Unit 21: Acoustic Artifacts

This paragraph introduces the concept of acoustic artifacts in ultrasound imaging, explaining them as any image element that does not accurately represent true anatomy. Artifacts can either create false anatomy or cause the disappearance of real anatomy, often due to the machine making assumptions about sound travel that are invalidated by actual tissue interactions. The assumption of a constant sound speed of 1540 meters per second in soft tissue is highlighted, along with other assumptions that can lead to artifacts, such as direct sound travel to reflectors, unidirectional reflections, fixed sound direction, and a narrowly defined beam. The paragraph also mentions mechanical and operator errors as sources of artifacts and categorizes them into resolution, position, and attenuation artifacts.

The second paragraph delves into resolution artifacts, which occur when image details fail to accurately represent true anatomy due to the beam's insufficient narrowness in various planes. It discusses axial, lateral, and elevational resolutions, explaining how they relate to the spatial pulse length and beam width. The summary highlights the consequences of poor resolution, such as the merging of separate objects into one in the image, and provides strategies to mitigate these artifacts, such as using higher frequency transducers and positioning the focal point correctly. The paragraph also reviews the physics behind resolution artifacts and emphasizes the importance of understanding and correcting them for clinical imaging.

This paragraph examines position artifacts, which cause anatomy to appear in incorrect locations due to sound direction changes. It covers various types of position artifacts, including refraction, mirror artifact, multi-path artifact, and others, that result from sound interacting with structures at oblique angles or reflecting off strong specular reflectors. The summary explains how these artifacts can create false replicas of anatomy and discusses the importance of the machine's timing mechanism in mapping echo returns to their paths. Strategies to resolve some of these artifacts, such as changing transducer position or understanding acoustic physics, are also mentioned.

The fourth paragraph focuses on multi-path and reverberation artifacts, which occur when sound changes direction before returning to the transducer. It differentiates between these artifacts based on the reflectors involved and the resulting image patterns. The summary explains that multi-path artifacts create similar but not exact replicas of anatomy deep to the true structure, while reverberation artifacts produce equally spaced reflectors due to sound bouncing between two strong reflectors. The paragraph also discusses methods to mitigate these artifacts, such as adjusting the angle of insonation and reducing gain.

This paragraph explores reverberation and ring down artifacts, which are caused by sound bouncing between reflectors. Reverberation artifacts are characterized by equally spaced lines parallel to the sound beam, while ring down artifacts appear as dense lines due to sound interacting with very small structures. The summary describes how these artifacts can aid in diagnosing certain conditions, such as the presence of air, and discusses the importance of understanding the physics behind these artifacts to interpret images accurately.

The sixth paragraph discusses speed error and range ambiguity artifacts, which are related to the speed at which sound travels through different mediums. Speed error artifacts occur when the sound speed deviates from the assumed 1540 meters per second, causing structures to appear shallower or deeper than they are. Range ambiguity artifacts happen when echoes return after a new pulse is sent, causing them to appear in the wrong location. The summary explains how these artifacts can affect image interpretation and suggests adjusting imaging depth and using different transducers to mitigate them.

This paragraph examines attenuation artifacts, which occur when sound energy is greatly or minimally affected by a reflector. It describes how shadowing, edge shadow, and enhancement artifacts are formed due to the interaction of sound with highly attenuating or low attenuation structures. The summary highlights the diagnostic value of these artifacts in identifying calcified structures and fluid-filled pathologies and discusses strategies for working around them to obtain clearer images.

The eighth paragraph discusses enhancement artifacts, which occur when sound energy is minimally attenuated, resulting in brighter echoes behind certain structures, and speckle, which is a grainy appearance on the image due to interference and represents tissue texture. The summary explains how enhancement can help distinguish fluid-filled structures from solid pathologies and how speckle can be reduced using higher frequency transducers for clearer images.

The final paragraph summarizes various techniques to reduce artifacts in ultrasound imaging, including spatial compounding, frequency compounding, and coded excitation. It emphasizes the importance of adjusting imaging settings and using different frequencies to minimize interference and speckle. The summary also encourages practitioners to continually assess and adjust their imaging techniques to ensure the highest image quality and artifact recognition.