Color Doppler Sonography in Genitourinary Ultrasound - HD

Colored Doppler Sonography in GU Ultrasound

I'm gonna be talking about colored doppler sonography in GU ultrasound and these are my disclosures.

Before I talk about more specific applications of color doppler in g ultrasound, I thought I'd show you a couple of examples of where color doppler is not only important, but it's actually critical in making the correct diagnosis.

Critical Examples of Color Doppler Use

This is the first case. This is a kidney. It looks like a normal kidney with what looks like a simple cyst in the inferior pole of the kidney. Who thinks it's a, it's a simple cyst. Well, nobody one.

I wouldn't be showing you this, a simple cyst because with doppler we see that it fills in and we see the yin yang appearance characteristic. Yin yang appearance. There's this area of aliasing feeding this very large pseudo aneurysm which occurred after a biopsy of this kidney.

This is a life-threatening condition which we would not have made without color Doppler. Here's a movie showing that sing and then that flow going into and out of this large pseudo aneurysm, we did an MRI, which confirmed that this is a pseudo aneurysm. And then this patient was then able to be successfully treated with coil embolization.

Color doppler save the day different patients. This is a transplant kidney To my eye, on gray scale it looks pretty normal, but with color doppler we see that the entire upper two thirds of the kidney, does not perfuse. There's no color here.

Whenever we see something like this on color, it's nice to verify with power, power is a little bit more sensitive for slow flow. So we have power here. There's still no detectable internal vascularity.

What looks normal on gray scale is actually a partially infarcted kidney transplant.

And then finally this is a different case. This is a case given to me by my colleague Shichi Rogers from Einstein. This is a woman who came in with severe right upper quadrant pain. At our institution. When we do a right upper quadrant ultrasound, we still look at the kidney and this helps to show why.

On gray scale, this kidney looks normal, but with color doppler we see that there is no detectable internal vascularity in this kidney. And this was a completely infarcted right kidney, which we would not have known if we had not looked at it with color doppler.

Those are some examples of where color doppler is really critical. But I actually want to show you, or talk about more specific applications of color doppler.

Kidney Background Review

I'm actually gonna give you a brief background, kind of like a review from medical school about the kidney. And then we'll talk about color doppler and evaluation of hydronephrosis color doppler and twinkling artifact and how that can help you. And then just briefly about the bladder.

Going back to medical school, the kidneys are a pair of retroperitoneal organs that help to filter your blood, remove waste, and maintain your electrolyte balance. And it does this by excreting urine in various concentrations.

The kidney also has some endocrine functions. The kidneys, secrete rein from the juxta glomerular cells. They activate erythropoietin, which is important for red blood cell production and convert vitamin D, which is important for calcium homeostasis.

The renal parenchyma can be broadly divided into the cortex and the medulla and the primary unit of the kidney is a nephron. The nephron in turn is composed of the glomerulus where we have an afferent arterial. It goes into a tuft of capillaries and then an efferent arterial. And that helps to filter the blood into Bowman's capsule where that fluid is then taken to the proximal convoluted toe, the loop of Henley and then to the distal convoluted tubule.

And it changes the concentration of the urine using this countercurrent osmolarity system. The urine then goes into the collecting duct and then into the ureters and bladder.

The cortex is where the glomeruli live. And just an aside, when you biopsy a kidney, you need to biopsy the cortex because we are trying to get glomeruli in order to make a diagnosis.

And then the medulla is where the loop of Henley and the collecting ducks live. The juxta glomerular cells are a set of smooth muscle cells that live in the afer and efer arterials and they detect the amount of blood going to the kidneys. And in response to low blood volume, it'll, they will secrete rein.

Rein in turn activates the rein angiotensin aldosterone cascade and that helps to regulate sodium chloride and water in your body. And also angiotensin two is a very potent vasoconstrictor.

That's why in patients who have refractory hypertension, we often do a renal ultrasound. We'll typically also do a renal ultrasound in patients who present with acute kidney injury.

And that is defined as an abrupt decrease in kidney function less within seven days where the creatinine increases by 0.3 milligrams per deciliter or where your oliguric with urine output less than 500 ccs over a 24 hour period. If it gets better within 48 hours, that is considered to be rapid reversal acute kidney injury. But if it goes on over 48 hours, that is persistent acute kidney injury. And then if it goes on for over seven days, that is now acute kidney disease.

