Dual-source CT brings the third CT revolution? !

Release date: 2006-09-13

Dual-source CT brings the third CT revolution? !
At the end of 2005, Siemens released the industry's first dual-source CT, and became one of the most eye-catching new CT products at the just-concluded RSNA2005. What is the significance of this new type of CT? What impact will it have on clinical medicine? Will its emergence establish a new direction for CT development?
With a question, I started a “dual-source CT exploration tour”. As a guide and told me in detail about the relevant knowledge: Professor Ji Ji, Chairman of the China Radiological Society, Mr. Bernd Ohnesorge, Vice President of Siemens Medical CT, and Medical Care of Siemens China Ltd. Mr. Zhong Hanming, Vice President of System Group, Mr. Wei Man, General Manager of CT Products Business Development of Siemens Medical Systems Group, and Mr. Zhang Dahai, Manager of CT Sales Support Department.
In recent years, with the development of multi-slice spiral CT, cardiovascular imaging has become one of the most promising areas of CT. Cardiovascular performance has also become a topic that cannot be separated from the evaluation of multi-slice spiral CT technology. Experts' introduction to dual-source CT began with cardiovascular imaging.
CT and cardiovascular imaging are endless. The heart is a problem for radiology. For a long time, radiologists have faced a heart rate that is too fast and arrhythmia. The relative quiescent period has to rely on invasive methods such as cardiovascular imaging to obtain the desired image of the heart.
In the 1970s, when CT was first invented, it took 7 minutes for each 360-degree scan, mainly for non-sports organs in the head, lungs, and body. Except for those savage science madmen, no one would have thought of using it for heart imaging. After 30 years of fighting, the CT has developed from the original axial tomography to spiral scanning, from single-row detectors to multi-row detectors. The scanning speed is increased, and the coverage of each scan is expanded to make cardiovascular CT (CardiacCT). From the impossibility to the possibility; the development of ECG gating technology, multi-sector image acquisition algorithm and image processing technology has gradually improved cardiovascular CT. In addition, CT has the advantage over traditional cardiovascular angiography: in addition to displaying images in the lumen of the blood vessel, it can simultaneously observe the vessel wall and the outside of the tube. The current diagnosis and treatment process for cardiovascular disease is:
Primary screening such as electrocardiogram----diagnosis: cardiovascular angiography---interventional therapy.
At the end of last year, Siemens released a dual-source CT-SOMATOMDefinition that combines two sets of imaging systems, making cardiovascular CT replacement angiography a reality. This process will be changed to: electrocardiogram and other screening tests---diagnosis: cardiovascular CT -- Interventional therapy --- review: cardiovascular CT
The significance of this change is to avoid negative and invasive patients receiving unnecessary invasive examinations, which makes the examination easier, more efficient, and cost effective.
The emergence of dual-source CT is not only a breakthrough in CT design ideas, it further solves some technical problems in the past cardiovascular CT. From the explanations of experts, the author understands that its two imaging systems are in the field of cardiac CT. With its unique technical advantages, its emergence will make CT perform better in the field of cardiovascular imaging.
SOMATOMDefinition
SOMATOMDefinition is the world's first dual-source computed tomography (DSCT) system. What is a dual source? In short, the two sets of imaging systems are integrated on one device: the two detectors are at a 90-degree angle, corresponding to a single tube. But this is not a routine arithmetic problem, and its answer is not limited to one plus one. two. The addition of two sets of imaging systems not only solves some of the problems existing in CT, but also opens up more possibilities for the future.
Time resolution reaches 83ms
The most important technological advance achieved by dual-source CT is its time resolution of 83ms. But the concept of this time resolution is slightly different from the time resolution calculated by multi-sector acquisition.
Why this 83ms is so important, we must start from the following three types of CT: electron beam CT (EBCT), multi-slice spiral CT with only one imaging system (for convenience of description, hereinafter referred to as "single-source CT"), dual-source CT .
Suppose there is an x-layer CT, an x-layer image can be obtained every revolution, and a heart scan is completed, which needs to be rotated n weeks to obtain n x-layer images. Because the heart is always moving, the acquisition of each x-ray image generally selects the relative stationary phase of the end-diastolic heart, that is, 200 to 100 ms before the R wave, and the images of the entire heart can be reconstructed from the images of the relatively stationary phase. .
Electron beam CT is a type of CT dedicated to the heart. Its time resolution can reach 100ms or even higher. For any heart rate patient, it can obtain the required 1/n part of information in a cardiac cycle, but it The low spatial resolution is an expensive and technically immature device.
Single-source CT is based on Siemens' 64-slice CT-SOMATOMSensation64. Its frame rotation speed reaches the industry's fastest 0.33s/week, but it still can't get the required 1/n part of information within 100ms, as hope. When the time resolution is higher than 100ms, multi-sector acquisition method must be adopted, for example, double-sector: divide the 180-degree scanning range into 2 times, and obtain half of the 1//n part of the information each time, so that its time resolution can be It reaches 83ms (0.33s divided by 2, divided by the number of divided sectors 2). In theory, the more time sectors are divided, the higher the resolution can be. But first, the state of the heart in each cardiac cycle may not be exactly the same; secondly, the gating technique has limitations for patients with arrhythmia, so the reconstructed image may be biased; third, the more the segmented sector, the more scanning time Long, the longer the patient needs to hold his breath; finally, the radiation dose increases as the scan time increases.
