Brief introduction of x-ray computed tomography

Directory 1 Pinyin 2 English reference 4 X-ray computed tomography indications overview 5 X-ray computed tomography contraindications 6 preparation 7 methods 8 precautions 1 Pinyin xx à n j ? su à n j ? du à n cé ng Shè y ǐ ng y ǐ ng

English reference computed tomography

Computerized x-ray tomography

X-ray computed tomography, also known as CT, is a method to obtain images of human internal tissues by using X-ray as the signal source. The basic theory of CT was laid by Cormac in 1963, while the technology and application of CT were published by British engineers Hounsfield and Dr. Ambrose in 1973. This photography method is to scan the human body with fan-beam X-rays (the first generation CT is a narrow beam), and the detector converts the X-rays passing through the human body into electrical signals, which are digitized and input into a computer for operation, thus obtaining a very clear X-ray profile image. The contrast range of CT images is about 4000 gray levels, which can distinguish the subtle differences of tissue structure. At present, the cross-sectional thickness can reach 1 mm, and CT can be divided into 1 ~ 4 generations according to scanning mode and scanning time. The first generation of X-rays is a narrow beam of 1 ~ 2 detector, and the scanning time takes 2 minutes. The second generation X-ray is a fan beam with dozens of detectors, and the scanning time is 20 seconds. The third generation adopts the scanning technology of continuous rotation of fan-shaped X-ray beam. The detector array is arranged opposite to the X-ray source and rotates synchronously around the subject, and the scanning time is only 2 seconds. The fourth generation uses a fan-shaped X-ray beam, and the detectors are arranged in a fixed ring. The X-ray tube can rotate 360 around the subject, and the scanning time is 2 seconds. CT is widely used in clinical examination of head, chest, abdomen, spine and other organs. At present, Chinese medicine also uses it to guide the objective research of clinical syndrome differentiation treatment.

Indications X-ray computed tomography is suitable for:

1. Hidden lesions were found, such as tumor metastasis, pelvic and retroperitoneal masses, retroperitoneal lymph nodes, paraaortic swollen lymph nodes, etc.

2. Differentiate clinically known mass properties (such as cystic, solid, fatty, bloody, abscess). Ovarian cysts and tumors, adnexal effusion, hematoma and abscess.

3. Assist in the diagnosis and staging of cervical cancer, endometrial cancer and ovarian cancer.

4. Focal localization, guided needle aspiration biopsy or conformal radiotherapy.

5. It is helpful to observe the size of the lesion and its response to radiotherapy, chemotherapy and antibiotics. And distinguish fibrous tissue hyperplasia from recurrent tumor after radiotherapy.

6. Diagnosis of congenital reproductive tract malformation.

7. The IUD is displaced and the position of the IUD is determined.

8. Others: diagnose endocrine abnormalities, such as pituitary adenoma.

5 contraindications ct examination X-ray may have an impact on the fetus, and CT examination is not allowed during pregnancy.

Before preparing for CT examination, the patient's preparation plays a vital role in the success of CT examination. The following is the general situation that patients need to pay attention to or must prepare before CT examination.

Before 1.CT examination, patients must carry relevant examination data, including previous CT, MRI, routine X-ray examination data and other clinical examination data.

2. Check that the patients and their accompanying families should change their shoes when they enter the CT room, and keep the computer room of the CT room clean and tidy to avoid dust from entering and affecting the normal operation of the machine.

3. Be patient to explain to the patient, including the sound made by the machine during the examination, to eliminate their nervousness and make the examination go smoothly.

4. Check and remove metal objects in the inspected parts, such as hairpins, keys, coins, buttons, etc. containing metal substances, to prevent artifacts.

5. For patients who can't cooperate, such as infants and coma patients, sedatives must be given in advance.

6. For patients with chest and abdomen examination, do necessary breathing training. For example, breathe regularly according to breathing instructions or indicator lights to avoid breathing or motion artifacts.

7. Patients who need enhanced scanning should be asked in detail whether they have a history of drug allergy, whether they have physical and mental diseases that are not suitable for the use of contrast media, and whether they should do or not do allergy tests according to the drug instructions.

8. For patients undergoing abdominal examination, oral contrast media or water must be prepared in advance according to the needs of the examination. In addition, before the examination 1 week, patients who have eaten barium meal and barium agent * * * in esophagus and gastrointestinal tract cannot have abdominal ct scanning, so as to avoid the influence of barium agent remaining in intestinal cavity on CT scanning.

