USG Basics, Part 9: Understanding Ultrasound Artifacts in Medical Imaging

In this Article - Unlock the secrets of ultrasound artifacts in medical imaging with our comprehensive guide. From refraction to shadowing, master the art of interpretation.

Ultrasound imaging relies on a set of fundamental assumptions to convert sound waves into detailed images. A pivotal assumption is the constant speed of sound in soft tissue, typically set at 1540 m/s. Additionally, the technology assumes that sound follows a straight path, the ultrasound beam is exceptionally thin, echoes originate solely from the beam's midpoint, and that these echoes are contingent solely upon tissue type. While these assumptions form the basis for ultrasound imaging, deviations can lead to the emergence of artifacts.

Artifacts in ultrasound imaging are crucial phenomena that can either assist or impede the accurate interpretation and diagnosis of medical conditions. A nuanced understanding of artifacts enables practitioners to scrutinize specific areas of interest more effectively. Artifacts may serve as valuable indicators or, conversely, introduce confusion and misdirection into the diagnostic process. Mastery of artifact recognition is paramount, as misinterpreting normal structures as abnormalities or vice versa could compromise the accuracy of diagnoses.

Diverse artifacts may manifest in ultrasound imaging, reflecting discrepancies between assumptions and real-world conditions. One prevalent type of artifact arises from variations in the speed of sound, potentially leading to distortions in tissue depiction. Refraction and reflection anomalies can occur when sound waves deviate from their anticipated linear paths, contributing to artifacts that complicate the interpretation of ultrasound images. Additionally, issues such as beam width and shape can affect the formation of echoes, giving rise to artifacts that necessitate careful consideration.

In essence, a practitioner's grasp of ultrasound artifacts serves as a crucial diagnostic skill. The ability to discern between genuine abnormalities and artifacts ensures that medical professionals make informed decisions, mitigating the risk of misdiagnosis. Whether artifacts offer valuable insights or pose challenges, their comprehensive understanding underscores the nuanced nature of ultrasound imaging and the importance of practitioner expertise in its accurate application.

1. Refraction artifact, also known as anisotropy, arises from alterations in the trajectory of the ultrasound beam when transitioning between different mediums.

2. Posterior Acoustic Enhancement (PAE) occurs when ultrasound waves traverse fluid-filled structures, such as cysts or large vessels, resulting in heightened brightness in echoes beyond the fluid compared to the surrounding normal structures.

3. Noise or speckle in ultrasound images manifests as a granular texture and is attributed to an artifact known as speckling. This artifact resembles the visual interference or "white noise" observed on an old-age television screen (CRT) when a channel isn't properly received. Speckling occurs due to interference from multiple echoes generated by microstructures that are closely spaced and too diminutive for the ultrasound machine to distinguish adequately.

4. Shadowing in ultrasound imaging emerges when sound waves encounter a medium or structure that entirely reflects or absorbs them.

Reverberation artifact with Needle

1. Reverberation artifact is a phenomenon in ultrasound imaging that occurs when sound waves become trapped between two strong reflectors, leading to the appearance of multiple parallel lines or echoes on the ultrasound image. This artifact is characterized by a repetitive pattern of echoes extending deeper into the image than expected.

2. The Mirror Image artifact arises when a sound beam encounters a structure capable of reflecting sound similarly to a mirror, producing an image that appears distal to the actual imaged structure. This artifact is a consequence of specular reflection, where the sound beam reflects off a large and smooth interface.

3. Side lobe and slice thickness artifacts occur when echoes are generated by beams situated on the periphery of the central axis of the ultrasound beam, commonly known as side lobes or grating lobes. The ultrasound device, however, assumes that all returning echoes originate solely from the central axis of the primary beam. This misalignment results in the superimposition of images from different reflectors, leading to the creation of artifacts.

About the Author -

Dr. Debjyoti Dutta is a renowned pain specialist and author affiliated with Samobathi Pain Clinic and Fortis Hospital in Kolkata. He currently serves as a registrar at the Indian Academy of Pain Medicine, specializing in musculoskeletal ultrasound and interventional pain management. Globally acknowledged for his expertise, Dr. Dutta has authored significant publications, such as "Musculoskeletal Ultrasound in Pain Medicine" and "Clinical Methods in Pain Medicine," providing profound insights into the field of pain management. Additionally, he is a faculty member of the Asian Pain Academy Courses, contributing to the delivery of top-notch pain management fellowship training in Kolkata, India.