If you have, if you have a GFR that is low less than 60 and that's been going on for over 90 days, then you are in the chronic kidney disease realm.

In patients who present for the first time with acute kidney injury, suspected acute kidney injury, the A CR does recommend doing an ultrasound as first line imaging. And the reason for this is that the renal ultrasound can help to evaluate for potentially reversible causes such as hydronephrosis or poor profusion to the kidney. And we can also assess for evidence of chronic kidney disease which may have otherwise not been known in that particular patient.

Color Doppler in Evaluation of Hydronephrosis

Moving on to color doppler in evaluation of hydronephrosis.

Urinary obstruction is a very common cause of acute and chronic renal failure. And I have to say that at our institution, it's one of the main reasons for doing a renal ultrasound. They're always come, they always come in and say rule out hydronephrosis. Well, it's not everything, but we are definitely looking for obstruction.

And a secondary sign of obstruction is dilatation. With obstruction, typically patients will have symptoms such as f flank, pain, fever, nausea, a vomiting or hematuria. Sometimes they'll have recurrent UTIs. They may have polycythemia because of their erythropoietin.

And then causes of obstruction can include calculi in the collecting system. Tumors, strictures we saw earlier, cases of endometriosis obstructing the urinary system and then you can have bladder outlet obstruction.

When we are assessing for collecting system dilatation, I think it's important to use, vocabulary that is consistent. And so, when we look at the collecting system, if the renal pelvis is dilated, we would call that pelviectasis.

Colored doper is really important in confirming pelviectasis to confirm that that is truly a dilated renal pelvis as opposed to vessels. This is a different patient who kind of looks like they have ectasis, but with colored doppler we see that it actually fills in completely with color. So these are just prominent renal vessels.

Color is really important in helping to differentiate between the two. Ectasis is where you have dilated CAEs and again, colored doppler is really helpful in confirming that those are lyes as opposed to prominent pyramids.

But once you have dilatation of your renal pelvis as well as your caly, then we would call that pelvic ectasis. And most people accept that that is synonymous with hydronephrosis that may or may not be accompanied with ureteral dilatation.

And hydronephrosis can be obstructive hydronephrosis or non-obstructive hydronephrosis. Hydronephrosis is just a state of dilatation. It doesn't imply the reason for that dilatation.

With hydronephrosis, we can then give kind of a gest all a grade of the degree of dilatation that we see. And I would have to say that in the literature there's not clear definitions. So I just took this from STAT dx.

In Stat DX they just say mild hydro necrosis is if you have mild dilatation of the collecting system. Moderate is when you have moderate dilatation and casal blunting. And then severe is where you have severe dilatation as well as renal parenchymal thinning or changes in the renal architecture.

Resistive Index

When we evaluate patients with color doppler, we typically also get a resistive index. And the resistive index should be measured in either the distal segmental or inter low bar renal artery.

The resistive index is calculated by taking the peak systolic velocity minus the end diastolic velocity divided by the peak systolic velocity. So you have velocity over velocity. That means it's unitless because the units cancel.

This example here, we're angle correcting, but you don't need to angle correct because by angle correcting you're just gonna be dividing cosign of theta by cosign of theta. So that also cancels. So you actually don't need to angle correct in the literature.

The resistive index is accepted to be normal. If it is between 0.5 to 0.7 elevated if it's over 0.7 and then low, if it's less than 0.5. And if it's this low, then you start thinking about parvis tardis.

In my experience and in the literature, the resistive index is non-specific but helpful. It is a, it's not perfect. It is a marker of renal dysfunction and it is typically elevated with interstitial or vascular diseases. And we very frequently see high ris with chronic medical renal disease.

But you need to kind of put this into context with the patient because the resistive index does increase with advancing age. So in somebody who's very elderly, a high resistive index may actually be normal for that patient. So you need to put it into context with the patient.

And then another caveat about the resistive index is that it may actually be normal even in the presence of glomerular disease. And so we think that's the case, be that is the case because glomeruli only comprise 7% of the renal parenchyma, which is not a lot. And so that may not be enough to affect the resistive index.

