Renal Duplex How to do it right including protocols - SD

Introduction

Hello, my name is Billy Zang.
I'm the formal technical director at Penn State,
Milton Hershey's Vascular Lab.
I presently am the clinical marketing manager at GE
Healthcare, and today I'd like to talk
to you about renal duplex imaging.

Equipment and Transducers

Okay, let's start with the lecture.
The first thing that's very important about this renal
duplex ultrasound exam
that we're gonna be performing today is the equipment
that you're gonna be using.
You really need to have a high end system to attempt
to do any abdominal work.
Especially if you're looking at the vasculature.
The transducers that you're gonna be using are going
to be the lower frequencies
because of the depth of the vessels
that you're trying to be interrogating.
So frequencies between two
and five megahertz are often used.
And you will also have to use color mode,
power mode, and any other advanced imaging applications
to help identify some of these really tough structures
that you'll be looking at when you're in the abdomen.

Looking at the arteries, the transducers
that you're gonna be looking at,
since they're the lower frequency transducers, many
of you are familiar with the curved linear as having those type of low frequencies as well
as the phased array transducers that we see right here.
Quite typically I'll start
with a curved linear transducer,
and then if I have a very difficult patient,
I'll move to my sector.
The sector can also help me out
because it allows a little better window
getting through the ribs.
If I'm have the patient in a lateral decubitus position
looking at that renal artery or the parenchyma,
or at the renal artery
as it moves back towards its origin at the aorta,
that sector scan helps me get through those ribs when
that patient is in that lateral decubitus position.
But as I just said, the curved linear transducer will
probably be your go-to transducer,
and a lot of major manufacturers have curved linear
transducers in several different frequencies.
And depending on your patient's body habitus,
you may find yourself in a situation
where you do not have to use a lower frequency.
And in fact, a higher frequency transducer will give you
better image quality and allow for better color sensitivity.
So based on your patient,
please choose your transducers appropriately.
That also being said, you may be in a unique situation
where a linear transducer may also serve that purpose.
And this really comes into play if you are doing a renal
transplant when you are scanning
for renal artery stenosis
or functionality within that transplant itself.

Patient Preparation

Patient preparation is really one
of the most important aspects of this exam.
If you can believe it or not,
the patient should come into your office, NPO
or in a hospital setting, be NPO
after midnight, diabetics will be a concern,
and we usually allow them to have a light breakfast,
no smoking or chewing is what we recommend
because that will allow air into the stomach area.
And obviously you're gonna be hunting
around in those areas for the artery.
We want the patients to take their morning medicine.
Obviously, most of these patients are sick
and have other problems going on,
and certainly for renal examination,
you're gonna have patients that have hypertension
and there are certainly most likely gonna be on some
antihypertensive medicine.
And then renal imaging should be done in the am also
to avoid any excess abdominal gas.
And we all know as the day goes on
and we see our patients for abdominal studies,
those patients seem to get gas.
We also wanna make sure that we have the patient
and they're aware of the fact that during this examination,
they're gonna need to hold their breath.
Very important
because these organs can move upwards to a centimeter
or two from the position that you see them in
as the patient is inhaling and exhaling.
So having to take patients take a deep breath in,
like these fine looking young ladies
and holding that breath or exhaling
and holding it, is really going to put the renal artery
or the other vessels that you're looking at in a favorable
position for you to take your doppler flow
and to take favorable B mode and color at duplex.
Imaging pictures really important when you're in the abdomen to be aware
of the anatomy and certainly more
than just the renal anatomy.
But we'll start with that since that's our target vessel.

Renal Anatomy

The renal arteries are located about two centimeters
below the xiphoid process,
that distal portion of the sternum.
If I place my transducer right
below the xiphoid process, I'm in pretty good shape
to see the celiac, the SMA and the renal arteries.
But certainly one of the landmarks I want to use when I'm in
that transverse approach is the left renal vein,
which is gonna come across the aorta on its way back to the IVC.
And that landmark really serves as a good position
for me to be in to identify both the right
and the left renal arteries.
These arteries will arise from the lateral
or posterior lateral walls of the abdominal aorta.
The left wall most of the time rise slightly
above the right.
We will definitely see these branching the branching effect of this renal artery
that moves towards the kidney.
And 20 to 30% of the patients will have an accessory
to renal artery, which we'll talk about a little bit.
And some of the problems and solutions
that we will come across when we are doing these renal duplex examinations when the patient has
more than one renal artery.

