In 1985, CT machine scanning adopted slip-ring technology to realize the feed and signal transmission between the rotating part and the stationary part. 1988, based on the increasing refinement and maturity of slip-ring technology, the spiral CT machine was successfully developed, which enabled the speed of data acquisition and the utilization of contrast agent to be improved substantially. A large range of volume scans can be performed in one screen and breath cycle, reducing motion artifacts, enabling improved image quality for multi-planar reconstruction and making three-dimensional image reconstruction possible. The efficiency of patient examination per unit time was greatly improved due to faster data acquisition. 1992 saw the introduction of CT machines with double-layer detectors. The two rows of detectors were designed in an arc shape to allow simultaneous 2-layer image count acquisition at one time, whether axial or spiral scanning, so its scan coverage was twice that of a single-layer detector, while improving image quality. The dual-detector CT machine was the forerunner of the multi-detector CT machine, and in 1998, a multi-detector CT machine was introduced that simultaneously acquired 4 layers of images at 4 times the data acquisition rate of a single-detector CT machine. In addition, multilayer CT machines that perform 2 revolutions per second are 1 times faster than most single-layer spiral CT machines, so these CT machines can scan 8 times faster than most single-layer spiral CT machines. 2000 saw the birth of CT machines that acquire 8 layers of images at once, reducing X-ray tube loss by nearly half compared to 4-layer acquisition, increasing scanning speed and detection efficiency by a factor of 1 for the same layer thickness, and reducing X-ray dose by half. It can be used for the examination of dynamic organs such as heart and large blood vessels.
In 2001, a 16-layer acquisition CT machine was launched, with the thinnest acquisition thickness of 0.5mm, realizing true isotropic voxel acquisition, and the acquisition time of 0.5s for the whole circumferential scan, which can achieve a breathless acquisition of dynamic organs such as the heart.
1.What is 16-layer CT?
16-layer spiral CT uses a conical X-ray beam and multiple rows of detectors, which greatly improves the scanning speed, and it can obtain 16 levels of images within 0.5 seconds of scanning a week. Since it is a fast volume scan, it can obtain a large amount of information in a short time with uninterrupted data acquisition over a long range of the body. After post-processing by computer, images as thin as 0.625 mm layer can be obtained not only, but also many kinds of techniques can be accomplished for imaging. Although some techniques have been accomplished on single-layer spiral CT, multi-layer spiral CT undoubtedly scans faster and makes the image quality higher. Such as three-dimensional reconstruction, without the step artifacts, the image is closer to the three-dimensional anatomical image, simulation of endoscopy is not only more “real”, and more small lesions and mucosal lesions detection rate increased.
2.How many patients can be examined by 16-layer CT in a day?
16-layer CT can scan 32 layers in 1 second, which is 16 times faster than normal CT. Normal CT can only examine 30 patients a day, while 16-layer CT can examine more than 150 patients a day.
3.What are the advantages of 16-layer spiral CT compared with conventional CT?
(1) The scanning speed can be increased by several times to tens of times depending on the scanning area. In the original cranial scan, the scanning time of each layer is 12 seconds, so it takes 120 seconds to scan a head with 10 layers, but now it only takes 4 seconds. For the chest, it took 240 seconds for 20 layers, but now it takes only 20 seconds. So agitated patients can get relatively clear images.
(2) Save the depletion of X-bulb tube, 1 rotation instead of 16 rotations in the past.
(3) The spatial resolution is improved, and the image quality is greatly improved. The original image of 7 line pairs/mm is now 24 line pairs/mm.
(4) In the past, it was a single layer scan, but now it is a volume scan. In the past, the X-ray bulb only obtained one level of image per rotation of one week, and if a thin layer was required, it was necessary to reposition the scan, but now it is a volume scan, and the application of solid self-scanning method to produce the layer thickness is the sum of the minimum layer thickness used. Therefore, while obtaining images with a layer thickness of 5 mm also obtains two layers of 2.5 mm and four layers of 1.5 mm, thus obtaining large scan coverage and uniformity of thin layer scans. In the past, we scanned the upper abdomen with 10 mm layer thickness, and then scanned the pancreas again with 2 mm layer thickness when we found problems with the pancreas, but now we do not need to do so, and we can obtain thin layer images by using the post-processing function.
(5) In the past, the thinnest layer thickness of CT was 2 mm, but now it can reach 0.625 mm, so small lesions can be clearly displayed.
(6) Enhancement examination can be set by high pressure rapid injector, and the injection and scanning time can be matched to achieve the most ideal enhancement examination. This is difficult to do with conventional CT.
(7) The dose of X-rays received by patients can be reduced by more than half, and if low-dose scanning is used, the amount of X-rays can be reduced by 90%, which can be used for the screening of lung cancer. This is definitely not possible with conventional CT.
(8) There are many software packages for post-processing, such as 3D and 4D reconstruction, evaluation of cardiac function, bone densitometry, and simulation of endoscopy, etc.
4.What are the benefits of 16-layer CT for patient examination?
The new concept of “Green Revolution of CT machine” has been realized.
