Non Invasive Testing vs Imaging Exams: When to Order What? - SD

Introduction

My name is Jim Betti.
I'm an interventional radiologist from the Baptist Cardiac
and Vascular Institute in Miami, Florida.
I also run our non-invasive vascular laboratory.
Today I'm going to talk to you about when
to order which test in non-invasive diagnosis.
We're gonna discuss the use of physiologic testing,
duplex ultrasound, MRA and CTA,
and try to determine when the best time
to order which test is.

Non-Invasive Testing versus Vascular Imaging Exams: When to Order What Study?

We're gonna look at both of these types of tests,
physiologic tests and imaging tests,
and try to determine when the best opportunity
to use these tests are.
Non-invasive vascular testing consists of physiologic
or indirect testing that includes segmental limb pressures,
doppler waveform analysis, and plethysmography anatomic
or direct testing includes duplex ultrasound,
MR angiography and CT angiography.

Determining the Right Test for Peripheral Arterial Disease

Whenever we see a patient with peripheral arterial disease,
we have to determine what it is that we want to answer
before we can determine which type of test we want to order.
There are about five basic questions that we have
to think about when we try to figure out what test to order.
The most important question is,
does the patient have disease?
When a patient comes in with symptoms,
it's not always clear that their symptoms are related
to peripheral arterial disease.
On the front end, we have to determine whether
or not the patient's symptoms are from
peripheral vascular disease.
Once we determine that, the next thing we need to answer is
where the disease is located.
Can we segmentize or compartmentalize the disease?
Is a disease in the aortic iliac segment,
the femoral popliteal segment, or the below knee segment,
or is it in combination of different areas,
probably the single most important question that we ask is,
how does a patient's disease relate
to the patient's presentation?
There are many patients who present with symptoms
and have vascular disease,
but the symptoms aren't related to the vascular disease.
There are also patients with very mild vascular disease
that may have very significant symptoms
because they have a very active lifestyle.
This is a really a physiologic question that needs
to be answered early on in the patient workup.
Once we determine the above three questions,
the next thing we have to figure out is
what are the therapeutic options?
And those therapeutic options can include medical therapy,
endovascular therapy, surgical therapy,
or actually doing nothing in certain patients.
Finally, once we decide to treat a patient, the final thing
that we want to know is what are the results of our therapy?
Did our treatment work?
And the way we determine that is by doing some sort of test
after the procedure so that we have a baseline
to follow patients by.

Who to Test

Who do we test? We can test symptomatic patients,
so all patients who present with claudication.
We can test patients with unexplained symptoms.
Remember, not all symptoms of claudication are classic
symptoms, so that sometimes patients come in with symptoms
that are a little bit confusing,
we can't really explain them.
We can test patients who have decreased or absent pulses.
We can test patients who have ulceration
or infection, patients with skin breakdown, poor ulcer,
healing patients with critical limb ischemia,
and then the emergent type patient
or the patients who have acute changes in
a physical examination.
For example, a patient who's completely normal
and comes into the ER with a four hour
or six hour history of a cold extremity
or a painful cold extremity.
Acute changes in physical examination,
while being the minority of patients are the group
that tend to be the most emergent.

Background: Value of History and Physical Exam

As a bit of background, we should point out
that there are some studies that look at the value of trying
to diagnose peripheral arterial disease
by history and physical.
And while it may seem obvious that you should be able
to do this, it turns out that there are a number of studies
that show that physical examine history alone
miss a significant number of patients with peripheral vascular disease.

PAD Awareness, Risk, and Treatment: New Resources for Survival (PARTNERS) Study

The first study I wanted to mention was a PARTNERS study,
the PAD awareness, risk
and treatment, new Resources for survival.
And this was a national investigation
to assess the feasibility
of detecting PAD in the office using the
ankle brachial index.
And this really assessed both patient
and physician awareness,
and it evaluated the intensity of use of risk
reduction, risk modifying strategies.
The summary from this study,
which was published in JAMA in 2001,
was that PAD is highly prevalent in the primary care setting.
And it's easily detectable despite the fact,
however, that it's highly prevalent
and easily detectable it's way underdiagnosed.
In fact, there are many instances
where patients knew they had PAD
and the physicians didn't pick up on it.
The patients had to inform their doctors that they had PAD.
It did show that males and females were affected equally.
And it also concluded that history alone may miss 85%
of the PAD diagnoses.
Clearly just a good history is not gonna be enough.
We're gonna need to do some sort of functional
or anatomic testing to find out whether someone has PAD.

