How to read lung CT

How to look at the lung CT, no obvious organic lesions were found. Guidance: Hello, smoking can cause blood vessels in the trachea and affect lung gas exchange. Long-term smoking can lead to pulmonary fibrosis and vascular fragility. It is very harmful to human health. A chest X-ray cannot show the color of the lungs. If you want to see the color of the lungs, you will need a needle biopsy. You are not an adult yet, and it is recommended that you do not smoke and quit smoking as soon as possible.

CT equipment mainly consists of the following three parts:

1. The scanning part consists of an X-ray tube, a detector and a scanning frame;

2. The computer system stores and calculates the information data collected by scanning;

3. Image display and storage system, which displays the computer-processed and reconstructed images on a TV screen or captures the images with multiple cameras or laser cameras. The number of detectors has grown from the original 1 to as many as 4,800. The scanning methods have also evolved from translation/rotation, rotation/rotation, rotation/fixed to the newly developed spiral CT scan. Computers have large capacity and fast computing speed, and can reconstruct images immediately. Due to the short scanning time, motion artifacts can be avoided, such as interference from respiratory movement, which can improve image quality. The layers are continuous, so lesions will not be missed, and three-dimensional reconstruction is feasible. Injection of contrast agent for angiography can obtain CT angiography (CTA).

The scanning method used by ultra-high-speed CT scanning is completely different from the former. The scanning time can be shortened to less than 40ms, and multiple frames of images can be obtained per second. Since the scanning time is very short, movie images can be acquired and artifacts caused by motion can be avoided. Therefore, it is suitable for cardiovascular angiography and examinations of children and patients with acute trauma who cannot cooperate well.

CT value

The CT value of a substance is equal to the difference between the attenuation coefficient of the substance and the absorption coefficient of water, compared with the attenuation coefficient of water, multiplied by the graduation factor. The CT value of a material reflects the density of the material, that is, the higher the CT value of a material is, the higher the density of the material is.

That is, CT value = α × (μm-μw) / μw

α is the graduation factor. When its value is 1000, the unit of CT value is Hounsfield unit (Hu). Different tissues in the human body have different attenuation coefficients, so their CT values ​​are also different. According to the CT values, they are bone tissue, soft tissue, fat, water, and gas. The CT value of water is about 0Hu.