An ultrasound scan, also referred to as a sonogram, diagnostic sonography, and ultrasonography, is a device that uses high-frequency sound waves to create images of the inside of the body.
Because sound waves are used instead of radiation, ultrasound scans are safe. Obstetric sonography is frequently used to check the baby in the womb.
The procedure is called an ultrasound scan and the image produced is a sonogram.
Ultrasound scans can be used to detect problems in the liver, heart, kidney, or abdomen. They may also be useful for a surgeon performing certain types of biopsies.
The word "ultrasound," in physics, refers to sound with a frequency that humans cannot hear. In diagnostic sonography, the ultrasound is usually between 2 and 18 megahertz. Higher frequencies provide better quality images but are more readily absorbed by the skin and other tissue, so they cannot penetrate as deeply as lower frequencies. Lower frequencies can penetrate deeper, but the image quality is inferior.
Contents of this article:
Fast facts on ultrasound scans
Here are some key points about ultrasound scans. More detail and supporting information is in the main article.
- Ultrasound scans are very safe and, therefore, widely used
- Ultrasound can be used for diagnosis or treatment
- These scans can be used by a range of medical professionals including anesthesiology and cardiologists
- In most cases, there is no necessary preparation for the patient before an ultrasound scan
How do ultrasound scans work?
Although ultrasound travels through soft tissue and fluids, it bounces back off denser surfaces. Ultrasound will travel through blood in the heart chamber, for example, but much of it will echo (bounce back) after hitting a heart valve.
If there are no solid gallstones in the gallbladder, ultrasound will travel straight through, but when there are stones, ultrasound will bounce back from them.
The denser the object the ultrasound hits, the more of the ultrasound bounces back. The bouncing back, or echo, is what gives the ultrasound image its features - varying shades of gray reflect different densities.
What are ultrasound scans used for?
Ultrasound is commonly used in medicine today. They can be used for either diagnosis or treatment (therapeutic procedures), as well as for guidance during procedures that require intervention, such as biopsies.
A medical professional who performs ultrasound scans is called a sonographer. Scans or images are then interpreted by radiologists, cardiologists, or other medical specialists. The sonographer usually holds a transducer; a hand-held device which is placed on the skin of the patient.
Below are examples of medical sonography:
Ultrasound in anesthesiology
Ultrasound is often used by anesthetists for guidance (accuracy) when injecting needles with anesthetic solutions near nerves.
As well as creating images of the cardiovascular system, echocardiograms can accurately measure blood flow and cardiac tissue movement at specific points using a technique called Doppler ultrasound.
A doctor can assess the function and state of cardiac valve areas, any abnormalities in the left and right side of the heart, valvular regurgitation (blood leaking from valves), and how well the heart pumps out blood.
Arterial sonography can be used to evaluate possible blockages or narrowing of arteries. Venous sonography can be used to evaluate for deep vein thrombosis (DVT).
Ultrasound in emergency medicine
The use of ultrasound in emergency medicine has grown considerably over the last two decades. In fact, for emergency medicine, ultrasound training has become increasingly popular.
Today, ultrasound is used in the FAST (Focused Assessment with Sonography for Trauma) scan, which assesses for trauma, pericardial tamponade (fluid buildup in the sac in which the heart is enclosed), or hemoperitoneum (blood leakage in the abdomen).
Abdominal Sonography (gastroenterology)
Ultrasound can be used to generate images of the spleen, kidneys, bile ducts, gall bladder, liver, aorta, inferior vena cava, pancreas, and other solid organs located in the abdomen.
If the appendix is swollen or inflamed, as may be the case with appendicitis, it may be detected by ultrasound.
Fat and gas in the bowel can sometimes block the ultrasound waves, making diagnosis more difficult.
Newborn infants (neonatology)
The sonographer can perform an ultrasound scan on an infant by placing the probe on the newborn's fontanelle (soft spot on the top of the skull) to check for abnormalities in the brain, hydrocephalus, and periventricular leukomalacia (a form of white-matter brain injury).
As the fontanelle grows smaller in time, the quality of the images becomes poorer.
Ultrasound and neurology
Ultrasound may be used to measure blood flow in the carotid arteries. Known as carotid ultrasonography, the scan looks for blood clots and plaque build-up.
A carotid duplex is a form of carotid ultrasonography using Duplex ultrasonography, which may include a Doppler ultrasound - a test which can reveal how blood cells move through the carotid arteries.