1979 JAMA Study on Objective Testing

In another study published in JAMA in 1979,
there was a study done that looked at the value
of objective testing.
This isn't just h and p,
but this is using now ankle brachial index plus a
non-invasive exam.
Surprisingly, patients who had an abnormal history
and physical had a normal non-invasive exam 44% of the time.
On the other hand, patients with a completely normal history
and physical had an abnormal non-invasive exam
19% of the time.
This very similar to the PARTNERS study,
this study concludes that history
and physical alone are not sensitive
or specific enough to diagnose PAD
with high accuracy and that other testing is needed.

Conditions Confused with PAD

What are some of the things we confuse for PAD?
Pseudo claudication is a term that's used,
and this is due to pain from spinal degenerative
disease neuropathy.
It can cause pain on ambulation,
it can be relieved by rest.
It can be associated with low back pain,
and the distribution can be from the feet
along the entire leg.
Arthritis, neuropathy, muscular pain
and pain from tumors compressing on nerves
or vessels can also be confused with peripheral arterial
or peripheral venous disease.
These are the things
that are in our differential diagnosis.

Physiologic Testing

Let's start with physiologic testing.
Physiologic testing is a general term that
includes a battery of different exams that can be done
and lumped into one non-invasive exam.
These include the use of pulse volume recordings,
segmental directional doppler waveform analysis,
segmental pressure and pressure gradients
and exercise testing.
In this image, you see both a normal
and an abnormal noninvasive exam.
If you look on the left image, you can see
that the pulse volume recordings are normal.
They're symmetrical from side to side.
The amplitudes of the waveform are good.
There's an excellent dichotic notch.
The ankle brachial indices are 1.09 on the right
and 1.16 on the left.
The segmental pressure starting at the high thigh are
symmetrical, and there's no significant drop off.
The image on the right shows you the right leg
is significantly diseased.
You can see the degradation
of the wave form at the high thigh and
above knee levels.
Interestingly, we still see augmentation of the wave form
below the knee indicating
that the femoral popliteal segment is open.
But in this patient, there's significant aortic
iliac inflow disease.
This is a physiologic test.
It's an excellent entry exam for a patient coming in
with peripheral arterial disease.
The physiologic test is a simple, inexpensive
reproducible test that can be performed just about anywhere,
by a well-trained technologist.
It provides a lot of advantages over some
of the more sophisticated imaging tests, such as CT and MR
because of the low cost and because of the accessibility.
It also, as you can see from these wave forms,
provides excellent physiologic information.
It lacks anatomic information,
but the physiologic information is vital in the
workup of these patients.

Value of Non-Invasive Testing Modalities

If we look at this chart,
we can look at the non-invasive testing modalities
and determine what their value is.
If we look at the first three,
the segmental limb pressures, the Doppler waveform analysis
and the plethysmography, we can see
that these all provide strong physiologic information.
The right hand column shows
that there is some anatomic information because we can localize
or compartmentalize the location of the disease.
But really the value of these tests is in their physiologic
determination.
The duplex scanning angiography, CT angiography
and contrast angiography on the other hand,
provide no physiologic information,
but provide exquisite anatomic information.
They're very high resolution studies.
They provide an excellent picture,
an excellent still photograph
of what's going on in the vasculature.
Again, we don't know
from these anatomic studies whether the findings correlate
with the patient's symptoms that can only be answered
by the physiologic testing.
You see that all these tests are important.
They complement each other,
they provide us different information,
and at times we need to do combinations
of all these tests to really figure out what's going on.
But there are times where we can be cost effective
and streamline care by ordering one test or another.

The vascular imaging studies lack all
the physiologic data.
As I mentioned, there's no exercise testing equivalent with anatomic testing,
and it limits the ability to relate the disease process
to the patient's presentation.

