DR image quality control

The specific performance of DR image quality control is as follows:

1, tube voltage (KV)

Influence of tube voltage (kV): When X-rays interact with human tissues, there are mainly two physical phenomena, namely photoelectric absorption and constance effect. These two effects have an influence on the formation of image contrast. Therefore, kV not only determines the penetration of X-rays, but also controls the contrast of images.

In low kV photography, the photon energy of X-rays is low, and the absorption of X-rays by human body is mainly photoelectric absorption. Because the effective atomic number z of human bones, muscles, fat and other tissues is very different, the photoelectric absorption increases with the increase of tissue z, so low kV photography shows high contrast image effect.

In high kV photography, the photon energy of X-rays is high, the absorption of X-rays by human body is mainly Compton effect, and the image contrast is mainly caused by the difference of tissue density. Coupled with Compton effect, scattering lines increase and image contrast decreases. Therefore, when shooting at high kV, the image shows a low contrast effect. Clinically, the contrast of images is often controlled by adjusting the value of kV.

The advantages of high kilovolt X-ray photography are:

1, rich images can be obtained, images of various structures of photographed tissues can be widely observed, more diagnostic information can be provided, and the diagnostic range can be expanded;

2. Improve the defect of great difference in image density caused by different limb thickness and tissue;

3, the milliampere second can be reduced or the irradiation time can be shortened;

4. The inspection of moving organs can reduce the image blur caused by exercise and improve the visibility of details;

5. Reduce the radiation received by the examinee.

6. Reduce the load of X-ray tube and prolong the service life of X-ray machine;

7. The improvement of exposure latitude is beneficial to the selection of photographic conditions such as tube current and exposure time.

What is a hierarchy? What is contrast?

70KV contrast 125KV: 70KV lungs are darker and thoracic vertebrae are whiter. However, at 125KV, the brightness of lung increases and that of thoracic vertebra decreases. 70KV is similar to a black-and-white image, and 125KV is similar to a gray-white image. 70KV black and white, of course, the contrast is relatively large. 125KV gray color, of course, reduces the contrast.

However, 125KV is rich in layers. When we look at 70kv lungs, we feel only black and white. When we look at 125kv lungs, we feel black, white and gray. This is the improvement of the level.

How to look at the level in the image?

125kv: You can see the bifurcation shadow of the trachea.

70kv: No shadow of tracheal bifurcation can be seen.

High kV X-ray photography avoids the defect that bone tissue completely blocks the images of other tissues in ordinary X-ray photography, thus displaying the images of other tissues with bone shadow. For high-energy X-rays generated by tube voltage above 120kV, the absorption and attenuation of matter is mainly Compton effect.

Because the probability of Compton effect has nothing to do with the effective atomic number, the image densities of bone, soft tissue and gas are similar, and even if they overlap, they will not be covered by bone shadow, so it is convenient to observe the fine structure of soft tissue or bone itself and the lumen containing gas.

High kV X-ray photography is often used for chest examination. When X-ray with tube voltage of 140kV or 150kV is used for chest radiography, lung texture or inflammatory lesions can be displayed through rib shadow; Even if mediastinum, trachea and bronchus overlap with sternum and spine, it is easy to be observed.