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Hello, and welcome to Noon Conference hosted by Medallity.

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Noon Conference connects the global radiology community through free live

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educational webinars that are accessible for all, and is an opportunity to learn

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alongside top radiologists from around the world.

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Today, we are honored to welcome Dr.

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Anup Shetty for a lecture entitled Approach to AIF

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Runoff Lower Extremity CTA. Dr. Shetty

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completed his internal medicine residency, radiology

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residency, and body MRI fellowship at Washington University.

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He currently serves as Associate Professor of Radiology, Advanced Abdominal

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Imaging Fellowship Director,

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and Service Director of Body MRI at Malenkrot

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Institute of Radiology.

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At the end of this lecture, please join Dr.

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Shetty in a Q&A session where he will address questions you

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may have on today's topic. Please remember to use the Q&A feature to submit your

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questions so we can get to as many as we can before our time is up.

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With that, we are ready to begin today's lecture. Dr.

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Shetty, please take it from here.

1:06

Thank you so much.

1:08

Welcome everyone who's joining for this topic.

1:10

I know this is something that many people are either

1:14

uncomfortable reading or would prefer not to read, given the option.

1:18

So I think it's helpful to have an approach to hopefully make you

1:21

feel more comfortable in approaching these cases.

1:25

I have no financial disclosures.

1:28

So what we're going to discuss today, some of the anatomy of what we image,

1:31

the inflow, outflow, and lower extremity runoff arterial vasculature.

1:35

We're going to be talking about some features of atherothrombotic and embolic

1:39

disease, as well as traumatic injuries.

1:43

So what is the role of AIF imaging? Most commonly, we're going to be performing

1:47

this to assess acute or chronic limb ischemia, whether

1:51

that's native vessel or potential complications related to

1:55

bypass or stents. We also often perform these

1:59

studies for trauma, whether that's a blunt trauma, motor vehicle collision,

2:03

or gunshot wound or other penetrating trauma, and then potentially also

2:07

for vascular access complications, and more rarely, inflammatory

2:11

diseases.

2:12

So we'll start just by talking about the anatomy of the abdominal

2:16

aorta and its proximal branches. It's important to start our

2:20

vascular evaluation with the aorta, since that is bringing the

2:24

blood supply to the lower extremities.

2:27

Then we divide the AIF into the

2:31

inflow first, what is bringing blood into the thighs.

2:34

So that is the aorta, our common and external iliac

2:38

arteries. The inguinal ligament is the dividing line, the

2:41

anatomic demarcator between the external iliac artery and the

2:45

common femoral artery. That is a bit more difficult to

2:49

see well on CT, so often I am using the deep inferior

2:53

epigastric artery that arises distally from the external iliac

2:57

artery as an anatomic dividing line.

3:01

Then we talk about the outflow,

3:04

which is going to be beginning with the femoral arteries, the

3:08

common femoral artery, which is going to branch into deep and superficial

3:12

femoral arteries. The deep femoral artery supplies the muscles of the thigh

3:16

and is an important source of collateral circulation when there is

3:20

disease of the superficial femoral artery.

3:23

The SFA is the longest vessel that we are going to be assessing, and that will

3:27

lead us from the outflow, what's bringing blood out of the

3:30

thighs, into the runoff or the most distal portion of the

3:34

circulation. The adductor hiatus is an important anatomic

3:37

landmark for distinguishing the superficial femoral artery from

3:41

the popliteal artery. The popliteal artery will have three

3:45

segments, an above the knee, at the knee joint, and below knee

3:49

segment. And now we are into the runoff, our calf vessels.

3:53

So we are going to have, in a typical branching pattern, the

3:57

popliteal artery giving rise to an anterior tibial artery and then a short

4:01

tibial peroneal trunk branching into peroneal and posterior

4:05

tibial arteries. And then when we reach the foot, we will see

4:08

continuation of the anterior tibial artery as dorsalis

4:11

pedis, and of the posterior tibial artery, most typically as the plantar

4:16

artery. So let's look at this in cross-section, just again to give

4:19

you an overview of the anatomy. These are the levels that we're looking at.

4:23

So here is our proximal aortic branches, more distal aortic

4:27

branches from the abdominal aorta.

4:29

Now getting into the inflow, our iliac arteries,

4:33

external, internal. And now we are heading into the

4:37

proximal outflow, our superficial and deep femoral arteries,

4:41

and then finally, our runoff in these bottom three images.

4:46

Okay, so moving from anatomy to technique, how do we perform this

4:50

exam?

4:51

We ideally like the patient's arms above their head to

4:55

reduce streak artifact. We ideally like to use as low a

4:59

kVp as possible to optimize your image contrast, recognizing

5:03

that some of these patients are going to be larger, or the arms may need to be

5:07

down in the setting of trauma, and so you may need to increase the kVp

5:10

to achieve a reasonable signal-to-noise ratio.

5:14

But ideally, as low a kVp as you can.

5:17

You want a high contrast injection rate.

5:20

We are typically bolus triggering or tracking, and then triggering off of the

5:24

descending thoracic aorta. So once we reach a threshold, we use

5:27

150 Hounsfield units. We wait an additional 10 seconds to

5:31

allow contrast to flow into the lower extremities and then

5:35

begin our scan. So our initial scan is from just

5:39

above the diaphragm to the toes, and then we wait anywhere from

5:43

15 to 30 seconds to do a delayed phase from just above

5:47

the knees to the toes. And the purpose of that delayed phase is

5:51

to avoid outrunning of the contrast bolus imaging before the arrival

5:55

of contrast that is most likely to occur in the distal portion

5:59

of the vasculature. So that is typically where we start our

6:02

delayAnd then you can add a non-contrast acquisition if

6:06

needed. For example, if you're scanning in the setting of trauma, wanting to be

6:10

able to distinguish bone fragments from active extravasation,

6:14

or if the patient is post-op and we want to know what is intrinsically dense before

6:17

we begin scanning. But we don't routinely perform non-contrast

6:21

imaging. I don't find it to add much use.

6:25

As far as reconstructions, we'll reconstruct our arterial and delayed phases in the

6:29

axial planes. I'm showing you just a coronal MPR of those.

6:33

Reconstruct separate lung windows.

6:35

And then from the scanner, we will get these coronal 30 by

6:38

5-millimeter MIPs, which can be useful sliding through to see an

6:42

overview of the vessels. And then eventually, our technologist will make

6:46

volume render 3D images, though you'll see plenty of those images in this

6:50

lecture. I think they look pretty, but I'm not typically actually using those for

6:53

diagnosis.