This is Dr. Netter's version of the anatomy.
It's very well drawn.
And everybody probably uses this
as a good starting point to get a feel for
what we should be looking at.
We can see the aorta coming through the diaphragm here,
and the first major branch being the celiac,
and the second one being the SMA.
And then we can see the renal arteries in
that location I just talked about in there.
In fact, is that left renal vein as it moves across anterior to the aorta on its way back to the IVC.
But the reality of it is that we're dealing
with very tortuous vessels.
And you'll note that when you're doing this examination
and these vessels when we meander their way to the kidney,
and the veins will meander away from the organs back
to the IVC,
and it's really very unusual to see them on a single plane.
So we have to take
that in consideration when we are doing this examination,
noting that we probably will have
to use multiple positionings of the patient
and of our transducer when we're trying
to assess these arteries.

As the arteries move to the kidney themselves,
we start calling them a little bit different.
You'll note that the renal artery is
not well collateralized.
So besides the accessory renal arteries
or the supernumerary renal arteries
that you may come across, that renal artery will leave the
origin of the aorta on its way to the kidney.
And when it gets to the kidney, it will divide itself
as it moves into the hilum and then into the parenchyma.
And we start to break up those specific arteries into
certain segments.
The first artery is a segmental,
and then the interlobar,
it moves out towards the periphery
and the arcuate,
which usually come across at a 90 degree angle.
And so sometimes the color filling is not as great
as the interlobar,
which is the most distant portion
of the tissue near the capsule region.
Those interlobar arteries will be identified.
Really need to have nice color settings to be able
to get a picture like this.
And we'll talk about how to make the color settings and the patient positioning very appropriate for you to obtain an image
that will give you a very clear demarcations of
where these arteries are within this kidney parenchyma.

Variants and Anomalies

We do have to know about variants,
and you can see with these percentages here that they're
a little bit seen more often than not the pre-K right renal artery.
Usually we would see this renal artery moving
underneath the IVC on its way to the right kidney.
But most some of the times between 15%
of the time we may see this right renal artery going
above the IVC and it may make it a little bit more difficult
or put more of a challenge on you to be able to look
for it in a different location.
Like we said before, the multiple renal arteries are the
majority of the anomalies that we may see within this system.
Early bifurcations, 10 to 15%.
This comes into play if we're looking at non atherosclerotic disease processes such as fibromuscular dysplasia,
which usually take place between the mid
and distal portion of the renal arteries.
A left renal vein that lies retro aortic as opposed to above the aorta
or a circumaortic left renal vein on both located in both the upper the anterior
and posterior to the IVC, which is in a whopping 9%.
And probably it happens and we see it,
but we don't actually document it because we're not looking for it.
'cause there's a lot of things going on in
that specific area.
And frankly, some of the times you're pushing down pretty hard to be able to maintain access to the renal arteries
and you may be actually including this left renal vein in
the process or making it so small
that you don't really see it.
And then multiple renal veins also,
25% are more often found on the right side,
which is a nice little thing
to remember when you're scanning.

Indications for Renal Duplex Examination

So indications for this renal duplex examination,
when the patient comes into your lab,
they're probably gonna have some type
of uncontrolled hypertension
that is the most likely indication
that you will come across.
You also know patients that have renal failure that have been requested to have this exam,
the ubiquitous abdominal flank bruit,
which really entitles you
to scan every artery in the abdomen.
But certainly if this patient has uncontrolled hypertension
coupled with their flank bruit,
the renal arteries are highly suspect that
that may in fact be causing that.
Following radiological surgical interventions, obviously
as we follow up the lower extremity arterial bypass grafts
and carotid endarterectomies, we would wanna do the same
for renal arteries and any known renal artery stenosis
that may not have been treated surgically,
maybe still doing a medicinal type of treatment
for the hypertension, but they want to follow it,
you will note that these patients will be coming back into the lab.
And then we have patients that have elevated creatinine
or BUN most of the time we see this
as an indication when we're looking at kidney transplants.
And I want another indication,
it seems like when patients come into your laboratory is,
you tend to have a larger patient come in,
not unlike some patient that we may see here.
Maybe you would see this patient with a for a liver duplex examination also.
But certainly this patient wouldn't come in
for a mesenteric duplex examination for gut ischemia,
but certainly they may have hypertension due
to their excess weight.
And this exam would be very challenging
and frankly, probably would not be able
to see anything from midline approach.
And we'd have to do everything laterally on these
larger patients, and we will talk about that.

