![]() ![]() (7) The ultrasound system is dependent on all components of the imaging chain, including the transducer array, gain and filter settings, and image display, to be functioning normally. Additionally, proper transducer frequencies must be selected to achieve the desired depth of penetration in the image. Pulse repetition frequency (PRF) settings must ensure adequate time for listening for echoes before the next pulse. (6) Improper use of user-adjusted overall receive-gain or time gain compensation (TGC) results in images that may not be representative of the acoustic properties at a given depth in the image. This results in ultrasound energy emitted outside of the main beam producing echoes that can appear as if in the beam and creating false information in the image. (5) Transducer crystal expansion and contraction in the thickness mode produces the main ultrasound beam, but at the same time radial contraction and expansion also occur. (4) Ultrasound attenuation varies greatly from high to low in typical tissues and structures encountered, with resultant artifactual shadowing or enhancement of tissues at greater depths in the image. (3) Multiple reflections of ultrasound occur from all directions within the complex environment of the human body, complicating the mapping of anatomic boundaries in the ultrasound image. The transmitted ultrasound beam is redirected at an angle of transmission different from the angle of incidence (known as refraction ), potentially causing mismapped anatomic locations. (2) Even minor differences in ultrasound speed between tissues alter the transmitted beam direction from a straight-line trajectory when the incident ultrasound beam is nonperpendicular to the boundary, causing a change in wavelength (the ultrasound frequency remains constant in stationary tissues). ![]() Most notably, for fat with a speed of 1450 m/s (about a 6% difference), echoes along the trajectory, including fat structures, are displaced farther in terms of depth from the actual location. The ultrasound system uses the average speed in soft tissue of 1540 m/s to map echo amplitude depths as a function of time in the image matrix. In respective order are responses to these assumptions: (1) Sound travels at different speeds in different media based on compressibility and density characteristics. Most artifacts arise from violations of assumptions for creating the ultrasound image, including but not limited to (1) ultrasound travels at a constant speed in all tissues (1540 m/s) (2) ultrasound travels in a straight path (3) reflections occur from the initial ultrasound beam with one interaction at a perpendicular incidence for each boundary (4) attenuation of ultrasound echoes is uniform (5) all of the energy emitted by the ultrasound transducer exists in the main beam (6) the operator has transmit, receive gain, and other settings properly adjusted and (7) all of the elements in the transducer array, as well as the remainder of the imaging system, are operating optimally.Īrtifacts are caused by a variety of mechanisms that contradict the assumptions listed above. Understanding how artifacts are generated and how they can be recognized is crucial, which places high demands on the knowledge of the sonographer and the interpreting physician. Ultrasound artifacts represent a false portrayal of image anatomy or image degradations related to false assumptions regarding the propagation and interaction of ultrasound with tissues, as well as malfunctioning or maladjusted equipment. ![]()
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