Clinical Applications of Color Comet Tail Artifacts - SD

Introduction

Hello everybody.

My name is Dr. Hampi.

I am from Wake Forest University Department of Radiology.

Today I'm gonna be discussing the clinical applications of color comet tail artifact, also known as twinkling artifact.

Understanding Color Comet Tail Artifact

Talking about color comet tail artifact.

As you know, this has been described in the past in 1996, there has been an extensive paper on that by Kammony, which discusses the artifact, which actually represents reflections occurring from rough surfaces behind echogenic foci, specifically calcifications.

Now, the explanation behind this remains unclear, but based on this paper you can see that.

And on the diagram on the right hand side shows the experiment that was done by the author at the time and his colleagues, and it shows that from rough surfaces in the mid portion here of the slide, you can see that there is more amplitude received back to the device, which can be perceived as a doppler shift by the machine.

Factors Influencing the Artifact

Now, in our experience, to summarize what we need to understand about this artifact is we need to understand that it depends on many factors.

The most important are the color write priority of the machine.

Unfortunately, as an ultrasound operator, as a sonographer or a sonologist performing the exam, you are limited to what you can do about this parameter.

The other one that you can really play with and can help you generating that effect is the pulse repetition frequency, and the gray scale.

Again, we're gonna see some examples of that on the next slides.

Now the third component here, which is color doppler frequency, which it is our personal experience.

When we started to experiment with this artifact, we found that the lower the frequency allowed by the transducer, the more intense the color comet tail artifact.

In other words, the more the chances to be able to produce the artifact to help you identify tiny calcifications.

Example: Calcification in the Carotid Artery

Now on this video clip, you can see an example of a calcification in the carotid artery outlined.

Here you can see the posterior shadowing on the gray scale image, but as you notice that we are not trying to optimize the image to identify flow within the carotid artery or the ICA nearby.

If you look here, you can see that our scale is pushed all the way up to the limit.

In other words, we're trying to wash out the color sensitivity filling the vessels, but unfortunately, as you can see, we're using a high frequency six megahertz probe, which is the lowest frequency allowed by the transducer.

And despite that lower frequency, we still cannot produce that artifact.

Next you can see that we switch the transducer to a curvilinear probe.

The purpose behind this, as we know that curvilinear probe is of very low quality to apply for small parts like in the sense of the carotid, but the purpose here is to demonstrate to you that the lower the frequency you can use, the better the chances of getting the artifact.

And in this instance, you can see the corresponding calcification in the carotid artery here producing the artifact nicely.

And the advantage is due to this lower frequency 1.75 megahertz allowable by the transducer.

Clinical Applications

Example: Kidney Stone

Now this is another example showing a kidney stone in the pelvis of the kidney.

And you can see we did not manipulate at this point the gray scale.

The gray scale is high enough as you can see there, and we can see color doppler in the vessels in the kidney as well.

But in the center of the kidney, we can see this color comet tail artifact.

And you can see the color comet tail effect extends a little bit behind the bulk of the stone due to non-manipulative of the parameters described.

But what I do next? I go and I switch that to a higher scale.

And you can see that when you switch to higher scale, and of course you lower your frequency, what happens is you wash out the vascularity in the vessels and you can see the big stone and you can see how accentuated the artifact behind the big stone.

But also at the same time, you are able to identify other stones, tiny stones as you can see here, anteriorly and another stone that was not really appreciated on the prior slide in the lower pole of the kidney.

Applications in Detecting Calcifications

Now, where can we use this or where can we apply this artifact?

Now, in our experience, this would help in every aspect where we are looking for calcifications.

Basically stones, small bile duct stones, not adequately producing or incompletely producing posterior shadowing, including those within non dilated ducts, small non shadowing kidney stones without hydronephrosis.

Actually, this one is the most important, our practice.

As you can see, if you review the literature on the validity of ultrasound and evaluating kidney stones in general with gray scale, you can see that the sensitivity and specificity and the literature is very dismal and is really not helpful in identifying kidneys, small kidneys without evidence of hydronephrosis or obstruction here where color comet tail artifact can be helpful.

And this has been stressed in recent papers in the literature.

So this is something you can always use if you do a lot of kidneys looking for stones.

Now the other thing is what really helps also is the same entity that relates to kidney stones, where you look for stones, distal distally within the ureters.

And these can be tough to identify due to the fact that behind the bladder there's an intense acoustic enhancement and the bright echoes may not be able to be appreciated by gray scale ultrasound alone.