This is a patient whose resistive index is pretty high, but if you look at this carefully, who believes this diastolic flow? Nobody. You guys are so smart.

This is not real diastolic flow. This is intrinsic machine noise, which we call clock phase jitter. And it is symmetric above and below baseline. It is, you see it in all silicone electronics, it's very hard to get rid of.

And that clock phase jitter can obscure the true diastolic flow. So if you use the clock phase jitter as your end diastole, you'll actually underestimate your true resistive index and that can lead to errors in interpretation.

In this patient, we redid it and redid the resistive index. And you can see there's still a little bit of clock phase jitter. I don't know if it projects, but we're able to make it less apparent and there's actually no diastolic flow here. So the resistive index is really close to one in this person.

The resistive index may also be elevated in patients who have acute high grade obstructive neuropathy. But again, there are some caveats with this. So there's this narrow window where the resistive index is typically elevated between six to 48 hours after the onset of symptoms.

This is a patient who has some mild hydro necrosis. I would say the resistive index is mildly elevated 0.76 on the left kidney that is asymmetrically elevated compared to the right, which is only 0.66 in the literature. It's felt that if you have, a resistive index difference of 0.6 to, I'm sorry, 0.06 to 0.1, that is significantly different.

And this patient difference was, caused by this UV J stone, which you can see because of twinkling artifact, which we'll talk about next.

In the setting of hydronephrosis, the resistive index has gotten kind of a bad wrap, I would say. First of all, it may not be elevated impartial obstruction. And if you have a for soil rupture, your resistive index may also not be elevated. So it's not perfect.

When it was first described by Joel Platt, also from Michigan in 1989, a long time ago, the diagnostic performance was reported to be excellent, 92% sensitivity in 88% specificity in differentiating obstructive hydronephrosis from non-obstructive hydronephrosis. And so everyone thought that was the greatest thing.

But then a few years later, Mitch Lin, and a few others, reported their experience with the resistive index and their diagnostic performance was not nearly as good with only a 44% sensitivity.

So we think that actually the resistive index in the setting of obstruction is affected by other things such as NSAIDs that can cause vasodilation and then can cause a resistive index to decrease, the degree of hydration, whether you got IV contrast that can affect your kidneys. And then your imaging technique like I just showed you with, the clock phase jitter that can, cause errors in your resistive index measurement.

Twinkling Artifact

Moving on to color doppler and twinkling artifact, it is twinkling artifact, not twinkle. I've heard a lot of people say twinkle twinkle is incorrect. It was, first described by uni etal. He's a Frenchman I guess from 1996. And so it might not sound correct to native English speakers, but twinkling is a gerand. And so if you wanna be correct about it, it is twinkling artifact.

Twinkling artifact, it is, it's a color doppler artifact and what you'll see is this alternating red and blue color doppler signal and actually all colors of the spectrum seen behind a rough, highly reflective surface.

And we think twinkling artifact occurs because of amplification of this intrinsic machine noise, this clock phase jitter. So what happens is, is you have a transducer here, it sends a brief pulse of sound and hits this rough surface. That sound gets reflected back to the transducer and the machine interprets that location.

The machine sends another brief pulse of sound. It thinks it's hitting the spot, but it's actually a slightly different spot. That slightly different spot has a different, path length and that gets interpreted as a frequency shift and then that gets interpreted as motion when nothing has moved. It's just a rough, highly reflective surface.

This is what clock phase jitter looks like I am using in this example. This is a, this is an image from this paper that I wrote a long time ago looking at twinkling artifact. And we used a pipette holder to image a flat surface. And so you get this clock face jitter, if you image even just a flat non-living surface that gets, that gets amplified with twinkling artifact.

And so with twinkling artifact you get this BroadB banded spectrum that fills the whole spectrum symmetrically above and below baseline. So that's what twinkling artifact looks like on spectral doppler.

And I think one of my CMA questions is how can you tell if it's twinkling artifact? If you wanna be sure you put a spectral tracing on it, you'll get this wave form.

A twinkling artifact, it's something that we see all the time. We see it with kidney stones, gallstones, adenomyosis, as well as biliary hematomas and then calcifications and other places like vascular calcs, pancreatic calcs, you name it.

