USG Artifacts.pptx..This presentation provides an overview of ultrasound artifacts, explaining their causes, appearance, and significance in diagnostic imaging, helping students and professionals identify common errors, and enhance the overall quality and

Ultrasound artifacts

1. ULTRASOUND IMAGING ARTIFACTS Presented by- Shipra Saroj [email protected]

2. IMAGING ARTIFACTS Artifacts are echoes on the screen that are not representative of actual anatomic features or occur when there are anatomic structures in the body that are not displayed on the screen. Artifacts may also occur as a result of electrical interference or a problem with the ultrasound machine. Artifacts result from assumptions that the ultrasound machine makes. These include: • Sound beams travel in a straight line and go directly from the transducer and back. • The only propagation speed in the body is 1540 m/s. • Any reflection that comes back to the transducer must have been along the path of the beam. • The slice thickness plane is razor thin.

3. Reverberation artifact A common artifact is reverberation, which is described as multiple reflections, and it occurs when the sound bounces back and forth between two closely spaced strong specular reflectors. This produces a "stepladder"-like appearance of parallel echoes that are equally spaced and decrease in brightness (amplitude) with depth. One subtype of reverberation is comet tall, which is caused by small structures like surgical clips or adenomyomatosis within the gallbladder wall. Ring-down artifact appears similar to comet tail, but is caused by sound interacting with small air bubbles, causing the bubbles to vibrate.

4. Mirror Artifact Mirror image artifact occurs when the sound is aimed toward a large specular reflector that acts like a mirror and directs some of the sound in a direction other than back to the transducer. This causes the reflector to appear equally spaced apart from either side of the strong reflector. This artifact is commonly seen near the diaphragm and pleura. Note that the duplicate object always appears deeper than the actual structure being duplicated.

5. Edge Shadowing Refraction causes artifacts as the beam is directed away from the path in which it was originally intended to go. One refraction artifact is edge shadowing, which is seen when sound strikes a curved reflector like the transverse gallbladder or carotid artery. Spatial compounding eliminates edge shadowing because the object is imaged from different angles. Thus, spatial compounding improves margin delineation. It also reduces speckle artifact and reverberation, resulting in a smoother image with improved contrast.

6. Side Lobes or Grating Lobes It is expected that sound energy travels along the main axis of the beam. If there is extraneous sound energy not along the main axis, the possibility exists that this sound will cause reflections back to the transducer. As the machine assumes that all reflectors lie along the path of the beam, the artifacts produced are called side lobes or grating lobes. Side lobes occur with single-element transducers, and grating lobes occur with array transducers. Tissue harmonics, apodization, and subdicing , which is a technique that slices the crystals into much smaller sections, are used to reduce or eliminate grating lobes.

7. Propagation speed errors Propagation speed errors can take place as well. Recall that although the ultrasound machine is programmed to assume that sound travels through all tissues at 1540 m/s, this does not actually occur because the body consists of many different types of tissue, with many different propagation speeds. Nonetheless, the machine uses 1540 m/s regardless of which type of tissue, or group of tissues, the beam encounters. If the actual propagation speed through which the sound is traveling is less than 1540 m/s, reflectors will be displayed on the screen too far away. Likewise, if the actual propagation speed of the tissue is greater than 1540 m/s, reflectors will be displayed too close. OR Speed displacement artifact, also known as propagation velocity artifact, is a gray scale ultrasound finding that can be identified as an area of focal discontinuity and displacement of an echo deeper than that its actual position in an imaged structure.

8. Shadowing Two potentially useful artifacts are shadowing and enhancement. Shadowing occurs when the sound travels through an area of higher attenuation (such as a rib or other calcified or bony structure) compared with the surrounding tissue (Figure 3-35). This artifact is useful because it helps with the identification of stones, such as those that may develop in the gallbladder or kidneys. Acoustic enhancement, formerly referred to as through transmission, occurs when the sound beam travels through areas of lower attenuation, such as fluid (Figure 3-36). Because less of the sound is attenuated when traveling through this region (e.g., a cyst), there is more signal strength distal to the object. This makes the tissue deep to the weak attenuator appear brighter. Note that solid masses may have enhancement.

9. Slice thickness artifact (Also known as partial-volume artifacts ) The ultrasound beam is not razor thin; it has a definite thickness in what is called the slice thickness, or elevational plane. Any reflectors appearing in this plane will appear in the image. An often-seen example of this is scanning through an ovarian cyst and seeing what appears to be echoes within it. After the transducer is turned 90°, the echoes disappear, indicating they are not really within the cyst. Slice thickness artifact occurs because the beam scanned through both the cyst and the soft tissue adjacent to the cyst, causing both to appear on the image. The solution to slice thickness artifact is better focusing in the elevational plane, such as with 1.5D transducers.

10. Electrical Interference The presence of electrical equipment near the ultrasound machine (e.g., unshielded ventilators) may cause an artifact related to electrical interference. This causes arc-like bands that move across the screen as long as the machine is in proximity to the unshielded equipment.

11. THANK YOU