Prevalence of Hypertension

So the prevalence of hypertension,
we get about 60 million patients within the United States
that have some form of hypertension
that hopefully are being treated for it if necessary.
If their doctor thinks it's appropriate within
that general population, less than 1% of them will have it.
That hypertension, if you would,
based on having renal vascular hypertension
or the cause of the hypertension being from a stenosis
within the renal artery
or proximal to the renal artery that's causing low blood flow to the kidneys.
If the clinical acumen
of the referring physician is pretty high,
they can select out a population within these this group
of individuals that will yield 17% of those patients having renal vascular hypertension.
And that's kind of the group that we want
to have selected out before they come to our lab.
That clinical selection that these physicians will be using is basically
that severe hypertension that I showed
as an indication on all these causes
with diastolic flows consistently
above 115 millimeters of mercury.
Malignant hypertension, hypertensive encephalopathy,
patients with uncontrolled hypertension.
And these are the patients that really are ones that really make me think
that there may be something going on.
The systolic pressures of above 165
and very high end diastolic pressures above 95
that are on three or more antihypertensive medications
and the hypertension is not being resolved.
Also, we look for patients
that have accelerated hypertension,
which is an increase in diastolic flow
of 15% within the last six months,
and then onset of hypertension between the lower end
before they get to 25 or greater than 45.
Abdominal flank bruit, like we also mentioned,
will buy you a pretty extensive examination.
But if that is coupled with hypertension,
that's a pretty good indication
to have this duplex examination caused.

Why Perform This Exam?

Now why do we do this type of exam?
I mean, a lot of people just do it
because they were told to do it.
Well, the kidney itself really helps
control your blood pressure.
And a lot of some people don't know that the kidney acts as a buffer zone in a fight or flight response.
If, for instance, you are losing a lot of blood,
the kidney reacts to that loss of blood
by releasing renin at the level
of the juxtaglomerular apparatus.
And that renin as it's into the system, will convert angio,
will convert angiotensin one,
and then angiotensin one converts to angiotensin two.
And that leads to a whole bunch of cascading things
of releasing aldosterone by incorporating
more salt into the system so that your blood pressure
increases, nervous system will then shut down
or clamp up some of your arterials in your peripheral.
So the system is conserving that pressure to the central portion of your body and your brain
and all these things take place
because the kidney, which has no brain cells, right,
is trying to compensate for this lack of pressure.
And of course, it can be fooled, right?
If you have a stenosis in front of that kidney in front
of that juxtaglomerular apparatus,
it will release the renin regardless of what is causing
that drop in pressure.
So if we can find that drop in pressure
to be a stenosis within the renal arteries,
and that can be fixed surgically, this patient should in fact, if it is renal vascular hypertension,
have a drop in their blood pressure
and possibly be able to come off their medicine.
So this is a fantastic examination to do
and a wonderful thing if we actually find renal artery
stenosis and even more wonderful, if that was the cause
of their hypertension, they can come off of their medicines.

Pathophysiology

The pathophysiology
that we will find within the renal arteries
and the aorta that will cause this type of problem within the system usually is
atherosclerotic disease.
And we're all very familiar with
that being vascular technologist.
And that mostly is located at the ostial
or proximal segments of this renal artery.
A lot of times you'll note that this disease is located
within the aorta and probably may start there and then
and encroach in
and go into the origin orifice of the renal artery
and extend to towards the kidney themselves.
But most of the time that proximal portion
of the renal artery will be
where you find the highest velocities.
And as I mentioned before, as you move mid distally,
you may not find that much atherosclerotic disease,
but if you do see an increase in flow, I would be very interested in the fact
that there may be fibromuscular dysplasia.
And also note that fibromuscular dysplasia,
if it's in the renal arteries,
it may also occur in the mid distal portions
of the internal carotid artery.
So you may want to call up the referring physician
and note that you saw this increase in velocity in the mid
distal portions of this patient and ask if they would like
or should they if they would like you to look at the internal carotid arteries
to see if they have any increase in velocity there.
And of course, we have some trauma
that may cause a dissection
or some disease states such as Marfans.
And you need to be aware that
that could cause a decrease in blood flow to the kidneys.
A lot of times this is not, the dissection is not located
within the renal artery itself, but within the aorta
and maybe is in the false or true lumen.
And that blood flow is then
therefore being hampered getting to the kidney
and that whole renin process starts
and you have an increase in blood pressure due to that.
And certainly aneurysmal disease may cause a lack of blood flow to the kidney
and that drop in pressure, which would also trigger it.
Aneurysmal disease will also need
to be noted within the aorta in this case.
'cause you have aneurysmal disease, obviously in any artery,
but within the aorta, because some of our parameters
that we use to define the disease from a velocity standpoint, we cannot use if we're using,
if we see an aneurysm within the aorta itself.

