The Siemens SOMATOM Definition System – the world’s first dual-energy computed tomography (DSCT) system – opens up a new era in medical imaging. It changes the current CT imaging system with one X-ray source and one detector used routinely to acquire CT images through two X-ray sources and two detectors. The system allows for unprecedented high quality examinations regardless of the patient’s own condition and heart rate. In addition, DSCT expands the scope of new clinical applications through dual-energy acquisition, where two X-ray sources operate at different energy settings. The technology can be applied to a large number of clinical practices, such as oncology, neurology, cardiology and acute care.
1. Scanning and Acquisition Faster than Every Heartbeat
SOMATOM Definition can image patients with rapid and irregular heart rates and those who have difficulty holding their breath, allowing cardiac studies to be completed in seconds. With the industry’s highest temporal resolution of 83 ms, the system is independent of the patient’s heart rate, enabling reliable cardiac image acquisition while avoiding beta-blockers and compelling multi-sector reconstructions. The system’s fast scanning allows for more accurate measurement of lesions, improved atheromatous plaque and stent imaging, and enhanced functional assessment.
2. Halved Radiation Dose Shows Complete Cardiac Detail
Although the SOMATOM Definition System uses two x-ray sources and twice the energy, it has the lowest radiation dose in cardiac CT scanning. This is due to its high temporal resolution, which enables the acquisition of cardiac images during a single heartbeat, thus making high-dose scanning methods using multi-sector reconstruction a thing of the past. To minimize the scan dose, the system automatically selects the fastest scan speed based on the heart rate. In addition, SOMATOM Definition employs ECG-based adaptive dose control – the industry’s most advanced ECG dose modulation technology – to minimize the radiation dose during the rapid motion phase of the heart. The combined use of these technologies doubles the image acquisition speed, while the SOMATOM Definition will deliver 50% lower radiation dose under normal heart rate conditions even when compared to the most energy efficient mono-energy CT scanners.
3.Providing one-stop emergency treatment
DSCT technology is capable of examining a large number of emergency patients with a single fastest scan and can provide excellent diagnostic image quality. The SOMATOM Definition’s 31″ (78 cm) aperture and 79″ (200 cm) scanning range allows for full-body scanning even in tall, obese patients, where the scanning range of conventional CT scans would be The range of conventional CT scans would be limited in this case. The SOMATOM Definition combines high power, high scanning speed, and the highest temporal resolution in the industry, enabling clinicians to perform timely examinations for critical emergencies.
4. (Dual) Energy CT beyond imaging significance
DSCT provides dual-energy scanning, generating different (energy data) information containing the same anatomical structure in a single scan, opening up new areas for research and clinical applications. For example, DSCT can separate anatomical structures and directly obtain separate images of bones or blood vessels with a single scan. In addition, it can further differentiate tissue types and characterize lesions, including atheromatous plaques found on cardiovascular CT scans and masses found on tumor examinations.
In September 2005, SOMATOM Definition was granted 510(k) market clearance by the U.S. Food and Drug Administration (FDA). The world’s first DSCT system is now successfully operating at the University of Erlangen, Germany. and New York University Medical Center.
Since 1998, multi-layer spiral CT has started to take off in a real sense, mainly in the increasing ability of simultaneous scanning (4 layers/loop — 6~8 layers/loop — 10~16 layers/loop — 32~40 layers/loop —-64 layers/loop), faster scanning speed (0.5s — 0.42s — 0.37s — 0.33s) image resolution Increasingly higher (Z-axis resolution: 1mm — 0.75mm — 0.6mm — 0.33mm, for example) Today, the speed and resolution of CT scans have reached unprecedented levels, which greatly meet various clinical needs, so will multi-layer spiral CT continue to develop to 128 layers, 256 layers or even more layers? In other words, is the development of CT only about the theme of “number of layers”? In fact, multi-layer spiral CT (including 64 layers and more layers and rows) of single-source CT has been facing insurmountable problems in clinical practice.
1. Effective cardiac imaging cannot be achieved at high and irregular heart rates (temporal resolution needs to be less than 100ms) When the minimum time for one rotation of the frame reaches 0.33s (SOMATOM Sensation CT), just like the infinite approach to the human body limit in the 100m race, a new limit speed has been reached for the mechanical manufacturing industry, with its high speed rotation of The centrifugal force reaches 28G and the temporal resolution of cardiac imaging reaches 165ms. l. And in order to adapt to the fluctuating heart rate situation, especially in the case of high heart rate and arrhythmia, the temporal resolution needs to be less than 100ms, when the corresponding frame rotation time must be around 0.2s and the centrifugal force will reach 75G, which is difficult to achieve and maintain with single-source CT.