9. Patients receiving pelvic scanning should also prepare oral contrast agent 1 0 days in advance, and pay special attention to its taking method, time and dosage.

Methods CT scanning can be divided into the following five steps:

1. Enter patient information.

This work is done on the operating platform through the keyboard or touch screen (usually prompted by the monitor screen). Including the patient's name, gender, date of birth, CT number, etc. Select the scanning direction, that is, head or foot forward. Whether the patient's position is supine, prone, left or right. If it is enhanced scanning, it should be indicated (such as C+), and other special scanning methods should be indicated if necessary.

2. Put the patient * * *

Swing * * is to put the patient on the examination table accurately and comfortably according to the examination requirements. Before setting, determine whether to lie on your back or face, head or feet, then help the patient lie flat, and use appropriate auxiliary devices to fix the patient's examination position according to the examination needs. For example, the skull scanning frame is used for skull examination, and the knee joint bracket is used for knee joint scanning. According to different examination positions, raise the bed surface of the examination table, turn on the positioning indicator light, and send the patient into the scanning hole. The specific depth of the bed entrance varies with the inspection position. Turn off the positioning indicator and reset the bed indication to zero. The main purpose of this action is to make the bed movement during scanning have a relatively fixed and easy-to-remember reference value.

3. Positioning before scanning

Positioning is to determine the scanning range. Two methods can be used. First, scan the positioning film. According to the need of examination, the positioning film can be in the front and back position or lateral position, and then the starting line and ending line of scanning can be determined by using the positioning function in the scanning software of CT machine. This method is intuitive and accurate. At present, this method is mostly used for CT examination. Another method is to determine the starting position of scanning directly from the patient's body surface by using the positioning indicator lamp when swinging. This method saves time and a positioning film, but the disadvantage is that the positioning is not as accurate as scanning positioning film. In addition, the positioning film not only determines the scanning range, but also is equivalent to a plain film of routine X-ray examination, which has certain diagnostic significance. The specific method of positioning scanning is to select positioning scanning by keyboard or mouse, and then determine the starting line, ending line and range of scanning directly on the image of the monitor screen according to the obtained positioning film.

scan

Scanning is the main step of CT examination. At present, most CT machines have special scanning functions such as transverse scanning (axial scanning) and spiral scanning (single-layer or multi-layer spiral scanning). The operator needs to choose which method to use before scanning. According to different machines, the scanning process can also be divided into manual mode and automatic mode. Manual mode means that after scanning one layer, you need to select the operation of the next layer and press the exposure key every time. The automatic mode only needs to press the exposure key once to complete the whole scanning range determined by the positioning film. The specific steps of scanning are: first determine the scanning mode, then select the scanning conditions and press the exposure button. During the whole scanning process, the operator should closely observe the image scanned each time, and sometimes adjust the scanning range as needed (such as whether the position of the scanned part in the image is appropriate, etc.). ).

Step 5 shoot and store

Photography and storage are the last step to complete the whole CT examination, and photography can be completed automatically or manually according to different machine conditions. Automatic shooting means that it can be preset on the CT machine, and the operator only needs to adjust the window width and window level at the beginning of each scan. After scanning, CT will automatically take all scanned images in turn according to the settings. Manual shooting is the manual shooting after scanning is completed. Automatic shooting is fast and simple, but it is impossible to select and post-process all scanned images. Manual shooting is slow, but it can be selectively shot, and post-processing work such as amplification, measurement and CT value can be carried out as needed. Usually, the scanned CT images are temporarily stored on the hard disk of the CT machine. If permanent storage is needed, you can choose storage media such as magnetic tape and optical disk. The operation of storing is usually to input the stored instructions after selecting the patient to be stored.

8 precautions 1. Prepare the previous X-rays, CT films, B-ultrasound, etc. And a summary of the illness for reference.

2. Fasting for 4 hours before scanning (fasting is not required for general scanning).

3. Do not do gastrointestinal radiography and take metal-containing drugs before abdominal examination 1 week.

4. People with a history of drug allergy, diabetes and cardiac and renal insufficiency may have anaphylactic shock, extravascular leakage of contrast media or other accidents. Therefore, before the examination, it is necessary to go through the signing procedures such as "medication consent form" and ask the patients and their families to cooperate.

5. Critically ill patients and restless patients should be examined after necessary clinical treatment.

6. Fill in every item of the application form carefully, such as X-ray number, CT number, symptoms and signs of the patient, especially the examination site, whether it is enhanced, etc.