Methods for Evaluation

Okay, so here's a little quote that I thought I came up
with, but frankly, maybe I heard it from somebody else.
But there is always more than one way to do something
and someone will always have an opinion
on which method is best.
And just like anything else that we've been scanning,
people have been looking at different ways to do or to define disease and the kidney is no different.
And here's a little analogy, course,
certainly there's a right way
to change a see if a baby diaper needs to be changed.
You can see this is a method that I would prefer,
but some other people prefer the direct method
for changing a diaper.
This is probably something I would try once
and note that it wasn't a good approach.
Now, ironically, I do prefer a direct method to look at the renal arteries specifically.
And I use the indirect method
or just looking at the parenchyma signal
and deriving some certain feeling that there may
or may not be something going on proximal
to it based on the wave form
and certain parameters that I'll set up when I'm doing the kidney,
only if I can't use the direct approach.
So we'll talk about both of these during this examination.
And you can pick which one works for you,
and I hope you base that on your internal protocols
and also the QA data that you get back from doing your studies and looking at the gold standard
that you use within your hospital
or your lab patient positioning.

Patient Positioning

I think I mentioned this a little bit before,
but is very very important.
Also something that you need to talk
to the patient about while you're taking an h and p
and you're letting them know about holding their breath
and all the other things that are gonna be happening
during this examination.
Mainly, you'll have the patient start in a supine position.
And here are two of my favorite sonographers
that I had the pleasure of working with at Hershey Medical Center.
And have Lori laying down here in a supine position while Stephanie
is scanning her.
You can see I have Lori's hands up in the
air and behind her head.
Now this position is very hard to hold for long periods
of time, so I don't often use this,
but it really can raise that rib cage up
and allow you access to that proximal portion of the abdomen right below that xiphoid process.
But like I said, this may be an exam
that you're gonna be performing for upwards of an hour
and that patient's not gonna be able
to hold that position for long.
So if I'm having trouble getting access below
that xiphoid process to look at those arteries in the
midline approach, I'll have this
patient go in this position.
But certainly I want the patient in a reverse trendelenburg
position, slight reverse trendelenburg position
because I want those organs to drop down a little bit,
giving me better access
to those proximal renal arteries in the proximal aorta.
When I go towards the kidney
and I look at the parenchyma, often I'll have
to put the patient in a lateral decubitus position.
And you can see that Stephanie has Lori in this position.
Her leg here is straight, which I really prefer.
A lot of people when they're put in the lateral decubitus
position will bend their leg into
what we call like a fetal position.
I allow this bottom leg to be in that fetal position,
but I want that top leg to kind of be straight,
'cause that'll bring that hip bone down a little bit.
And by raising this hand up here, you'll raise up that rib cage and it'll give you a nice little access
to this flank approach that will give you great imaging
of that kidney, especially when you're doing the indirect
approach, which we talked about before.
Which all that information is gained from signals
within the kidney itself.

Direct Evaluation Protocol

So the direct evaluation, this is the method that I prefer,
and the method that I kind of look forward to define whether
or not there's renal artery stenosis.
We want to go through a certain protocol in
that protocol includes taking
velocities at the proximal aorta
because you'll use that as the denominator within the renal
aortic ratio calculations that will define the disease.
I also like to evaluate the celiac
and superior mesenteric artery, mainly
for the waveform morphology kind of gives me another marker
to know where I am within the body,
and we'll talk about that in a little bit.
Doppler spectral interrogation must take place along the
entire length of the renal artery,
if you're gonna call this a direct evaluation, that interrogation then therefore may have to take place be
in the supine position and the lateral decubitus position
because of that tortuosity that I mentioned before.
And then obviously, I wanna go to the end organ
and obtain a length
because we know if blood flow has been restricted to a organ, that organ will become will atrophy and become smaller.
So I'm looking for a certain length to make me feel like
that this organ is getting enough of blood.
And if I see it being way off from what I expect,
then I am looking probably for some type of occlusion
or critical stenosis that's been at chronic stages
and should be found before I let that patient go.