6:55

Okay. How about more advanced techniques?

6:56

So if you have access to a dual energy CT scanner

7:00

performing low virtual mono-energetic reconstructions, this example is

7:04

at a keV of 50 will increase your contrast.

7:08

So this is the native reconstruction, a blended image, and we can

7:12

see looking at our outflow vessels, or excuse me, our runoff vessels,

7:15

that we get increased contrast and conspicuity of those

7:19

vessels on both the arterial as well as the delayed phase compared

7:23

to our standard acquisition. So if you have the ability to do that, it

7:27

can be useful. What is even better is photon counting CT,

7:31

because you will essentially have this capability on every scan that you perform

7:35

without needing to choose

7:38

a special type of acquisition technique.

7:41

So what you can reconstruct as a standard image is in what's called quantum

7:45

mode, is a virtual low mono energy.

7:47

This is at 55, so you get very nice enhancement with this.

7:50

And then we can use a more complex material decomposition

7:54

to reconstruct a pure lumen. This is using a Siemens photon

7:59

counting scanner. You can do a virtual calcium removal, so

8:02

this removes the calcium. Helps you identify the vessels perhaps a little bit more

8:06

easily, particularly distally. And then you can also perform a pure

8:10

calcium, which is a virtual non-iodine, essentially a more

8:13

sophisticated virtual non-contrast image that would allow you to see

8:17

calcium. We don't reconstruct the pure calcium, but we do reconstruct the pure

8:20

lumen. And this is where I find it to be particularly useful.

8:24

So if we look at this coronal maximum intensity projection,

8:29

this is just in regular quantum mode.

8:30

You can see quite a bit of calcium in the vessels, potentially a stent

8:34

here. But then the vessels from really the distal thigh

8:38

through the toes are often obscured by overlying bone.

8:43

The pure lumen or virtual non-calcium

8:46

image is able to remove much of that cortical bone.

8:50

So you can kind of still see the outlines of the bones, but the vessels you're

8:53

actually able to see through the bone.

8:55

So for your maximum intensity projections, in particular,

8:59

this pure lumen reconstruction can be helpful.

9:04

Okay. So how about protocol considerations if you want to modify that

9:07

protocol? Adding a chest to the acquisition, it can be

9:11

helpful in the setting of trauma if they have additional trauma

9:15

involving the chest. If you have a clinical suspicion for embolic

9:18

disease, then it is really imperative to try and scan the chest so that you are

9:22

able to assess for cardiac or aortic causes, some of which I've listed here and

9:26

we'll go through in more detail. If there is clinical suspicion for an acute aortic

9:30

syndrome compromising the lower extremity circulation, then doing the

9:34

chest obviously will be helpful. And then if the patient has an axillofemoral

9:37

bypass graft, we want to be able to assess the proximal attachment site

9:41

and flow through that graft.

9:44

How about if you are only dealing with a trauma in lower extremities, then you

9:48

could potentially just do a lower extremity angio and omit the

9:51

abdomen portion since there really is no concern in that region, but that's really

9:55

not appropriate for peripheral vascular disease.

9:58

We want to assess the inflow as well.

10:00

And then if you have a patient who has a triple A, you may want to modify this to

10:04

be able to assess their endovascular repair and look for

10:07

endoleak, potentially adding a non-con as well as a 90-second delay

10:11

to assess for that endoleak. And then, as I mentioned, adding a

10:15

non-con to an AIF can be useful if there's a concern for bleeding,

10:20

particularly post-operatively, but we don't routinely perform this.

10:24

So this is just my approach. You can do this in a lot of different ways, but I

10:28

essentially read this exam like a normal abdomen and pelvis.

10:31

I ignore the vessels on my first pass.

10:33

I dictate how I would normally dictate an abdomen and pelvis, and then I look at

10:36

the vessels because I know that that is where I'm going to need to spend the most

10:40

time and pay the most attention, and I try to go through the vessels

10:44

really just from top to bottom. That is the way our template is organized as well

10:48

to try and stay organized. You will find

10:51

extravascular findings of importance on many of these patients are often older,

10:55

have comorbidities. Here's an example of a patient with an infiltrative

10:59

adenocarcinoma, cholangiocarcinoma of the liver that is

11:02

incidentally seen on an AIF.

11:06

So I report those non-vascular findings first, make sure that I'm

11:09

using a comprehensive template. And as I'm reading the

11:13

exam, I'm really thinking about synthesis from the very beginning.

11:16

What does a vascular surgeon want to know? What needs to go in the impression?

11:20

So what they're interested in, and we'll talk about this in more detail, is where

11:24

is their vascular disease the worst or most significant?

11:27

Is it unifocal or multifocal? Where is the abnormality?

11:31

And then what are potential revascularization targets distally?

11:34

If they're going to do an intervention, is there a distal vessel that is

11:38

suitable for, say, a bypass or a stenting?

11:42

Some of the pitfalls that you need to be aware of are bolus timing.

11:45

So one of the issues that we can encounter is that we scan too rapidly

11:49

or outrun the bolus. We scan before the arrival of contrast.

11:53

This is accentuated more with poor cardiac output, and it's hard to know

11:56

prospectively who this is going to affect.

12:00

But one of the

12:01

ways you can identify this is that you'll notice in this patientIn the

12:05

left lower extremity, that the density of this contrast column is just getting

12:09

gradually lighter and lighter and then fading away, which is not what thrombosis

12:13

looks like. So that can help you identify that we are outrunning the bolus in

12:17

one of the extremities, and we'll talk about why that might happen.

12:19

You can kind of see the same thing here.

12:21

It's getting less and less and less dense as we scroll down.

12:24

So that is the purpose of the delay, is to be able to give you

12:28

another opportunity, and certainly you can start the delay higher.

12:32

So if you have a patient who has, say, a femoral popliteal bypass graft, you

12:36

may want to change the protocol to start the delay at the

12:39

level of the proximal attachment site of that graft so you can make sure

12:43

that you're fully evaluating it if the bolus is outrun.

12:48

On the other side, you can also have venous contamination if you scan the patient

12:52

too late. So here was the initial scan of this patient who was moving,

12:56

and then by the time we re-scan, you can see that the veins paired with the

13:00

arteries are already opacified. You can still read the study, but it

13:03

requires far more scrutiny, narrower windowing to make sure that

13:07

you're really following the arteries and not the veins.