Right: feet of fetus at 18 Weeks.
Ultrasound is used to create images of the fetus or embryo in the uterus. Today, it is part of standard prenatal care. Obstetric ultrasonography can reveal various aspects of the fetus' health, as well as the mother's. It can also help doctors assess the progress of the pregnancy.
The probe or transducer is typically placed on the mother's abdomen, but may also be placed in her vagina - transvaginal sonography. A transvaginal scan can provide a clearer picture during early pregnancy, and it may be a better option for obese mothers.
A Doppler Sonography shows the fetus' heartbeat and can help the doctor detect signs of abnormalities in the heart and blood vessels.
Ultrasound and urology
Ultrasound is used in urology for many purposes. For instance, one can check how much urine remains in the patient's bladder after urinating.
Organs in the pelvic region can be checked, including the uterus and testicles. In young adult male patients, ultrasound is sometimes used to distinguish hydrocele or varicocele (swelling in the testicular area) from testicular cancer.
Pelvic sonographies can be carried out internally or externally. In a male, the internal sonogram may be inserted into the rectum, in a female it might be inserted into the vagina.
Ultrasound scans of the pelvic floor can help the doctor determine the extent of, for example, a pelvic prolapse, incontinence, or obstructed defecation.
Ultrasound can be used to examine ligaments, bone surfaces, soft tissue masses, nerves, muscles, and tendons.
Doppler ultrasound is a type of ultrasound that depends on the Doppler effect, a change in the wave's frequency, which can occur from the motion of a reflector, such as a red blood cell.
As an example, we experience the Doppler effect when an ambulance approaches us, passes, and then drives away. The siren sounds as if it becomes higher-pitched as it approaches and then progressively lower-pitched as it travels further away.
Put simply, Doppler ultrasound is used to assess the flow of blood in a vessel - this includes determining blood velocity and looking for any obstructions.
Doppler ultrasound can also be used to check the fetus' heart and heartbeat.
In the majority of cases, a transducer is used that is placed on the surface of the patient's body. However, there are transducers that are placed internally - these tend to provide clearer and more informative images.
The following ultrasound transducers can be used for internal use:
- An endovaginal transducer - enters through the vagina
- An endorectal transducer - enters through the rectum
- A transesophageal transducer - enters through the esophagus (down the patient's throat)
Some tiny transducers can be placed onto the end of catheters and inserted into blood vessels so that images of vessel walls can be examined.
Preparing for an ultrasound scan
In most cases, no special preparation is needed before a routine ultrasound scan. Experts advise patients to wear loose-fitting and comfortable clothing.
If the doctor wants to check the liver or gallbladder, the patient may be asked to eat nothing (fast) for several hours before the procedure.
For individuals going for a scan during pregnancy, especially early pregnancy, the doctor or nurse will ask them to drink plenty of water and to avoid urinating several hours before the test.
When the bladder is full, the nearby loops of intestine are displaced, and the scan produces a better image of the uterus.
Ultrasound scan process
The majority of scans take 15-45 minutes and usually take place in the radiology department of a hospital. The test is performed either by a doctor or a sonographer.
In most countries, the sonographer has specialized training in viewing, analyzing, and modifying the scan to optimize the data in the image. Sonographers need to understand the physics involved in ultrasound, as well as having solid knowledge of anatomy, pathology, and physiology.
- External ultrasound - The sonographer puts lubricating gel onto the patient's skin and then places a transducer over the lubricated skin. The transducer is moved over the part of the body that needs to be examined. Examples include ultrasound examinations of a patient's heart or a fetus in the uterus. The patient should not feel discomfort or pain. They will just feel the transducer over the skin. Pregnant women may feel slight discomfort only because it is recommended to come in with a full bladder.
- Internal ultrasound - The probe is placed into the vagina (in females) or the rectum (in males). Internal ultrasounds may be used when the doctor wants to have a better look at the prostate gland, ovaries, or uterus.
- Endoscopic ultrasound - An endoscope is inserted into the patient's body, usually through the mouth. This type of scan is used when the doctor wants to have a better look at the esophagus, chest lymph nodes, or the stomach.
There is a light and an ultrasound device attached to the end of the endoscope. Patients are given medications to reduce pain and/or sedatives before the procedure.
There is generally more discomfort with internal ultrasound scans compared to external ones, as well as a slight risk of internal bleeding. However, ultrasounds are, overall, incredibly safe.