Mesenteric Arterial Anatomy and Waveform Morphology

So the mesenteric arterial anatomy,
while I'm gonna look at the celiac artery
and the superior mesenteric and inferior,
and you may be thinking, what is this guy talking about?
Why? I just mentioned I really want
to see the waveform morphology.
So I really don't care about the left gastric in this
situation, nor do I care about the inferior mesenteric,
but I really care about that splenic artery
and that superior mesenteric artery.
And if I see some problems with the celiac artery, I want
to kind of take a peek of that splenic and the hepatic,
because it's gonna it should match up
with the wave form morphology
that I'm seeing in the celiac artery,
unless there's a problem there.
The reason I want to do this is
because I feel that that wave form morphology is another marker, like I said,
to help me define where the renal arteries are,
because quite often I do not have a great window,
and I don't have a great look at this wonderful picture that Dr.
Netter has right here where I have the celiac and the SMA
and the renal arteries right in front of me,
and everything looks hunky dory.
That waveform also or that view also allows me to take my doppler signal right
where I want to every time for that equation.
That renal aortic artery equation that I was mentioning
before, where that proximal aorta will serve
as the denominator within that equation.
And you can see that I have nice parallel sample volume with the doppler cursor parallel
to the vessel wall right at the level of the celiac.
And that's another reason I like to interrogate that, to say
that I know exactly where I was in that vessel.
But the uniqueness
of the waveform is really what I'm going for.
Like I've mentioned, the celiac artery is gonna feed the
splenic the splenic,
the celiac artery is gonna feed the splenic artery
and hepatic artery, which will go to the hepatic artery going to the liver,
and the splenic artery going to the spleen,
which are very high end organs
that are always demanding blood flow, right?
So very high diastolic flow is needed to flow
to feed these organs.
And I use the fact
that this waveform is gonna be a little bit
different than the spleen.
These all these waveform,
the hepatic artery also will have this type
of waveform pattern, and the splenic artery will also have
this type of waveform pattern.
But the SMA should have a much more resistant wave
pattern, waveform pattern.
Because remember, I asked the patient to come in NPO
and coming in NPO means that that SMA really doesn't have
to do much work, right?
It doesn't have any food in the system that it has
to go down and supply blood for.
So it usually in a normal state will be a very
resistant pattern, especially when compared to the celiac.
So I have a situation set up here
where the celiac artery is low resistant.
The SMA, I'm sorry, is high resistant.
And then I'm gonna go into the renal arteries,
which would also be a high resistant signal.
However, sometimes you'll note
that the renal artery will look like the SMA,
and you can look how this signal looks very resistant
because the kidney itself is not functioning properly,
not from the standpoint of renal artery stenosis,
but from the standpoint of the renal system itself, that kidney itself has medical renal disease
and it is not accepting blood the way we would like
to at the end organ level.
And we have a very resistant pattern instead
of the very open pattern that we like to see
with high diastolic flow.

So that's something to note there is the ratio
that we've talked about with the renal aortic ratio equaling
the peak renal artery velocity over the proximal
aortic velocity, which we took at the level
of the celiac artery.
Certainly you don't have to take it at that level,
but you should take it at a level above the renal artery.

Examination Protocol and Criteria

All right, when we start this examination
and we've taken the aortic signal, we wanna move down into the kidney itself by via the renal artery.
So we'll start at the aorta from the midline approach
and walk ourselves into the proximal portion
of these renal arteries.
As we obtain all these signals, we want
to put the highest peak systolic velocity,
either whether it was in the proximal
or distal portion of the renal artery
and the numerator of the equation with that denominator
or beating that aortic signal
that you took proximal to this level.
And if it's below 3.5, we consider this
to be a normal renal artery in the sense
that we don't think there's significant disease
that's causing hypertension.
If we can't use that, we also look for a mark
of 180 centimeters per second.
And if I say I can't use that,
what I mean is if the ratio cannot be used in some
situations that we're gonna talk about,
we can't use this ratio.
I'll look for a velocity
of a hundred centimeters per second.
Quite often you'll find
that other people will move these velocities around.
Some people prefer higher velocity.
Some people prefer lower velocities when they're looking
purely at velocities.
But for any of these cases, I want to be at a lower
velocity than 180
and certainly a lower renal aortic ratio than 3.5.
If I'm gonna say this is normal, that coupled
with no increases in velocity throughout any other portion
of the renal artery, no evidence of turbulent flow
and a low resistant spectral pattern kind of tells me
that the kidney is probably adequately
being supplied with blood.

Like I said before, that kidney length is very important.
It kind of gives me a marker that the things
that I'm seeing, if I think they are right should be,
then proven by having a pretty nice sized kidney.
And a normal sized kidney is
between nine and 12 centimeters.
Anything less than nine, I start getting a little concerned
that there may be some type of stenosis
or occlusion proximal.
Certainly I want to compare the kidney size to the other, the other side of the body.
So the ipsilateral compared
to the contralateral kidney is
also gonna be a marker for me.
I never rely on just one thing,
and I don't think anybody should when they're doing a duplex
ultrasound, always having more than one thing
as a marker really boost your confidence whether
there's disease or there's not disease.