Exercise Testing in Non-Invasive Vascular Testing

Non-invasive vascular testing is something that we have
to talk about in the context of exercise testing.
It's my belief and the belief of many
that exercise testing should be mandatory in all patients
with normal resting physiologic studies who have exertional symptoms.
If a patient comes in complaining of claudication
and their non-invasive exam is normal
or near normal, an exercise test is mandatory.
If we don't test patients with some sort
of exercise testing, then we will miss a lot of mild
and moderate disease, especially in active patients.
It's completely plausible to have a normal resting exam
and a significantly abnormal non-invasive physiologic exam.
We also want to use exercise testing in patients
who have unusual presentation of their symptoms.
It allows us to correlate the symptoms
with the physiologic changes of exercise.
Exercise testing demonstrates exercise induced ischemia.
We can see drops in ankle brachial indices.
We can see degradation of the plethysmography tracings
and again, allows the correlation of symptoms
with the induction of ischemia.
It's very important to realize that all pain in patients
with vascular disease is not vascular in etiology.
Many patients with vascular disease have degenerative
spine disease neuropathy, muscle contractions,
diabetes,
and all vascular pain is not typical claudication.
The typical claudication patient who complains of fatigue
or tiredness or pain in their calves
or thighs when they walk,
that is not all patients.
It may be the majority.
There are patients who come in
with different types of symptoms.
And the only way we can really correlate those symptoms
with their findings is to exercise them.
And the best way to exercise patients really is
to use treadmill testing.
And if you have a treadmill,
you can then repeat the ankle brachial indices
and the pulse volume recordings at rest and then
after exercise.

Example: Physiologic Testing with MRA Correlation

Again, if we look at this non-invasive,
this is a functional test.
This non-invasive exam,
we see an ankle brachial index on the right
of 0.63 on the left of 0.57.
We know that there's moderate disease already.
We see the degradation in the waveform below the knees.
We know that there's significant femoral popliteal disease
because the abnormality
and the waveform lies
between the high thigh and below knee segment.
If we look at the high thigh segments, we know
that those wave forms are essentially normal.
We doubt that there's any aorta,
iliac inflow disease on this patient.
And here's the MRA of this patient.
And just as we suggested,
the aorta iliac segment shows no
significant vascular disease.
There actually is atherosclerotic plaque
and you can see a small abdominal aneurysm,
but none of that is causing any narrowing in his arteries,
and therefore he has no significant occlusive phenomena going on
in the upper extremities in the aorta iliac segment.
Now, if we come down and look at the femoral popliteal
segment, we can see that on the image on your left,
there's a complete superficial femoral artery occlusion.
We see a large profunda femoral artery coming down
and reconstituting the distal superficial femoral artery
and popliteal artery at the knee joint
on the left side on the left extremity.
We see that the superficial femoral artery is diseased,
but widely patent below the knee.
We see that there's good two vessel runoff bilaterally.
The question on this patient, if I asked you,
which side is he more symptomatic on, one might be inclined
to say that he's more symptomatic on the right side
because of that long superficial femoral artery lesion.
But in fact, this patient presents
with left leg claudication.
This is a perfect example of
how anatomic testing provides us no functional information
from looking at these images.
Again, one might guess
that the patient's more symptomatic on the right,
but in fact, the majority of his symptoms are left sided.
When we do a catheter based angiogram,
you can see this heavily calcified plaque in the
common femoral artery.
This plaque is causing a significant obstruction to flow.
And even though the superficial femoral artery is,
as we identified earlier, is patent,
this patient's more symptomatic on the left
because of this focal plaque.
This is something that's not appreciated on the anatomic testing
and was much better appreciated
with the physiologic functional testing.
And here's this superficial femoral artery we looked at
with a good reconstitution of the popliteal artery
and tibial vessels.

Example: Bilateral Buttock Claudication

Let's look at this other example now of a 63-year-old male
who has bilateral buttock claudication.
We have a non-invasive exam
that you can see on the screen.
If we look at that non-invasive exam
and compare the waveforms from side to side, what we see is
that there's a degradation in the waveform at the high thigh
below knee and ankle level.
We know that the left side has significant disease,
and based on that waveform analysis, we know
that there's some inflow disease in the
aortic iliac segment on the right
and significant femoral popliteal disease on the right.
The left side, however, is relatively normal.
How does that functional non-invasive exam explain a
63-year-old gentleman with bilateral buttock claudication?
I put up these questions
and you can ask yourself, does this,
are the symptoms explained by this exam,
are the symptoms not explained by the exam
because the exam is inaccurate?
Are the symptoms not explained by the exam?
And you would recommend a neurologic evaluation
or the symptoms not explained by the exam,
and you recommend a vascular imaging study.
This is a perfect case
where we can use physiologic testing,
but it does have limits in this particular case.
A physiologic test does not explain the patient's symptoms
before this patient gets sent for a neurologic evaluation
or for some other type of workup by another specialist.
It's completely reasonable
to obtain a vascular imaging study, an anatomic study.
And here we can see an MRA performed on this patient.
And if we look carefully in both oblique projections,
we can see that the origins
of the hypogastric arteries are very highly stenotic.
This clearly explains the patient's buttock claudication
stenosis in the hypogastric artery limit flow
to the superior gluteal artery causing pain in the upper
thigh and buttocks.
There's nothing in a physiologic test
that would identify this.
Since the physiologic tests focus on flow
and the common iliac
and external iliac arteries in this particular patient,
again, we come down, we look in the thigh region,
and we can see and confirm, as we knew
before, that there is a right superficial
femoral artery occlusion.
And we can see that.
That however does not explain the buttock claudication.
The buttock claudication is explained by the anatomic testing.
Here's a catheter based angiogram in two obliques,
and you can see the stenosis at the origin
of both hypogastric arteries.
In this particular patient.
We stented the origins of those vessels,
and you can see the post stent angiograms here
with excellent flow
and no significant residual stenosis on either side,
the patient's buttock claudication resolved the next morning
on a treadmill test.
This is an excellent example of the need
for anatomic testing.
Although we champion the use of physiologic testing to get patients
in their initial workup
to enter them into their initial workup,
we sometimes realize that we need other testing as well.