13:10

And in the setting of trauma, so this is a reason why you may see asymmetry of

13:14

this. This patient had a traumatized left lower extremity, so there's increased

13:18

blood flow to that left lower extremity and therefore earlier venous

13:21

return. So you'll see hyperemia in the left lower extremity and

13:25

not the right. So that is something to be aware of when you're evaluating these

13:29

patients.

13:30

And then, of course, dense calcification or blooming artifact can obscure the

13:33

vessels. You really want to use a wider window width that can be helpful,

13:38

especially relevant with renal and mesenteric arteries, as well as the calf

13:41

arteries. And if you really are not able to assess it and it is of

13:45

clinical importance, then MR angiography can potentially help with this

13:49

limitation since we don't see the calcium.

13:52

And then if you're using maximum intensity projections or 3D

13:56

renderings in particular, where the technologist may need

13:59

to select the vessel, you want to make sure if you see something that doesn't make

14:03

sense, that it is backed up by the source data.

14:05

Here's an example where it looks like there's a focal occlusion, and for whatever

14:08

reason, the vessel probe did not catch the

14:12

superficial femoral artery segment here.

14:14

So if you see an abnormality there, just make sure that it's truly real.

14:19

And then streak artifact, whether that's from metallic implants such as

14:23

knee arthroplasties or internal fixation, bullets in the setting of

14:27

trauma will create streak artifact that is worse when you are

14:31

acquiring your images with a lower kVp.

14:33

So in that setting, if you have the ability to perform metal artifact

14:37

reduction, most of the CT vendors offer this, that is able

14:41

to help. And here is an example of that.

14:45

So in this patient, we can see a bullet that is near

14:48

probably the popliteal artery, and we can see that there is

14:52

streak artifact that is obscuring our evaluation on our

14:56

standard reconstruction. When using iterative metal artifact reduction, in this

15:00

case, we are able to ameliorate that.

15:04

There is not a specific metal artifact reduction technique for bullets,

15:08

but I find that the dental implant setting tends to work fairly well.

15:14

Okay, so now armed with that background, we're going to talk about some

15:17

disease processes, and then we'll get to the bulk of this

15:21

presentation, which is going to be going through some sample cases.

15:25

So when thinking about peripheral arterial disease, we can see many

15:29

different patterns of disease, and often it will be symmetric.

15:32

It can be helpful as you're synthesizing your findings, looking through the study,

15:36

seeing if it happens to be the same on both sides.

15:38

So we're going to be looking at examples of stenosis and occlusion, what can happen

15:42

with bypass grafts and stents, embolic disease, peripheral aneurysms, the whole

15:46

gamut.

15:47

So when a patient presents with acute limb ischemia, this is the clinical

15:51

evaluation and our stages, you'll notice here there's

15:55

no radiology at this stage. I guess Doppler is radiology in a sense, but

15:59

this is not being performed by us typically.

16:02

So they are trying to determine, is this limb viable?

16:05

Maybe not immediately threatened based on their sensory and

16:09

findings, their neurologic findings, as well as Doppler signals.

16:13

Is a limb threatened, progressing all the way, potentially to a

16:17

stage three of acute limb ischemia, where there's irreversible damage and this

16:21

is not going to be a salvageable limb?

16:23

So when we're thinking about acute limb ischemia, you will notice

16:27

that in terms of our options for evaluation, that

16:31

CT is going to be your primary modality.

16:34

Duplex ultrasound can be useful for problem-solving, like for bypasses, for

16:38

example, as well as potentially invasive angiography for diagnosis.

16:42

But CTA is going to be the workhorse with MRA reserved if

16:46

CTA is contraindicated in that particular patient for whatever reason.

16:50

And for subacute limb ischemia, same thing.

16:52

CTA is really going to be the workhorse for assessing

16:56

this.

16:58

So when we think about the causes of acute peripheral arterial occlusion, the

17:01

majority of time, this is going to be thrombotic occlusion at a site of

17:05

pre-existing atherosclerotic stenosis.

17:08

This is often less severe when that occlusion occurs than

17:11

embolic disease because these patients have had time to develop collateral

17:15

circulation. And because vascular interventions are

17:19

fairly common now, you'll see thrombosis of bypass grafts as the most

17:23

frequent cause of acute limb ischemia.

17:25

In fewer cases, but it's important to keep in the back of your mind when you're

17:29

encountering thrombosis, is embolic disease, which is about 15% of these

17:33

cases. It's usually cardiac in origin, but the aorta

17:37

can be a potential source as well. So when we say cardiac, we're thinking about

17:41

left atrial appendage thrombi in the setting

17:45

of atrial fibrillation or potentially a left ventricular apical thrombus from an

17:49

MI. And we want to evaluate the aorta as well

17:53

because it can be a potential source of embolic disease.

17:55

And we will see some examples of the pattern of embolic disease where these tend to

17:59

lodge at bifurcations or vascular branch

18:02

points.So just a simple way

18:06

for grading vascular stenosis, kind of how I think about it, if it is less

18:09

than 50%, I would consider it mild, 50 to 70 moderate,

18:14

70 to 99 severe, and of course, 100% occluded.

18:17

I don't think there is really much of a role in trying to

18:21

precisely quantify the degree of stenosis in most cases.

18:25

You're already spending enough time going through this case.

18:27

So, I think you can really use your gestalt, but

18:31

just try to apply it consistently.

18:34

So thinking about some of the types of bypass grafts that you will encounter,

18:38

this is an aortobifemoral bypass graft.

18:41

So those patients typically have bilateral iliac occlusive

18:45

disease. You can have a crossover or

18:48

femorofemoral bypass graft that's typically for unilateral

18:52

iliac occlusive disease where the other iliac vessel is

18:56

relatively undiseased, and this is a fairly short, simple

19:00

bypass graft to be able to place. When you see an

19:03

axillobifemoral bypass graft, that is typically the last resort.

19:07

The patient has exhausted all of their other avenues for blood

19:11

flow to that extremity. This is typically what is going to precede

19:15

amputation. This is the last-ditch effort, and given the length of that bypass

19:19

graft, you can understand why this has a tendency to thrombose.

19:24

And then some of the other bypass grafts that you will encounter, this is

19:27

above-knee femoral to popliteal

19:30

artery bypass graft. You can also see femorotibial

19:34

bypass grafts, a large variety, but it's just important to

19:38

recognize some of the anatomic configurations that you may encounter.

19:43

For endovascular therapy, such as stent placements, we should also

19:47

be thinking about potential complications at the puncture site, such as bleeding or

19:51

development of pseudo aneurysms or AV fistulas.

