CT substitute tube technology has been playing a role in hospital imaging diagnosis for many years. With the continuous development of CT technology, its clinical significance is also constantly improving. According to the technology of X-ray CT, there are several stages that can be divided into: non slip ring CT, slip ring CT, spiral CT, and multi row spiral CT. Soon, X-ray beam CT with flat panel detectors will also be available. However, in terms of clinical function, the role played by each new technology is different, some are only a quantitative accumulation, while others constitute a qualitative leap. And we can see the development of CT technology from the perspective of performance application.
（1） Performance request oriented technology development
For hospitals, the main requirements for CT application performance are examination speed, image quality, and resolution and processing capabilities. These three aspects are the basic guarantees of clinical performance. Of course, we will also consider the scalability of the software and the issue of X-ray dosage. The inspection speed includes: scanning speed, reconstruction speed of images, and the speed at which the user operates the machine. The three factors jointly affect and check the patient's circulation volume. Among them, the improvement of scanning speed is particularly crucial. The improvement in scanning speed has brought significant changes to CT. Earlier CT scans required several tens of seconds to scan a single layer of images, and the quality of chest and abdominal images affected by respiratory movements cannot be guaranteed.
To understand and solve this problem, slip ring technology emerged, which also brought about the first qualitative advancement in CT clinical technology. The X-ray tube ball and detector of the sliding ring CT can rotate continuously in the same direction, significantly improving the scanning speed, allowing one to scan a layer of image with just one breath, ensuring image quality, significantly improving the diagnostic ability of CT in the chest and abdomen, and also improving the examination speed.
However, it is difficult to grasp the false negatives and false positives (missed or repeated scans of lesions) caused by changes in the position of organs during each breath hold when using sliding ring CT as a substitute for the balloon tube. To understand and solve this problem, it is necessary to improve the scanning speed from time to time, but the continuous stepping method of the examination bed poses a great obstacle to the progress of scanning speed. Spiral acquisition (volume acquisition) technology has addressed this challenge and brought about a second leap in CT clinical technology. Spiral CT obtains the overall volume data within the scanning range while the scanning frame rotates at a constant speed and the examination bed moves continuously at a constant speed. It can reconstruct cross-sectional images of arbitrary positions within the scanning range. This has greatly improved the continuous acquisition capability and acquisition speed of CT, relying on this technology to scan a specific area with one breath held, eliminating false negatives and false positives caused by respiratory movements. This not only provides a technical foundation for ensuring image quality and diagnostic accuracy, but also generates clinically significant analytical methods such as CTA (CT angiography), CEV (virtual endoscopy), and 3D reconstruction. Nowadays, spiral CT can achieve scanning times of 1 second or less.
The next goal is to counter the impact of cardiac pulsation, and multi detector technology and gating technology have found a solution for this. This progress is the third qualitative leap in CT clinical technology. It is impossible to complete the scanning of the heart in one cardiac cycle, but gating technology allows us to selectively remove data from the systolic phase of the heart when collecting data, so that we can select data from the same time phase in each cardiac cycle to reconstruct the image. Multi row CT scans with 4 or more layers (including 4 layers) can display coronary arteries and their branches through injection of contrast agents and gating technology. Compared with previous coronary artery examination methods, this examination is a minimally invasive examination method. Its ability to display coronary artery branches and diagnostic value for lesions have been compared and evaluated with catheterization coronary angiography and clinical comprehensive diagnosis, and it has entered the clinical application stage. The acceleration of scanning speed also occasionally improves the temporal resolution of enhanced scanning.
In order to reduce X-ray exposure, automatic milliampere control technology has been applied on CT scans. The previous automatic control method used to calculate and determine the current of each layer of scanning image based on the scanning positioning image. However, due to the difficulty in distinguishing the patient's breath holding position between the scanning positioning image and the cross-sectional image, and the significant difference in body thickness between the frontal and lateral positions of the human body, this method is not easy to maintain the stability of image quality. The new automatic milliampere control technology achieves accurate automatic control of X-ray quantity during the scanning process, through automatic reaction function and real-time adjustment of tube ball current.
