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Today we are honored to welcome

0:39

Dr. Chang for a case review of CT colonography cases.

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Dr. Chang completed his radiology residency

0:45

at Boston University and his cross-sectional

0:47

imaging fellowship at Johns Hopkins Hospital.

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He's an associate professor of radiology at Boston

0:52

University's Chobanian and Avedisian School of Medicine,

0:56

and an adjunct associate professor of diagnostic

0:58

imaging at Brown University's Alpert Medical School.

1:01

At the end of the lecture, please join Dr.

1:03

Chang in a Q&A session where he will

1:05

address questions you may have on today's topic.

1:08

Please remember to use the Q&A feature

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to submit your questions so we can get to

1:12

as many as we can before our time is up.

1:14

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

1:17

Dr. Chang, please take it from here.

1:20

Good afternoon.

1:21

My name is Dr. Kevin Chang.

1:22

I'm a, I'm a radiologist at Boston Medical

1:25

Center, Boston University Medical Center,

1:27

and currently the section chief for abdominal

1:29

imaging at, uh, Boston Medical Center.

1:32

I'm an associate professor in radiology at,

1:35

uh, Boston University School of Medicine.

1:36

The, uh—

1:37

The Chobanian and Avedisian School of Medicine,

1:41

also an adjunct associate professor, uh,

1:43

in diagnostic imaging at Brown University.

1:47

I've been a long-time reader of CT colonography

1:50

and a teacher of CT colonography for,

1:52

for, uh, over a decade and, uh, and have—

1:55

Had experience at, uh, multiple institutions

1:58

other than Boston University as well, including,

2:01

uh, Newton-Wellesley Hospital and the Rhode Island

2:04

Hospital, and the Rhode Island Medical Imaging system.

2:07

Uh, today I'm gonna be showing you a bunch of, um,

2:10

interactive cases, uh, on the TeraRecon platform.

2:14

I have multiple teaching cases to show

2:17

you how I read CT colonographies using both a

2:21

primary 2D read as well as a primary 3D read.

2:25

And I'll show you, uh, an example of multiple

2:27

different kinds of pathologies—polyps,

2:29

cancers, other interesting, um, features

2:32

that you need to be able to describe.

2:34

And I'll also, uh, show you how we use the C-RADS,

2:38

uh, system—the CT Colonography Reporting and

2:43

Data System—to classify lesions and

2:47

to guide management for, uh, for the findings.

2:50

That's what we're gonna be doing today.

2:52

So from our list of, uh, anonymized

2:55

cases, I'm gonna be choosing the case

2:58

with the supine and the prone dataset.

3:01

So usually CT colonography, we get at least two data

3:04

sets in two different positions. At our institution,

3:07

we usually will scan the patient once on their

3:10

back and once on their belly, but you can choose

3:11

any two different, um, uh, positions you like,

3:14

uh, as long as you give the tagged fluid and the tagged

3:18

stool a chance to, to, to redistribute on the two

3:22

views so that you can get a chance to look at, uh,

3:25

the entire circumference of the colonic mucosa,

3:29

uh, in air relief on one of the two positions.

3:32

So we choose supine and prone, but

3:34

it can be any two that you'd like.

3:37

I make sure I'm choosing the thin cuts,

3:39

the ones that are 1.25 millimeters thin.

3:42

And basically we recommend scanning with,

3:44

uh, thin cuts at, uh, no greater than 1.25

3:47

millimeters. I would say it can be thinner than that.

3:51

And then I load it up in the colonography fly-through

3:54

package here, and it will choose the, um, centerline.

3:59

It's gonna try to—the package is gonna try

4:02

to automatically select out the gas-filled colon

4:06

and render a camera line through the center of the

4:08

lumen in both the supine and the prone dataset.

4:11

So on the left, we have the supine images and it's

4:14

automatically picked the colon out in green here.

4:17

And you can turn the 3D model around and

4:19

make sure that the, um, the segments that

4:21

are selected are colon and not anything else.

4:24

For example, here we've got a little bit of

4:26

the rectum here, so I'm gonna unselect that.