2, a scan is difficult to complete the entire organ scan: all current multi-layer spiral CT are used in the scanning direction (Z-axis) of multiple rows of sub-millimeter detector combination, the maximum coverage of a single circle scan is only 20-40mm, it is difficult to complete more than the entire organ instantaneous scan. Especially for the scanning of moving organs such as the heart, the acquisition method is pitch less than 1 (pitch value is generally 0.2-0.4), i.e., multiple real-phase overlapping scanning method, which requires multiple turns to generate volumetric data for image reconstruction, but the perfusion of the whole organ over time cannot be observed by this method, and the spatial resolution of the image It is difficult to further improve the spatial resolution of the image to the level of conventional X-ray plain film.
3. Difficult to maximize the volume coverage speed and sufficient power to accomplish clear imaging: Nowadays, there is an increasing clinical need for large-area, high-velocity, ultra-thin layer scans. Previously often had to make a choice and compromise between the above three according to the actual situation, because the single-source CT scan power is limited, even though its power value is increasingly large, but the actual effective power value and reserve value is not significantly improved. For example, the scanning of obese patients often need to increase the scan dose to obtain high-quality thin layer images, but often need to sacrifice the scan speed or range.
4, the ability to distinguish between tissue structures is not enough: density resolution is the main advantage of CT imaging, but also the basic starting point of CT imaging principles. For single-source CT, density is the only basis for its ability to distinguish tissues. If density contrast is lost, it is difficult to make diagnoses and differential diagnoses – Now, with the introduction of dual-source CT technology at the 2005 annual meeting of the Radiological Society of North America (RSNA), Siemens has once again demonstrated its revolutionary innovation in technology and clinical use, going beyond the simple accumulation of scan layers (or detector rows), which has been the main competitive point of CT technology over the past few years, to redefine and redefined and reinterpreted the concept of CT. It expands the clinical applications of CT in all its aspects and takes the field of diagnostic imaging to a surprisingly high level!
The Siemens SOMATOM Definition system is the world’s first Dual Source Computed Tomography (DSCT) system, which changes the conventional use of one X-ray source and one detector for CT imaging.
With a temporal resolution of 83 ms, the SOMATOM Definition is independent of heart rate and is capable of supporting cardiac scanning at all heart rates, accomplishing everything from the assessment of acute chest pain to coronary artery imaging and cardiac function analysis. It combines a spatial resolution of less than 0.4 mm, enabling high-quality imaging of extremely small anatomical structures. With its large 78 cm frame aperture and imaging field of view, as well as its 200 cm scanning range and high voltage generator power, the system allows the most appropriate scans to be performed on acutely ill patients, regardless of patient size or physical condition – and importantly, all at extremely low doses. In addition, SOMATOM Definition expands the range of clinical applications, enabling faster, more confident diagnoses in minutes. The computer-assisted visual reading tool helps physicians perform early detection, rapid evaluation, and close follow-up of malignant disease, sometimes even before the patient is out of the examination bed. More meaningfully, the superiority of SOMATOM Definition will greatly facilitate the performance of new functions of advanced clinical examinations.
How it works
SOMATOM Definition uses two X-ray sources and two detectors simultaneously to achieve a doubling of temporal resolution, scanning speed and power, while further reducing radiation dose.
Cardiac Imaging Ideal cardiac imaging is best performed during the diastolic phase of the cardiac cycle, which becomes shorter the faster the heart rate. With single-source CT, the X-ray source/detector system would have to acquire a 180o data projection during the diastolic phase of the heart in order to complete image reconstruction. Now with dual-source CT scanners, each X-ray source/detector combination only needs to be rotated 90o to acquire superior quality cardiac images. Based on a frame rotation time of 0.33 s, dual source CT provides a temporal resolution of 83 ms and cardiac CT imaging will no longer be affected by heart rate. In addition, SOMATOM Definition uses extremely low radiation exposure doses for cardiac CT exams. Because it is a dual source CT, the CT frame only needs to be rotated 90o to acquire cardiac images of excellent quality. With real-time ECG gating, Siemens’ adaptive ECG pulse dose modulation technology adjusts accordingly to any change in heart rate. Compared to single-source CT, dual-source CT acquires cardiac images twice as fast, and with the dose modulation technology reducing high dose exposure during cardiac acquisition, it reduces the cardiac acquisition dose by more than half. Dual-source CT has very high temporal resolution, allowing cardiac images to be acquired within a single cardiac cycle at any heart rate, even in higher heart rate cases, without the need for multi-sector reconstruction (i.e., acquisition of cardiac images using data from multiple cardiac cycles). At faster heart rates, the SOMATOM Definition can increase the pitch of the scan by automatically adjusting the bed feed speed, speeding up the bed feed and reducing the exposure time accordingly. In other words, the higher the heart rate, the shorter the time required for cardiac imaging and the lower the dose required.