The occasional acceleration of reconstruction time has improved the examination speed, and during enhanced scanning, it allows the examiner to see the scanned image as early as possible, in order to decide whether to stop scanning at other time periods. The ideal reconstruction speed is synchronous reconstruction, which means the scanning time is the same as the reconstruction time, ensuring that the examiner can immediately see all the images when the scanning is completed.
The time required to operate the machine is related to the sensitivity and convenience of the software, which is crucial for improving patient circulation. The image quality is constantly improving after years of technological development, and its spatial resolution limit is the human eye's resolution ability -0.2mm.
The progress of analytical processing ability mainly manifests in the improvement of processing speed and image display methods. In the era of rapid development of information technology, the scalability of machine software is an essential requirement for users.
The existing multi row spiral CT substitute tubes have been developed from single row to 64 row detectors, constantly improving scanning speed, image quality, and analytical processing capabilities. However, due to the conical shape of the rays emitted by the X-ray tube ball, the detector being too wide can cause the image near the edge to tend from an ideal cross-section to a funnel-shaped shape, which limits the width of the detector and also limits the leap in scanning speed.
To address this issue, some manufacturers are discussing cone beam CT for flat panel detectors. Believing in the constant progress of technology will bring us one surprise after another.
（2） Clinical demand oriented CT market
The technology of CT is advancing rapidly, and we roughly classify the existing CT in the market into three categories based on clinical needs:
(1) CT scans that meet the needs of regular clinical examinations. Like regular sliding ring CT scans.
(2) Fast speed, high image quality, suitable for all examinations except cardiovascular CT. For spiral CT scans with a scanning time of 1 second or less and below 4 rows. In terms of checking patient flow, there is no significant difference between single row and 4-row CT scans (taking 50 people per day and each person scanning 30 layers as an example, the scanning time for a 1-second single row CT scan is only 25 minutes. A faster scanning speed is only saving more than 25 minutes per day.)
(3) Not only does it require fast examination speed and high image quality, but it also needs to meet the requirements of CT for cardiovascular examination, that is, multi slice CT with 4 rows or more (including 4 rows), which requires gating technology.
The type of CT to purchase is not only related to the level of the hospital, but also to the hospital's purchasing ability and clinical needs. Hospitals should choose equipment based on their own research, teaching, and clinical needs. Regarding most hospitals in our country, spiral CT between 1-second single row and sub second 4-layer multi row can meet clinical needs. As for large hospitals with higher demand for multi row CT scans and scientific research and teaching tasks, due to the large number of patients undergoing CT examinations, it is not enough to meet the demand with just one multi row spiral CT. Often, a spiral CT with less than four rows is also needed at the same time. Therefore, the demand for spiral CT between single row 1-second to sub second 4-layer multi row will be high in the Chinese market in recent years. Of course, some hospitals may also consider ensuring that their technology does not fall behind during the service life, but the term "not falling behind" here should be compared to the development of the hospital, rather than compared to the development of CT technology. We believe that it is an advanced device that can always meet the clinical needs of the hospital within its normal service life.
Nowadays, competition among domestic hospitals is also very fierce, forming a competitive understanding of purchasing equipment. The central government's formulation of charging standards for CT substitute tube examinations will also guide the standardization of hospital equipment procurement. It is not easy for some hospitals to apply for funding from their superiors at once, so they try to purchase equipment as much as possible within the scope of funding. Due to numerous reasons, some hospitals have purchased equipment that exceeds their practical needs, resulting in some advanced equipment not fully utilizing its performance and causing a certain level of resource waste. The phenomenon of inadequate allocation of these resources will be improved with the institutional changes of the country and the strengthening of people's economic awareness from time to time.