Abdominal Doppler - SD

Introduction to Abdominal Doppler

Hello, my name is Franklin Tesler.
I'm from the University of Alabama at Birmingham
and I'm going to be talking about abdominal doppler.

The Doppler Effect and Its Namesake

This is a stamp honoring Christian Doppler
for whom the Doppler effect is named.
I suppose a little bit of consolation
for him only getting this stamp was the fact
that he had a stamp with a small physics
tutorial at the bottom that you could see those two diagrams
showing the Doppler effect diagrammatically.

Importance of Angle in Doppler Imaging

But when it comes to doppler
to borrow the tagline from the folks@overstock.com,
it's really all about the o
and naturally it's not the O I'm talking about,
it's the angle and that's illustrated in this image
of a color doppler sonogram of a carotid artery.
It may look that we're nicely below the magic angle
of 60 degrees here set at 42 degrees,
but if you take a close look at the color Doppler image on
top up, you can see
that the angle correction doesn't match the flow in the
vessel as it should.
It should really be set like this.

Why is this so important?
As we'll see as we go through the abdomen, some
of the diagnosis you're going
to be making within the abdominal vessels depend on
accurate velocity measurements.

Doppler Equation and Velocity Calculation

To illustrate the importance of this, we go back
to the Doppler equation, which you see at the top.
If you rearrange the terms, you show
how the machine is calculating
the velocity within the vessel.
See, the velocity of sound is known.
The doppler shift is measured by the machine.
F is the incident frequency, so the only variable left is
that angle theta, the angle correction
or more correctly in this case, the cosign of that angle.
The machine has no way of knowing what that is.
You tell it what it is
by setting the doppler angle correction cursor.

Example of Angle Correction Error

Let's look at an actual example here of a vessel
with a true flow velocity
of a hundred centimeters per second
and an angle of insulation of 60 degrees.
All the other values are either
constants or have been measured.
In this case, the shift is 3,250 hertz.
So if you're diligent
and you set the angle correction properly,
as I'm illustrating here,
the measured velocity will be very close
to the actual velocity of a hundred centimeters per second.
But what if you make a mistake
and you're off by only 10 degrees?
As is shown here, you've set a correction
of 50 instead of 60.
Remember, the machine doesn't know that it should be 60.
You've told it the calculated velocity in that case as shown
by the machine will be 78 centimeters per second.
That's a big difference.
So angle correction is absolutely critical.
If you don't do it properly,
you'll make errors in velocity measurements
and that can translate to errors in diagnosis.
Note that that's not the same
as a true 50 degree doppler angle as is shown here.
If the angle is really 50 degrees, that's
where you should set your cursor.
The doppler angle correction cursor should
therefore be set parallel to the vessel
or more correctly parallel to the flow stream in the vessel,
which usually is parallel to the vessel wall.

Tour Through the Abdomen

So with that introduc introductory technical point,
let's do a quick tour through the abdomen.
I'm going to cover the liver vasculature followed
by the renal vessels, a little bit on mesenteric arteries
and close with the IVC.

Hepatic Vasculature

Let's start off with the hepatic vasculature.
The most prominent feature
of the liver vasculature is the portal venous system,
which we look at on pretty much every abdominal sonogram.
The portal venous system accounts for about 70 to 75%
of flow to the normal liver flow is usually monophasic,
but it can be pulsatile in patients
with right-sided cardiac dysfunction, right heart failure,
tricuspid regurgitation,
and in fact in some young individuals
and the normal velocity is extremely variable.
This color doppler sonogram shows a normal main portal vein
with monophasic flow.
In this case a velocity measured at the peak.
Although the use of the term peak here is a little bit
different from the way it's used in arterial flow
because it's not pulsatile,
but in this case about 29 centimeters per second.
As I said, the velocity varies widely
and as I also just mentioned, it can be quite pulsatile
as in this case of a patient
with right-sided cardiac dysfunction.

Portal Hypertension

Portal hypertension, which we are asked often asked
to look at in our patients may be classified
as intra hepatic either pre or post sinusoidal
or extra hepatic pre or post hepatic.
It's defined as a portal vein to hepatic vein
or IVC gradient of greater than
or equal to 12 millimeters of mercury.
The signs include dilation of the portal veins, SMV
and splenic vein
and detection of collaterals with he petal ugal flow.
And these collaterals are myriad including the coronary
vein, the short gastric veins, the umbilical vein
or spontaneous breal shunts
and the most commonly seen
or looked for sign reversal of flow in the portal.
Vein dilation of the portal vein is really not a very
sensitive sign of portal hypertension,
but when the portal vein is as large as we see here,
almost 2.2 centimeters, that's a pretty good indication
that flow within the portal venous system is abnormal.
Here we have an example
of reversal flow in the main portal vein as is shown by the
blue color within the vein showing flow away from the
transducer and hence out of the liver.
And here is the same patient shown on a spectral doppler
tracing with reversal of flow.