The technology based on dual-source CT is also the technology of multi-slice spiral CT. The simple meaning of combining two sets of imaging systems is that the two-sector scan that was previously performed twice by a set of imaging systems becomes Simultaneous scanning by two sets of image systems, each 1/n part of the image is obtained at the same time, is the real state of scanning the instantaneous heart state. As mentioned earlier, the time resolution of dual-source CT is 83ms. This value is the same as the time resolution of the SOMATOMSensation64 just calculated for dual-sector acquisition of 83ms, but their meanings are different.
The emergence of dual-source CT is an important advance in the field of CT The emergence of dual-source CT solves some problems in CT technology, and is a very important development in the field of CT, mainly reflected in the following aspects:
1. Fast scanning speed Due to the scanning speed of 83ms, dual-source CT can image patients with too fast heart rate, irregularity and difficulty in holding their breath, complete heart research in a few seconds, and do not need to use b receptor to lower heart rate. Blockers do not have to be multi-sector acquisition and reconstruction.
2. Radiation dose halving dual-source CT uses two imaging systems to work simultaneously, but its radiation dose under normal heart rate is reduced by 50% even when compared with the most energy-efficient single-energy CT scanner. Because: First, multi-sector acquisition is not required, and heart images can be acquired during one heartbeat. Second, SOMATOMDefinition can automatically select the fastest scanning speed according to the speed of heart rate. Third, Siemens has also developed an electrocardiogram based on Adaptive dose-regulation techniques that reduce radiation dose during rapid cardiac motion. The combined use of these technologies doubles the speed of image acquisition.
3. Dual-source CT is especially suitable for emergency diagnosis and treatment. Dual-source CT technology can perform a variety of examinations for emergency patients through a quick scan, and can provide excellent diagnostic image quality. With a total energy of 160 kW, the two X-ray sources ensure excellent image quality even at the fastest scanning and bed-in speeds. With a 78cm rack aperture and a 200cm scan range, SOMATOMDefinition enables full-body scans even in patients with high obesity. This is especially important when clinically requiring a systemic examination, such as a compound trauma or a patient requiring a systemic vascular examination. SOMATOMDefinition combines high power, high scanning speed and high time resolution to enable clinicians to perform critical emergency examinations in a timely manner.
Because of these characteristics, dual-source CT not only has advantages in the diagnosis of coronary heart disease, but also its rapid scanning speed and low dose is especially suitable for patients with pediatric congenital heart disease.
Dual-source CT opens up a new field of clinical research. Dual-source CT not only greatly enhances the performance of CT in the existing fields in the above three aspects. The two imaging systems installed together bring more new opportunities for CT. Pushing the door to a new field of clinical research.
1. Dual source makes CT work in new fields such as tissue resolution. Siemens is an expert in dual-source radiation equipment. The dual C-arm vascular intervention system introduced several years ago has verified its data acquisition and processing in dual-source sources. Aspect technology.
The successful development of dual-source CT has made it possible to carry out research on technologies such as dual-energy subtraction in the field of CT. With dual energy subtraction, images of only bones can be separated as needed by one scan, and images of only blood vessels can be isolated. It can further distinguish tissue types and describe lesion characteristics, including atheromatous plaques found by cardiovascular CT. And the mass found in the tumor examination. This is the first time in CT history to make a difference in organizational resolution.
2. Cardiac systolic imaging In the past, cardiac images were diastolic images. Due to the fast scanning speed of dual-source CT, multi-sector reconstruction is not needed. At present, research institutions have used dual-source CT for systolic imaging.
The author believes that with the increasing popularity of dual-source CT in the clinic, more new research areas will be discovered. Will multi-source CT appear?
Dual-source CT has so many advantages, so is more source CT the future direction?
In the 1980s, CT systems with five detectors were conceived. Prof. Jiji told the author: “The installation of a set of imaging system, the rack will have to withstand 20G centrifugal force, Siemens' dual-source system is very clever way to solve this problem.” Mr. Zhong Hanming said: “In designing this system At the time, Siemens' Straton tube was critical because it was only 1/4 of the size and weight of a conventional tube, which is what makes dual sources possible."
Mr. Zhong continued: “There are currently no systems that can make more detectors. The main reason is that they are limited by physical factors such as limited space and centrifugal force. And dual-source CT can fully meet the requirements of the fastest heart rate, more sources. The system has no clinical need in this regard. But multi-source systems may make a difference in improving organizational resolution."
Conclusions Reviewing the history of CT, from tomography to spiral scanning is the first technological revolution. From single-row detectors to multi-row detectors is the second technological revolution. Now we have witnessed the progress from single source to dual source. Will it be the third important technological revolution of CT? !
—— Information from: World Medical Devices

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