Now, the other application we can do is whenever we identify cystic lesions, before we say that these are benign cystic lesions, we need to apply color doppler on those cysts.

This is part of our practice.

This is specifically important also in the kidneys and virtually in any cystic lesion that you can identify in the body.

Now, another applications is evaluation and trying to figure out the presence or absence of chronic calcific pancreatitis by ultrasound.

The other application is you can use it to identify calcification in many other organs like the scrotum, the thyroid.

And as I've shown you in one example within the arteries, another application that really helps us in our practice as radiologist is when we look for surgical clips, catheters, stents.

And also when you do and perform interventional procedures in very big, thick patients, you'll be surprised to see that this artifact can help you localize the tip of your biopsy needle.

We're gonna see some examples of those.

Now, the other clinical area that's really important to stress is the role of this technology or this artifact in nephrocalcinosis.

You can this can really help you differentiate cortical and medullary nephrocalcinosis, specifically cortical nephrocalcinosis can be easily appreciated and not be missed, as we are gonna see a few examples along this lecture.

Optimizing Machine Parameters

So, before we go further, let me talk to you about how we do it.

In other words, how can you optimize your machine parameters so that you can get the best out of this artifact in your clinical practice?

So you identify the object of interest where you feel that the color comet tail artifact would improve your diagnostic confidence or even it may yield abnormal findings that were not considered in the first place.

So as I said earlier, the most important thing is to manipulate your color scale because you have the ability to do that on any ultrasound machine.

So decrease the color to decrease the color sensitivity.

In other words, you're trying to get rid of the normal frequency shifts from the vessels within the organs, and keep the artifact on the background so that you appreciate it better.

The other thing is switch to the lowest frequency allowed by the transducer.

This will also enhance the artifact.

We also found that if we move the transmit focus below the level of the object or area of interest, the artifact get more accentuated.

Example: Tiny Stone in Common Bile Duct

Now you can see here on this video clip, this is an example of a tiny stone within the common bile duct.

We lowered our sensitivity so that we try to get the artifact.

We still get some color in the nearby vessels, but you can see nicely that small little stone in the common bile duct is well appreciated.

And beyond that point, proximal to that point, you can see that there is not much of bile dilatation in this patient with normal bile duct diameter and a tiny stone in the distal common bile duct.

Example: Distal Common Bile Duct

Now this is another example of a similar patient, and you can see the intense color comet tail artifact within the distal common bile duct at the level of the head of the pancreas.

So on gray scale image here, this is a second example to show that there are multiple echogenic foci within the liver.

And you can see that these are in the expected anatomic location of the biliary duct.

When we apply color doppler to the same area in the liver, we can see there are multiple color comet tail artifacts from most of these echogenic foci, and this represent biliary lithiasis.

Example: Cystic Fibrosis Patient

Now another example is this case here, this is a 17-year-old with cystic fibrosis.

The clinicians were concerned about biliary stones as the liver function test indicates biliary obstruction.

So we scan this patient, we didn't find any evidence of extrahepatic biliary ductal dilatation, but as you can see here on the gray scale, it's really hard to appreciate the abnormality.

But you can see that there's maybe something here that's not quite obvious.

So we apply color doppler to this specific area and you can see that there is a nice color comet tail artifact and you can see just a little bit of ductal dilatation above that level.

So obviously patients with cystic fibrosis, they have the tendency to form very, very tiny stones within the intrahepatic biliary ductal system, which creates a picture of cholestasis and maybe obstruction in these patients.

And that's very important way of identifying these tiny little stones.

Now, without using that color doppler, you may have definitely missed that opportunity to make the diagnosis and explain the disease process in this patient and the clinicians, based on our findings, we're happy to explain why the patient is having the abnormal liver function tests.

Example: Gallbladder

Now we move on to show you another example.

This is a gallbladder.

And you can see within the gallbladder there are non-dependently echogenic foci with a gray scale color comet tail artifact or ring down artifact.

And when we apply color doppler to that area, you can see the color doppler is produced, not from all of these echogenic foci, but mainly from one or two of those.

But again, you have to keep in mind that the color comet tail artifact may not be produced or be expected to be produced all the time, as we said earlier, because it depends on the degree of the roughness of the surfaces to create the artifact or to produce the artifact.

Now this is another example where color doppler artifact can help you figure out the exact problem going on with this gallbladder.

Now you look at the gallbladder and if you don't carefully look in the region of the fundus of the gallbladder, you may think that all these shadowings maybe related to the nearby duodenum or stomach.

But what happens is when you apply color doppler, you can start to appreciate that there is a color comet tail artifact from the fundus of the gallbladder.

