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Mentions: The mirror artifact occurs when the sonographic waves are reflected by an angle by a high acoustic impedance tissue, for example like the diaphragm. The mirror artifact will mimic a virtual object similar to a true mirror on the opposite side of the structure [Figure 4]. The mirror image is more hypoechoic and somewhat more blurred and distorted than the image of the original structure as a result of absorption the of the ultrasound beam when passing through a long pathway. Reverberation artifact occurs when ultrasound bounces between two interfaces especially with high acoustic impedance like the pleura. The waves will move forward and backward between these interfaces. The machine will recognize these waves as parallel lines with equal distances between them, and decreased density for the deeper lines, because the reflected waves become gradually lesser in number. This results in a stripped pattern having alternating dark and clear lines at regular intervals [Figure 5].
Clinical ultrasound physics
Bottom Line: Depending on the acoustic impedance of different materials, which depends on their density, different grades of white and black images are produced.The operator should know sonographic artifacts which may distort the studied structures or even show unreal ones.The most common artifacts include shadow and enhancement artifacts, edge artifact, mirror artifact and reverberation artifact.
Affiliation: Department of Surgery, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
Understanding the basic physics of ultrasound is essential for acute care physicians. Medical ultrasound machines generate and receive ultrasound waves. Brightness mode (B mode) is the basic mode that is usually used. Ultrasound waves are emitted from piezoelectric crystals of the ultrasound transducer. Depending on the acoustic impedance of different materials, which depends on their density, different grades of white and black images are produced. There are different methods that can control the quality of ultrasound waves including timing of ultrasound wave emission, frequency of waves, and size and curvature of the surface of the transducer. The received ultrasound signal can be amplified by increasing the gain. The operator should know sonographic artifacts which may distort the studied structures or even show unreal ones. The most common artifacts include shadow and enhancement artifacts, edge artifact, mirror artifact and reverberation artifact.