At first glance, this sonogram looks pretty normal.
We see the main hepatic vein with flow into the liver
and we see it here in the clip with a lot
of hepatic arterial flow around it.
And in fact that could be a little bit of a clue
because that's a common finding in cirrhotic patients.
But if you follow flow through the liver
and look diligently through the collaterals I mentioned,
you'll find flow directed from the left hepatic vein
along in this case a patent rec canalized
periumbilical collateral vessel.
And this vessel can be followed along the anterior abdominal
wall indicating that there is portal venous hypertension.
Often we see varis near the splenic hilum on gray scale.
The spleen here is shown to be enlarged,
but there are a number of sono lucin structures near the
hilum which on color doppler imaging light up
and these are varice in a patient
with portal venous hypertension.

Portal Vein Thrombosis

Portal vein thrombosis is another diagnosis we get asked
to look for quite frequently,
but it's important to note that it may be very difficult
or even imp impossible
to distinguish very slow flow from actual thrombosis.
Gray scale imaging is as important as doppler interrogation
because non-obstructive portal venous thrombus can be very
difficult to see with color doppler
where the color signal overrides the thrombus.
It's also important when you see thrombus in the portal
venous system to look
for flow in tumor thrombus in the setting
of hepatocellular carcinoma.
And I'll say more about that, how to detect that later.
Here's a case of portal vein thrombus in this case.
There's no doubt that all these echoes within the portal
vein are abnormal and indicate true thrombosis.
And here's another case in this case, a clip, a lot
of arterial flow
but no flow in the main portal vein, which is filled with
low to medium level echoes indicating thrombus.
In some cases with longstanding thrombus you can get
so-called recanalization of the portal vein
that is development of multiple collaterals
and in some cases those collaterals can as in this case,
simulate a patent portal vein on color
or spectral doppler imaging.
And it's important not to fall into this trap
and call this a patent portal vein.
Usually the collaterals are smaller,
more tortuous than the main portal vein
and it's important to follow the portal venous system
from outside the liver.
That is the slen portal confluence into the liver
and that usually makes it obvious vs.
Portal Vein thrombosis, as I just said, can also be related
to hepatic cellular carcinoma as in this case,
especially in a cirrhotic.
If you see portal vein thrombus, you need
to look diligently at the hepatic parenchyma
for the associated HCC.
In some cases the portal vein thrombus can be biopsied if
there is no other suitable biopsy target.

Hepatic Veins

As I'm showing here,
there are usually three major hepatic veins, right, middle
and left, but variations in accessory vessels
are quite common.
The waveforms are normally phasic.
This slide shows the right
and middle hepatic veins coated in blue
with flow toward the IVC where they converge.
And this is a typical spectral doppler tracing in this case
from the middle hepatic vein showing the normal
phasic waveform Monophasic waveforms,
as in this case in the right hepatic vein may be seen
in a number of conditions.
Most notably cirrhosis as in this case

Budd-Chiari Syndrome

the Bud Chiari syndrome is something we get asked to look
for fairly commonly as well.
It's really an amalgam of diagnoses
and it results from hepatic vein obstruction at any level
from the IVC to the main hepatic veins to the small vens.
The gray scale findings include enlargement of the liver,
hypertrophy of the caudate lobe, inability
to visualize the hepatic veins, which usually
unless the liver is very abnormal, otherwise are easy to see
and thickening of the hepatic vein walls
or intraluminal clot or webs.
In this case, the clot
or webs would be the actual cause of the syndrome.
On doppler, we may see no
or reversed flow in the hepatic veins
or development of intra hepatic collaterals.
Here's an example of a patient
with Bud Chiari syndrome showing a small bit
of color in the hepatic veins,
but you can see the path
of the right hepatic vein in this case on the gray scale
image and there is no flow on it.
And here of course attention to technique is very important.
And this is for an an older,
an older article from 1993 from our group at UCLA
where we looked at color Doppler in uh,
the Bud Chiari syndrome in this case showing development
of collateral vessels on the left
and the actual site of stenosis in the IVC as indicated
by the arrow on the right.