With twinkling artifact, it's useful because it is not affected by the ultrasound beam. The focus of your ultrasound beam. So sometimes you'll see an area of twinkling where you're not actually focusing on and it helps to draw your eye to that spot.

It's also not affected by the ultrasound frequency, but it is affected by other machine parameters such as color, right? Priority. If you increase your color right priority, you'll increase the amount of twinkling artifact that you see.

If you increase your gray scale gain, you'll decrease the amount of twinkling artifact you see see. And then if you increase your PRF, you'll actually decrease the amount of twinkling that you see.

Here's some examples of where twinkling artifact can be helpful. This is a patient who has kidney stones on gray scale. I think it's kind of hard to see. Sometimes stones, they kind of blend in with the renal sinus fat.

The sonographer here put calipers because they thought that was a stone. But with colored doppler we can see that, oh, there's twinkling artifact here so maybe it is a stone. And there's another spot here with more twinkling artifact that helps us to draw our eye back to the kidney.

Oops, my arrows and the second area of twinkling corresponds to this other echogenic focus that maybe I didn't see as well originally. And then we can confirm that that is twinkling artifact and not aliasing by using spectral tracings over. And we see this broad broadband at spectrum different patient where the kidney is a little bit tough to see.

There's this echogenic area with color doppler. We can see that there is twinkling artifact. That helps us to draw our eye back here. And we can see this fairly perceptible, posterior acoustic shadowing that corresponds to that area of twinkling artifact.

And we can be sure that that's twinkling artifact by putting a spectral tracing on it. And you see that broadband at spectrum and that corresponds to this kidney stone here.

If you wanna be absolutely sure or very, very sure that you're really looking at a kidney stone, you can't just rely on the twinkling artifact. So you need to use your other stenographic features and that includes an echogenic focus, posterior acoustic shadowing. And then twinkling artifact is very helpful.

Here's an echogenic focus, posterior acoustic shadowing and twinkling artifact. Another example where we have this echogenic focus poster acoustic shadowing and twinkling artifact.

So there was a paper, really nice paper a couple years ago by Bill Mash etal also from Michigan. Michigan's just a powerhouse I guess. Run. Okay fine. Anyway, so, there's this paper that was published two years ago by Bill Mash etal looking at twinkling artifact and kidney stones.

And they looked at these three sonographic features, echogenic focus, shadowing and twinkling artifact. If you only use twinkling artifact in their paper, they had a positive predictive value for stone of 68%.

But if you add additional sonographic features like an echogenic focus, you increase your positive predictive value to 74%. And then if you add shadowing, you increase that p, positive predictive value to 92%. But you're gonna be much more specific for stone.

If you use all three but your sensitivity goes way down to 31%. So it's a compromise. If you can use twinkling to help improve your sensitivity, that's great. And then you kind of compliment that with these other sonographic features to improve your positive predictive value.

And there's another paper also from University of Michigan looking at just twinkling artifact in diagnosis of stones. And this is a paper by Jonathan Dillman et all from 2011 where they complain or compared twinkling artifact to five millimeter slice, non-contrast cts.

So if you only use twinkling and none of the other sonographic features, you're actually only gonna be correct 50% of the time or close to 50%. So in their paper, if they only looked at twinkling, the positive predictive value for stone was 78% anywhere in the kidney.

But if you look focus per fo, look at each individual focus, the true positive for stone was actually only 49% and they had a 51% false positive rate. So you're only gonna be correct 50% of the time if you only rely on twinkling. That's why you need to use your other sonographic features.

And the reason for that is that not all stones have twinkling artifacts. So here's an example of a pretty obvious stone to my eye. There is this echogenic focus and shadowing, but there is no corresponding twinkling artifact. So a twinkling is not perfect. Not all stones have twinkling.

Different example of a distal ureteral stone with shadowing, but there is no twinkling artifact. So it's not perfect. And then the converse is also not true. Not all twinkling equals stones.

In the kidneys we see twinkling artifact very commonly in debris layering in cysts. And here's an example. So this patient has lots of areas of twinkling artifact. You need to look at that carefully with gray scale.

And this patient, we see that that area corresponds to this little cyst and there is layering debris here that layering debris for some reason is really, really prominent on colored dopper as twinkling artifact very frequently.