19:54

You can also have distal issues such as embolization or dissection.

19:58

And these endovascular treatments tend to not work quite as well for

20:02

patients who have diabetes or end-stage renal disease, kind of brittle

20:05

calcification. They don't tend to work quite as well for long segment

20:08

occlusion. They're better for short stenoses, though I will say, I think that

20:12

these statements are really based on how these

20:15

devices tended to perform because we do see more and more

20:19

patients who have a multiplicity of stents rather than a bypass, as we might have

20:23

expected in yesteryear.

20:26

All right, so now we are going to go through some cases to illustrate some of these

20:30

points. So this first case was a 63-year-old man who had undergone an

20:33

aortobifemoral bypass nine years ago, presenting with decreased

20:37

pulses, increased claudication in the right foot.

20:42

So again, I'm not necessarily reading these cases

20:45

using these 3D renderings, but they do provide a more

20:49

straightforward way of depicting the vascular findings on a single image rather

20:52

than having to scroll through. So here we can see this

20:55

aortobifemoral bypass. So from the infrarenal

20:59

aorta, kind of plugging into the common femoral artery on each side.

21:04

And as we follow our blood flow on the right side, we're coming

21:08

down through the popliteal artery and where we would expect to see the

21:12

tibioperoneal trunk between that and the popliteal artery,

21:16

we see a segmental occlusion about seven centimeters in length.

21:19

So this is a popliteal artery occlusion.

21:21

You can see in the contralateral extremity a more

21:25

normal appearance of the vasculature to kind of give you a sense.

21:28

So for this popliteal artery occlusion, they ended up doing

21:32

a reversed greater saphenous vein above-knee to

21:36

tibial peroneal trunk bypass. So we can see

21:39

after they have performed that intervention that we have restored

21:43

flow. So a fairly straightforward example of what

21:47

is presumably thrombotic disease.

21:51

How about this 85-year-old man with leg pain?

21:54

This is a more unusual manifestation of peripheral arterial

21:58

disease to be aware of. As we look at the right popliteal artery

22:02

above the knee, we can see this vascular outpouching

22:06

with mural thrombus indicating a popliteal artery aneurysm.

22:10

This patient had a unilateral aneurysm, but you will see

22:14

bilateral aneurysms in many of these patients.

22:17

And so as this aneurysm expands, we can see that there's likely

22:21

non-laminar or turbulent flow, which is leading to development of this

22:24

thrombus. So this patient was treated essentially with

22:28

endovascular repair to make sure that this did not expand and

22:32

rupture. So thinking about popliteal artery aneurysms, these are defined

22:36

as focal dilation of the artery more than 50% of the normal diameter,

22:41

most commonly affecting the popliteal artery in the lower extremity,

22:44

presumably the repetitive mechanical trauma from bending the knee.

22:48

These have a variable growth and natural history.

22:51

Some of these will stay stable for years, others will grow fairly

22:54

rapidly. As I mentioned, about half these patients will have

22:58

bilateral aneurysms. So we want to treat these

23:02

to prevent continued growth of the aneurysm, thrombosis, distal

23:05

occlusion, or even rupture. So two centimeters is typically

23:09

the cutoff that is used because they have an increased risk of thrombosis or

23:13

distal embolic events. And so when it is two centimeters, they

23:17

can potentially be able to stent that if it's ruptured or

23:21

distally thrombosed, then it's going to be a more complicated repair.

23:26

So that is the location in the lower extremities to be on the

23:30

lookout for aneurysms most commonly.

23:33

All right, our next case, you may be able to guess the diagnosis based just on the

23:37

history. This patient presented with buttock claudication.

23:40

And so if we look at the maximum intensity projection as well as this

23:44

3D rendering, we can see after the renal arteries have come off that we seem to be

23:48

missing a fairly large chunk of the aorta.

23:51

So this patient has infrarenal aortoiliac occlusion,

23:55

and we can see reconstitution of our femoral arteries and as

23:59

well as our external iliac artery from

24:03

collateral. So we've got a very large, robust collateral network

24:07

fromCircumflex iliac arteries, as well as deep

24:10

inferior epigastric arteries. And you can see some of those

24:14

collaterals illustrated on this axial slice.

24:18

So this is a pretty common pathway, particularly from

24:21

the superior epigastric, inferior epigastric to external iliac, the

24:25

pathway Winslow, that is able to provide collateral blood

24:29

flow when there's aortic or aortoiliac occlusion,

24:33

but these patients tend to develop butt claudication and impotence, which

24:37

is what we call Leriche syndrome.

24:40

So this patient underwent an aortobifemoral

24:44

bypass, and we can see a complication after some time, I

24:48

think this was six months to 12 years later, where we have soft tissue around the

24:52

graft extending posteriorly into the adjacent

24:56

vertebral body. You can see this kind of long segment soft tissue thickening,

25:00

this rind of tissue around the iliac limbs.

25:03

And on the MRI, we can see adjacent enhancement of

25:07

both the phlegmon as well as that vertebral body.

25:10

So this patient had Leriche syndrome, that chronic aortoiliac

25:13

occlusion, as well as subsequent infection of an

25:16

aortobifemoral bypass graft. So complications

25:20

of grafts can include infection. Seeing some fluid or gas around

25:24

the graft fairly soon after surgery is normal, but we expect that

25:28

to either the gas to resolve, the fluid and soft tissue thickening to

25:32

either stay the same or decrease. So certainly if it's getting larger, we want

25:36

to be raising the possibility of infection.

25:40

Okay, so now we're going to turn to embolic disease.

25:42

So this is a 54-year-old woman who had rheumatic heart disease, a bioprosthetic

25:46

mitral valve replacement, dry gangrene of all 10 digits.

25:50

And so if we look at this patient's coronal image, we can

25:54

again see aortoiliac occlusion. So

25:58

we have this thrombosis from the most distal portion of the infrarenal aorta

26:01

extending through the common iliac arteries.

26:04

And then if we take a peek more distally, we can see a

26:07

fairly normal

26:10

runoff in the right lower extremity.

26:12

And in the left lower extremity, we can see this abrupt occlusion of

26:15

the tibial peroneal trunk, as well as restoration of flow

26:19

more distally. So that appearance, when we have a

26:23

proximal thrombosis, we have flow, which is collateral

26:27

flow, and then we have a more distal thrombosis.

