What Is the Difference Between an Ultrasound and a CT Scan?

CT examination is a modern advanced medical imaging examination technology. CT scans generally include plain CT, contrast-enhanced CT scans, and CT angiography.

Chinese name: CT inspection
Species: Three kinds

Types of: Medical check
Pin pair: Scanning the human brain

CT examination classification

CT diagnosis is usually plain CT, enhanced CT scan and cerebellar angiography CT.

The plain CT scan is generally a cross-sectional scan, mostly using the auditory line as the baseline, and successively scanning upwards or downwards. The contrast agent commonly used for enhanced CT scans is iodine contrast agent, 1.5 to 2.0 ml per kilogram of body weight. Those with a history of iodine allergy and heart and kidney failure are contraindicated.

Cerebrovascular CT is usually injected with non-ionic contrast agent or gas through lumbar puncture or large occipital puncture to make the cerebellum to be examined full. For abdominal CT, fast before the test. Orally dilute the iodine solution against the outline of the organs. During the test, the patient should hold his breath and scan.

Middle ear cancer can be manifested as bone destruction centered on the middle ear, the auditory ossicles completely disappeared, and soft tissue mass shadows can be seen locally. Sinusitis CT manifests as thickened mucosa, increased intraluminal density, and the formation of fluid or pus. Most liver cancers show low-density areas during plain scans. CT manifestations of liver cirrhosis include unevenness of the liver surface, improper proportion of each leaf, uneven liver parenchyma density, and splenomegaly. Patients with acute pancreatitis show chronic enlargement of the pancreas, deformation and blurring of the edges, disappearance of the fat layer around the pancreas, and thickening of the renal fascia; chronic patients show enlargement or shrinkage of the pancreas, deformation and calcification, enlarged pancreatic ducts, and renal tendons The film is thickened. The bronchus on CT of patients with bronchiectasis can be columnar, sac-like, or mixed. CT showed curved shadows on the inside and outside of the chest wall, indicating the presence of pleural effusion.

CT examination features

1. High density resolution, can directly display organs and lesions that can not be displayed by X-ray examination.

2. The examination is convenient, fast and safe. As long as the patient does not move, the examination can be successfully completed, it is easy for the patient to accept, and it is convenient to follow up, especially for the emergency patients who can make a diagnosis quickly and play a role in fighting for time to rescue the patient. Important role. In addition, CT can also be repeated in the short term for emergency, which is beneficial to observe the evolution of the lesion.

3. It overcomes the shortcomings of the traditional X-ray flat-film images, the density of adjacent organs and tissues is not so different to form a contrast image, and the soft tissue constituent organs cannot be developed or poorly developed. Compared with nuclide scanning and ultrasound images, CT images are clear, anatomical relationships are clear, and lesions are displayed well. Therefore, the inspection rate and diagnostic accuracy of lesions are high.

4. X-ray absorption coefficients (or attenuation coefficients) of various normal tissues and diseased tissues can be obtained for quantitative analysis, that is, not only images of organs, tissues or lesions of different densities are displayed, but the respective X-ray absorptions are directly obtained. How much is the absorption coefficient.

5. As the image is converted from the absorption coefficient, image processing can be performed to adjust the density or grayscale of the image to be suitable for observing a certain tissue or lesion, while the density of each image of the X-ray photograph cannot be adjusted.

6. If necessary, an enhanced scan can be added to make the image clearer. Differential diagnosis of certain lesions can be made to improve the accuracy and display rate of the diagnosis of the lesions. The non-ionic iodine contrast agent currently used has high safety.

CT examination indications

1. Nervous system lesions: craniocerebral trauma, cerebral infarction, brain tumors, inflammation, degenerative diseases, congenital malformations, etc. It is the earliest application of the human body system, especially in the diagnosis of traumatic craniocerebral emergency. It shows cerebral contusion and laceration, acute intracerebral hematoma, epidural and subdural hematoma, craniofacial bone fracture, intracranial metal foreign body, etc., and it is more sensitive than any other method. CT diagnosis of acute cerebrovascular diseases such as hypertensive cerebral hemorrhage, subarachnoid hemorrhage, cerebral aneurysm and arteriovenous malformation rupture and bleeding, cerebral infarction, etc. are of great value. Acute bleeding can be considered as the first choice for examination, and acute cerebral infarction is particularly morbid. Within 6 hours, CT is not as sensitive as MRI.

2. Cardiovascular system: it can be used for the diagnosis of pericardial tumors and pericardial effusions. CT of acute aortic dissection aneurysms has a positive diagnostic significance, especially enhanced scans have characteristic features and can be used for qualitative diagnosis.

