Since childhood, eating for decades, walking for decades, and entering the hospital countless times, I believe there is one thing that you have not been able to figure out until now. X-rays, CT, ultrasound and MRI are four types of imaging examinations, what exactly are their imaging principles and differences? What are their advantages and disadvantages? In the end, which parts of the body are they each suitable for examination? In order to clear your mind of the many doubts about these four imaging examinations, below, let’s carefully sort it out with you! X-ray photography (flat film) X-ray will pass through the body, different parts of the absorption of radiation, the negative will not be exposed or partially exposed, the part is white after the film is washed. Advantages: fast and inexpensive. Disadvantages: The images of deep and shallow tissues overlap and are hidden from each other, and sometimes it is necessary to take X-rays from multiple angles to see clearly. CT The principle of CT examination is that X-rays will pass through the body in layers, which are processed into secondary imaging through computer calculations. Advantages: It can be viewed in layers, and post-processing can show more information. Disadvantages: The cost is more expensive than X-ray photography, and the radiation dose of CT examination is usually higher than that of a single X-ray photography. Ultrasound The principle of ultrasound is to penetrate the body with ultrasound waves, and when the sound waves encounter human tissue, reflected waves are generated and imaged by calculating the reflected waves. Advantages: multi-directional observation, real-time imaging. Disadvantages: Ultrasound is greatly disturbed by gas, and for organs containing more gas, such as the intestine, the accuracy of ultrasound diagnosis will be reduced, so the general intestinal examination using colonoscopy. Magnetic resonance imaging (MRI) Magnetic resonance imaging is an imaging technique that uses the signals generated by the collection of magnetic resonance phenomena to reconstruct images. Simply put, it is equivalent to shaking your hand to make hydrogen protons vibrate, then calm down and feel the vibrations inside. Advantages: Compared with CT, it has no radiation, no bony artifacts, multifaceted and multiparametric imaging, and a high degree of soft tissue resolution. Disadvantages: It is relatively expensive. Which body parts are suitable for which kind of examination? 1, traumatic bone – a rough look at radiography, a closer look at CT When encountering a variety of trauma, if you suspect that the injury to the bone, the priority is to choose radiography, the results of the examination is fast and easy to obtain. To further observe, you can choose CT observation details, or even magnetic resonance imaging to observe hidden injuries or soft tissue injuries. 2, cervical lumbar spine – the best choice of MRI, the second choice of CT cervical spondylosis, lumbar disc herniation and other intervertebral disc disease need to observe the disc and the corresponding nerve roots, to better observe these soft tissues, the optimal choice is magnetic resonance imaging. Likewise, MRI is a good choice for joint, muscle and adipose tissue examination, tumor, inflammation, trauma, degenerative lesions and various congenital diseases. CT can be used as a powerful supplement to observe spinal osteophytes and intervertebral foraminal stenosis. 3, chest – a cursory look at X-ray plain film, a closer look at CT X-ray chest film can be a cursory examination of the lungs, heart shadow, aortic arch, ribs, etc. It can check for increased lung texture, larger masses in the lungs, calcification of the aortic nodes, etc. CT chest examination shows a clearer structure and is more sensitive and accurate for detecting chest lesions than conventional X-ray chest films, especially for screening early lung cancer, which is of great significance. Magnetic resonance imaging, on the other hand, has very limited application for the diagnosis of diseases in the lung. 4.Abdominal pelvis – except for the intestines, general ultrasound can be checked The well-known one should be the examination related to the fetus during pregnancy, which can be seen clearly with ultrasound; in addition, the ultrasound diagnostic accuracy is higher for superficial organs such as the thyroid gland, and parenchymal organs such as the liver, spleen, pancreas, kidneys, and pelvis. 5, heart – exclude coronary heart disease with CT, see the heart function with ultrasound Conventional heart structure and function examination, cardiac ultrasound can almost meet! CT is available for congenital heart disease involving the examination of coronary arteries and structural abnormalities. magnetic resonance imaging is used to examine myocardial lesions, such as myocardial infarction. Reminder that after all this, you should have some knowledge of these four tests! However, doctors have some other examination precautions to remind you: before using iodine contrast agent, if you have a history of drug allergy, hyperthyroidism, iodine allergy (ever have a history of eating food with high iodine content allergy), etc., you should tell your doctor in advance in order to decide whether you can receive the examination; if the patient is equipped with a pacemaker, or has shrapnel, metal implants, “insulin pump” in the body “and other absolute or relative contraindications to MRI, you must inform your doctor in advance; Although PET-CT examination can detect cancer lesions in many parts of the body due to its ultra-high inspiration, like other imaging devices, PET-CT also has certain limitations, and false positives and false negatives may occur in a very small number of cases, so it is recommended not to do PET-CT blindly and follow medical advice. It is recommended not to do PET-CT blindly, but to follow medical advice.