4:31

Looks like you can't unselect that without un-

4:33

selecting the ascending colon and the cecum.

4:35

And that's fine.

4:36

And then here we've got most of the colon

4:38

selected except for the, uh, the rectosigmoid.

4:41

And now I've added that back in because the,

4:44

um, if there's a fluid-filled segment of

4:47

the bowel, it may not know how to trace the

4:50

centerline through the lumen quite as well.

4:53

So you have to manually select that.

4:55

But these look like they're both appropriate.

4:56

Then hit the, the next step button and it'll

5:00

try to render the, the centerline through.

5:03

So basically this part is just

5:04

a game of connect the dots.

5:06

You wanna make sure that it's starting in the, in

5:09

the right place and ending in the right place and

5:10

going through the segments in the right order.

5:12

So this looks like it's doing a pretty good

5:14

job of that, although in the beginning it

5:16

looks like it's going right down the barrel

5:18

of our rectal catheter, which is fine.

5:21

You're not gonna find polyps

5:22

inside the rectal catheter.

5:24

But, but we will get into the,

5:25

uh, the rest of the colon.

5:27

Then I hit okay.

5:29

And then we should be ready to,

5:30

um, to do our, our 3D fly-throughs.

5:34

But for, for the time being, I think we will start

5:38

with the 2D, um, evaluation because that's probably

5:42

the, the easiest way to, uh, pick up CT colonography.

5:46

Just to make sure that the 3D images look appropriate.

5:50

I want to, um, window it so that there's,

5:52

uh, to minimize the amount of noise on the,

5:55

um, on the, um, the wall of the structures.

6:00

And given that we are using a very, uh, low radiation

6:03

dose protocol, uh, I tend to have to adjust this

6:07

just a little bit to make it a little bit less noisy.

6:10

So these are our 3D settings.

6:12

Basically the, um, the rendering

6:14

thresholds for the surface render.

6:17

And I do that for both positions here.

6:22

So basically you could see how

6:23

there's a little bit of, um—

6:26

Noise along the wall of the colon here,

6:28

and I'm just adjusting the, um, the

6:29

threshold to make it a little bit smoother.

6:33

All right, so that's basically that.

6:35

And then you can choose on this package,

6:37

you can choose a, a variety of different

6:39

workflows, uh, and different layouts.

6:44

Uh, for a primary 2D read, you can either

6:47

use the 3D read here or you, we can try the

6:50

primary 2D, which does, which aligns both the

6:54

supine and the prone together at the same time.

6:56

I don't like to scroll 'em at the same time,

6:58

uh, because, uh, I like to look at each

7:01

side individually, but basically the, um—

7:05

The next step here is to, the first

7:08

step is just to judge the quality of the

7:10

distension and the quality of the bowel prep.

7:13

So I'm looking through, uh, on small

7:16

field of view windows through the colon.

7:18

And basically the job is to, to fly through, basically

7:22

to assess the entire colonic lumen from the anal

7:25

verge all the way to the cecum on both positions.

7:30

And, uh, you want to set your window wide enough

7:33

so that you can see through the tagged fluid.

7:36

'Cause here you can see the oral contrast

7:37

tagging any residual fluid and stool in the

7:40

colon, while still being able to differentiate

7:45

a, a soft tissue density polyp from, from the

7:48

adjacent fat, or from a lipoma, for example.

7:52

Basically the definition of your target lesion

7:54

on CT colonography is either a polyp or a mass

7:58

that's, um, soft tissue attenuation and density.

8:01

So you don't want any mixed attenuation within it.

8:04

If you see something that has gas bubbles inside it

8:08

or contrast inside of it, or fat attenuation inside

8:11

of it, then you're dealing with either a tagged,

8:14

um, stool or bubbles, uh, or fecal material, or

8:20

in the latter case, uh, something like a lipoma.

8:23

So it needs to be soft—

8:24

Have a soft tissue core.

8:26

So here you can see the rectal catheter here.

8:28

There's a balloon in here, um, which is filled

8:31

with, uh, with air, and you could see that better.

8:34

If you go to a long window, you'll see

8:36

the, the wall of the balloon there.