You can see in retrospect that this area represent a focal thickening in the fundus with these echogenic foci representing a clinical picture of adenomyomatosis.

Now, we also found in our practice, in our experience that the artifact can also be reproduced by using power doppler.

And you can see in this example there are multiple artifacts produced from the fundus of this gallbladder by power doppler.

Example: Pancreas

Now show another example.

This is a patient who presented with abdominal pain.

And you can see we all know that it's really hard to evaluate the pancreas by ultrasound because of the patient's body habitus, extensive bowel gas overlying the pancreas.

You can't really appreciate the pancreas, but really it's really hard to see what's going on.

But you see there is some area of shadowing here in the region of the head of the pancreas, but you may say, maybe it's due to bowel, maybe not.

And you can maybe say that there may be some echogenic foci within the body and the head of the pancreas.

But what happens is when you apply color doppler and you use the same setup that we described above by utilizing the lowest frequency and the high scale that you can get to, you wash out all the vessel markers.

And this shadowing may be related to stones, but obviously there are multiple calcification within this pancreas indicating that this patient is having a chronic calcific pancreatitis, another patient with chronic pancreatitis with more extensive disease in the head of the pancreas.

Well, here there's no doubt that you can make the diagnosis with a gray scale, but if you supplement this with color doppler, as we said earlier, you can definitely improve your confidence of the diagnosis and look how beautiful and intense these artifacts coming from these calcifications within the pancreatic parenchyma.

And you can appreciate nicely the duct, the minimally dilated duct in the head of the pancreas on both images.

Example: Staghorn Calculus

Now this is a straightforward image that anybody can diagnose without any problem.

You can see it on the gray scale.

You can see there's a big staghorn calculus occupying the collecting system of the left kidney.

But just for purposes of demonstration, you can see that how intense and nice the color comet tail artifact from these stones on these images.

Applications in Renal Sonography

Alright, now we move on to one of the most important areas where we think that this color comet tail artifact or the twinkling artifact is really of help to radiologists and practice, because this area is evaluating kidney stones or calcifications in the kidneys.

And you can see in this example here, this is a fairly thick patient.

You can look at the kidney and you can see this echogenic area here within, you don't know whether it is within the kidney or outside of the kidney.

You apply color doppler in the same technique and you can see nicely there's a color comet tail artifact produced from this cortical calcification in this kidney.

Now, now things get more complicated when you start to evaluate kidneys that show evidence of cortical disease.

Like in this instance there's the some cortical scarring.

Again, you can see the patient is fairly of good size and you get a lot of shadowing.

There's coming down from the ribs and you don't know what is this a stone or this is not, not a stone vascular calcification.

So we apply color doppler and we can see that that this is a stone there within the kidney and that's the cortex of the kidney over there.

So we managed to do this again by using the lowest frequency we can have and with using a very, very high scale, i.e. less color sensitivity.

Okay? We stay in the kidney and we look at another entity here and you can see this is a patient with polycystic kidney disease.

And you can see there are multiple cysts of variable sizes.

You can see there are some echogenic foci with ring down artifact, gray scale ring down artifact and you can appreciate it nicely there, but you don't know what is what.

So when you apply color doppler and you can see that this patient definitely had multiple echogenic foci.

Now there might be stone sitting among these areas of echogenic cysts.

However, these most likely the bulk of these echogenic foci with the color comet tail artifact represents calcification in the wall of many of those cysts in the kidney, most likely related to prior hemorrhages.

Example: Exophytic Cyst

Now this is a video clip with a gray scale and you wonder what's going on.

So if I ask you where is the calcification? What do you think the calcification is gonna be?

Is it gonna be in the kidney, is it gonna be in the spleen or where do you think that's gonna be?

And there you go, you apply color doppler and you can see that there's an exophytic cyst, which we thought of initially, maybe just a simple exophytic cyst.

Now this cyst is demonstrating evidence of color comet tail artifact.

And now this is not a simple cyst, this is a complex cyst and we need to keep an eye on this and monitoring the patient closely.

Alright, another example patient is having a cyst here looks simple and has all the features of simple cyst, acoustic enhancement thin wall and everything is fine.

Then we go apply color doppler and we can see that adjacent to this cyst there is a color comet tail artifact.

So this may be a calcification in the wall of the cyst that really also needs to be further investigated with CT to make sure that there is no evidence of something more advanced than just a simple cyst.

Example: Pitfall in Renal Ultrasound

Now this is, I wanna show you an example of where you can get into a pitfall when you read this kidney ultrasound.