Arterial Duplex Examinations

What about arterial duplex examinations?
Arterial duplex is an incredibly valuable tool
that we use in the workup of patients
with peripheral arterial disease.
But when do we use it as a question?
It does provide us excellent anatomic information,
and the waveforms do give us a small amount
of physiologic information.
There are duplex criteria that can be used to determine
how significant a stenosis is,
and these criteria may vary from author to author.
One basic criteria can basically categorize patients
as having less than 50
or greater than 50% stenosis based on a twofold increase in
the systolic velocities through a stenosis.
Duplex scanning is a primary modality,
is an exhaustive examination of the arteries.
It's very time consuming.
It takes a long time
to scan someone from the lower aorta
all the way to the ankles.
And the best way to really deal with duplex scanning
is to use it as an adjuvant
to physiologic studies.
Use it as a site specific evaluation tool.
That is, you could do a physiologic test,
and then once you identify where the disease is,
you can use duplex
to determine whether the vessel's occluded, stenotic,
diffusely diseased, or focally diseased.
In doing this, you cut the scan time down,
you decrease the patient's time in the laboratory
and you streamline your exam.
It should be noted that if you are using duplex scanning
as your primary testing modality,
you must do an ankle brachial index to have a complete exam.
The ankle brachial index is one bit
of physiologic information that can be added
to a duplex scan to make it a relevant test.
The duplex scan alone without an ankle brachial index is
nothing more than a snapshot of a vessel
and doesn't really tell you whether
or not the disease you're seeing is significant.

Advantages and Limitations of Duplex Testing

Some of the advantages
to duplex testing is it provides us very good anatomic
information in the region scanned.
When done as a site-specific interrogation,
it can tell us occlusions versus stenosis.
Identify focal complications such as pseudo aneurysms,
evaluate extravascular lesions such as lymph nodes,
baker cyst, and other abnormalities in the soft tissues.
It can give us an estimation of vessel size
and it can allow us to plan treatment
for endovascular therapy
and even planned treatment for surgical bypass.
The limitations include bowel gas in the pelvis,
heavy calcium in vessels,
which may make identifying flow difficult.
The fact that there's diffuse multifocal disease can add in
prolonged scan time.
There's limited physiologic data.
It lacks an exercise testing equivalent.
And as we mentioned previously,
a complete exam is difficult.
It's a very lengthy exam.
As a limited examination, it's a fantastic adjuvant
to physiologic testing.

Summary of Arterial Duplex Scanning

If we summarize arterial duplex scanning,
it supplements physiologic testing
provides good anatomic information.
It's excellent for post intervention assessment.
If you wanna look at a stent or an angioplasty site
and look at velocities through your treated area,
it provides an excellent baseline for follow up.
And in patients who have bypass graft,
it is the preferred method of evaluation.
We often don't wanna put blood pressure cuffs on bypass
grafts, so using duplex is an outstanding way
to evaluate the graft.
It gives us anatomic information.
We can see the graft anastomosis, we can measure velocities,
we can follow velocities,
and we can establish baselines from which the patients will
be followed moving forward.
For bypass graft evaluation, it is the imaging modality of choice.

Other Imaging Exams: MRA and CTA

Other imaging exams include MRA and CTA.
These both provide exquisite anatomic information
that may be of critical importance.
Again, there is no physiologic data.
These exams also have issues with access.
They're not readily available to everyone.
They're very costly,
and if they're done improperly, the quality can be an issue.
If younger patients radiation may be an issue
with CT angiography.
And in patients with elevated creatinines, both MRA
and CTA may provide significant limitations
because of the need for contrast.

