It has been many years since the CT substitute tube technology began to play a role in the imaging diagnosis of the hospital. With the continuous development of CT technology, its clinical role is also constantly improving. According to the development process of X-ray CT technology, it can be divided into several stages. : Non-slip ring CT, slip ring CT, spiral CT, multi-slice spiral CT. Soon, there will be X-ray beam CT with flat panel detectors. However, in terms of clinical function, the role of each new technology is different. There are differences, some are just the accumulation of quantity, and some constitute a qualitative leap. And we can look at the technical development of CT from the perspective of application performance.
(1) Development of performance request-oriented technology
For hospitals, the main requirements for CT application performance are: inspection speed, image quality, and analysis and processing capabilities. These three aspects are the basic guarantee of clinical performance. Of course, the scalability of software and X-ray dose issues will also be considered. The inspection speed includes: the scanning speed, the speed of reconstructing the image, and the speed at which the user operates the machine. The three together affect and check the patient's circulation. Among them, the improvement of the scanning speed is particularly critical. The improvement of the scanning speed brings changes to CT It's a big deal. The previous CT took tens of seconds to scan a layer of images, and the image quality of the chest and abdomen affected by breathing motion could not be guaranteed.
In order to solve this problem, the slip ring technology was born, which also brought the first qualitative progress in CT clinical technology. The X-ray tube and detector of the slip ring CT can always rotate in the same direction, which is a significant improvement. The scanning speed makes it possible to scan one layer of images while holding one’s breath, which ensures the image quality, significantly improves the diagnostic ability of CT in the chest and abdomen, and also improves the inspection speed.
However, the false negatives and false positives (missing or repeated scanning of lesions) caused by the positional change of the organs during each breath-hold of the slip ring CT substitute tube are difficult to grasp. In order to solve this problem, it is necessary to improve the scanning speed from time to time. , but the continuous stepping method of the examination bed constitutes a huge obstacle to the progress of the scanning speed. The spiral acquisition (volume acquisition) technology solves this problem and brings the second leap in CT clinical technology. Under the condition that the gantry rotates at a constant speed and the examination table moves at a constant speed, the overall volume data within the scanning range can be obtained, and cross-sectional images at any position within the scanning range can be reconstructed. This greatly improves the continuous acquisition capability and acquisition speed of CT. , Relying on this technology, one part can be scanned by holding one's breath, eliminating false negatives and false positives caused by breathing motion. This not only provides a technical foundation for ensuring image quality and diagnostic accuracy, but also produces CTA (CT angiography). Angiography), CEV (virtual endoscopy), 3D reconstruction and other clinically significant analytical treatment methods. Today's scanning time is within 1 second and within 1 second, spiral CT can do it.
The next purpose is to restrain the influence of cardiac beating. Multi-row detector technology and gating technology have found a reasonable solution for this. This progress is the third qualitative leap in CT clinical technology. It is impossible to scan the heart in one cardiac cycle. Complete, but gating technology allows us to selectively remove systolic data when collecting data, and even select the same phase of data in each cardiac cycle to reconstruct the image. 4 layers and above (including 4 layers) Multi-slice CT can visualize coronary arteries and their branches through injection of contrast agent and gating technology. The diagnostic value of lesions has entered the stage of clinical application after being compared and evaluated with catheter-based coronary angiography and comprehensive clinical diagnosis. The acceleration of scanning speed has also improved the temporal resolution of enhanced scanning from time to time.
In order to reduce the amount of X-ray exposure, the automatic mA control technology has been applied to CT. The previous automatic control method was to calculate and formulate the current of each layer of scanned images based on the scanning positioning image. During imaging, the position of the patient's breath-holding is difficult to differentiate. In addition, the difference in body thickness between the frontal and lateral positions of the human body is very large. This method is not easy to maintain the stability of the image quality. The new automatic mA control technology is in the process of scanning. Automatic response function, real-time adjustment of tube current, complete automatic control of accurate X-ray quantity.
The reconstruction time is constantly accelerated, which improves the examination speed, and allows the examiner to see the scanned image as soon as possible during the enhanced scan, so as to decide whether to stop the scan in other phases. The ideal reconstruction speed is synchronous reconstruction, that is, scan time and reconstruction. The time is the same to ensure that the examiner can see the image of everything immediately when the scan is completed.
The time to operate the machine is related to the sensitivity and convenience of the software, which is very important to improve the patient's circulation. The image quality is constantly improving after years of technological development, and the limit of its spatial resolution is the ability of the human eye to distinguish —— 0.2mm .
The improvement of analytical processing ability is mainly reflected in the improvement of processing speed and the way of image display. In the era of rapid development of information technology, the scalability of machine software is an indispensable requirement for users.
The existing multi-row spiral CT substitute tube has been developed from a single row to 64 rows of detectors, so that the scanning speed, image quality and analytical processing capabilities have been constantly improved. Too wide will make the image near the edge tend to be funnel-shaped from the ideal cross-section, which limits the width of the detector and limits another leap in scanning speed.
In order to deal with this problem, some manufacturers are studying the cone beam CT of flat panel detectors. I believe that the continuous progress of science and technology will bring us one surprise after another.
(2), clinical demand-oriented CT market
CT technology is developing rapidly, we roughly divide the existing CT in the market into 3 categories according to clinical needs:
(1) CT that meets the needs of ordinary clinical examinations, such as ordinary scanning slip ring CT.
(2), fast speed, high image quality, CT for all inspections except cardiovascular. For example, spiral CT with scan time of 1 second and less than 4 rows. In terms of checking the flow of patients, single row and There is no significant difference between 4-slice CT (taking 50 people every day and scanning 30 slices for each person as an example, the scanning time of 1 second single-slice CT is only 25 minutes. A faster scanning speed saves more than 25 minutes per day. )
(3) Not only fast inspection speed and high image quality are required, but also CT for cardiovascular inspection, that is, multi-slice CT with more than 4 rows (including 4 rows), requires gating technology.
What kind of CT to purchase is not only related to the level of the hospital, but also related to the hospital's purchasing ability and clinical needs. Hospitals should purchase equipment according to their own scientific research, teaching and clinical needs. For most hospitals in my country, 1 second single row Spiral CT between sub-second 4-slice multi-slice can meet clinical needs. For multi-slice CT with more demand, large hospitals with scientific research and teaching tasks, because the number of patients examined by CT is very large, only one multi-slice spiral CT is required. CT cannot meet the demand, and a helical CT with less than 4 rows is often required at the same time. Therefore, the helical CT between single row 1 second to subsecond 4 layers and multiple rows will be in great demand in the Chinese market in recent years. Of course, some hospitals will also consider to ensure that their technology does not fall behind during the service life, but the "not backward" here should be compared with the development of the hospital, not with the development of CT technology. We think , As long as the equipment can meet the clinical needs of the hospital within the normal service life of the equipment, it is an advanced equipment.
Nowadays, the competition among domestic hospitals is also very fierce, forming a comparative understanding of the purchase of equipment. The central government's formulation of the charging standards for CT substitute tube examinations will also lead to the standards for hospital purchase of equipment. Therefore, within the range allowed by funds, try to purchase the equipment as much as possible. For many reasons, the equipment purchased by some hospitals exceeds the practical needs of the hospital, resulting in some advanced equipment not fully exerting its performance, resulting in a certain level of resource waste. These The phenomenon of unreasonable allocation of resources will be improved with the institutional reform of the country and the continuous enhancement of people's economic understanding.
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