 Hello friends and welcome to Indian Radiologist. Today's lecture is a physics lecture on ultrasound artifacts and this lecture is going to be useful for radiology residents especially when they are giving their viva as we have created an acronym as well for these artifacts so that you can remember these artifacts when you ask this question in your examination. So what is an ultrasound artifact? ultrasound artifacts are echoes on the received ultrasound image that is not directly similar to the actual tissue being scanned. So let us try and understand what this means. So when the ultrasound beam from the probe hits the tissue it is ideally supposed to reflect back but all tissues give back different signals and hence a different digital image to us on our ultrasound screens and many tissues may either refract the sound it may scatter the sound or some tissues may also absorb the sound and it is these characteristics within a particular tissue that give rise to ultrasound artifacts. However artifacts are not bad as it is with these artifacts that sometimes and many times we can actually diagnose certain conditions as we about to find out. The acronym for this is ABC stream as simple as that and we are going to discuss these artifacts in this very order. Acoustic shadowing occurs as an area of low amplitude echoes behind an area of strongly attenuating tissue. So this is caused actually by severe attenuation of the beam at a particular interface. This results in very little sound being transmitted beyond that particular interface. Usually that tissue will be a dense structure for example like a stone in a gallbladder or in the kidney like we see here and it always occurs at interfaces with large acoustic mismatch such as soft tissue and bone or calculus. This attenuation is usually due to absorption or reflection of the sound waves. So we have here a couple of examples. We can see acoustic shadowing behind a renal stone that we see in the mid aspect of this kidney and you can see that shadowing very clearly. Most commonly you see it in gallstones where you see that acoustic shadowing taking place behind the stones and of course we can see some calcification here in a thyroid gland and we can see a dense black shadow occurring beyond this calcification. So more often than not when we see acoustic shadowing we are looking at calculi or calcification. Now the exact opposite of acoustic shadowing is acoustic enhancement and this artifact is seen as a localized area of increased echo amplitude behind an area of low attenuation. Hence it is seen behind fluid filled structures such as the urinary bladder or a cyst or even the gallbladder and this occurs because sound travels very easily through fluid filled structures and those structures will create a very low level of attenuation to the ultrasound beam allowing it to pass fast through that particular area and hence create a raised signal distilled to that particular structure. An example of this is this renal cyst as we see at the lower pole of this kidney. We can see the cyst move and we can also see the ultrasound artifact as an area of increased acoustic enhancement distilled to the cyst. The B in the ABC is beam width artifact and this is identified by understanding the shape of the ultrasound beam. Normally the main ultrasound beam exits the transducer at approximately the same width as the transducer and then it narrows down as it approaches the focal zone as we see here and then widens again distilled to the focal zone. Now this distilled beam may widen beyond the actual width of the transducer and that is what causes the beam width artifact. If there is a highly reflective object located within this widen beam beyond the margin of the transducer it can generate certain echoes and most commonly we see these echoes around the urinary bladder. So basically we can recognize beam width artifacts when a structure that should be completely an echoic such as the bladder will contain peripheral echoes as we can see here along the posterior aspect of the urinary bladder and if we see during scanning we can just improve the image quality by adjusting the focal zone down to the level of interest that is right down up to the posterior aspect of the bladder and this will help in reducing the beam width artifact. The C in the ABC is the comet tail artifact. Now to understand comet tail artifact we must understand that all objects do not reflect back the sound back to the ultrasound probe as we see on this image. Sometimes the structure may be highly reflective for example like cholesterol crystals in the gallbladder wall and this causes the sound beam to get reflected back and forth. Thus due to this back and forth motion the beam takes more time to reach back to the transducer. This delay causes the false echo to be displayed at a further distance from the transducer hence giving rise to the comet tail artifact. So where exactly do we see this comet tail artifact? We see it within the gallbladder. The advantage of seeing this artifact in the gallbladder is that once you see it you know that this is because of the rockitancy ascoff sinuses that create this particular artifact and we can safely diagnose adenomyomatosis of the gallbladder. Now the S in this stream is side lobe artifacts. Again to understand this we have to understand that normal structures reflect back the sound but there are low amplitude ultrasound energy beams that project radially from the main beam axis as we see here in figure B. So what happens with these low amplitude ultrasound energy beams that come out radially from the transducer is that they can hit structures which are on either side of the main image that we are imaging and if those