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ULTRASOUND ARTIFACTS M.D. ALEJANDRO MONTALVO R1 – RADIOLOGÍA E IMAGEN

Ultrasound Artifacts

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ARTEFACTOS COMUNES EN LA ECOGRAFIA

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Ultrasound artifacts and contrast

Ultrasound artifacts m.D. Alejandro Montalvo r1 radiologa e imagen

definicinARTEFACTO

Se utiliza para describir cualquier parte de una imagen que no representa con precisin las estructuras anatmicas presentes en el sujeto que est siendo evaluado.Los equipos de ultrasonido se basan en supuestos fsicos para asignar la ubicacin y la intensidad de cada eco recibido.Supuestos ecogrficos1.- Los ecos detectados se originaron desde dentro del haz de ultrasonidos principal.

2.- El eco vuelve al transductor despus de una sola reflexin.

3.- La profundidad de un objeto est directamente relacionada con el tiempo que tarda en regresar el ultrasonido al transductor.

4.- La velocidad del sonido en el tejido humano es constante.

5.- El haz de sonido y su eco de viajes en lnea recta,

6.- La energa acstica en un campo de la ecografa es uniformemente atenuada.

Tipos de ARTEFACTOSArtifacts associated with ultrasound beam characteristics.

Artifacts associated with multiple echoes.

Artifacts associated with velocity errors.

Artifacts associated with attenuation errors.

Artifacts associated with ultrasound beam characteristics.Ultrasound beam exits the transducer as a complex three-dimensional bow-tie shape with additional off-axis low-energy beams side lobes.

A strong reflector located outside of the main ultrasound beam may generate echoes that are detectable by the transducer. These echoes will be falsely displayed as having originated from within the main beam.

----- Meeting Notes (1/16/14 22:49) -----most likely occur when e----- Meeting Notes (1/16/14 22:50) -----occur when misplaced echoes overlap an anechoic stucture.6Beam width artifactCaused due to the widening of the main beam after the focal spot.

Image quality may be improved by adjusting the focal zone to the level of interest and by placing the transducer at the center of the object of interest.

Longitudinal scan of the bladder

Beam width artifact

Side lobe artifactsSide lobes are multiple beams of low-amplitude ultrasound energy that project radially from the main beam axis, mainly seen in linear-array transducers.

----- Meeting Notes (1/16/14 23:37) -----most likely recognized when in an anechoic area.11Side lobe artifact

----- Meeting Notes (1/16/14 23:37) -----the air in the bowel is a strong reflector12

Artifacts Associated with Multiple Echoes

Reverberation artifactsUS assumes that an echo returns to the transducer after a single reflection and that the depth of an object is related to the time for this round trip. In the presence of two parallel highly reflective surfaces, the echoes generated from the ultrasound beam may be repeatedly reflected back and forth before returning to the transducer for detection.

RETORNO LENTO LUEGODE YA HABERSE REFLEJADO!

The echo that returns to the transducer after a single reflection will be displayed in the proper location. The sequential echoes will take longer to return to the transducer, and the ultrasound processor will erroneously place the delayed echoes at an increased distance from the transducer. At imaging, this is seen as multiple equidistantly spaced linear reflections and is referred to as reverberation artifact.

Comet tail artifactComet tail artifact is a form of reverberation.

In this artifact, the two reflective interfaces and thus sequential echoes are closely spaced. On the display, the sequential echoes may be so close together that individual signals are not perceivable.

In addition, the later echoes may have decreased amplitude secondary to attenuation; this decreased amplitude is displayed as decreased width.

The result is an artifact caused by the principle of reverberation but with a triangular, tapered shape.

Ring down artifactIn ring-down artifact, the transmitted ultrasound energy causes resonant vibrations within fluid trapped between a tetrahedron of air bubbles. These vibrations create a continuous sound wave that is transmitted back to the transducer. This phenomenon is displayed as a line or series of parallel bands extending posterior to a gas collection.

The display shows a bright reflector with an echogenic line extending posteriorly.

Left lateral decubitus US image of the gallbladder shows air and fluid in the duodenum causing ring-down artifact.Mirror image artifactsMirror image artifacts are also generated by the false assumption that an echo returns to the transducer after a single reflection. In this artifact, the primary beam encounters a highly reflective interface. The reflected echoes then encounter the back side of a structure and are reflected back toward the reflective interface before being reflected to the transducer for detection.

Artifacts Associated with Velocity Errors

Speed displacement artifactWhen sound travels through material with a velocity significantly slower than the assumed 1540 m/sec, the returning echo will take longer to return to the transducer.

The image processor assumes that the length of time for a single round trip of an echo is related only to the distance traveled by the echo.

The echoes are thus displayed deeper on the image than they really are.

This is referred to as the speed displacement artifact

This artifact is encountered when the ultrasound beam encounters an area of focal fat.

Refraction artifactsA change in velocity of the ultrasound beam as it travels through two adjacent tissues with different density and elastic properties may produce a refraction artifact. In refraction, non-perpendicular incident ultrasound energy encounters an interface between two materials with different speeds of sound. When this occurs, the incident ultrasound beam changes direction.

The ultrasound display assumes that the beam travels in a straight line and thus misplaces the returning echoes to the side of their true location.

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Artifacts Associated with Attenuation Errors

When the ultrasound beam encounters a focal material that attenuates the sound to a greateror lesser extent than in the surrounding tissue, the strength of the beam distal to this structure will be either weaker or stronger than in the surrounding field.

IMPORTANTE PARA REALIZAR DIAGNOSTICOS DIFERENCIALES ECOGRAFICOS

Attenuation is also dependent on the frequency of the ultrasound. Attenuation increases with increase in frequency. In soft tissues, the relationship between attenuation and frequency is linear. In bone and water, attenuation increases as the square of the frequency. In clinical imaging, the different tissues an ultrasound beam encounters attenuate the beam differently.

REferencesUS Artifacts. Myra K. Feldman, Sanjeev Katyal, Margaret S. Blackwood. Radiographics, 2009.RadioGraphics.