How do ultrasounds produce images

In some cases, the radiologist may discuss results with you after the exam. You may need a follow-up exam. If so, your doctor will explain why.

Sometimes a follow-up exam further evaluates a potential issue with more views or a special imaging technique. It may also see if there has been any change in an issue over time. Follow-up exams are often the best way to see if treatment is working or if a problem needs attention.

Ultrasound waves are disrupted by air or gas. Therefore, ultrasound is not an ideal imaging technique for the air-filled bowel or organs obscured by the bowel. Ultrasound is not as useful for imaging air-filled lungs, but it may be used to detect fluid around or within the lungs. Similarly, ultrasound cannot penetrate bone, but may be used for imaging bone fractures or for infection surrounding a bone. Large patients are more difficult to image by ultrasound because greater amounts of tissue weaken the sound waves as they pass deeper into the body and need to return to the transducer for analysis.

Ultrasound has difficulty penetrating bone and, therefore, can only see the outer surface of bony structures and not what lies within except in infants who have more cartilage in their skeletons than older children or adults. Doctors typically use other imaging modalities such as MRI to visualize the internal structure of bones or certain joints.

Please type your comment or suggestion into the text box below. Note: we are unable to answer specific questions or offer individual medical advice or opinions. Some imaging tests and treatments have special pediatric considerations. The teddy bear denotes child-specific content.

Please contact your physician with specific medical questions or for a referral to a radiologist or other physician. To locate a medical imaging or radiation oncology provider in your community, you can search the ACR-accredited facilities database. This website does not provide cost information. The costs for specific medical imaging tests, treatments and procedures may vary by geographic region.

Web page review process: This Web page is reviewed regularly by a physician with expertise in the medical area presented and is further reviewed by committees from the Radiological Society of North America RSNA and the American College of Radiology ACR , comprising physicians with expertise in several radiologic areas. Outside links: For the convenience of our users, RadiologyInfo.

Toggle navigation. What is General Ultrasound Imaging? What are some common uses of the procedure? How should I prepare? What does the equipment look like? How does the procedure work? How is the procedure performed?

What will I experience during and after the procedure? Who interprets the results and how do I get them? What are the benefits vs. What are the limitations of General Ultrasound Imaging? A Doppler ultrasound study may be part of an ultrasound examination. Power Doppler is up to five times more sensitive in detecting blood flow than color Doppler, and it is less dependent on the scanning angle.

Thus, power Doppler can be used to identify the smaller blood vessels more reliably. The drawback is that power Doppler does not provide any information on the direction and speed of blood flow Figure A single beam in an ultrasound scan can be used to produce a picture with a motion signal, where movement of a structure such as a heart valve can be depicted in a wave-like manner.

M-mode is used extensively in cardiac and fetal cardiac imaging; however, its present use in regional anesthesia is negligible Figure Ultrasound machines convert the echoes received by the transducer into visible dots, which form the anatomic image on an ultrasound screen. The brightness of each dot corresponds to the echo strength, producing what is known as a grayscale image. Two types of scan transducers are used in regional anesthesia: linear and curved. A linear transducer can produce parallel scan lines and a rectangular display, called a linear scan, whereas a curved transducer yields a curvilinear scan and an arc-shaped image Figures 17A and 17B.

In clinical scanning, even a very thin layer of air between the transducer and skin may reflect virtually all the ultrasound, hindering any penetration into the tissue. Therefore, a coupling medium, usually an aqueous gel, is applied between surfaces of the transducer and skin to eliminate the air layer. Theoretically, 3D imaging should help in understanding the relationship of anatomic structures and the spread of local anesthetics.

There are three major types of 3D ultrasound imaging: 1 Freehand 3D is based on a set of 2D cross-sectional ultrasound images acquired from a sonographer sweeping the transducer over a region of interest Figures 18A and 18B. The transducer elements automatically sweep through the region of interest during the scanning; the sonographer is not required to perform hand motions Figure 18C.

However, typical spatial resolution of 3D imaging is about 0. At present, 3D imaging systems still lack the resolution and simplicity of 2D images, so their practical use in regional anesthesia is limited.

The echoes exhibit a steady decline in amplitude with increasing depth. This occurs for two reasons: First, each successive reflection removes a certain amount of energy from the pulse, decreasing the generation of later echoes. Second, tissue absorbs ultrasound, so there is a steady loss of energy as the ultrasound pulse travels through the tissues.

This can be corrected by manipulating time-gain compensation TGC and compression functions. Gain is the ratio of output to input electric power; it controls the brightness of the image.