(1) Safer
The biggest advantage and innovation of 16-layer CT machine is to reduce the X-ray dose to the patient during the examination and increase the safety of the patient. 16-layer CT machine adopts advanced intelligent filtering technology, automatic mA modulation and setting technology, variable speed scanning and phase selective exposure technology, automatic ECG delay algorithm technology, etc., which greatly reduces the X-ray dose during the scan.
(2) Faster
Able to carry out a rapid scan of 0.5s or less; a scan, can simultaneously obtain multiple levels of image data, significantly reducing the scanning time. For example, the lung and abdomen examination originally required 5 breaths and 120 seconds, but now 1 breath and 10 seconds can be held.
(3) More comfortable
The patient’s waiting time and examination time have been greatly reduced, and it is no longer necessary to hold the breath repeatedly during the examination, and it is no longer necessary to receive repeated scans, which is especially suitable for old and frail patients and critically ill patients.
(4) Better image quality
Good image quality is the primary prerequisite for accurate diagnosis of diseases. 16-layer spiral CT adopts a variety of state-of-the-art imaging technologies, with the thinnest examination layer thickness up to 0.625mm, and its spatial resolution and density resolution are the highest in the field of CT at present. At the same time, 16-layer spiral CT adopts the continuous volume scanning technology without interval, which greatly improves the detection rate of small lesions.
(5) More powerful image processing function
16-layer spiral CT has a very powerful image post-processing function. As long as a volume scan is performed on a patient, even if the patient leaves, we can still perform the various reconstructions needed for the image. For example, while a typical CT has a single cross-sectional image, a 16-layer spiral CT can reconstruct the image in any direction. In short, what could only be seen “horizontally” before can now be seen not only “vertically”, but also upside down, or even turned forward and backward, or turned up and down; what could not be seen before, such as blood vessels, intestines and bronchial cavities, can now also be “drilled” in to see clearly. The “drill” into the cavity to see clearly.
The special examination techniques used include: multi-plane thin-layer reconstruction technology, simulation endoscopy technology, vascular reconstruction technology (CTA), transparency technology, perfusion functional imaging technology and many other technologies.
5 .What is the difference between CT and MRI?
CT and MRI are two very different examination methods. MRI is the abbreviation of Magnetic Resnane Iamge, which is the Chinese word for Magnetic Resonance Imaging. MRI is to place the human body in a powerful magnetic field, and excite the hydrogen protons in the human body through radiofrequency pulses, and then receive the MRI signal from the protons, and after the gradient field is positioned in three directions, and then after The computer’s calculation constitutes the image of each direction.
CT can only do cross-sectional imaging because the X-ray tube and detector rotate around a certain part of the body, while MRI can do cross-sectional, sagittal, coronal and arbitrary cross-sectional imaging.
MRI can form various images from different scan sequences, such as T1-weighted image, T2-weighted image, proton density image, etc. There are also water imaging, water suppression imaging, fat suppression, diffusion imaging, spectral imaging, functional imaging, etc. CT can only discriminate tissues with density difference, and the resolution of soft tissues is not high while MRI has better resolution of soft tissues, such as muscle, fat, cartilage, and fascia with different signals. Therefore, CT and MRI are very different examination methods.
6.Can MRI replace CT?
No, MRI cannot. Although MRI has many advantages, it is a very different imaging method from CT, and the resulting images are very different.
MRI has many advantages such as multi-directional imaging, no harm to the body, better resolution of soft tissues, various imaging methods, and images that reflect not only the anatomical structure of the body, but also provide physiological, pathological, and biochemical information, and are considered to be imaging at the molecular level. Because of the long imaging time of MRI, comatose and agitated patients cannot obtain clear images, and of course patients with metallic foreign bodies in their bodies cannot access the magnetic field, which is a contraindication. Therefore, MRI examination also has insurmountable shortcomings, it cannot replace CT, and of course, CT cannot replace MRI, the two should complement each other, which is why sometimes you have to do CT after MRI, or MRI after CT.
7, Why do you advocate CT-enhanced examination?
CT scan cannot show small lesions of a few millimeters, for example, small nodules of liver cancer are often missed, and it is not easy to distinguish complex lesions. It is also possible to observe whether the blood vessels inside the lesion and the surrounding structures are altered and whether there is tumor thrombus formation inside. It is of great importance in clinical work. In many large hospitals, this examination is nearly half of the plain scan.
8.What are the general clinical applications of 16-layer CT?
For general CT, general spiral CT routine whole body examination of various diseases
9.What are the advanced clinical applications of 16-layer CT?
(1) Multiplanar thin-layer reconstruction technology (2DMPR)
With this technology, various lesions of the whole body can be reconstructed, and the fine structure of the lesion and the relationship between the lesion and the surrounding tissues such as blood vessels can be shown more clearly, which can provide more information for diagnosis. Through cross-sectional, coronal, sagittal and surface reconstruction, all organs of the body can be observed in multiple directions and from multiple angles, especially after enhancement, such as the observation of lung cancer, liver cancer, bile duct cancer, pancreatic cancer, etc.
