What Is a Multi Slice CT Scan?

With the rapid development of microelectronics and computer technology, the basic theory and settings of CT research have been improved and updated. Multi-slice csCT (MSCT), developed in 1997, is referred to as multi-slice CT ^[1] , which has a multi-row wide detector structure, and multiple levels can be obtained at the same time by a single exposure of the tube (usually 4, 8 and 16-layer) imaging system for image data.

With the rapid development of microelectronics and computer technology, the basic theory and settings of CT research have been improved and updated. Multi-slice csCT (MSCT), developed in 1997, is referred to as multi-slice CT ^[1] , which has a multi-row wide detector structure, and multiple levels can be obtained at the same time by a single exposure of the tube (usually 4, 8 and 16-layer) imaging system for image data.

Chinese name

Multislice spiral CT

Foreign name

multisliecs helieal CT, MSCT

profession

Imaging system

Multislice spiral CT background

Since spiral CT was put into clinical application in 1989, it has gradually replaced the previous tomographic CT. The advantages of spiral CT over tomographic CT are: spiral CT can continuously collect projection data, can reconstruct the volume data of the object, shorten the scanning time, improve the Z-axis resolution, and reduce motion artifacts and missed scans Can reconstruct high-quality 3D images. Multi-slice helical CT (multisliecs helieal CT) was developed on the basis of single-slice helical CT, and was first launched by Elscint in 1991. The main difference between a multi-slice spiral CT and a single-slice spiral CT is that the detector of a single-slice spiral CT is a single row and collects projection data one layer at a time, while the multi-slice spiral CT detector is multi-row and can collect Layer projection data ^[1] . The performance of multi-slice spiral CT is a step higher than that of single-slice spiral CT. The scanning coverage is larger, the scanning time is shorter, the Z-axis resolution is higher, and a better 3D reconstructed image can be obtained ^[2] . In 1998, GE, Siemens, Toshiba, and Philips introduced 4-slice spiral CT. In 2001, GE launched 8-slice spiral CT. In 2002, GE, Siemens, Toshiba, and Philips introduced 16-slice spiral CT. At present, multi-slice spiral CT scans have reached sub-second levels in one week. Multi-slice spiral CT has been used in three-dimensional imaging of the human body, angiography imaging, cardiac imaging, and cerebral perfusion imaging ^[3] , and also plays an important role in computer-aided technologies (virtual endoscope technology and radiation treatment planning).

MSCT Principles and Structural Features of Multislice Spiral CT MSCT

Compared with single-slice spiral CT (singleslice helieal CT, SSCT), the MSCT is different in design principle and structure ^[1] : In addition to the multi-row detector structure on the Z axis, there are multiple data acquisition channels, The calculation methods used for image reconstruction are also different, mainly

Internal structure of spiral CT

There have been significant improvements in scanning frames, detectors, data acquisition systems (DAS) ^[2] , image reconstruction systems, and computer systems ^[3] .

Scanning method and driving system

SSCT is a spiral scanning imaging system that uses slip ring technology and continuous advancement on the basis of rotary scanning. MSCT has two scanning methods: axial helical scanning and non-spiral scanning ^[1] . The former means that the bed surface moves while the tube is continuously rotating, and the latter means that the bed surface remains stationary while the tube is rotating. On the drive system, MSCT mostly adopts magnetic levitation technology to drive the scanning frame faster by 0.3 seconds per week, and the centrifugal force generated is 13G, and the vibration is small. These are conducive to the fast and stable precession scan of MSCT.

X-ray utilization

The MSCT produced by some companies uses fly-focus technology, which greatly improves the effective output utilization rate of X-ray tube ^[4] . If the tube is exposed once, 4 layers of scanning can be performed at the same time, that is, the utilization rate of X-rays is increased by 4 times compared with SSCT, and the life of the tube is prolonged. The reduction of the scanning time and the number of scans greatly reduces the patient's X-ray absorbed dose. At the same time, the heat capacity of the tube has also increased to 5.3 to 7.5 MHU or higher.

Design of the detector combination

The most significant difference between MSCT and SSCT is the difference in detector design. The main characteristics are three parameters ^[5] : detector array, detector accuracy, and the precession distance of 360-degree bed rotation. SSCT has only one row of detectors in the Z-axis direction, and the slice thickness is adjusted by the X-ray collimator. During the exposure, all the detectors are in the excited state, and the X-ray beam always gathers at the center of the detector, so that the detectors outside the effective layer thickness range also absorb a small amount of scattered rays, so the volume effect is significantly increased, and the edges of the image are blurred. MSCT's multi-row detectors have different design methods, which are 8, 16, 24, and 34 rows, respectively, and the detector array can be divided into fixed array and variable array ^[1] .