Certainly when I'm looking at the kidney,
I wanna turn on my color and that can be a good marker.
Also, even before I take my renal artery signal, I know
that this vessel is perfusing pretty well.
I don't know if there's medical renal disease really based on this image right here,
but I can tell you that this kidney is getting
a lot of blood flow to it.
I have a very nice result when I put my color box on.
I do wanna make sure that my PRF is set appropriately
and then my gain is set appropriately
to obtain at windows like this.
And to obtain an image like this,
I also wanna make sure those same parameters
are set appropriately.
If I am in fact looking for and looking at a kidney that I think does not have much
blood flow to it, such as this one that we see right here,
we can also use some of the other modalities within the machine itself, such as color,
power angio or power angio which will give us some perhaps some better sensitivity within the abdomen,
but it's very flash sensitive too.
So you really have to have the patient hold their breath
while you're doing any type of power angio.

When we're at the kidney, we also want to pay attention
to any other anomalies that are outside
of the arterial system also that we can relay back
to the interpreting physician.
And some of those will be the ones that I'll show you here.
A horseshoe kidney, very very difficult exam.
Many times a horseshoe kidney will have multiple renal
arteries coming off of it.
Very challenging for you. Very cool thing to see though.
And if you have students, it's certainly something
that you wanna bring that student into
the room and show them.
You don't see it that often,
but when you do see it it is a challenging exam and something that you probably will,
even if you're an experienced sonographer,
may wanna bring in another technologist to help out with
and make sure that you didn't miss anything.
Kidney stones obviously could be causing some type of abdominal pain in these patients and are noted,
but usually by these shadows that we see here,
hydronephrosis most often we see this from a standpoint
of vascular lab when we're looking at kidney transplants.
Polycystic disease is often found when you're doing this examination, it must be noted.
These signals are very resistant, obviously when they get into the parenchymal
and even to the renal artery.
'cause remember there's not much collateralization here.
So these resistant signals are caused
by probably some compression with all these cysts around.
And then of course unfortunately if we see some type
of mass in the region of the kidney, we want
to pass that information on to the interpreting physician
and the requesting physician for further testing.

Disease States: Less Than 60% Stenosis

As we move into a higher disease state,
there's another category that's less than 60%,
but we think that may be approaching 60%
and that we need to note,
and we see that when the RAR is still less than 3.5,
but the peak systolic velocity is above 180,
but we do not see that post stenotic signal.
You really wanna pay attention
to your angle correction here.
You wanna make sure that you have multiple locations
that you have looked at
and locations, I mean, throughout the entire length.
And from a midline approach
and from a lateral decubitus approach
and that lateral decubitus approach, I prefer, I think that
that velocity really gives me a better feel whether
or not there's disease there
because I'm coming at probably a less than 30 degree angle,
and a lot of times right around is zero degree angle.
And that comfort zone
of knowing I'm getting the strongest upper shift back.
And if that velocity is very high
and sits itself into the RAR above 3.5
or close to 3.5
and a higher velocity, I really think
that there is some type of disease state.
And coupled with the same type of velocities or
or high velocities from the midline state, I am very very confident that we are in some type of we have some type of problem within the renal artery.

Severe Disease: Greater Than 60% Stenosis

For the patients with severe disease.
We really have some high velocities here.
It's not uncommon to have bruits associated
with these high velocities.
Also, not uncommon for your system
to go into a high PRF setting
because of the depth of these vessels.
Greater than 60% stenosis in this case is denoted
by an RAR now above 3.5.
And to get that 3.5 RAR, you certainly are gonna be
above 180 centimeters per second in most cases, if not all.
And you will have that post stenotic turbulence and a low
or a high resistant spectral pattern depending on
what is also going on within the kidney itself.

So here is a angiogram that shows
that renal artery stenosis on the left side,
and you can see that very well.
And this usually is a confirmatory test for the patient and one that you'll be using
as a gold standard that with MRI
and some cts may be taking place in your lab,
but you'll be using this for your gold standard to compare
to the stenosis that you have recorded
during a duplex examination.

