Ultrasound Physics: Artefacts and Principles

The three fundamental assumptions about sound wave propagation that are key to creating accurate ultrasound images are:

1. Sound travels in a straight line.
2. Sound travels into tissue, encounters a structure, and travels back directly to the transducer.
3. Sound travels at a constant speed in tissue (approximately 1540 m/s).

The assumption of a straight narrow sound beam contributes to accurate image formation by ensuring that echoes detected by the transducer originate from structures within the beam's path. This helps to minimize the occurrence of artefacts caused by echoes from structures outside the beam's intended range.

The assumption of constant sound speed is crucial for accurate depth measurement because the time it takes for an echo to return to the transducer is directly proportional to the distance traveled. If the speed of sound varies significantly throughout the tissue, the calculated depth will be inaccurate, leading to potential misinterpretations in the ultrasound image.

<p>Sound attenuation refers to the gradual decrease in the intensity of the sound wave as it travels through tissue. This weakening of the signal can make it difficult to detect echoes from deeper structures. It also impacts image interpretation, as structures at greater depths may appear less bright or even absent in the image.</p> Signup and view all the answers

<p>An artefact in ultrasonography is a spurious echo or an echo that does not correspond to an actual anatomical structure. It can also be an echo that is missing, misplaced, or incorrectly displayed in terms of size, shape, or brightness. Artefacts introduce inaccuracies into the ultrasound image, potentially leading to misinterpretation and diagnostic errors.</p> Signup and view all the answers

<p>Attenuation artefacts are caused by the uneven attenuation of sound waves within different tissues. This means that sound waves can attenuate at different rates in different structures, leading to variations in echo strength.</p> Signup and view all the answers

<p>Acoustic enhancement occurs when the ultrasound beam encounters a structure that attenuates sound less than the surrounding tissues. The TGC system overcompensates for the reduced attenuation, resulting in a brighter signal from the area behind the structure. This often occurs behind fluid-filled structures like cysts.</p> Signup and view all the answers

<p>Shadowing is a decrease in echo strength distal to a highly attenuating or reflective object. This happens because the strong attenuation of sound waves in the object reduces the intensity of the beam reaching the tissues behind it. This results in a darker region posterior to the structure. For example, calcifications or bones are known to cause shadowing.</p> Signup and view all the answers

<p>Clean shadowing occurs when sound waves are completely absorbed by a structure with high attenuation, resulting in a clear, dark shadow. Dirty shadowing, on the other hand, is seen behind highly reflective surfaces, like gas, where some echoes are still reflected back but appear scattered and disorganised, creating a less defined shadow.</p> Signup and view all the answers

<p>Attenuation artefacts can affect the accuracy of ultrasound images, potentially leading to misinterpretations. It is crucial to recognise these artefacts and distinguish them from actual tissue changes or pathologies. This allows for a more precise diagnosis and treatment plan.</p> Signup and view all the answers

<p>Examples of structures that typically produce shadowing include calcifications, bones, and gas bubbles.</p> Signup and view all the answers

<p>Acoustic enhancement can aid in the identification of cystic masses, as they are often fluid-filled and tend to exhibit this artefact. It also provides information about the acoustic properties of tissues and can help distinguish between different types of pathology.</p> Signup and view all the answers

<p>Failing to recognize and interpret attenuation artefacts can lead to misinterpretations of the image, resulting in incorrect diagnosis and potentially inappropriate treatment decisions. It can also contribute to missed diagnoses of pathology, delaying appropriate intervention.</p> Signup and view all the answers

<p>Less attenuating tissue results in stronger echo intensity from deeper tissues due to overcompensation of the TGC.</p> Signup and view all the answers

<p>Reverberation artifacts occur when sound waves bounce back and forth between two highly reflective interfaces, causing multiple echoes interpreted at increasing depths.</p> Signup and view all the answers

<p>Comet tail artifacts arise from closely spaced reflective interfaces where individual echoes are not resolvable, resulting in a tapering echogenic triangle or cone.</p> Signup and view all the answers

<p>Strong reflectors can cause sound to bounce between different structures, resulting in multiple echoes being received by the transducer.</p> Signup and view all the answers