8:38

And then I basically, this is the tip of the

8:41

rectal catheter here, and I'm just scrolling

8:43

through and bringing up the field of view here so

8:47

that you can look for any bumps along the wall.

8:49

Of, um, the colon, either the, the lateral walls,

8:53

or you have to also scroll through the top and the

8:55

bottom of each turn, looking for any polyps on the

8:58

top or the bottom side of a, of a, of a loop of bowel.

9:02

So here we're in the distal, um, sigmoid colon here,

9:07

and basically we're scrolling through, looking for

9:10

any bumps, anything that doesn't look like a haustral

9:12

fold, that might be soft tissue in attenuation.

9:18

So in this case, I'd be scrolling through the

9:20

top of the sigmoid colon here through the, the

9:26

proximal sigmoid colon here, and then now we're

9:29

in the descending colon, scrolling all the way up.

9:34

And the, the more experience you have

9:35

with this, the faster you can do this.

9:37

Looking through the contrast, making sure that

9:39

there's no submerged polyps that you may not

9:42

necessarily be able to see on the 3D view.

9:47

And then going all the way up

9:48

through the splenic flexure here,

9:54

scrolling through the transverse colon now,

10:00

and then this is your transverse colon.

10:01

I'm gonna scroll through the bottom and the top of

10:04

each turn, and then you see our first finding here.

10:07

So right in there

10:12

to confirm that finding.

10:13

So, so you can see there's something here that looks

10:15

a little bit different from the adjacent folds.

10:18

You can go to our soft tissue windows.

10:20

You can see that the center of it does look like

10:22

it's soft tissue in attenuation, similar to, uh,

10:25

muscle or, or liver, for example, different from

10:28

the adjacent fat, uh, outside of the colonic wall.

10:32

There's a little bit of contrast

10:34

between the, this polyp,

10:36

the adjacent fold here, and that's fine.

10:39

Contrast on the surface of a

10:40

polyp is, is, uh, acceptable.

10:42

In fact, sometimes it's the best way to

10:44

see a polyp, especially on these 2D views,

10:47

is if it's, um, coated with contrast.

10:49

But the center of the, um, of the finding

10:51

needs to be soft tissue in attenuation.

10:53

And if you look at that same area on the 3D

10:57

images—so if you set up the 3D images here—you

11:00

can see what this, uh, polyp looks like in 3D.

11:04

And this is probably the best way you can

11:05

appreciate the morphology of a finding.

11:07

You can see it's, there's a polyp with

11:10

a stalk and it looks like the stalk

11:12

is arising from a, a haustral fold,

11:18

just like you can see it on the 2Ds.

11:21

So there's a couple different ways of, uh,

11:24

figuring out what to do with this polyp.

11:25

Basically, a lot of our management

11:28

is based off polyp size.

11:30

The larger the polyp is, the higher the

11:32

likelihood that it's going to represent

11:34

a, uh, uh, a high-grade adenoma.

11:37

Uh, the, the larger it is, the more precancerous

11:40

or the potentially cancerous a polyp may be.

11:43

So in this case, you know, you can, you can try

11:45

to—the best way to measure it is actually off

11:47

the 3D images because you can get the maximal

11:50

dimension of the polyp excluding the stalk.

11:53

And that's how a polyp is classified by the

11:55

gastroenterologist at the time of, uh, colonoscopy.

11:58

Um, and, uh, the best way to figure out what the

12:02

long axis—the maximal dimension—of

12:05

a polyp is, is by looking at it on the 3D views.

12:08

'Cause there's no guarantee that the 2D

12:09

views is gonna be the maximal dimension.

12:12

And I'll give you an example of that here.

12:13

You wanna measure from edge to edge

12:15

without shooting off the edge of the—

12:19

And this is—you have to be a little bit careful

12:21

of where you put the caliper because, um, if

12:23

you place the caliper a little too far off

12:26

the edge of the polyp, you can over-measure

12:28

because the, uh, 3D workstation thinks that

12:31

you're measuring from this point to a point

12:33

on the far wall of the colon, for example.

