Us artefacts

physics ultrasound

1. US ATRFACTS Dr. Kamal Sayed / MSc US AAU OK What is the principle of ultrasound? An electric current passes through a cable to the transducer and is applied to the crystals, causing them to deform and vibrate. This vibration produces the  ultrasound  beam. The frequency of the  ultrasound  waves produced is predetermined by the crystals in the transducer.

2. Artefacts US Artifacts  are any alterations in the image which do not represent an actual image of the examined area. They may be produced by technical imaging errors or result from the complex interaction of the  US  with biological tissues . Reverberation   artifacts  appear as a series of equally spaced lines . One can avoid artefacts by turninig off all electric equipment so that artefact does not hinder cardiac anatomy exam. Cauterization  artifact  is another example of how external electrical equipment can cause distorted  ultrasound  images.

3. What does artifact mean in medical terms? In  medical  imaging,  artifacts  are misrepresentations of tissue structures produced by imaging techniques such as ultrasound, X-ray, CT scan, and magnetic resonance imaging (MRI). ... Physicians typically learn to recognize some of these  artifacts  to avoid mistaking them for actual pathology.

4. Examples of tools causing artefacts include :  include stone tools, pottery vessels, metal objects such as weapons and items of personal adornment such as buttons, jewelry and clothing. Bones that show signs of human modification are also  examples . Artifacts  are items, usually found at an archaeological dig, are any things made by or used by humans. Some  examples  would be whole pottery, pot shards, stone tools, decorative and religious artworks, bones of the animals that the group ate, and sometimes human remains. Things such as shelters, firepits , etc

5. Artifacts https://radiopaedia.org/articles/blooming-artifact-ultrasound?lang=gb acoustic enhancement acoustic shadowing aliasing artifact anisotropy beam width artifact blooming artifact

6. comet tail artifact colour comet tail artifact double aorta artifact electrical interference artifact hardware-related artifacts transducer-related artifact mirror image artifact multipath artifact colour bruit artifact colour flash artifact

7. reverberation artifact refraction artifact ring down artifact side lobe artifact speckle artifact speed displacement artifact side lobe artifact twinkling artifact

8. An  image artifact  is any feature which appears in an  image  which is not present in the original imaged object. An  image artifact  is sometime the result of improper operation of the imager, and other times a consequence of natural processes or properties of the human body

9. . Mirror image artefact  is one of the beam path  artefacts . These occur when an  ultrasound  beam is not reflected directly back to the transducer after hitting a reflective surface, but rather takes an indirect return journey. The primary beam reflects from such a surface (e.g.  diaphragm ) but instead of directly being received by the  transducer , it encounters another structure (e.g. a nodular lesion) i n its path and is reflected back to the highly reflective surface (e.g. diaphragm). Slide (13)

10. It then again reflects back towards the transducer . To avoid this artifact, change the position and angle of scanning to change the angel of insonation of the primary ultrasound beam. In rhematology , mirrors nearly always are bone surfaces. The mirror artefact is easily seen as such when the true image as well as the mirror and mirror image are all in the image . The mirror image is slightly trickier when only the mirror and mirror image are present

11. . The ultrasound machine makes a false assumption that the returning echo has been reflected once and hence the delayed echoes are judged as if being returned from a deeper structure , thus giving a mirror artifact on the other side of the reflective surface

12. . It is a friendly artifact that allows the sonographer to exclude pleural effusion by the reflection of the liver image through the diaphragm. Examples : @ reflection of a liver lesion into the thorax (the commonest example) @ reflection of abdominal ascites mimicking pleural effusion @ duplication of gestational sac (either ghost twin or heterotopic pregnancy)  3 @ duplication of the uterus Images slides ()

13. Scrotum (upper image) /Liver lesion (lower image)

14. Acoustic enhancement Acoustic enhancement  also called  posterior enhancement  or  enhanced through transmission , refers to the increased echoes deep to structures that transmit sound exceptionally well. This is characteristic of fluid-filled structures such as cysts, the  urinary bladder  and the  gallbladder . The fluid only attenuates the sound less than the surrounding tissue. Slide (15)

15. Acoustic enhancement: upper ( hep cyst + GB)/ lower (epidermal inclusion cyst)

16. The  time gain compensation  (TGC) overcompensates through the fluid-filled structure causing deeper tissues to be brighter. Simply it is seen as increased echogenicity (whiteness) posterior to the cystic area. The presence of acoustic enhancement aids in the identification of cystic masses but some solid masses, especially  lymphoma , may also show acoustic enhancement posteriorly .

17. Acoustic shadowing (posterior acoustic shadowing)   is characterised by a signal void (dark or black area) behind structures that strongly absorb or reflect ultrasonic waves. it is a form of  imaging artifact . This happens most frequently with solid structures , as sound conducts most rapidly in areas where molecules are closely packed, such as in bone or stones. Slide (18)

18. LT image ( cholelithiasis )/ MID image (renal calculus)/ RT image (gas in colon diverticulum )

19. Beam width artifact Occurs when a reflective object located beyond the widened ultrasound beam,  after the focal zone , creates false detectable echoes that are displayed as overlapping the structure of interest. it occurs when scanning an anechoic structure and some peripheral echoes are identified, i.e. gas bubbles in the duodenum simulating small gallstones and peripheric echoes in the bladder. 