structures are highly reflective they will pick up a signal from those structures and give it back to the main transducer. This is known as a side lobe artifact. Commonly we see it as extraneous echoes that come within a normal anechoic structure like in the urinary bladder or like we see here in this ovarian cyst. Actually this is a clear thin walled cyst that we see on the transverginal image. However because of the side lobe artifact that we see depicted by the green arrow here we see a linear bright structure within the cyst. We should understand that this is an artifact and not any internal components that are usually seen within the cyst like loculations or internal separations. Another example of the side lobe artifact is senior because the bladder is partially distended and we're getting some signals, linear signals that are seen at the superior aspect of this pregnancy sac and again these are nothing but side lobe artifacts. So side lobe artifacts actually look like beam with artifacts but the physics behind it is completely different. A twinkling artifact is actually a colored Doppler artifact but we could slip in this point as well in a regular ultrasound artifact QNA. So the concept is almost like that of acoustic shadowing that we see on a regular ultrasound machine. So what we see on Doppler is actually a focus of alternating colors behind the reflective object which is usually a calculus and this gives an appearance of turbulent blood flow. Many a time knowing this artifact you could actually switch on the color if you're trying to hunt for small stones and you will end up seeing a small twinkle distilled to the calculus thus confirming your diagnosis. It also depends on the machine setting so when the focal zone is located below the reflecting surface this twinkling artifact will become more obvious than when it is above it. Ringdown artifact is the R in the stream and ringdown artifact is a type of reverberation artifact. This occurs due to a ring of bubbles with fluid trapped centrally. Because of sound that is coming from this pocket of fluid there's a continuous source of sound energy that comes and goes back to the transducer for detection. This is seen as a very bright line and a dirty shadow almost that we call representing air from the bowel but it is because of that fluid that is trapped in between the air bubbles. Electrical interference is basically caused because of some problems in the machine output. It could be related to voltage fluctuation, frequency fluctuation and sometimes just some electrical interference which is coming from adjacent electrical machines that are on at the same time as the ultrasound devices. On this video we can see it as linear lines that are coming at the distal part of the screen where shadowing occurs at the edges of rounded structures and this occurs because of a combination of refraction and reflection. So when the ultrasound beam reaches the edge of the rounded structure there's a reflection which occurs with an angle of incidence that is equal to the angle of reflection. So when the ultrasound beam reaches the rounded edge of a particular structure the outer part of the beam gets reflected but the remainder of the beam passes through the rounded structure and is refracted. This combination of reflection and refraction of the beam at the edge of the rounded structure causes a thin strip of tissue that is behind the edge to not get insomniated at all by the ultrasound beam. It is this tissue that creates a shadow that is depicted as a very thin line going distal to the rounded structure as we can see on this image. Anisotrophy is an artifact that is encountered in ultrasound especially in muscles and tendons during a musculoskeletal examination. Why does this occur? When the ultrasound beam is incident on a fibrillar structure such as a tendon or a ligament these fibrils may reflect the majority of the insonating sound beam away from the transducer and hence the transducer does not get the signal back. The transducer thus assumes that the insonated area should be hypoechoic and here lies the trick because what could happen is that because of this artifact we might make an incorrect diagnosis of tendinosis or tendon tear. As we can see on this image of the biceps tendon we see a hypoechoic area seen within the tendon. This is not an abnormality this is the artifact of anisotrophy. Now the M in the stream is the mirror image artifact and these artifacts result in a mirror image of the structure that is seen on the ultrasound display. In this diagram you can see the gray arrow that represents the expected reflective path of the ultrasound beam that goes back to the transducer. However there are some other black arrows that we see from the edge of the structure which shows an alternate path of the primary ultrasound beam. Here the primary ultrasound beam has encountered a deeper reflective interface and because of that it takes longer time to return to the transducer and is misplaced on the display. This is commonly seen along the right lobe of livers especially on lesions that are sub diaphragmatic as we can see on both our examples. In one of the examples you can see what was later proved to be a hemangioma on CT. We can see the hemangioma on the other side of the diaphragm. Next video we can see a cyst which is seen at the sub diaphragmatic aspect of the right lobe of liver again which is reflected at a loculated area seen above the diaphragmatic surface. Okay friends thank you for watching this video I hope you liked it and if you did you can like share or comment on this video. You could also share this with radiology colleagues and students who are appearing for the examination shortly. Thank you.