26:29

This should alert you or at least

26:32

make you consider the possibility of distal embolic disease from a more

26:35

proximal thrombosis. This patient developed this

26:39

aortoiliac occlusion because of a vegetation on

26:43

their mitral valve.

26:45

So this is an example of embolic disease.

26:47

I'm going to show you another here in just a moment.

26:50

This is a 54-year-old man with metastatic testicular cancer.

26:55

And so if we look at this patient's sequential images, we have

26:59

embolic disease within the right common femoral artery

27:03

extending down into the popliteal artery, and then we can see that there's

27:06

flow. And on the contralateral side, popliteal artery

27:10

occlusion, we can see emboli

27:14

within the peroneal artery, as well as the posterior

27:17

tibial artery.

27:19

This patient's imaging of the chest shows the culprit, a large

27:24

left ventricular apical thrombus in the setting of a

27:28

prior infarct. And this is just, again, showing you the

27:32

maximum intensity projections of those embolic foci.

27:35

So this patient had an LV infarct and thrombus with bilateral lower

27:39

extremity embolic disease. So when should you think about embolic

27:42

disease? If you see abrupt focal occlusion with expansion of the vessel,

27:47

this is where the non-vascular findings can inform your

27:51

vascular interpretation. So as I'm looking through the

27:54

organs, the bowel, if I see renal infarcts or splenic infarcts,

27:59

potentially bowel ischemia in really severe cases, that should alert you to the

28:02

possibility of embolic disease. If the patient doesn't fit the demographic,

28:06

they're younger, there's really no athero in the lower extremities, that's another

28:10

reason to consider embolic disease.

28:12

And then, of course, if you happen to see a source, whether that's a triple A with

28:16

mural thrombus, a left atrial appendage clot in the setting of AFib,

28:20

a left ventricular apical thrombus in the setting of MIs in this patient, valvular

28:24

disease, ARS disease. This patient had a thoracic aortic mural

28:28

or mobile thrombus or TAMTE. Those are a potential nidus for

28:31

distal embolic disease as well, and as well as patients of hypercoagulable

28:35

states. So for my residents who read these cases, I

28:39

really hammer home to keep embolic disease in the back of your mind.

28:43

It's not the most common cause, but if you don't think about it,

28:47

no one may be thinking about it. So we need to just be mindful of that.

28:53

Okay, how about other things that you may encounter in this setting?

28:56

So a 55-year-old man with abdominal pain and hypotension.

29:01

We don't really need the contrast to make this diagnosis, but we can see on these

29:04

upper two images a markedly expanded abdominal aorta, so an

29:08

aneurysm, this hyperdense mural thrombus, as well as a

29:12

significant volume of adjacent left retroperitoneal hemorrhage extending

29:16

down along this aneurysmal left common iliac artery.

29:20

So this patient has a ruptured abdominal aortic aneurysm

29:24

with aneurysmal dilation extending into that left iliac

29:28

system. So this patient was able to undergo

29:31

an endovascular repair. And so because of the

29:35

aneurysmal left iliac system, they did an interesting

29:39

repair here. So we can see an

29:41

aortoiliac-uniiliac endovascular repair, as well

29:45

as a femoro-femoral bypass graft.

29:47

So this is how they were able to restore blood flow to

29:52

this left lower extremity. And then they have used an

29:55

Amplatzer occluder device to embolize the internal iliac artery

29:59

to try and prevent retrograde flow into that left

30:03

external or left common iliac artery aneurysm.

30:07

So this is what a patent femoro-femoral bypass graft should look like.

30:10

This is just an axial maximum intensity projection to be able to show the entire

30:14

graft on one image. And so you can see there is just normal blood flow,

30:18

no ingraft stenosis or

30:21

thrombus.Okay. So unfortunately, this patient's journey was not done.

30:25

On subsequent imaging, we can now see interval thrombosis of

30:29

the aortic, as well as the iliac components of this

30:33

bypass graft. We can also see thrombosis of the

30:36

femoral bypass graft. And then we can see how is blood flow

30:40

getting to the legs. Our familiar friends, the circumflex iliac and

30:44

deep inferior epigastric arteries, are providing collateral blood

30:48

flow to the external iliac artery.

30:51

The flow that you see above this, you will see this frequently, this is presumably

30:54

retrograde flow back up the external iliac artery

30:58

to supply the internal iliac artery.

31:01

So you will see that frequently, but really the source where

31:04

the collateral flow is going through is going to be the external

31:08

iliac artery.

31:10

So this patient had the ruptured AAA and the endovascular

31:14

repair, and then subsequent occlusion of their grafts, and many

31:18

more procedures that I'm not going to show for this particular case.

31:22

All right, so next we have a 69-year-old man, remote history of

31:26

aortobifemoral bypass,

31:28

as well as a left femoral pseudoaneurysm repair, now presenting with a

31:32

pulseless cold mottled left leg, as well as a pulsatile left

31:36

inguinal lump. So we can probably make the diagnosis from the history, but

31:40

the imaging is pretty interesting here.

31:41

So this patient, for whatever reason, tends to be an aneurysm

31:45

former. So they've had an aortobifemoral bypass graft.

31:48

We can see an aneurysm at the distal graft site on the right, but

31:52

on the left we can see a much larger aneurysm, and it looks like there's

31:56

some adjacent hemorrhage around it.

31:58

So an unstable aneurysm at the

32:01

anastomotic site on the left side.

32:05

And then what do we see as we come down?

32:07

You can kind of see this even beginning here.

32:09

If you look at the degree of contrast enhancement of both of

32:12

these

32:13

pseudoaneurysms, you can see far more enhancement on the right.

32:16

So there's sort of diminished flow or more turbulent flow on that left

32:20

side, and we can see that borne out as we follow their runoff.

32:24

We can see at the level of the knee as we're coming down that we can

32:28

see blood flow within the right-sided vessels, but not so much on the

32:31

left. Given the fact that this is sort of gradually diminishing, again, this

32:35

looks more like outrunning of the contrast bolus rather than distal

32:39

occlusion on the left side. And if you encounter this and are not

32:43

sure, have we outrun the bolus or is there thrombosis?

32:46

This is where

32:47

a conversation with whoever's taking care of the patient can be very useful.

32:51

If that leg, that foot is warm, there's pulses, then that is

32:55

far more likely that we have outrun the bolus rather than being a true

32:58

occlusion.

33:00

So this patient underwent repair of that, and then four years later

33:04

came back with a pseudoaneurysm on the right side.

33:07

So they unfortunately had bad luck.