20. It is possible to avoid this beam width artifact by 1- adjusting the focal zone to the depth level of interest 2- and by placing the transducer at the centre of the object being studied . 

21. Mirror image artifact   is seen when there is a highly reflective surface (e.g.  diaphragm ) in the path of the primary beam. The primary beam reflects from such a surface (e.g.  diaphragm ) but instead of directly being received by the  transducer , it encounters another structure (e.g. a nodular lesion) i n its path and is reflected back to the highly reflective surface (e.g. diaphragm). It then again reflects back towards the transducer . To avoid this artifact, change the position and angle of scanning to change the angel of insonation of the primary ultrasound beam.

22. In rheumatology, mirrors are nearly always bone surfaces. The mirror artefact is easily seen as such when the true image as well as the mirror and mirror image are all in the image . The mirror image is slightly trickier when only the mirror and mirror image are present . The ultrasound machine makes a false assumption that the returning echo has been reflected once and hence the delayed echoes are judged as if being returned from a deeper structure , thus giving a mirror artifact on the other side of the reflective surface.

23. It is a friendly artifact that allows the sonographer to exclude pleural effusion by the reflection of the liver image through the diaphragm. Examples: @ reflection of a liver lesion into the thorax (the commonest example) @ reflection of abdominal ascites mimicking pleural effusion @ duplication of gestational sac (either ghost twin or heterotopic pregnancy)  3 @ duplication of the uterus Images slides (24)

24. Liver lesion (upper image) Scrotum / scrotum (lower image)

25. reverberation artifact Reverberation artifact  occurs when an  ultrasound  beam encounters two strong parallel reflectors. When the ultrasound beam reflects back and forth between the reflectors ("reverberates"), the ultrasound transducer interprets the sound waves returning as deeper structures since it took longer for the wave to return to the transducer. when the ultrasound beam reflects back and forth between the reflectors ("reverberates"), Slides (29/30)

26. the ultrasound transducer interprets the sound waves returning as deeper structures since it took longer for the wave to return to the transducer. Reverberation artifacts can be improved by changing the angle of insonation so that reverberation between strong parallel reflectors cannot occur.

27. Comet-tail artifact  is a specific type of reverberation artifact. This results a short train of reverberations from an echogenic focus which has strong parallel reflectors within it (e.g. cholesterol crystals in  adenomyomatosis ). It is advisable always to let the colour box go to the top of the image to be aware of possible reverberation sources Slide (31).

28. With comet tail artifact, the space between the two strong parallel reflectors may be less than 1/2 the space pulse length, causing the echoes to be displayed as triangular lines (the later echoes get attenuated and have a decreased amplitude, manifesting on the display as decreased width).

29. Anisotropy   artefact is an angle-generated artifact. It is produced in tissue that contains multiple, parallel linear sound interfaces (e.g., tendons, ligaments) that lead to the preferential reflection of the beam in one direction . When the ultrasound beam is incident on a fibrillar structure as a tendon or a ligament, the organised fibrils may reflect a majority of the insonating sound beam in a direction away from the transducer.  When this occurs, the transducer does not receive the returning echo and assumes that the insonated area should be hypoechoic .

30. This anisotropic effect is dependant on the angle of the insonating beam. The maximum return echo occurs when the ultrasound beam is perpendicular to the tendon.  Decreasing the insonating angle on a normal tendon will cause it to change from brightly hyperechoic (the actual echo from tightly bound tendon fibres ) to darkly hypoechoic . If the angle is then increased, the tendon will again appear hyperechoic Slide (35).

31. If the artefact causes a normal tendon to appear hypoechoic , it may falsely lead to a diagnosis of tendinosis or tear . In some situations, anisotropy may be useful in diagnosis. If a tendon is surrounded by other brightly hyperechoic structures (e.g. fat), then altering the angle of the transducer will cause the tendon to become hypoechoic , differentiating it from the other structures.

32. Anistropy : upper: TXR NOT perp. To volar ( palmar ) wrist lower : TXR perpendicular to volar wrist

33. Grating lobes Artefacts  are the maxima of the main beam. Side  lobes  and  grating lobes  are both unwanted parts of the US beam emitted off axis that produce image artifacts due to error in positioning the returning echo.

34. POINT SPREAD ARTEFACT This  artifact  occurs when two reflectors are perpendicular to the beam's main axis create one reflection on the image . It is also called  point spread artifact . Lateral resolution is determined by beam width. Point spread artifact is another term of describing suboptimal lateral resolution.

35. 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. Depth determination by an US machine is based on the principle that the average propagation velocity of sound in human tissue is 1540 m/s, and as such the { go return } time between transmission and detecting the returned sound wave to the transducer is multiplied by this number and halved to determine distance , regardless of tissue type

36. As a result, if the true propagation velocity of a tissue falls significantly below or above 1540 m/s, such as fat or bone, then the distance calculated by the machine will be false , displaying an inaccurate depth measurement. By this same principle, if there is differential variation in tissue composition of the tissues under the same ultrasound beam, then different return times to the transducer will be processed as different depths of tissue as opposed to differences in propagation velocity between the tissues. 

37. This may result in discontinuity in the displayed ultrasound image , and as such is referred to as a propagation velocity misrepresentation .  A commonly encountered scenario is speed displacement artifact due to slowing of the US beam by focal fat , such as in focal fatty sparing in case of hepatic steatosis .