Hepatic Arteries and Shunts

The hepatic arteries are most important
to look at in transplants
because unlike in the uh, non-transplant patient,
the where the portal venous system accounts for most
of the flow post-transplant,
the hepatic artery is extremely important.
Anatomic variations such as a replaced main right
or left branch are common,
although we typically don't diagnose those sono graphically.
Normally. The arterial waveform is
of a low resistance pattern as is shown here
in this normal hepatic artery.
Shunts are also frequently seen
spontaneous operative
or trans hepatic in the past operative shunts as therapy
for portal venous hypertension were fair, fairly common.
We don't see those so frequently anymore
and the main types of shunts we look at these days are trans
hepatic shunts and I will concentrate on those,
but here is an example, a rare example in the case
of my institution of an operative porta caval shunt
and it's a little bit easier if I label the vessels
for you here in this case the portal vein and the IVC
and there is the shunt.
You can actually see the flow communication through
from one vessel to the other in gray
scale and then in color.
But those shunts you have to look for really carefully.
The communication site is often not very large
and deep, so it can be somewhat difficult to see.

The most frequent type of shunt we see these days are tips,
transjugular, inpe, porter, systemic shunts.
The most important take home point in these is
that angle correction.
Going back to what I said earlier is critical
and I always do the angle correction using the gray scale,
not the color doppler image,
you want the angle correction cursor to be parallel
to the flow stream and that's often easier
to tell on the gray scale images they'll show you.
It's also important to know
that the shunt may not be seen in the first few days
because of gas around the shunt and that can shadow
and completely obscure the shunt.
So we tend not to do baseline sonograms early.
It's important to measure the velocity at at least three
points in the shunt.
The so-called portal vein terminus mid shunt
and the hepatic vein terminus thrombosis is indicated
by lack of flow on doppler imaging.
Whether color or spectral stenosis is more difficult
to diagnose and a variety of criteria have been published
for this, including velocities less than 90 centimeters per
second or what I think is more important
a decrease from baseline.
Here's an example of normal flow at the portal vein terminus
of a shunt and it illustrates the importance
of angle correction using the gray scale image.
I like to zoom up the image quite a bit
so I can see the vessel wall
of the shunt rather very clearly
and set the angle correction cursor that way.
In this case the velocity is 57 centimeters per second,
but this was a normal shunt.
It had not changed from baseline.
That's why I think that a change from baseline can be a more
important indicator of impending stenosis than just an
absolute velocity.
And here we see the flow velocity measured
at the other end of the shunt.
In this case, the operator has elected it to do it
with the color doppler image,
but you can see that the color doppler makes it a little
harder to tell where the walls of the shunt are,
although in this case we're probably not too far off.
This is a case of a thrombo shunt shown in this clip
and you can see there's no flow here.
Remember that early on you may not see anything
because of gas shadowing, but that's not true in this case.
We can see the shunt, we just don't show the flow.
And this is a thrombo shunt.
Here is another shunt with a stenosis with a velocity
of almost 48 centimeters per second at the
portal vein terminus.
And this did represent a significant drop from the previous
scan and looking further distally in the shunt in this case
in the mid, the velocity increased
to 2.4 meters per second indicating a shunt stenosis.
Here's another common site for shunt stenosis.
This is where the shunt enters into the hepatic vein.
You can see that as color doppler aliasing.
And here's the corresponding spectral doppler tracing
showing a high velocity
of 2.7 meters per second

Post-Transplant Hepatic Artery

The role of ultrasound is
to detect vascular complications early
so they can be corrected and not require explanation.
As I mentioned, the hepatic artery
is very important post-transplant,
it assumes a predominant role in blood supply to the liver.
Normally it has a low resistance weight form
with a resistant index of 0.55 to 0.80.
But it's important to remember
that high resistance flow is common in the early
postoperative period.
It is not abnormal complications include stenosis
thrombosis and much less common pseudo aneurysms.
Here's an example of uh, an arterial tracing
post-transplant Normal.
And here's one post-transplant early in the postoperative
period with essentially no diastolic flow.
This is normal
thrombosis is indicated by lack
of flow in the proper hepatic artery
or intra hepatic branches,
Whereas stenosis which usually occurs at the anastomotic
site, is associated with a focal elevation of velocity
with turbulence just like stenosis elsewhere.
The problem is that the site
of anastomosis is often difficult to see in these patients,
particularly if they're in the ICU setting.
So we rely on indirect signs quite a bit, such
as a TARDIS parvis waveform in intrahepatic branches
and a resistive index of less than 0.5 in
as indicated in this case, the main hepatic artery.
This is almost a monophasic waveform with a resistive index
of 0.32 in this patient with hepatic artery stenosis.
It's also important to look at the portal in hepatic veins
post-transplant in the portal vein, looking
for thrombus stenosis or aneurysm
and the hepatic veins in IVC to look for stenosis
or thrombosis.
But these complications are less common.