33:12

Okay, this next case is a 68-year-old woman with a left femoral

33:16

popliteal bypass graft and repair of a common femoral artery

33:20

pseudoaneurysm, now with an exposed wound.

33:22

So in these postoperative patients, we want to be thinking carefully about

33:26

infection, and it can be challenging because you're going to see some soft tissue

33:30

thickening, some fat stranding, maybe even some hematoma after

33:34

a repair. But the clinical scenario, I think, is important

33:37

for being able to assess that. Here we can see that there's quite a bit

33:41

of soft tissue thickening around this common femoral artery pseudoaneurysm repair

33:45

and a wound that is extending all the way to the skin surface.

33:48

This patient has a pretty unusual manifestation of infection.

33:52

So they have this bypass graft, and you can see these little

33:55

vascular outpouchings from these.

33:58

So they have graft pseudoaneurysms, which are extremely

34:02

uncommon, but should make you think about the

34:05

possibility of infection.

34:08

So they end up explanting this patient's graft, and she ultimately

34:12

needed an above-the-knee amputation due to not being able to

34:16

salvage that lower extremity.

34:20

Next case is a 41-year-old man with a cold right foot and chest pain.

34:24

And I show this case, at least this slide, to illustrate that on

34:27

most AIFs, you're going to, because you have a good systemic arterial phase of

34:31

contrast, you should also have quite a bit of contrast in your pulmonary artery.

34:35

So you should look for pulmonary emboli within the distal

34:39

pulmonary artery branches. In this case, we can see both the pulmonary

34:43

embolism in a left lower lobe artery, as well as the peripheral

34:46

infarct.

34:49

I've seen those missed on occasion, so try to make that part of your vascular

34:52

search pattern. And we can see deep vein thrombosis, which was likely the culprit

34:56

in the right femoral vein.

35:01

And so now as we look down, this patient not only had deep vein

35:04

thrombosis, they also had arterial occlusion.

35:07

We can see at the level of the right popliteal artery that both

35:11

the artery and the vein are occluded.

35:14

And so you can kind of see that segmental occlusion here.

35:18

So this patient underwent a right lower extremity embolectomy and

35:21

unfortunately also subsequently required an amputation.

35:25

But keep venous thrombosis in the back of your mind when

35:29

you are reading these cases as well.

35:32

All right. We are now going to move to trauma.

35:35

So we have a 24-year-old woman, motor vehicle collision, so blunt trauma.

35:39

And fairly straightforward, we can see a fracture in the

35:43

midshaft of the femur, as well as a short segment occlusion of the

35:47

mid superficial femoral artery at the site of this displaced

35:51

femoral artery fracture.

35:53

In the acute setting, you will often see that there is still blood flow distally.

35:57

There are collaterals, often muscular collaterals from the deep femoral

36:01

artery that are providing blood flow.

36:03

So you can see that the distal vasculature looks quite normal.

36:07

And when you see this proximal occlusion, make sure that you are carefully

36:10

scrutinizing for distal embolus disease.

36:12

We don't see any on these images.

36:15

So this was a traumatic left SFA occlusion.

36:19

All right, this is a patient who had another motor vehicle collision,

36:23

tibia and fibula fractures in this case.And we can see those fractures

36:27

here. And now we see this interesting phenomenon where they have

36:31

the fractures on the right side, and we can see that there is, on the

36:34

arterial phase, opacification of the right popliteal artery, but no

36:38

contrast in the left. And on our delayed phase imaging, we can now see both

36:42

the artery and the vein are opacified on the right, and now the artery is

36:46

opacified the vein to a lesser degree.

36:48

And if we look at the maximum intensity projections, we can see a

36:52

couple of things that are interesting here.

36:55

On the left side, where we are outrunning the contrast bolus, we can see that

36:59

contrast column gets less and less bright. It gradually diminishes.

37:03

That's a good look for outrunning of the contrast bolus.

37:06

And on the right side, the traumatized lower extremity, they had tibia and fibula

37:10

fractures. Although we don't see an occlusion, we do see this sort of thready

37:14

appearance of our calf vessels, indicating that this is likely

37:18

vasospasm. Those vessels have been irritated by that blunt

37:22

trauma or potentially subcutaneous hemorrhage.

37:24

So vasospasm is something to be aware of in these patients.

37:28

We'll see an example here in just a few cases.

37:32

So this was hyperemia in that right lower extremity

37:35

and outrunning of the contrast bolus in the left lower extremity,

37:39

but no vascular injury.

37:43

All right, this was an unusual trauma.

37:45

72-year-old man who lost his balance and fell attempting to sweep kick another

37:49

person.

37:50

And so fairly straightforward diagnosis here.

37:52

We can see a proximal tibia fracture, and then we

37:56

see this rounded contrast blush adjacent to

38:00

the anterior tibial artery. So this is going to be a pseudoaneurysm of

38:04

a branch of the anterior tibial artery.

38:06

This is also a good example of satisfaction search, because what was missed on the

38:10

initial interpretation of this is that there's a small amount of active

38:13

extravasation more anteriorly within the

38:17

knee. So something to just keep an eye out.

38:19

When you see hemorrhage, make sure you look within that hemorrhage to

38:23

identify any foci of pseudoaneurysm or active extravasation.

38:28

So this was a traumatic anterior tibial artery branch pseudoaneurysm.

38:33

Our next case is a 60-year-old man who had undergone a heart transplant several

38:37

years prior, more recently, a cardiac catheterization presenting with right

38:41

groin and flank pain.

38:43

So what we can see on this case are the classic features on CT

38:47

angiography of an arteriovenous fistula.

38:50

So we can see that there is a direct communication between the right

38:54

superficial femoral artery and the adjacent femoral vein, which is expanded.

38:58

If we look at its size of the iliac vessels, as we come up a

39:02

little bit more proximally, it's a bit larger.

39:05

And on our maximum intensity projection, you can nicely see what looks like an

39:08

extra artery, because the vein is now nearly the same density as the

39:12

artery. So these are all sort of the classic features that one should look for.

39:16

It makes it fairly easy to make the diagnosis.

39:19

It can be a little bit more challenging when it's more subtle.

39:23

This patient also underwent a Doppler evaluation, and so we

39:27

can see these low resistance waveforms in the common femoral and superficial

39:31

femoral arteries, as well as an arterialized waveform in the right

39:34

superficial vein. And then this interesting Doppler phenomenon of tissue

39:38

vibration. When you're looking with color Doppler, you're able to see

39:42

this storm of both red and blue

39:45

around these vessels at the site of turbulent increase to blood flow.