Data Acquisition System (DAS)

MSCT has multiple data acquisition channels, and a layer of image is generated from the data of one channel. Each channel is independently connected directly to the detector. Therefore, increasing the data acquisition channel is also important to increase the CT imaging speed ^[5] .

computer system

In addition to the high requirements of the MSCT on the tube and the detector, the computer system is also very critical ^[2] . Due to the large amount of information obtained during MSCT scanning, the computer must be fast, and some MSCT computers have a computing speed of more than 1.9 billion times per second. The larger the memory capacity, the more data can be stored, and the longer the case data can be stored. Some memory can be as high as 75GB or higher.

CT Application of Multislice Spiral CT

Multi-slice CT technology makes it possible to examine patients faster, better, and more widely, and also expands the clinical application of CT, such as isotropic imaging, musculoskeletal examination, and multi-directional reconstruction in special cases. , CT myelography, large-scale and multi-phase studies, CT angiography, cardiac evaluation, cerebral perfusion imaging, examination of large patients, evaluation of patients with acute chest pain or shortness of breath, virtual endoscopy and retrospective image fusion Layer scanning, etc. It can be said that multi-slice CT is superior to single-slice spiral CT in almost all aspects of the clinic ^[6] .

Musculoskeletal applications

Multi-slice spiral CT for bone imaging

Multi-slice spiral CT introduces the concept of isotropic imaging, which refers to using the original tomographic data to generate other orientation images with the same spatial resolution ^[7] . For small-scale scanning, isotropic imaging can use small focus exposure and ultra-thin sectioning (0.5mm). The multi-directional image obtained is comparable to the original tomography.

Cover a larger anatomical area

Many CT examinations include internal organs of the chest, abdomen, and pelvis, or imaging the entire spine. With multilayer C

Study of Multislice Spiral CT on Chest Injury

Scanning of small quasi-values and high milliseconds of T can obtain images with a large range, high space and high contrast resolution, and based on multi-layer CT axial position data, the coronal position and For sagittal images ^[8] , single-layer spiral CT is incompetent ^[6] .

CT angiography

Multi-slice CT can quickly scan a large area without loss of spatial resolution, making the carotid artery display better, the aorta, iliac artery, and femoral artery can also be observed in one scan, effectively using intravascular contrast agent ^{[ 6]} . Because multi-layer CT can choose thinner layer thickness, the vascular tree of each part can be displayed with higher contrast, which is unmatched by single-layer spiral CT ^[9] .

Cardiac evaluation

Coronary calcification indicates the possibility of coronary heart disease, and the amount of calcification is related to the severity of the disease ^[10] . Heart score is single-slice spiral CT, but multi-slice spiral CT has better temporal resolution (time resolution of four-slice CT is 0.3 seconds) ^[9] .

Brain perfusion imaging

Dynamic multi-slice CT can be used to evaluate the cerebral ischemic phase of acute stroke. The use of a full-width detector array allows a dynamic scan of 4x5mm layer thickness to improve spatial resolution and reduce image noise ^[6] .

Examination of large patients

The imaging of large or overweight patients is difficult in single-slice spiral CT, which is mainly limited by the heat capacity of the tube, and the image quality is poor. High-heat-capacity tubes and wider detector arrays configured for multi-layer CTs enable scanning of large or overweight patients to obtain high-quality images ^[6] .

Virtual endoscopy

CT virtual endoscopy has been widely used in cavity organs or organs with ducts, such as gastrointestinal tract, trachea and bronchus, urinary tract, inner ear and paranasal sinuses. Multi-slice CT allows faster, smaller quasi-values, and large-scale scanning to reduce motion artifacts and increase tissue contrast. Multi-dimensional image reconstruction can show the anatomical details of these organs. High-performance workstations combined with easy-to-use software make simulated endoscopy as a routine inspection and a powerful complement to fiber endoscopy ^[6] .

Multislice spiral CT outlook

Multi-slice CT is superior to single-slice spiral CT in almost all aspects of clinical application ^[8] . The fast scanning of multi-slice CT can be used to improve the temporal, spatial and contrast resolution of images ^[4] . In addition, multi-slice CT can be used in areas where single-slice spiral CT is limited or not applicable, such as cardiac imaging, organ perfusion imaging, and multiphase studies of blood vessels. Multi-layer spiral technology has also introduced isotropic imaging into the field of CT. It is no exaggeration to say that multi-slice spiral CT has reached the top of the new century imaging technology ^[1] .