Structure and function of medical diagnostic machine

Basic structure and working principle of CT machine

Basic structure and working principle of CT machine

Key words: CT machine; Computed tomography; )

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Chapter VII CT diagnosis

Computed tomography

, is a major breakthrough in the application of electronic computer and X-ray in the medical field, which makes the traditional X-ray diagnosis technology enter a new era of computer processing and TV image display. Therefore, Hounsfield, the inventor of CT, won the Nobel Prize in Medicine.

The first CT scan was 197 1, and only brain examination was done, and the effect was good. 1974 did whole body CT, and the examination extended to chest, abdomen, spine and limbs. CT shows cross-sectional images to avoid overlapping; High density resolution, clear image; This method is simple, rapid, non-invasive, painless and non-dangerous. Therefore, it has been widely used and promoted the development of medical imaging.

Section 1 Basic structure and working principle of CT machine

First, the basic structure of CT machine

Including scanning part, computer system, image display and recording system and central console (Figure 7- 1).

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Fig. 7-7-1basic structure of CT machine

Second, the working principle of CT machine

The scanning part of CT machine is mainly composed of X-ray tube and different number of detectors, which are used to collect information. X-ray beam scans the selected slice, and its intensity is absorbed and attenuated due to its interaction with tissues with different densities. The detector converts the collected X-ray signals into electrical signals, which are converted into digital signals by A/D converter, and then input into the computer for storage and processing, so as to obtain the CT values (CT numbers) of each unit volume of this layer and arrange them into a digital matrix.

(Figure 7-2). These numbers can be stored on hard disks, floppy disks and magnetic tapes.

Magnetic tape, MT), can also be printed with a printer. The digital matrix is converted into the image on the display by D/A converter, which is the cross-sectional image of this layer. Images can be shot on film by multiple cameras for film reading, archiving and consultation.

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Figure 7-2 Digital Matrix

Third, the development and types of CT machines

CT machine can be divided into skull CT machine and whole body CT machine according to its application scope. Common development generation of CT machine (G

Eneration) to express.

The first generation of CT machine adopts rotation/translation mode (rotation/translation

Mode) to scan and collect information. First, the X-ray tube and the corresponding detector perform the first synchronous parallel motion. Then, rotate 1 degree around the patient to prepare for the second scan. Repeat this process until all data are collected within the range of 180 degrees. Because the X-ray beam is pen-shaped, there are only 1-2 detectors, and less data is collected, so the scanning time of each layer is long and the image quality is poor.

The second generation CT machine is developed on the basis of the first generation CT. The X-ray beam is changed into a fan, and the number of detectors is increased to 30, which expands the scanning range and increases the collected data. Therefore, the rotation angle is increased from 1o to 23o, which shortens the scanning time and improves the image quality, but still can't completely avoid the artifacts caused by the patient's physiological movement.

The main feature of the third generation CT machine is that the number of controllers and detectors is increased to 300-800, and the X-ray tube only rotates. Therefore, more data can be collected, and the scanning time is less than 5 seconds, which greatly reduces the artifacts and obviously improves the image quality.