<p>Partial shadowing occurs when part of the ultrasound beam is attenuated, causing the distal tissue to appear less intense yet not completely obscured.</p> Signup and view all the answers

<p>TGC is used to amplify echoes from deeper tissues to compensate for uniform attenuation, ensuring better visualization of structures.</p> Signup and view all the answers

<p>Echo time refers to the duration it takes for an echo to return to the transducer, which is crucial for calculating the depth of a structure based on the speed of sound.</p> Signup and view all the answers

<p>Speckle is caused by the interference of scattered ultrasound waves from small tissue structures, resulting in a granular appearance on the image.</p> Signup and view all the answers

<p>Ring-down artifacts occur when a sound wave encounters gas bubbles, causing them to resonate. These resonant vibrations produce a continuous sound wave that is transmitted back to the receiver, appearing as a streak or series of parallel bands extending deep to the focus of gas bubbles.</p> Signup and view all the answers

<p>A mirror image artifact occurs when a sound wave encounters a target after being reflected off a strong specular reflector. A portion of the beam is reflected back along its initial path, creating a second image of the target that appears deeper than the true location.</p> Signup and view all the answers

<p>A mirror image artifact appears as an identical structure to the original target, located above, below, or to the side of a strong reflector. It can occur adjacent to structures like the pleura, bladder, or bowel.</p> Signup and view all the answers

<p>Multipath artifacts occur when the sound beam encounters multiple reflectors along its path to or from a primary reflector. The beam may reflect off the primary target, then off a secondary reflector, before returning to the transducer. This increases the path length, making the object appear deeper than its actual location.</p> Signup and view all the answers

<p>Speckle is the granular appearance within tissues on an ultrasound image, resulting from scattered sound waves interacting with small interfaces. The beam interacts with these interfaces and scatters in all directions, creating a grainy texture.</p> Signup and view all the answers

<p>Speckle Reduction Imaging (SRI) is a technique that reduces the amount of speckle noise in an ultrasound image. It makes the image appear smoother and less grainy, improving visualization of tissue textures and boundaries.</p> Signup and view all the answers

<p>A twinkle artifact is a specific type of color Doppler artifact. It appears as a dynamic, flickering pattern of colors within the ultrasound image.</p> Signup and view all the answers

<p>Potential causes of twinkle artifacts include strong reflectors, such as small stones, dense calcifications, or moving air bubbles within the tissue.</p> Signup and view all the answers

Echoes or reflections that do not accurately represent actual structures in an image.

Includes missing echoes, mislocated echoes, or incorrectly representing size/shape/brightness.

Key beliefs in ultrasound: sound travels straight, at constant speed, and returns to the transducer.

Sound travels at a constant speed of 1540 m/s in human tissue for accurate imaging.

The thin layer where the ultrasound image is captured, crucial for depth and clarity.

Artefacts resulting from sound attenuating unevenly in tissue.

Increased brightness behind fluid-filled structures due to less sound attenuation.

Reduction in echo strength behind highly attenuating objects.

Includes enhancement and shadowing effects in ultrasound imaging.

Absorption of energy leading to no reflections past an object.

Hypoechoic (dark) area distal to a highly attenuating soft tissue.

Hypoechoic area distal to a highly reflecting surface, typically gas.

An artefact caused by inaccurate assumptions about sound speed in different tissues.

Artifacts occurring when sound reflectors cause echoes to return to the transducer inappropriately.

Artifact caused by sound bouncing between two strong reflectors, leading to false depth readings.

A subtype of reverberation artifact seen as a tapering triangle, caused by closely spaced reflectors.

Occurs when sound reflects off a boundary and back toward the transducer, misleading depth information.

Artifact caused by sound traveling different paths to the transducer, resulting in incorrect depth perception.

Artifacts arising from resonant vibrations in trapped air bubbles causing streaks in ultrasound images.

Grainy patterns on ultrasound images from acoustic interference, giving texture to tissues.

A control in ultrasound that adjusts the visible speckle for a more uniform texture.

Color Doppler artifacts that create a sparkling effect in ultrasound images.

The inherent dot-like echoes within tissues resulting from small-scale reflectors in imaging.

Reflectors that bounce sound waves back in a single direction, creating strong images.