(2) Volume rendering technology: Volume rendering VR uses all voxel CT values to perform deep and surface masking technology combined with rotation, plus pseudocolor coding and transparency technology to display surface and deep structures simultaneously. For example, in the chest, structures such as bronchi, lungs, blood vessels, and musculoskeletal structures of the chest wall are visualized, and the anatomical structures are clear and realistic at a glance. By cutting and presenting the image, the structure inside the lesion can be observed, showing its scope and morphology, such as the observation of minor rib and rib cartilage fractures and fractures of the nasal bone and mandible.
(3), volume segmentation display technology: the use of special software can be three-dimensional three-dimensional image cutting, splitting and false color processing, so that each tissue and structure and its lesion display more clearly and explicitly.
(4), real-time imaging and CT fluoroscopy
16-layer MSCT can complete a long distance scan of 150cm in less than half a minute, and can complete the scan of chest, abdomen and pelvis in one go. For example, for dynamic CT scan of the liver, it is not difficult to obtain accurate phase images such as hepatic artery phase. 1 second or sub-second acquisition of volume data line continuous imaging (continuous imaging) can display 6~8 frames in 1 second, which achieves the effect of near fluoroscopy. The effect is called CT fluoroscopy, which is useful for carrying out CT interventional techniques.
(5).Heart examination
Coronary heart disease is one of the most common diseases that endanger people’s health, and its basic lesion is coronary atherosclerosis, and the risk of soft plaque in atherosclerosis is greater than that of calcification. 16-layer spiral CT scan time can be less than 100MS, which can complete many examinations that could not be done before.
Reconstruction and post-processing techniques can directly visualize atherosclerotic soft plaques of 0.16 mm in size and are the only effective methods available today.
Coronary artery imaging (CTA): shows the main trunk and secondary branches of the coronary arteries close to DSA, but is safer, faster and less invasive than DSA.
Coronary artery endoscopic techniques: the ability to show coronary stenosis and soft plaques, etc. has shown encouraging potential.
Myocardial CT perfusion imaging technology: can show the blood supply and function of the myocardium.
(6), lung examination
Early lung cancer screening: Due to the fast scanning speed and low X-ray dose, it is increasingly used in the early lung cancer screening work;
Pulmonary function test: the use of rapid scanning to obtain the maximum inspiratory and expiratory end images of the lung, the lung function parameters can be measured, the development process of emphysema and lung function evaluation after lobectomy is significant.
Bronchial endoscopy technology: it can directly display the lesions in the bronchial lumen;
(7), gastrointestinal examination
Transparency and simulation navigation endoscopy technology: it can show the suspicious segmental structure of the inner and outer wall of the cavity, which is beneficial to the early screening of colon cancer.
(8) Simulation endoscopy technology
The simulation endoscopy (VE) function, developed by combining computer simulation technology with CT, can simulate the endoscopic examination process. It is recognized for its advantages such as non-invasive and realistic. Currently, it is possible to simulate endoscopy in almost all lumen, such as nasopharyngeal and sinusoscopy, larynx and hypopharynx, trachea, bronchoscopy, gastroscopy, colonoscopy, uroscopy, angioscopy, and middle otoscopy. Simulated bronchoscopy can show up to grade 5~6 bronchus beyond what can be observed by fiberoptic bronchoscopy, and can reveal polyp-like lesions, airway narrowing, occlusion, etc. Simulated gastroscopy and colonoscopy can also detect small polypoid lesions and can be used as a screening test. Simulated angioscopy can observe areas that cannot be examined by fiberoptic angioscopy, diagnose stenosis, atheroma and thrombus, find aneurysms larger than 3 mm in diameter, and observe endothelial flaps and openings of aortic coarctation.
(9) Vascular imaging technology (CTA)
At present, CTA shows blood vessels more perfectly than in the past, with good display of cerebral vessels, renal arteries and pulmonary arteries, but the display of small vessels is still not satisfactory. Compared with MRA, CTA gives more information, and compared with DSA, CTA does not require intubation and is less invasive. With further improvement of image resolution, it could become a more practical method for displaying blood vessels.
MSCT may show stenosis, atheroma and calcium plaques, etc. MSCT may also be useful for coronary artery calcification score.
(10), CT perfusion-functional imaging technique (cerebral perfusion imaging)
CT cerebral perfusion imaging (brain perfusion imaging) principle and method such as dynamic brain CT scan and MRI perfusion imaging. A rapid intravenous doughnut injection of contrast is followed by continuous scanning of selected levels. Using special software, time density curves, peak time, mean passage time, local cerebral blood volume, local cerebral blood flow and other parameters are obtained to provide a feasible new way to diagnose acute or hyperacute cerebral ischemic diseases, to differentiate local cerebral ischemia from cerebral infarction and to observe the microcirculation of brain tumors. Perfusion CT is also applied to the study of heart, lung, liver, kidney and other organs to observe the normal and abnormal capillary perfusion, which can help further qualitative diagnosis of lesions.