The gain is usually measured in decibels dB. Increasing the gain amplifies not only the returning signals, but also the background noise within the system in the same manner. TGC is a time-dependent amplification.

TGC function can be used to increase the amplitude of incoming signals from various tissue depths. The layout of the TGC controls varies from one machine to another. A popular design is a set of slider knobs. Each knob in the slider set controls the gain for a specific depth, which allows for a well-balanced gain scale on the image Figures 19A , 19B , and 19C.

Amplification is the conversion of the small voltages received from the transducer into larger ones that are suitable for further processing and storage. There are two amplification processes considered to increase the magnitude of ultrasound echoes: linear and nonlinear amplification.

Currently, the ultrasonic imaging system with linear amplifiers is commonly used in medical diagnostic applications. However, the strength of echoes attenuates exponentially as the distance between the transducer and the reflector increases.

Ultrasonic imaging instruments equipped with logarithmic amplifiers can display echo signals with a wider dynamic range than a linear amplifier and remarkably improve the sensitivity for a small magnitude of echoes on the screen. Dynamic range is the range of amplitudes from largest to the smallest echo signals that an ultrasound system can detect.

Dynamic range less than 50 dB or greater than dB is probably too low or too high in terms of visualization of peripheral nerve. Compression is the process of decreasing the differences between the smallest and largest echo-voltage amplitudes; the optimal compression is between 2 and 4 for a maximal scale equal to 6. As previously discussed, it is common to use electronic means to narrow the width of the beam at some depth and achieve a focusing effect similar to that obtained using a convex lens Figure There are two types of focusing: annular and linear.

These are illustrated in Figures 22A and 22B , respectively. Adjusting focus improves the spatial resolution on the plane of interest because the beam width is converged.

However, the reduction in beam width at the selected depth is achieved at the expense of degradation in beam width at other depths, resulting in poorer images below the focal zone. The mechanisms of action by which an ultrasound application could produce a biologic effect can be conceptually categorized into two aspects: heating and mechanical.

In reality, these two effects are rarely separable except for extracorporeal lithotripsy, the therapeutic application of mechanical bioeffects alone.

The generation of heat increases as ultrasound intensity or frequency is increased. For similar exposure conditions, the expected temperature increase in bone is significantly greater than in soft tissues. Ultrasound scans, or sonography, are safe because they use sound waves or echoes to make an image, instead of radiation. Ultrasound scans are used to evaluate fetal development, and they can detect problems in the liver, heart, kidney, or abdomen.

They may also assist in performing certain types of biopsy. The person who performs an ultrasound scan is called a sonographer, but the images are interpreted by radiologists, cardiologists, or other specialists. Ultrasound is sound that travels through soft tissue and fluids, but it bounces back, or echoes, off denser surfaces.

This is how it creates an image. For diagnostic uses, the ultrasound is usually between 2 and 18 megahertz MHz. 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. Ultrasound will travel through blood in the heart chamber, for example, but if it hits a heart valve, it will echo, or bounce back. It will travel straight through the gallbladder if there are no gallstones , but if there are stones, it will bounce back from them.

This bouncing back, or echo, gives the ultrasound image its features. Varying shades of gray reflect different densities.

Some very small transducers can be placed onto the end of a catheter and inserted into blood vessels to examine the walls of blood vessels. Ultrasound is commonly used for diagnosis, for treatment, and for guidance during procedures such as biopsies. It can be used to examine internal organs such as the liver and kidneys, the pancreas, the thyroid gland, the testes and the ovaries, and others.

An ultrasound scan can reveal whether a lump is a tumor. This could be cancerous, or a fluid-filled cyst. There are no known risks.

Ultrasound is a valuable tool, but it has limitations. Sound doesn't travel well through air or bone, so ultrasound isn't effective at imaging body parts that have gas in them or are hidden by bone, such as the lungs or head. Wear loose clothing to your ultrasound appointment. You may be asked to remove jewelry during your ultrasound, so it's a good idea to leave any valuables at home. An ultrasound uses sound waves to create an image. This ultrasound shows a liver tumor. These images show how ultrasound can help guide a needle into a tumor left , where material is injected right to destroy tumor cells.

During a transvaginal ultrasound, your doctor or a medical technician inserts a wandlike device transducer into your vagina while you are positioned on an exam table. The transducer emits sound waves that generate images of your uterus, ovaries and fallopian tubes. Gel is applied to your skin over the area being examined.

It helps prevent air pockets, which can block the sound waves that create the images. This water-based gel is easy to remove from skin and, if needed, clothing.