Scanning Obese Patients When scanning obese patients, single-source CT is often difficult to balance between scan speed and image quality. Dual-source CT overcomes the power reserve limitation with a second X-ray source. In other words, it can pool the power of two independent sources to reach an unprecedented 160 KW to provide sufficient X-ray power reserve to achieve high image quality with maximum volume coverage speed and minimum scan time, regardless of the patient’s height. At the same time, due to the increased scanning speed, the SOMATOM Definition uses higher power to improve image quality while maintaining the same dose as single source CT. In addition, the device’s large aperture design makes patient positioning easier.
Tissue differentiation Collecting as much information as possible for tissue differentiation – this has always been the goal of Siemens Medical Systems Group. Dual source CT ushers in a new era, taking CT from single tissue imaging to a new realm of tissue classification and characterization. By using two X-ray sources of different energies simultaneously, the SOMATOM Definition’s two spheres of different voltage values allow two data sets to be acquired simultaneously in a single scan. The result is that the two data sets provide different information that can be used to distinguish, identify, separate and discriminate between the imaged tissues or objects, thus obtaining more specific details of the scanned object beyond morphology. Arguably, dual-source CT lays the groundwork for a wider range of clinical applications and more recent research topics in possible areas such as direct subtraction of blood vessels or bone in scans, tumor classification in oncology, characterization of vascular plaques, and identification of the nature of body fluids in emergency medicine.
Noninvasive cardiac CT imaging is the driving force behind the development of multilayer CT technology. There are 3 challenges that need to be addressed in cardiac CT examinations: 1) breath-holding time during scanning; 2) temporal resolution; and 3) spatial resolution. Since the introduction of 64-layer CT into the clinic, cardiac CT examinations can be completed in less than 10s, and there is basically no problem for patients to hold their breath. However, in patients with high heart rates, it is often necessary to make the necessary clinical preparations or wait to ensure the success of the examination. Spatial resolution is somewhat limited in the assessment of severe coronary artery calcification or stenosis with metal stents. Temporal resolution can be achieved by both “soft” and “hard” improvements – “soft” meaning The software “multi-sector” reconstruction is performed by superimposing multiple cardiac cycles to shorten the imaging time window, which leads to a significant decrease in spatial resolution and a significant increase in dose due to the long scan time and misalignment of different cardiac cycles. ” is achieved by boosting the frame rotation speed, which requires strong hardware support, with a centrifugal force of 17 G for multilayer CT 0.42s/360º rotation and 28 G for 0.33s/360º rotation, and the experience of EBCT is that the ideal temporal resolution for freezing the heart needs to be less than 100 ms. And from the imaging In principle, modern CT for 180º data imaging requires a rotation speed of 0.2s/360º, in such a high-speed rotation of the scan, the centrifugal force will be as high as 75G, but the current mechanical industry is not yet able to meet such high requirements. Therefore, Siemens SOMATOM Definition, based on the proven SOMATOM Sensation64 technology and Straton zero-trillion spherical tube, integrates two 64-layer CT imaging systems in the frame, with significantly improved temporal resolution and conventionalized single-sector cardiac imaging. In addition to cardiac imaging, dual-source CT offers unparalleled advantages in “one-stop” emergency medicine and dual-energy subtraction imaging.
The Dual Source CT SOMATOM Definition is based on Siemens’ proven 64-layer CT technology, which provides excellent scan speed, temporal resolution and spatial resolution.
1. Straton zero-megapixel metal bulb, which resembles a compact EBCT and is 1/4 the size and weight of a conventional glass bulb, with real-time control of the tube current mA through electromagnetic deflection coils controlling the electron beam. Another important reason for using Straton bulb tube is that, to place two sets of X-ray bulb tubes and detector systems in the existing 64-layer CT rack space, the bulky ordinary bulb tube is obviously unable to do so, and the tolerance of centrifugal force under high-speed rotation is also a great challenge, which is difficult for ordinary glass bulb tubes to take up this task.
2.Electromagnetic direct drive technology, net sound scanning technology.
3.Special scattering ray correction reconstruction technology.
4, special ray dose control technology, especially the adaptive ECG gated dose control technology.