You can see a lot of flash here
and I'll have a lot of pretty pictures here.
But the reality of it is that it gets pretty tough to optimize your system perfectly when you're in the abdomen.
You may see some images that aren't pretty,
but the proof in the pudding is really
with this doppler spectral data.
And here you can see a stenosis that is playing right here of something I found in the right renal artery
and I from a midline approach.
'cause you can see that straight up and down angle.
But my angle of insonation is parallel to the walls here
with my line right here.
My angle right here,
very nicely shown at 60 degrees.
Now, you don't have to maintain a 60 degree angle here.
Anything less than 60 degrees is much appropriate.
In fact, like I just mentioned
before, anything close
to zero is really really appropriate.
What you do have to maintain is if you're gonna see this
patient back again and you're trying to compare velocities,
please look back at the old studies
and make sure that you're angle is matching up
to the angle that you used before.

Here is some waveforms
that you need to be able to recognize.
There's that tight stenosis.
Here's in the aftermath
and you need to know
that this turbulent signal happens right after this.
If you go too far out, you may see some normalization
of this amid this post stenotic turbulence
and really really high stenotic lesions.
You will have this tardus parvus waveform,
which is a pure sign.
And really you can almost bet the bank on it,
but you probably never do that in
medicine because you never know.
But seeing something like this really is a good indicator
that there is a severe stenosis in front of it.

Indirect Study Interpretation Criteria

The interpretation criteria
for the indirect study really has to do
with acceleration time and acceleration.
And that really is telling you, I'm trying to find out
how fast and how long it takes for a signal
to reach end diastole to peak systole.
And we can see that acceleration times greater than 0.07
seconds is a problem
and something that we think may be caused
by a more proximal stenosis.
And acceleration time of less than three meters
per second is also something
that we think may cause it.
Some people also use early systolic peaks,
and this is this little notch
that we see right here within the kidney.
To obtain this waveform, you really need
to have some pretty good skill levels within
that parenchyma signal.
And the artery that we're gonna be really trying
to interrogate is that segmental artery,
that larger artery that we see that comes right
through the hilum and is in that middle portion of the kidney itself.
And you can see some very good images right here denoting where our location of our calipers need to be
for the acceleration time
and acceleration, as well as
that early systolic peak over here.
You can see they do not have that type of waveform, more
of a tardus parvus type of waveform.
And we do not see that early systolic peak.
This is something that you will take you a long time
to master and you really have to have a pretty firm control of your ultrasound system.
You can see that my waveform timeline is a little bit different.
I've decreased it to two right here, between two
and three is really where you should have it
to really spread out that waveform
and to obtaining these waveform in the proximal mid
and upper poles or the upper mid and lower poles.
I'm sorry, I'm so used to seeing pro
and distal are very essential to make sure
that you're not missing any stenosis
that may be an accessory renal artery.

Also renal artery occlusions can be very very difficult also to see
because you're looking for an artery
that's not patent anymore.
And it's like finding a needle in a
haystack in a lot of these cases.
The real indicator is probably that kidney itself,
which has shrunken in size in this situation
where it's been a chronic problem.
And in fact that is a good marker for you to realize
that probably there is no renal artery.
And also when you do find that renal artery,
you may have these staccato type signals,
certainly within the parenchyma
or within that renal artery itself before that occlusion.

Renal Parenchymal Evaluation

The renal parenchymal system also can
give you some information.
I mentioned this before about medical renal disease
and there's several ways to look at this.
Some people use an RI mean not RAR
and resistive indices of 0.75 or greater.
Other people have manipulate that equation
and kind of put the end diastolic above or below the thing.
We used a four as a marker for that.
So our peak systolic and our end diastolic value are
used to give us a whole number.
And anything greater than four we thought was medical renal disease.
And you can really eyeball this also.
You really don't need to quantify it.
You can note that this is pretty normal diastolic flow,
whereas this is not.
And you can say that the patient has medical renal disease that is always coupled with the blood work that you'll see has high that the patient will have high creatinine levels.
So those two have to come together for this to make sense.
So always use the patient history also as a marker
of medical renal disease quickly.

Special Considerations

Some things to remember, you don't want to use
that renal aortic ratio.
When there's an aneurysm, you want to have velocities
that you're obtaining in that proximal aorta segment
that are between 50 and a hundred centimeters.
Anything above or below that you don't wanna use
the renal aortic ratio.
Also young patients, the data that was collected
that we're using is really not based on
a young patient population.
In fact, these patients are oftentimes very old that we see.
And therefore all the data
that we collected we're all in these older patients.
And younger patients are not part of that cohort.
So the criteria does not hold for them.
And then renal artery stents, a lot
of people have done a lot of work and there's some
some good publications out there,
but I don't think anybody has really landed on a certain criteria to use when you're dealing
with renal artery stents.
Yet. Remember those multiple renal arteries, 20
or 30% of the population.
In fact, you'll probably see the one that has the stenosis
and miss the one that doesn't.
So works out well for us, but pay attention to them.
It's nice to identify both of them.
You labeling them correctly is also nice too.
But these patients are probably on their way to an angiogram
or some other testing modality that can kind of let you know whether it was in the inferior portion
or the superior portion.