Renal Vessels

Now let's shift to the renal vessels starting off
with the renal arteries.
And the main reason we get asked
to look at the renal arteries is for stenosis.
In patients with refractory hypertension,
the diagnosis can be based on either direct
or indirect criteria.
For the indirect criteria,
you interrogate the segmental arteries
and look for absent early systolic peaks
and TARDIS parvis waveform.
The direct criteria require accurate angle corrected
velocity measurements in the main renal artery
of at least 200 centimeters per second.
There are a wide variety of criteria here as well,
or as we use in our lab, a renal artery
to aortic satic velocity ratio of 3.5 to one or greater.
It's important however to look distally,
especially in younger patients
who may have fibromuscular dysplasia which tend, which tends
to involve the distal vessel.
Whereas in the older population
with atherosclerotic narrowing the stenosis US is usually
very close to the osteum To
get the ratio that I talked about.
Of course, you have to measure the velocity
and the proximal aorta as is shown here in this case at uh,
a systolic velocity of 0.8 meters per second.
And that's the basis for the ratio measurement later on.
This is one of the first things we do in the renal artery
doppler sonogram, but then of course we go on
to look at the vessels indirectly
and directly in this case within the kidney.
Looking at the intraarterial waveforms, these are normal
with sharp upstrokes.
We also pay some attention to the resistive index,
although an increase in the resistive index tends
to be nonspecific
and of course we look at the main renal arteries.
Doing that can be technically very challenging,
especially in large patients.
It's facilitated by having the patients fast overnight
to reduce bowel gas,
but it can be still be very difficult to do.
In this case, we have an abnormal intrarenal wave
form in this case.
The uh, middle
of the kidney showing a TARDIS parvis waveform in this
patient with renal artery stenosis further proximally
and in the same patient interrogating the main renal artery
showing very high velocity flow
with aliasing due to stenosis.

Renal Vein Thrombosis

We sometimes get asked to look at the renal veins
for thrombosis as well,
although we have an adult popul patient
population at our institution.
And this is a more common diagnosis in children than adults
and can be associated
with various conditions including dehydration,
nephrotic syndrome, hypercoagulable states.
Those are some of the predisposing factors.
And more commonly we see renal vein thrombosis related
to renal tumors, primarily renal cell carcinoma
with associated with tumor thrombus.
Here's one such case a clip showing this kidney with
a large mass in the anterior part of the kidney
and in this other clip showing the right renal vein,
which is distended with tumor.
Thrombus. More on that in a little bit.
There's also an incidental gallstone.

Mesenteric Vessels

Next I wanna talk
to you a little bit very quickly about the
mesenteric vessels.
There are a variety of indications
for looking at the mesenteric vessels,
the arteries primarily with ultrasound, including brue,
suspected aneurysms,
and most commonly suspected mesenteric insufficiency.
This like the renal sonogram, is best done
with the patient fasting
and early in the day it's important
to examine all the vessels as best you can.
The celiac axis in its branches, the SMA and the IMA,
and I won't go into this in great detail just to mention
that various thresholds have been published.
These are the ones that I use in the celiac axis
and the IMA 200 centimeters per second
and the SMA 275 centimeters per second.
Here's an example of an abnormal case of celiac axis
with a acephalic velocity
of greater than four meters per second in this case
with celiac axis stenosis.

Inferior Vena Cava (IVC)

I want to close by talking about the IVC.
The hepatic segment of the IVC is easiest to see
and in fact, looking at the IVC is part
of every normal abdominal sonogram,
even if doppler isn't being performed, you have
to look at the IVC structurally.
The wave forms within a are variable,
but usually similar to the hepatic veins to monophasic.
And as I mentioned, you can get tumor thrombus in patients
with renal cell carcinoma
or you can get bland thrombus in other conditions.
And this in fact is the same patient
that I showed you earlier with the IVC
and right renal vein thrombus related
to a large renal cell carcinoma in this case.
The IVC is distended with echogenic thrombus.
And one trick that I found useful in showing
that this is tumor thrombus
and not bland thrombus is not to use color or power doppler
because I think that can be very difficult
and you can see a lot of artifact and superior signals
and you really want to know
that you're looking at a pulsatile signal.
So what I do is I put the spectral doppler le cursor
with a very large sample volume, uh,
or sample gate on the thrombus as I've done here.
In this case, I've shown
a low resistance arterial pattern related to neovascular
in this tumor thrombus.
We can occasionally see thrombus in the IVC from other
causes, whether it is propagation from below in patients
with lower extremity DVT or as in this case thrombus,
and the IVC related to a filter
as is shown in this color Doppler image.

Summary

So to summarize, I'd like to reiterate two points.
One is to play close attention to angle correction.
As I've said before, if you are incorrect in your correction
as it were, you'll get incorrect velocity measurements
and that can lead to incorrect diagnoses.
And second, to use gray scale and Doppler color
and spectral imaging in concert in making your diagnoses.
Thank you very much.