When you go to the hospital, medical terms such as “CT”, “MRI”, “X-ray” and “B-ultrasound” are not unfamiliar to people. These terms are not new to people, but these similar-looking medical imaging devices often make people “confused”. Why do you use “CT” sometimes and “MRI” sometimes, because your condition has worsened?
In fact, they work on different principles and have their own division of labor. It is a matter of concern how to do the correct and appropriate examination without wasting the examination cost. A preliminary understanding of the characteristics, advantages and scope of application of these devices can help patients save time and money.
Different principles, different advantages
CT (Computed Tomography) means X-ray computed tomography, which is a tomographic scan of a part of the human body with an X-ray beam to obtain a cross-sectional or stereoscopic image of the examined part of the human body. CT can provide complete three-dimensional information of the examined part of the human body and can make organs and structures clearly visible and show lesions clearly.
X-rays are highly penetrating rays that can penetrate the body. The principle of using X-rays for fluoroscopy or photography of the inside of the body is the use of the penetrating effect of X-rays. When penetrating the body, it is weakened by absorption of calcium-containing components (bone), water (blood, etc.), and soft tissue (muscle), so that the basic shape of the area being examined can be presented.
Unlike CT and X-ray, ultrasound examinations use the principle of ultrasound to produce echoes for examination. Ultrasound can propagate in a certain direction and can penetrate objects, and if it encounters an obstacle, it will produce an echo. people collect and display this echo on the screen through the instrument, which can be used to understand the internal structure of the object and assist in diagnosis. ultrasound is 2-dimensional ultrasound information, which constitutes a planar graphic and reflects the structure of the human body.
With the emergence of color-Doppler ultrasound technology, color ultrasound (color B-ultrasound) has emerged, i.e., color Doppler is added to black-and-white B-ultrasound. Color ultrasound also provides rich information on hemodynamics, and the practical application is widely valued and welcomed, and color ultrasound is often used in current clinical practice.
MR, MRI (nuclear magnetic resonance imaging), or magnetic resonance, is a biomagnetic spin imaging technique that uses the characteristics of the spin motion of the atomic nucleus to generate a signal within an applied magnetic field after excitation by a radiofrequency pulse, which is detected with a detector and input to a computer and converted into an image.
Unlike CT and X-rays, the greatest advantage of MR is that it is not damaging to the body and there is no ionizing radiation damage. Compared to CT tomography, MR can obtain native 3D cross-sectional imaging in multiple directions, such as stereoscopic images of the brain and spinal cord. It is particularly accurate for the diagnosis of bones, joints, spinal cord, pelvic organs, prostate, bladder, uterus, ovaries, cardiac macrovascular lesions and myocardial infarction.
For the examination of the lungs, the choice of X-ray or CT is superior to MR. For the examination of the liver, pancreas, adrenal glands, and prostate, MR is not superior to CT, but rather expensive. In addition, MR examinations are not recommended for patients with metal objects in their bodies, those who are less than 3 months pregnant, those with pacemakers, or those who are critically ill.
X-rays or CT for chest examinations
A chest X-ray can examine the heart, lungs, mediastinum, ribs, pleura, and aorta, such as increased lung texture, calcified spots in the lungs, and calcified aortic nodes. Compared to X-rays, CT chest examinations show a more pronounced clarity of structures and are more sensitive in detecting chest lesions and more accurate in showing lesions than conventional X-rays of the chest. CT chest examination is good for detecting minor lesions and hidden lesions and showing lesion characteristics, especially for early lung cancer diagnosis.
However, the radiation dose of CT examinations is significantly higher than that of X-rays. In addition, X-ray is one of the important examinations in clinical orthopedics, and its effect is to check whether there are organic lesions in bone, spine, joints, etc., and to clarify the location, size, degree and relationship with surrounding soft tissues, so as to provide reference for treatment. And CT can diagnose bone itself lesions, fracture or dislocation, bone joint and soft tissue lesions, etc.
Ultrasound for gallbladder diseases
Ultrasound has a high degree of accuracy in the diagnosis of gallbladder diseases, such as gallbladder stones, with a general accuracy rate of over 95%, while CT has a lower diagnostic compliance rate. Since CT scans every 1-5 seconds, it is not easy to obtain accurate information for examination of organs such as heart, normal people breathe at least once in 3 seconds when calm, and abdominal organs affected by breathing, such as liver and spleen, patients are required to pause for breathing when doing CT examination, and the young, mentally disturbed and lung functionally incompetent cannot cooperate and cannot be examined, while there is no such limitation for doing B-ultrasound.
Ultrasound is the most commonly used method for clinical examination of biliary tract diseases, and can confirm the diagnosis of gallbladder stones, gallbladder inflammation, tumors, etc. Moreover, ultrasound has a higher accuracy rate for cirrhosis, fatty liver, splenomegaly, liver cancer, and intestinal lesions.
In addition, the purpose of ultrasound examination during pregnancy is to determine whether the fetus grows in accordance with the gestational week, to determine whether the fetus has any malformation, and to understand whether the fetus is safe in the womb.
CT is mostly used for tumor diagnosis
CT has a higher resolution than B ultrasound for tumor diagnosis. For small masses of 1 to 2 cm, CT shows 88%, while B ultrasound shows 48%; for kidney cancer diagnosis, CT has an accuracy rate of 90%, while B ultrasound shows 44%. For liver and pancreas, CT can diagnose hepatocellular carcinoma, hepatic hemangioma, fatty liver, pancreatic cancer, acute pancreatitis, chronic pancreatitis, etc., while MR is suitable for examining diseases such as primary liver cancer.
CT is superior to ultrasound for the diagnosis of kidney, adrenal, bladder and prostate diseases. CT can show not only the renal pelvis, calyces and internal cavity of the bladder, but also the renal parenchyma and bladder wall, and can diagnose adrenal tumors, subperitoneal hemorrhage, etc.
Choose MR for soft tissue diseases
MR can examine muscles and soft tissues. MR uses a completely different imaging principle than X-rays, and the resolution of soft tissues is far from that of CT and X-rays, and is mainly used to observe soft tissues in the spinal canal such as nerves and spinal cord, so it can be used to detect and diagnose central nervous system diseases and posterior lumbar disc protrusion.