Introduction to clinical ultrasound: glossary of the most frequently used terms

Clinical ultrasound is a medical imaging technique increasingly used by healthcare professionals to enhance the physical examination. This non-invasive, radiation-free technique provides real-time images of the human body's organs and soft tissues. However, clinical ultrasound uses specific terms that may seem complex to novice practitioners.

In this article, we offer you a glossary of clinical ultrasound that brings together the most commonly used terms in this practice. Mastering these terms is essential to be able to learn about clinical ultrasound and correctly interpret the images obtained.

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Echogenicity: Refers to a structure's ability to reflect sound waves and produce echoes in ultrasound. A structure can be hypoechoic (few echoes), hyperechoic (many echoes) or anechoic (no echoes).

Anechoic: Refers to a structure that produces no echoes and therefore appears black on an ultrasound image. This is typical of liquid structures (effusions, cysts, etc.).

Hypoechoic: Refers to a structure that produces relatively fewer echoes than the surrounding tissue, resulting in a darker image than the reference tissue.

Isoechogenic: Refers to a structure whose echogenicity is similar to that of the surrounding tissue.

Hyperechoic: Indicates a structure that produces more echoes than surrounding tissue, appearing whiter on an ultrasound image. Hyperechoic structures often include dense tissue such as bone or calcifications.

Echostructure: General term for the overall appearance of tissues seen on ultrasound, including echogenicity and texture. Echostructures can be homogeneous or heterogeneous.

FAST (Focused Assessment with Sonography for Trauma): A rapid ultrasound protocol used to evaluate trauma patients. It aims to rapidly identify the presence of effusions in the abdominal or pelvic cavities, or in the pericardium, which may indicate internal bleeding.

eFAST (extended Focused Assessment with Sonography for Trauma): An extension of the FAST protocol that also includes assessment of the thoracic cavity for gas (pneumothorax) or fluid (hemorrhagic) effusion, in addition to the standard FAST abdominal and pericardial examination.

Acoustic terms

Image mode: Modern ultrasound scanners offer several imaging modes, such as B mode (for 2D images), M mode (for assessing the movement of structures, such as heart valves), and Doppler mode (for assessing blood flow).
Mode B (Brightness Mode): the most common display mode in ultrasound, representing the intensity of echoes received as bright dots of varying intensity on the screen.
Scanning: Technique of moving the probe over the patient's body. Scanning can be longitudinal, transverse or oblique, depending on the axis of the desired image. It is essential for complete coverage of the organ under study.
Spatial resolution: The ultrasound scanner's ability to distinguish between two objects in close proximity. High spatial resolution is essential for visualizing fine structures and small tissue defects.
Acoustic window: Area of the body that allows optimal transmission of sound waves for ultrasound imaging, without significant obstruction by structures such as bone or air.
Transducer: Device used in ultrasound to send sound waves and receive echoes. There are different types of transducer for different clinical applications.
Gain: Ultrasound scanner setting that modifies the amplification of received echo signals. The gain setting optimizes image quality according to the characteristics of the explored tissue.

Artifacts

Artifact: Incorrect or misleading representation on an ultrasound image, which may be caused by various technical or physiological factors, such as multiple reflections or aberrations.
Reverberation artifact: This artifact occurs when sound waves bounce repeatedly between two highly reflective structures, creating multiple echoes that appear as a series of parallel lines or repetitive echoes behind the structure.
Comet tail artifact: This is a specific type of reverberation artifact, appearing as a series of converging linear hyperechoic bands. Typical examples are B-lines in interstitial lung disease.
Posterior shadow cone: often seen behind highly reflective structures such as gallstones or surgical staples.
Acoustic shadow artifact: This manifests itself as a dark area behind a dense structure that blocks the transmission of sound waves, such as stones or bone. This creates a shadow with no ultrasound signal.
Posterior enhancement artifact: the opposite of acoustic shadowing, this artifact appears as an area of greater echogenicity behind less dense structures, such as cysts or fluid lesions, due to less attenuation of sound waves.
Mirror artifact: This artifact occurs when sound waves reflect off a highly reflective surface (such as the diaphragm), giving the impression that structures on the other side of this surface are mirrored.
Side lobe artifact: Occurs when secondary beams emitted by the transducer are reflected by objects off the main beam axis, creating images of these objects next to their true position.
Edge artifact: Appearance of dark or shiny bands along the edges of a rounded structure, caused by refraction and deflection of ultrasound waves.

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Conclusion

Although ultrasound may seem complex at first glance, it's important to note that it's not difficult to learn. Once you've mastered the theory and terminology, you can start training to integrate it into your medical practice.

Clinical ultrasound can provide invaluable information on the structure and function of organs and soft tissues, which can help you make a more rapid and accurate referral diagnosis. What's more, clinical ultrasound can be used as often as required to monitor the progression of pathologies and assess response to treatment, which can improve the management of your patients.

Finally, integrating clinical ultrasound into medical practice can strengthen the doctor-patient relationship, offering a more personalized approach and giving your patients a better understanding of their condition.

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