Ultrasound science tips
Whether it's a health check-up or a visit to the hospital, doctors always ask patients to have an ultrasound examination. Most people understand ultrasound to mean that a pregnant woman needs an ultrasound, but the truth is that ultrasound is not only used to examine the foetus, it is only a small part of the clinical use of ultrasound. What exactly is ultrasound? How is it used to examine the human body?
Ultrasound, or ultrasound, is a mechanical wave. The frequency of sound waves that can be heard by the human ear is between 20 and 20 000 Hz. When the frequency of sound waves vibrates above 20 000 Hz or below 20 Hz, we cannot hear them. Therefore, we call sound waves with a frequency higher than 20 000 Hz "ultrasound". Ultrasound has good directionality, strong penetrating ability, easy to obtain more concentrated sound energy, in the water to spread far and so on, can be used for measuring distance, speed, cleaning, welding, stone crushing, etc., in medicine, military, industry, agriculture is widely used.
The frequency of ultrasound used for medical diagnosis is 2-10 MHz, and it can be transmitted in the human body and reflected back to different tissues after touching them. Based on this physical property, scientists have developed various ultrasound instruments. Ultrasound waves are generated and emitted by a probe, and after entering the body, according to the differences in the acoustic properties of human organs and tissues, some of the ultrasound waves are reflected back, and then accepted by the probe and processed by a computer to display and describe the waveform, curve or image, and the ultrasonographer makes a diagnosis of physiological and pathological conditions according to the characteristics of the image.
Is ultrasound harmful to the human body? Ultrasound can cause changes in the function, structure or state of a biological system when it propagates through it. The severity of the biological effects caused depends mainly on the size of the ultrasound dose and the length of the examination. The dose and duration of ultrasound used in clinical diagnosis are now within a very safe range and the effects on the human body are almost negligible.
Others may ask whether ultrasound has any effect on the foetus. The answer to this question is not yet clear internationally. The following are some of the more unified understandings in China: 1. If there is a definite diagnostic purpose, ultrasound imaging and other diagnostic techniques should be actively used; 2. The fetal brain, eyes, medulla, heart and reproductive organs should also be examined within 3-5 minutes of the scheduled ultrasound. If these points are followed, ultrasound examination of the fetus should be safe.
In summary, the advantages of ultrasound diagnosis are that it is painless and non-invasive to the patient, easy to examine, intuitive and clear, so it is very popular with clinicians and patients. Together with X-ray CT, magnetic resonance imaging and isotope scanning, it is considered one of the four major diagnostic imaging techniques in modern medicine, complementing and improving each other.
There are many types of diagnostic ultrasound, which can generally be divided into type A, type B, type D, type M and so on. Ultrasound A and ultrasound M are both one-dimensional images, and ultrasound A has been largely eliminated in other fields except in the field of ophthalmology, while ultrasound M is mainly used for cardiac ultrasound. ultrasound B is the basis of all ultrasound diagnostics, and it can directly display two-dimensional spatial images, so it is also called two-dimensional ultrasound. ultrasound D, also known as Doppler, is used to detect blood flow and organ activity through Doppler. The Doppler frequency shift signal of blood flow and organ activity is superimposed on the two-dimensional image of B-mode ultrasound after processing and colour coding by autocorrelation techniques, which is generally known as colour ultrasound. Many people think that colour ultrasound is a colour television set and that all images seen should be in colour, however, colour ultrasound is by no means full-screen colour and only partially displays red or blue when observing blood flow signals. As a result, colour ultrasound provides both morphological and haemodynamic information in two-dimensional images and is now the mainstream of ultrasound diagnosis.
In recent years, new technologies such as three-dimensional ultrasound and ultrasonography have emerged, both of which are under rapid development. At present, three-dimensional ultrasound is mainly used clinically in obstetrics for the examination of the foetus, and ultrasonography, which is performed by injecting a contrast agent into a vein for the purpose of visualisation, has been carried out in major hospitals across the country, making the scope and level of ultrasound diagnosis greatly enhanced.
Conventional ultrasound examinations are done on the surface of the body. Some organs or lesions are located deep within the pelvic cavity, etc. In this case, in order to avoid the influence of other tissues, intracavitary detection methods can be used, such as transesophageal examination of the digestive tract and heart, transrectal examination of the prostate, transvaginal examination of the uterus and adnexa, etc. The correct insertion or injection of puncture needles, drainage catheters or drugs under ultrasound guidance into the lesion, cystic cavity, body cavity, ducts and other specific sites to be reached for diagnostic or/and therapeutic purposes is called interventional ultrasound. In addition, ultrasound can be used to guide the treatment of tumours or directly to treat tumours using high energy focused ultrasound.
Ultrasound is used extensively in the body, in the cranium, heart, blood vessels, liver, gallbladder, pancreas, spleen, chest, kidneys, ureters, bladder, urethra, uterus, pelvic adnexa, prostate, seminal vesicles, as well as in the eyes, thyroid, breast, salivary glands, testes, peripheral nerves and tendons of the limbs. However, there are limitations to ultrasound diagnosis, such as limited diagnostic value for lesions of the bones, lungs and gastrointestinal tract. Ultrasound diagnosis is based on the analysis of the images by the physician after taking the patient's medical history and other clinical information, and does not directly reveal the pathological findings.
