China News Service, Beijing, September 3rd, "Do I need a CT for the physical examination?" "Is it better to have an enhanced CT?" "I do CT so often, will it hurt my body?"...

  Now, it is the peak period of school physical examination and entry physical examination. Many people have various doubts about CT examination. How does CT work?

How to choose when to check?

A few days ago, experts from Peking Union Medical College Hospital's "'Zhihui Thoracic Surgery' Science Team" gave a detailed interpretation on this topic.

Data map: Chengdu, Sichuan, doctors discuss the patient's condition through CT images of the patient's lungs.

Photo by China News Agency reporter Liu Zhongjun

  According to Guo Chao, the attending physician of the Department of Thoracic Surgery of Peking Union Medical College Hospital, chest CT is a very broad concept. HRCT) and chest enhanced CT.

  "Generally speaking, the standard chest plain CT scan is generally 5mm layer, and a set of chest plain CT film has about 60-70 layers of images. If the film layer in your hand is less than 30 layers, it is undoubtedly a set of quality. With poorer films, there may be missed diagnosis for lesions whose diameter is smaller than the thickness of the slice." Guo Chao said.

  According to experts, the slice thickness of high-resolution CT is generally 2-3mm, and slices of this thickness can basically cover all suspicious lesions in the lung.

  What if the 1-2mm lesion is "invisible"?

According to Zhao Ke, a thoracic surgeon at Peking Union Medical College Hospital, in fact, for thoracic surgeons, it is difficult to judge the nature of lesions of 1-2mm. Even if they are not found, there is no need to worry. Generally speaking, nodules above 5mm are needed. Object of focus.

  CT can be divided into low-dose CT and non-sweeping CT according to the different sharpness.

The “low dose” of chest low-dose CT mainly refers to the radiation dose. The radiation dose is about 1/6 of that of the chest plain scan CT, but it can meet the basic inspection needs, that is, “find lesions”.

But it does lead to a decrease in CT resolution to a certain extent. In short, it is "indiscernible", which mainly affects doctors' judgment on the nature of some atypical lesions.

  Zhao Ke said that studies have shown that low-dose CT has a detection rate of 10.0%, 52.0%-88.1% and 100.0% of nodules with a diameter of ≤3mm, 3-5mm or >10mm, respectively, and it is not easy to find the lung apex or hilum. Nodules at the junction of blood vessels, endobronchial lung cancer, small central lung cancer, and nodules adjacent to the heart border or diaphragm.

  There is also a special chest enhanced CT, its main function is to distinguish components with similar densities in the body, that is, components with similar colors on CT.

  "If we have a coconut cheese toast in front of us, the ingredients are butter and cheese. They are all light yellow. If they are mixed together, they cannot be distinguished from each other with the naked eye. If there is a 'magic little pigment' that can make cheese If the color changes but the butter does not change color, then the two ingredients can be easily distinguished.” Guo Chao gave an example.

  Guo Chao said that there are some similar situations in the human chest cavity. For example, tumors, lymph nodes and blood vessels in the hilum all show soft tissue density, which is gray on CT. At this time, the "magic little pigment" of contrast agent is used to make blood vessels. Turns white, thereby distinguishing the boundaries between blood vessels and tumors, identifying what's going on in the body without opening the chest cavity.

  Experts said that the so-called enhancement is not the case of enhancing the lungs. If you want to see the lung parenchyma more clearly, you should choose high-resolution CT instead of enhanced CT. Of course, it will not bring more radiation.

Image source: WeChat public account of Peking Union Medical College Hospital

  When it comes to CT examinations, radiation is the most worrying thing for people.

Experts said that if low-dose chest CT is used as an annual physical examination item, it will not cause a serious burden on the body.

  Even the radiation dose of chest plain scan/high-resolution/enhanced CT is not enough to cause serious physical damage. Usually, the safe radiation dose range cannot exceed 100mSv a year. The impact is still negligible.

  For the choice of CT examination, experts suggest that if it is an annual physical examination, a low-dose chest CT can be selected, which has a relatively small radiation dose and can detect most of the lesions that need attention; if it is a follow-up of existing lesions or postoperative review, It is recommended to do chest CT scan; if it is a relatively small lesion or if you want to identify whether the nodule is "ground glass" or "solid", then choose high-resolution chest CT; if the lesion and the normal structure of the hilum are mixed, the most It is good to choose enhanced chest CT (recommended to be prescribed by a thoracic surgeon).

Of course, the most important thing is to follow your doctor's orders.

(Guidance for popular science: Li Danqing, Director and Chief Physician of Thoracic Surgery, Peking Union Medical College Hospital) (End)