.27 seconds to rotate a circle. Dual-source CT system Figure 2 Dual-source CT imaging Simultaneous use of two radiation sources and two detector systems enables the acquisition of cardiac and coronary artery images synchronized with the ECG with a time resolution of 83ms. This system enables cardiac imaging of patients with high heart rate, irregular heart rate, and even arrhythmia without the need for heart rate control. At the same time, 2 radiation sources are capable of outputting X-rays of different energies. The tissue resolution of CT is significantly improved with dual-energy exposure technology. The DSCT is structurally similar to a conventional CT machine, but has some advantages over a conventional CT machine in terms of clinical application analysis. Cardiac imaging The greatest advantage of DSCT is in cardiac imaging. Dual energy imaging is imaging at two different energies. This is based on the idea that different tissues have different CT values when exposed to different X-ray energies, and by using image fusion and reconstruction techniques, a CT image is obtained that reflects the chemical composition of the tissue, i.e., a characteristic image of the tissue. General Scanning For general examinations, DSCT uses only Data Acquisition System A. Data Acquisition System B is turned off, which is equivalent to a normal 64-slice CT machine. Radiation Dose The issue of CT radiation has long been a concern. Although the existing CT equipment will generally control the radiation dose within the safe dose range, but we still hope that the CT examination radiation dose can be as low as possible. Although a dual source CT system uses 2 x-ray bulb systems and 2 detector sets, the radiation dose in a cardiac scan is only 50% of that of conventional CT. Due to its high temporal resolution, cardiac images can be acquired in a single heartbeat, making high-dose scanning methods utilizing multisector reconstruction a thing of the past. In addition, Dual Source CT employs ECG-based adaptive dose control to minimize the radiation dose during the rapid motion phase of the heart. The combination of these techniques has resulted in a doubling of the speed and efficiency of image acquisition, and even compared to the highest energy effect monoenergetic scanners, dual source CT will reduce the radiation dose at normal heart rate by at least 50%. Conclusion and Outlook The DSCT is a new device based on Siemens' proven 64-slice CT technology, which provides a breakthrough in scanning speed, temporal resolution, and spatial resolution. The overall superior performance of the DSCT relies on the Straton zero-megabit metal bulb, electromagnetic direct drive technology, silent scanning technology, special scatter correction reconstruction technology, and special dose modulation technology, especially the adaptive ECG gated dose modulation. Adaptive cardiac gating dose modulation techniques are applied. In terms of coronary imaging, it has the incomparable advantages of ordinary CT machines, and dual-energy imaging also has its unique advantages, but due to the many problems that need to be solved urgently, its actual clinical value still needs a lot of clinical verification. But in general, DSCT is a new revolution in CT technology, which opens a new era in CT history.