And this is the same patient on CT that corresponds to that little tiny cyst that layering debris sometimes is way more obvious on ultrasound than on ct. In fact, it's not calcified on CT in many cases a different patient where we have lots of twinkling.

And there you can see that there's layering debris within the cyst and that corresponded to a cyst with a little bit of layering debris. You can see on the MRI, you can also have twinkling artifact in layering milk of calcium, which we can see with larger cysts or with CIL diverticula.

And this is a patient who has very prominent shadowing and really prominent twinkling artifact.

Twinkling artifact is really helpful in looking at UVJ stones. When we look at the bladder, we typically look for URE jets. And in this patient we have a unilateral jet on the left side, no jet on the right side, but with color doppler it's really nice to put that window just over the uuv js. That helps us to identify this little stone, with their twinkling artifact here.

I think twinkling is really helpful in looking for a UPJ stone. Sometimes stones in the UPJ are really hard to see because they're kind of deep or they may be obscured by bowel gas In this patient they have moderate mild to moderate hydro nephrosis.

Kind of hard to see, maybe you see it 'cause you guys are all great at ultrasound but hard to see on the gray scale. But when you look at it with colored doppler, you can see this area of twinkling artifact really obvious. And that corresponded to this stone that in retrospect was actually there.

I have some stills here. Here's a twinkling artifact that really helped us identify this up. PJ stone, this person did go on a CT and there is a stone here.

Color Doppler in Bladder Evaluation

Moving on to color doppler in looking at the bladder.

Going back to obstruction and hydronephrosis, this is a patient who has asymmetric dilatation of the collecting system on the right compared to the left. Whenever we see this, we wanna look at the bladder. And when we look at the bladder, what we're looking for are the jets.

The jets are really helpful in this patient. They have a left-sided jet but no right-sided jet. So unilateral jet, or obs jet is absent and that was caused by a, an obstructing right-sided UPJ wait UVJ stone.

Jets, are really helpful in figuring out whether your obstruction is complete or high grade versus partial or incomplete. So if you have a unilaterally absent jet, that actually corresponds very well with high grade obstruction with the caveat that the urine that's coming into the bladder needs to be of a different tonicity than the urine within the bladder.

Jets typically are best seen with color doppler, and they're usually one to three seconds and duration they'll alternate depending on the peristalsis. And the frequency of the jets appearing actually depends on how well how well hydrated the patient is.

If the patient has not been drinking for a long time, you may not be able to see their jets. And then typically you want the bladder to be at least moderately full to help improve your jet visualization.

Usually we see jets with color doppler. Sometimes we see jets with gray scale. I don't know if that projects, but there's some gray scale jets here.

Different patient where I don't know why the right jet you can see with gray scale. And then the left jet we could see with color doppler. So it's good to look at the jets in both gray scale and color.

Different patient who has mild hydronephrosis, of the kidney. And we can see the cause. There's this UVJ stone here. We can see that it's trying to make its way into the bladder.

We look at it with color doppler and we can see that there is this slow amplitude continuous jet, which is a pattern that we sometimes see with partially obstructing EVJ stones. So again, color is really helpful in showing that this is not a high grade obstruction, it's a partial obstruction.

Color is really helpful in looking at bladder stones. This patient has bladder stones to my eye I think it's hard to see on gray scale. Maybe you guys see it. But with color we can see all of this twinkling artifact and that corresponds to this area of shadowing.

And this patient did have a ct, I can't remember if it was before or after the stones. They're mobile. So on the CT they're on the opposite side, but you can see these layering little tiny stones.

And then finally an obvious example where a colored lar is really helpful in looking at the bladder. This person had gross hematuria. They have this large mass like thing in the bladder. Is this a hematoma or is this a tumor?

With gray scale it's a little bit tough to tell, but with color doppler we can see that there is internal vascularity and that has arterial waveform. So that is clearly a bladder cancer.

Conclusion

In conclusion, color doppler is really useful in gu sonography. It's really important in global assessment of the kidneys and collecting system in evaluation of patients who have obstruction and hydronephrosis.

Color doppler twinkling artifact is really, helpful in identifying kidney stones, but it's not perfect. You need to use those additional stenographic features to improve your specificity.

And then, color doppler is helpful in evaluation of the bladder, especially those jets. Thank you so much.