When you're looking at it FMD, remember
that this is the second most common cause
of renal vascular hypertension.
It most commonly will affect the mid
to distal segments of the renal artery.
But like I said before, don't count on it.
Not affecting the proximal portion.
But I would most likely
and have most likely seen it in that mid to distal portion.
It's commonly found in young women.
So if you see a young woman approach your lab
for this type of study, be suspicious
that it's probably FMD,
especially if you're looking at the aorta
and that mesenteric and celiac artery levels
and you see no disease whatsoever, it can occur bilaterally.
So make sure that you look at both sides which is commonly done when you do a renal duplex examination.
And then remember, like I said
before, the internal carotid artery
distally is also affected.

And here's a nice angiogram
of this fibromuscular dysplasia.
You can see that that proximal portion is perfect.
But the distal portion of this artery does have this, what they call a string
of pearls right here.
And you can see there are a string of beads.
You can see that same effect very nicely done by I think I got this from Cindy Owen and Mike Wigg.
One of my friends that are also educators.
And you can see that that correlates very very well kind of historically.

But we need to know about, there are renal bypass grafts
out there and sometimes they're still being placed,
but most of the time we'll see stents
or aorta renal bypass graft, spleen renal,
hepatic renal and iliorenal.
I always use the same renal aortic ratio,
but they are located in different locations.
Here is what we'll see most of the time now
and that are these stents.
And you can visualize 'em pretty well
'cause they they do are bright metal objects
that will be shown
and that stent will follow itself
and track itself in the same anatomical location.
So it's a little bit easier than bypass grafts, right?
'cause it's within the same renal artery itself.
What I like to do is kind of 'cause it's an artificial thing
and a lot of times it stent extends into the aorta.
I like to start in the aorta
and walk myself into the renal artery.
If that is possible based on the image that I'm allowed
to obtain based on the patient's body habitus.
So you can see me doing that right here
as I move from the aorta into the renal artery
and obtain that velocity.

Take Homes

So some take homes, the direct method you know,
the combination probably works the best,
but if you use a direct method alone,
it may be inaccurate if stenosis is undetected in the accessory renal artery if that is missed.
But I think that in most cases you will find
that accessory renal artery
because of that high color bruit.
If it does in fact have the disease.
And the other artery is the one that's widely patent,
inability
to visualize the entire length of the renal artery.
Which is not that uncommon because of obesity.
Bowel gas, patient unable to hold their breath,
a lot of other factors.
So if you can't see the entire length
and you're uncomfortable that you miss some sections,
especially if they're the proximal sections,
you certainly don't wanna put
that you think this exam is completely normal.
You can improve your accuracy by having angles
of less than 60 degrees and I've already mentioned that.
So you do not need to obtain 60 degrees
and please do not think that that is part of the renal duplex examination
or any abdominal examination having
to maintain a 60 degree angle.
Do not want to go above it, but you certainly can go below.
And in fact, the lower the angles that you get,
the better it's gonna look.
Demonstration of post stenotic turbulence is a must.
If you are going to say that this in fact is a flow.
Reducing stenosis maintain all those waveforms
so you can show them to the interpreting physician to prove
that you in fact were able
to see the proximal mid distal segments.
And then always patient always position your patient appropriately
when you are doing this examination.
'cause it can really help you open up different windows.

That indirect method that we mentioned
before inaccurate when their RI is greater than 0.75.
So we know there's probably some type
of medical renal disease going on
and if they have AAA, just like the renal artery,
RAR is inaccurate if we have AAA in the proximal midsection
of the renals actually will improve if angles are used
that are less than 30 degrees.
And the way you do that, as you bring that kidney as close
to the surface as you can and you use the appropriate transducer sometimes since
you're trying to get that parenchyma tissue as close
to the surface, you can in some patients,
especially the thinner ones you'll note, you'll note
that is really really close to the surface
and you can go drop down to a linear transducer
and it may help you get better angles of insonation.
Sweep speed should be changed to two to three seconds
to really elongate that signal.
Lower PRF larger sample volume should be used in
and when you're looking at anything in the kidney,
parenchyma and waveform should be obtained in the
upper, mid and lower poles.

Conclusion

And with that, I'd like to thank you
and hope you have learned something from this lecture
and you continue to scan renal arteries
and if you haven't tried them, you now attempt to do that
after hearing this.