This patient came with renal impairment and the ultrasound evaluation was done.

And you can see that if you don't pay much attention or you don't apply color doppler, you can easily say that the cortical echogenicity is increased and you would just go and label the diagnosis as renal parenchymal disease.

However, once you apply the color doppler to this kidney, you can see that all these are color comet tail artifact.

There is no cortical flow in this area.

So this is an extensive cortical nephrocalcinosis in this patient.

So your diagnosis now switch from just chronic renal disease based on echogenic kidney to a potential diagnosis that can help the clinicians pursue the possibility or the possibility why this patient is having cortical nephrocalcinosis.

The other entity that is more commonly seen than cortical nephrocalcinosis is medullary nephrocalcinosis.

You see the kidney, you can make the diagnosis nicely with gray scale, but sometimes the early nephrocalcinosis may be a challenge to make.

So you apply color doppler and you can see nicely that there are multiple color comet tail artifacts representing artifacts from tiny, tiny calcifications in this patient with nephrocalcinosis.

Example: Bladder Stone

Alright, here we can see on the video clip that there is an echogenic focus in the base of the urinary bladder and you can see with the posterior shadowing, but the thing is we don't know if this stone is causing complete obstruction or partial obstruction, but we use color doppler and you can see nicely there is the color comet tail artifact coming from the stone.

And you can see offside that there is a jet.

So this stone is not producing a complete obstruction, so the obstruction is partial and that's of important information can be relayed to the clinicians so that they don't have to panic and act on a completely blocked system.

Example: Distal Ureter Stone

Okay? This is another example of a stone in the distal ureter, but the example here is showing you that the stone is sitting.

If you freeze this, you can see that the stone is going within the bladder and there is more of a bladder tissue on both sides of the stone.

Now the color doppler shows the artifact nicely, and you can see that this artifact is produced within the lumen of the bladder.

There is a bladder on both sides of the stone, and you can see nicely that there's a jet and this was actually a stone within a urothelial polyp.

Example: Ureteral Stone with Hydronephrosis

Okay, we move on now to the next slide.

Alright, here you can see that there is an echogenic focus along the course of the right ureter at the level of the iliac vessels.

And you can see that there is some shadowing there.

Maybe that's the ureter you would say dilated above that.

So this dilemma can be solved by the fact.

You can see that this is the ureter coming nicely here.

These are the iliac vessels, and this is the stone blocking the passage of urine.

And you can see the proximal dilatation over there and you can see that this is the patient, a different patient with hydronephrosis.

We can appreciate the hydronephrosis, we can with gray scale, maybe assume that there's a stone there, but definitely this patient may have obstruction distal causing this hydronephrosis.

But when we apply color doppler in our technique, we can anchor and appreciate more stones.

There's a stone here, stone there, and there's another stone in the lower pole of the kidney.

Example: Spleen

Now another example is, let's look at this spleen.

The spleen has multiple echogenic foci.

You can make the diagnosis when the gray scale.

In this instance, you really don't need the color doppler.

But for purposes of illustration, I would like to show you that you can even produce the color comet tail artifact from some of these calcifications within the splenic parenchyma.

And again, as I said, don't expect to get the artifact all the time from any echogenic focus.

You see, and this is a good example demonstrating that.

And the reason why is maybe these are not too rough to be able to produce the artifact.

I mean, the surfaces of these echogenic foci are not that rough to produce the artifact.

Example: Post-Whipple Surgery

Now, another thing that helps you identify problems is before you jump to conclusions here, what is this going on and stuff like that.

Look, this is the area of the common bile duct in the porta hepatis.

And this patient had a Whipple surgery presented with abdominal pain.

And this is the corresponding CT and you can see the CT there in the porta hepatis and the level of the head of the pancreas, which corresponds to the same area.

On the ultrasound, there are multiple surgical clips and these surgical clips in this instance are producing the color comet tail artifacts.

Example: Foreign Body in Abdominal Wall

This is an interesting case of a patient who presented to the emergency department with right lower abdominal wall swelling.

And he didn't tell the full story to the ED physician at the time, and they sent him to rule out an abscess or fluid collection by ultrasound.

And if you look at this ultrasound image, you can see that there is abdominal fluid collection in the subcutaneous tissues of the lower abdomen.

And you can see that there is an echogenic focus there with the ring down artifact.

You can appreciate the ring down artifact on this one here.

And again, the same concept we apply color doppler and you can see how beautiful that the barely seen object here is producing this nice color comet tail artifact.