39:49

So all features

39:51

confirming the presence of an arteriovenous fistula.

39:54

This is a companion case. So this is an example of where early venous

39:58

enhancement may mimic an arteriovenous fistula.

40:01

This patient had undergone an aortic valve and mitral valve

40:04

replacement, as well as a CABG, coming in with right groin pain.

40:08

And we do see similar to our last case, but not to the same degree, that

40:11

this right femoral vein is asymmetrically opacified relative to the

40:15

left. But comparing this to the degree of enhancement, I think

40:19

that's quite helpful. You can see that this is enhancing nearly as much as the

40:23

artery, whereas this almost looks like there's a mixing within this.

40:26

There's some brighter components, some less bright components, not quite as

40:30

dense as the adjacent artery. So in a case

40:34

like this, I would be more suspicious of hyperemia,

40:38

asymmetric blood flow to that right lower extremity compared to the left.

40:42

But in an equivocal case like this, and particularly when

40:45

that vessel is accessible for Doppler evaluation, that is going to be

40:49

helpful. This patient underwent a Doppler, and we can see we don't have the tissue

40:53

vibration, nor did we see either grayscale or Doppler evidence of an

40:57

arteriovenous fistula. So this was just a case of hyperemia.

41:02

When should you expect to see an arteriovenous fistula?

41:05

If the patient has end-stage renal disease and has had a lower extremity

41:10

dialysis fistula. So here we can see they've got a catheter in

41:14

their left iliac vein, the dialysis catheter.

41:16

And on the right side, we can see that vein looks like the artery, the

41:20

external

41:22

iliac vein, because this patient has a right thigh

41:26

dialysis fistula. They've had some other failed fistulas as well.

41:29

So before you get too excited about a fistula,

41:33

as you're scrolling through, make sure they don't have a specific reason to

41:37

intentionally have one.

41:40

All right, this is a 28-year-old man who was shot through

41:44

the left leg, and so I need to get off of

41:48

the laser pointer mode to play this video.

41:51

So as we scroll down, we're looking at the

41:54

superficial femoral artery.

41:58

And as we come down, we can see that there is

42:01

this contrast blush where there's active extravasation, and then we do not

42:05

see any flow below that for a short segment.

42:08

So that is transection with active extravasation from

42:12

this gunshot injury. Then as we come down more

42:16

distally, we can see reconstitution of

42:20

the popliteal artery.

42:23

And as we come down even furtherWe're going to

42:27

have some problems. So here now we can see the sort of thread-like filling

42:31

defect, what looks like most likely an embolism to the

42:35

distal popliteal artery extending into the tibial peroneal trunk.

42:39

And so we have a proximal vascular injury occlusion

42:43

and then distal embolic disease.

42:47

In the contralateral extremity, this is a nice example.

42:50

Let me put the laser pointer back on for showing you what

42:54

vasospasm looks like. So we can see the superficial femoral artery has a nice

42:58

straight contour. The deep femoral artery, we can see

43:02

has that somewhat beaded or thready appearance that would make us think about

43:06

vasospasm, and this patient happened to get a follow-up CTA

43:10

the next day after repair of their contralateral injuries, and now we can

43:14

see that that vasospasm has nearly completely resolved.

43:16

We have a much smoother contour of those vessels.

43:20

So this patient had a left SFA transection with active extrav,

43:24

embolic disease to the popliteal and calf arteries, and right profunda

43:27

vasospasm resolved the next day. There was a question about the

43:31

previous case asking about why, and I think that was coming back here,

43:35

that why was there hyperemia in one leg versus

43:39

the other? And it can happen for a number of reasons.

43:42

If you're able to see in the chart that maybe the patient has cellulitis in one

43:46

leg, or they had vascular access in one leg versus the other.

43:50

Anything that essentially irritates that extremity could

43:54

potentially lead to hyperemia. So I typically think about

43:57

infection, trauma, or postoperative state, and then

44:02

occasionally if they have cellulitis or something like that.

44:07

Okay. Case 19. This, I think we're getting towards the end here.

44:10

So this is a gunshot wound to the right leg.

44:13

We can see this comminuted ballistic fracture, proximal

44:16

tibia. And when we take a look at

44:20

the vasculature, the runoff here, we can see

44:24

for the tibial peroneal trunk, there is a short segment

44:27

occlusion, and then we see blood flow.

44:30

And so this was mistakenly attributed

44:34

to vasospasm at this time. So the patient had

44:38

an orthopedic repair, but no vascular intervention.

44:41

And as we saw earlier, that vasospasm is not the complete absence of

44:45

flow most of the time. It is going to be kind of thready flow or a

44:49

beaded appearance to the vessel. So this patient presented 10 months later, and now

44:53

we can see the consequences of missing that.

44:55

So there was obviously recanalization of that blood flow at some point, but

44:59

because there was a vascular injury, this dumbbell-shaped

45:03

pseudoaneurysm developed and has eroded into the bone.

45:07

So now it's a little bit more complicated of a problem for vascular

45:11

surgery and orthopedic surgery to repair

45:14

together. All right, so that was a lot of cases, a lot of

45:17

information. Our take-home points for you, trying to

45:21

understand the goals of aortoiliopemoral imaging, whether

45:25

that is in assessing peripheral vascular disease or trauma.

45:29

Trying to use a consistent search pattern.

45:31

I prefer to do my non-vascular assessment first and then look at the

45:35

vessels.

45:36

But you certainly can approach it in whatever manner works the best for you.

45:40

Dividing this into the inflow, what is bringing blood into the thighs, the aorta

45:44

and iliac arteries, the outflow, what is taking blood out of the thighs, the

45:48

femoral and popliteal arteries, and then the runoff, our calf

45:52

vessels and foot vessels. It is very helpful

45:55

to investigate the surgical history or prior interventions,

45:59

particularly before, if you are in a circumstance to be able to actively

46:03

protocol cases as you may want to make

46:06

alterations to the standard imaging protocol.

46:10

And then thinking about what information the vascular surgeon wants and really

46:13

trying to put that in the impression. Where is the disease burden the worst?

46:16

What are potential outflow targets?

46:19

And then trying to avoid satisfaction of search after finding a potential

46:23

injury or pseudoaneurysm or an occlusion.

46:25

Really look carefully about the fracture sites and be on the

46:29

lookout for embolic disease.

46:33

And then finally, be cautious in calling an arteriovenous fistula.