3. Thoracic lesions: It has a very satisfactory effect for displaying lung lesions, and has a high diagnostic value for lung trauma, infectious lesions, tumors and the like. It is also satisfactory for the display of masses, lymph nodes, and pleural lesions in the mediastinum, which can show the relationship between lung masses and the mediastinum.

4. Abdominal organs: Clear display for parenchymal organs such as liver, gallbladder, spleen, pancreas, kidney, adrenal gland, etc. For tumors, infections, and trauma, it can clearly show the exact part of the anatomy and the degree of lesions, and is of higher value for staging of lesions It is helpful for the clinical development of treatment plans, especially for the surgical positioning of the surgical department. It is of great value in the diagnosis and differential diagnosis of abdominal masses.

5. Pelvic organs; there are rich fat spaces between pelvic organs, which can accurately show tumor invasion to adjacent tissues, so CT has become a diagnosis and clinical staging of ovarian, cervical and uterine, bladder, seminal vesicles, prostate and rectal tumors. And important means of radiotherapy design.

6, bones and joints: (1) small lesions in bones and muscles, X-ray plain films are often covered by bone cortex and cannot be displayed. (2) Bone and joint with complicated structure, such as spine and sternoclavicular joint. (3) X-ray suspicious lesions, such as small fractures of the articular surface, soft tissue abscesses, bone cortical damage caused by intramedullary bone tumors, and observation of tumor infiltration into soft tissues. (4) Display of internal and surrounding structures in the bone destruction area: such as dead bone, calcification, ossification, and bone hyperplasia, soft tissue abscesses, and tumors around the destruction area are significantly better than conventional plain radiographs. (5) For articular cartilage, ligaments, meniscus, synovium, etc., MRI examination is appropriate.

7. Liver lesions: CT examination can show the shape, contour, necrosis, bleeding, and growth patterns of intrahepatic mass lesions, primary liver cancer or metastatic liver cancer, and can also understand gall, pancreas, kidney and other organs As a result, patients with chronic hepatitis, cirrhosis, and suspicious lesions or liver cancer need a CT examination.

Liver CT examination has a high sensitivity for the diagnosis of early liver cirrhosis. It can be used as a routine examination item for patients with CHB, which can help the diagnosis of early liver cirrhosis and guide active antiviral treatment. The CT manifestations of liver cirrhosis include: liver shrinkage, obtuse shape; abnormal proportion of the size of each liver lobe, more often the right lobe shrinks; liver parenchyma is often uneven, and in severe cases the liver is covered with nodules of different sizes, which can be pineapple-like; Splenomegaly; ascites; widening of the hilum, shifting of the gallbladder, varicose veins around the hilum and stomach.

CT inspection principle

CT uses an X-ray beam to scan a slice of a certain thickness in a part of the human body. The X-rays transmitted through the slice are received by the detector, converted into visible light, converted from photoelectric conversion into electrical signals, and then passed through an analog / digital converter (analog / digitalconverter) into numbers and input to the computer for processing. The process of image formation is like dividing a selected slice into several cuboids with the same volume, which is called voxel. The information obtained from the scan is calculated to obtain the X-ray attenuation coefficient or absorption coefficient of each voxel, and then arranged into a matrix, that is, a digital matrix (digitalmatrix). The digital matrix can be stored in a magnetic disk or an optical disk. A digital / analog converter (digital / analogconverter) converts each digit in the digital matrix into small squares ranging from black to white, that is, pixels, and arranges them in a matrix to form a CT image. Therefore, the CT image is a reconstructed image. The X-ray absorption coefficient of each voxel can be calculated by different mathematical methods.

CT examination precautions

CT inspection instructions

In order to increase the difference between the density of diseased tissue and normal tissue, and to make a clear diagnosis, contrast agents are often used for enhanced scans in CT examinations. The non-ionic iodine contrast agents currently used are safe, but the following are contraindications and high-risk factors:

CT contraindications

1. Allergy to iodine contrast.

2. Severe liver and kidney damage.

3. Severe thyroid disease (hyperthyroidism).

High-risk factors for CT examination

1. Renal insufficiency.

2. Diabetes, multiple myeloma, dehydration, severe cerebral arteriosclerosis and cerebral vasospasm, acute pancreatitis, acute thrombophlebitis, severe cachexia and other serious diseases.

3. Asthma, hay fever, hives, eczema and other allergic diseases.

4, heart disease: such as congestive heart failure, coronary heart disease, arrhythmia and so on.

5. Patients with allergies to contrast media and other drugs.

6. Children under 1 year old and elderly over 60 years old.