And the same thing here corresponding to this image, you can see the corresponding image with color showing the color comet tail artifact.

And this is the same patient with the corresponding CT.

And you can see the foreign body there, you can see the abscess in the subcutaneous tissues.

And this actually was a bullet fragment.

So when the patient was asked, he said, I was shot a week ago.

And I thought it didn't, the bullet did not retain in my body and I thought it will go away.

So, and that was an abscess related to a retained bullet in the abdominal wall.

Example: Calcified Appendicolith

This is another example of calcification that I said.

You can see it anywhere in the body.

And this is an calcified appendicolith, which has no clinical significance.

But again, for purposes of demonstration, you can see the color comet tail artifact on the corresponding color image.

Applications in Procedures

In our practice, we do a lot of procedures and biopsies.

And as you know, the population is, we don't have everybody thin and easy to do.

So this is a fairly good sized patient who had a kidney transplant and the clinicians want to rule out rejection and they ask us to perform a biopsy.

And you can see here that this is the needle biopsy coming down, but you really cannot determine this is exactly where is the tip of the needle.

So before you fire, you really wanna know where you're going, so you can utilize the artifact to help you identify the tip of your biopsy needle.

And you can see here the tip of the biopsy needle with the artifact is close to the surface of the kidney.

And then we felt comfortable that we can proceed and perform the biopsy.

And this is the biopsy of the kidney.

And I wanna tell you that even though this is a very large needle, it's a 16 gauge needle and that was not easily seen in this thick patient.

Example: Prostate

Another example for the color comet tail artifact is you can see it also within the prostate.

This is a calcified prostate focus there, which was identified by color comet tail artifact and we managed to exclude another focal lesion in the prostate.

But we know that ultrasound remains limited for transabdominal evaluation of the prostate.

Example: Pelvic Mass

This is another example of a lady who presented with a large pelvic mass, and you can see there is a large irregular pelvic mass with extensive shadowing there.

And we didn't know what exactly going on, but we assumed that this is a large uterine mass.

And this was actually a large fibroid with areas of calcification.

And the color comet tail artifact helped us identify these calcification.

But also we need to remember that shadowing from a large fibroid like this may not be solely related to calcification, but may also be related to the dense fibrous stroma of the fibroid.

Example: Subendometrial Cyst

This lady came for transvaginal ultrasound for pelvic pain, and incidentally we found this cystic lesion that has little calcification.

So we thought that this is a small subendometrial cyst and we managed to commit to that diagnosis.

Example: Appendicitis

Another example where this can be helpful is when you identify patients for lower quadrant pain, this patient was referred from the emergency department to rule out gallstones, but the patient during the examination pinpointed that the pain is in her right lower quadrant rather than the upper quadrant.

Clinically we know that pain in the lower quadrant can refer to the upper quadrant and vice versa.

So we evaluated the right lower quadrant and we managed to identify this focal calcific area with posterior shadowing.

And we applied compression is not compressing, but you can see that this calcified area is producing a little bit of a color comet tail artifact, and we thought that was from an appendicolith.

The patient was taken to the OR and operated on, and this was surgically proven acute appendicitis with an appendicolith.

Example: Thyroid Nodule

We all know that the thyroid evaluation is really challenging and we still don't have current exact sonographic differentiation between what is benign and what is malignant.

We have features that may tell us to suspect malignancy, and one of those is micro calcification.

So you can see that there is a nodule, which is solid cystic, and it has this little area of papillary projection.

So we applied color doppler trying to figure out if we can produce anything from that.

And our surprise, we managed to get a color comet tail from that micro calcification.

So we thought that this may be a micro calcification rather than colloid, as we did not appreciate any comet halo around the echogenic focus on the gray scale.

And this subsequently was biopsied and came back papillary thyroid cancer.

Conclusion

So in conclusion, color comet tail artifact or a twinkling artifact is a very helpful artifact.

It can help you identify problems, it can really influence your reports.

And we feel that the most important role for this artifact is in renal sonography because it improves stone detection rate dramatically.

And really in our practice where we are, we have a large population with kidney stones and the clinicians are happy with our ultrasound yield for stones.

And there is nowadays less and less CT scans for follow up of these patients.

And hopefully in the future, the technology will improve and we'll be able to see the artifact better.

But again, I have to tell you that as of today, you cannot have this artifact produced on all manufacturers machines on the market.

And that an issue we need to address to manufacturers to bring the artifact back because many of them they obviously suppress the artifact and thinking that we do not need it.

And this is the artifact that I call a friendly artifact that can help us improve things.

And thank you for your time.