46:36

Try to find direct evidence of that connection, if you can.

46:39

Markedly abnormal venous enhancement that ideally is nearly the same as the artery.

46:44

Think about every time I'm going to call an AV fistula, I will try and ask

46:48

myself, could this be hyperemia? It is helpful to try and

46:52

avoid that pitfall.

46:54

And if you're interested in further reading, I published this almost a

46:57

decade ago with a couple of my fellows, and then this was our more recent

47:01

publication last year in Radiographics, where you'll see many of these

47:05

concepts discussed in further detail.

47:08

And with that, I thank you for your attention, and I am happy

47:12

to answer any questions. And I do see

47:16

a few in the Q&A, so let

47:19

me unshare my

47:22

screen, and then we will try and answer these questions.

47:26

Okay, so

47:27

first question is, "When you're scrolling on axial CT images, how do you know

47:31

when you are at the adductor hiatus to determine where the popliteal artery

47:35

origin is?" So you will see that the femoral

47:39

artery, superficial femoral artery is kind of coursing through the adductor

47:43

compartment, and you will see this last little slip of the adductor

47:47

muscle kind of fade away, usually about maybe two-thirds to

47:50

three-quarters of the way down the thigh, and that is when you reach

47:54

the popliteal artery. So you're really looking for it to go

47:58

to sort of leave the adductor musculature where it's no longer

48:02

completely surrounded, and that kind of alerts you to when you reach that

48:06

point.

48:08

Other questions. How to differentiate an

48:12

aneurysm from a pseudoaneurysm? Yes, and that can be

48:16

challenging. I think often the clinical context is the most

48:20

important. If you are encountering an aneurysm

48:24

in the non-traumatic or non-iatrogenic setting,

48:28

it's probably fairly unlikely to be a false

48:31

aneurysm. If it is

48:34

moreSaccular rather than fusiform, that

48:37

might give you an indication that it is a pseudoaneurysm that

48:41

is only contained by adventitia, not by all three layers of the

48:46

vessel wall. So I think clinical circumstance and

48:49

morphology are helpful, but sometimes you don't know, and you'll just have

48:53

to make a decision on giving it one designation versus the other.

48:59

Okay, so the next question, calcifications.

49:02

"I find the runoff very challenging due to calcifications.

49:05

Do you always comment on three vessel or two vessel or one vessel runoff?" That's a

49:08

great question. So when they are really dense

49:12

calcifications, particularly in the calf vessels or foot vessels,

49:16

then sometimes you just have to give a caveat that the vessels are

49:20

so densely calcified that adequate assessment is precluded.

49:23

In terms of where I will say that there is vascular runoff

49:27

to the foot or the ankle, I will vary that based

49:31

on how well I can assess those vessels.

49:33

So if I see that blood flow is definitely getting to the ankle, and

49:37

then it's getting kind of thready, but my suspicion for a actual

49:41

vascular issue is low, then I might say three vessel runoff to the ankle.

49:45

But if I can see

49:47

the anterior tibial artery going into dorsalis pedis and it's really

49:51

well delineated, and then I really don't see the plantar artery, then I'm probably

49:55

going to call an actual occlusion.

49:57

But I think you have some leeway in describing it as long

50:01

as your description is accurate.

50:06

Other questions. "In a traumatic setting, how can

50:10

we differentiate on CT and an arterial

50:14

post-traumatic dissection, a contusion with

50:17

thrombosis, and vasospasm?" So for the

50:21

vasospasm, when I've seen these, I am

50:25

not usually seeing a problem inside the vessel itself.

50:28

It's more that the contour of the vessel is abnormal.

50:31

It's that kind of beaded appearance or thread-like appearance.

50:34

With a dissection, it could be challenging, too.

50:37

Is it a dissection? Is it embolic disease?

50:40

With a dissection, it's usually reasonably long segment.

50:43

You kind of see a flap that's emanating from the edge of the vessel.

50:46

But when the vessels are so small, it's just a few pixels large as you're

50:50

getting down into the distal thigh, the proximal calf, I think it can be

50:54

really challenging. And probably what's more important is just identifying the fact

50:58

that there is a vascular injury that they may need to

51:02

assess at catheter angiography.

51:06

This other question, "Is the radiologist really helpful in assessing the

51:10

foot arteries, the dorsalis

51:14

pedis and the plantar artery? I find that these are often sub-optimally

51:17

opacified on CTA. And would you say that a 10-second delay

51:21

helps opacify them more reliably?" No, I think 10 seconds is too early.

51:25

I will say it is all over the place for our technologists,

51:29

sometimes 15, sometimes 30, sometimes a minute, and they

51:33

can't really win. Either they scan too early or they scan too

51:37

late. It's really hard to know.

51:39

So I will say that there are cases where you really see those

51:43

arteries beautifully and have found that with photon counting CT and

51:47

the improved contrast, that you are

51:51

able to see those in some cases. But yeah,

51:55

it is often challenging to be able to follow those

51:59

vessels all the way out. And when it really matters,

52:02

I will not say that we do this frequently,

52:06

you can do time-resolved MR angiography of the foot

52:10

so

52:11

then you're not really having to worry about timing because you can do a

52:15

TWIST or a TRICKS sequence and be able to image repeatedly over

52:19

several minutes and ensure that you're not missing the optimal

52:23

enhancement of those arteries. But practically speaking, we don't really need to do

52:27

that very often at all.

52:30

And I think I addressed the slow flow in the one leg in

52:34

trauma case.

52:36

Are there other questions that I can answer?

52:39

Happy to answer others.

52:46

All right. Looks like,

52:49

yeah, looks like you got through all those.

52:52

All right. Well, thank you everyone for your attention again.

52:55

I think the

52:56

publication in Radiographics has probably as many of these examples since

53:00

they've used these for multiple purposes, but it does go

53:03

into many of these topics in greater detail.

53:07

You'll see those anatomic illustrations, and

53:10

I think it's really to try to design it as a helpful reference for

53:14

reading what can be a challenging study.

53:18

Well, Dr. Shetty, thank you for that lecture today, and thanks to everyone for

53:22

participating and asking such great questions.

53:25

Thank you.

53:26

Be sure to join us next week on Thursday, May 14th, where

53:30

Dr. Ronit Kampelath will deliver a lecture

53:34

entitled "CT and MR Enterography in the

53:38

Evaluation of Crohn's Disease." You can register for that at

53:41

modality.com and follow us on social media for updates on future noon

53:45

conferences. Thanks again and have a great day.