Examples of MRA

These are two demonstrations of an MRA
of moderate quality.
However, with this MRA, we can see
that there's diffuse aortic disease,
almost a Leriche type syndrome, with bilateral common iliac artery stenosis
at the aortic bifurcation.
This is an exquisite MRA showing the distal abdominal aorta
and extending into the iliac system
with no significant arterial disease.
We get a look at the renal artery in a patient
with a solitary right kidney.
We see the SMA,
and this is an example of an excellent evaluation
of the abdominal aorta as we come down in the legs.
This MRA provides us excellent anatomic information,
especially on the left side
where it shows a popliteal artery occlusion.
And then it's excellent
for picking up the reconstituted vessels
below the occlusion.
And we can see the runoff clear into the foot,
providing the surgeon with good anatomic targeting
for the distal bypass,
or providing an endovascular specialist good anatomic
targeting for their endovascular therapeutic strategies.

Examples of CTA

CTA also provides an exceptional highly anatomic imaging.
This is a study with the highest resolution,
the highest degree of accuracy.
When we look at images in this particular case, you can see
that there's a penetrating ulcer in the abdominal aorta,
it's seen in both cross-section and longitudinal imaging.
While this could be identified with ultrasound,
the CT does provide us extremely accurate measurement
for treatment planning.
Shows us the adjunctive calcification, the relationship to
the vessels such as intercostals, the aortic bifurcation,
the renal vessels, and the mesenteric vessels.
And overall provides us the best assessment
of these type of focal anatomic lesions.
CT also has a very valuable role
when we use CT and runoffs.
We can get highly accurate runoffs,
but one of the problems with CT angiography is
that calcium can be a barrier.
When we look at these images,
we can clearly see a left superficial femoral artery
occlusion with good one vessel reconstitution.
However, depending on how we process these images,
we can get very pretty pictures,
but it's sometimes hard to tell whether the vessel's patent
because of the calcification.
Therefore, if calcification is an extreme issue,
sometimes MR angiography in the distal lower extremities has
an advantage over CT angiography.
In these cases, we have pictures of runoff vessels,
but it's very difficult to determine the patency
of these vessels because of the diffuse heavy calcification.
Rarely, sometimes conventional angiography is required
for therapeutic planning, especially
for distal limb targeting,
but with the high resolution studies that we can obtain.
This is almost unheard of.
In fact, this type of angiography is reserved for the angiograms
that have performed on the day of treatment.

Returning to the Original Questions

Let's go back to the original questions we asked.
Does a patient have disease?
If P is physiologic
and I is imaging, we can say that both
of these modalities can answer this question.
Imaging in a prettier picture,
physiologic in a more functional way,
but physiologic, much less expensive
and much easier to perform.
However, both modalities answer the question,
where is the disease located?
Clearly imaging has an advantage over physiologic testing.
But as I showed you in many examples, physiologic testing
does provide segment and compartmentalization of disease.
But it's really imaging that tells us this the best,
the most important question, as I mentioned
before, how does the disease relate
to the patient's presentation?
That can only be answered by physiologic testing.
Anatomic testing has no role in this situation.
What are the therapeutic options?
Anatomic testing imaging
actually provides us the best role for this
between duplex, CT and MR.
We can plan endovascular surgical strategies.
We can look at the vessel length,
the diameter of the vessel.
We can determine which tools we want to use.
We can streamline our therapy.
What are the results of therapy?
Only provided by physiologic information?
Showing a widely patent vessel
after therapy does not answer the question as
to how well we did.
The only way that we can answer how well our treatment is,
is to test the patient and see if he's still symptomatic.
The results of therapy come primarily from
physiologic testing.

Conclusion

As we conclude, each test has strengths
and weaknesses when done properly
with appropriate clinical correlation, both anatomic
and physiologic testing provide valuable information
when done improperly
or without appropriate clinical correlation.
Both sets of testing are prone for significant error.
Proper interpretation requires understanding of the test
and the disease, and it also requires trained technologists
and physicians to interpret these studies.
Physiologic testing continues
to be an extremely important part of the workup for patients
with peripheral arterial disease, it's best to start simple
answer functional questions
before committing to expensive exams
that don't provide physiologic information.
Duplex is an excellent adjunct to physiologic testing.
And then once PAD is confirmed, proceeding to an MRA
or a CTA or directly
to intervention would be the way one should go.
Thank you very much.