12:36

So when you place this caliper, I, I rotate around

12:39

the polyp just to make sure that I'm staying on

12:41

the polyp and I'm not putting the, the, um, the

12:43

marker down, uh, on the far wall of the colon.

12:47

'Cause for example, if I move it to over here,

12:50

you can see that, uh, it may not necessarily

12:54

be measuring, uh, the polyp itself anymore.

12:56

And the, the, the point may be placed on a, on a part

12:59

of the colonic wall, on the other side of the polyp.

13:02

So we've got something that's

13:03

over a centimeter in size here.

13:05

If we try to measure it off the 2Ds, uh, usually

13:08

you may end up underestimating the size of the polyp.

13:12

See for example here, if you measure it off of

13:13

just the 2Ds, you could potentially get a,

13:15

a number that's less than a, a centimeter, and

13:19

that one-centimeter, um, size threshold

13:22

is an important one in the C-RADS system.

13:25

So C-RADS is how we, um, how we manage

13:28

polyps of different size and number.

13:31

So basically, um, C1 would be,

13:33

uh, a normal colonography or benign

13:36

findings like lipomas, for example.

13:39

Uh, a C2 would be if you have one or two

13:43

subcentimeter polyps, and polyps we define as

13:46

being, uh, six millimeters or larger in size.

13:50

So if you have one or two polyps that are six to

13:52

nine millimeters in size, rounding to the closest

13:54

millimeter, then, uh, we give the patient two options.

13:58

One would be a, a short-term follow-up

14:00

CT colonography within three years.

14:03

Which is, uh, perfectly acceptable and safe.

14:05

Uh, option for, for following up these, uh,

14:08

these low-risk polyps or in the, uh, refer or

14:13

the patient's, um, preference if they prefer

14:15

a colonoscopy, uh, for a polypectomy, that's

14:18

also an appropriate, uh, management option.

14:21

And then at the one-centimeter size threshold,

14:24

the 10-millimeter size threshold, we start

14:26

putting the patients into a C3 category.

14:29

So if you have one polyp that's 10 millimeters

14:31

or larger in size, or you have three sub-

14:34

centimeter polyps or more, then, uh, generally

14:38

the recommendation for C3 is to go on

14:41

to the, uh, colonoscopy for polypectomy.

14:44

And then we use the C4 category for, uh, masses.

14:48

And these are our classic, uh, colon cancers

14:51

that I will show you a little bit later.

14:53

The, um, the large annular, uh, apple

14:56

core lesions or, or saddle lesions.

14:58

Big, big mass.

15:01

So this is our first finding here.

15:03

And the other thing that you want to do once

15:05

you find a finding is to confirm that you're

15:06

also seeing it on the other view, because

15:08

you have two chances to see this same polyp.

15:12

Uh, another way to differentiate a, a polyp

15:14

from a stool ball is to show that it's in

15:16

the same general location on both positions.

15:19

So basically, a polyp should have a pretty

15:21

fixed location, um, relative to the colon and

15:26

the adjacent haustral folds, uh, despite

15:28

changes in patient position, whereas a stool ball

15:31

may fall independently, uh, without a stalk

15:34

or without an attachment to the colonic wall.

15:37

So in this case, in this same location here,

15:39

you're seeing that there is a filling defect

15:42

within this pool of contrast in the same location,

15:44

in the mid-transverse colon, and you're able to

15:46

see the stalk connecting it to the, um, to that

15:49

haustral fold in the mid-transverse colon.

15:52

And you're not seeing it on the 3D images here

15:54

because it's obscured, it's submerged by the contrast.

15:58

And if we had not used our fluid tagging

16:00

material, you wouldn't be able to see this on

16:02

the, on, on the 2D images either because there's

16:05

not enough of an attenuation differential

16:07

between, um, untagged fluid and a polyp.

16:12

Although depending on your software package,

16:15

you could see the, the, if the, the—

16:19

Gas-fluid level here is being rendered as a solid

16:23

in appearance, but occasionally you can do a remove

16:25

stool function to try to subtract out electronically,

16:29

subtract out fluid above a certain threshold.

16:33

Uh, but you need to have enough, uh,

16:35

contrast tagging to be able to do that.

16:37

And it tends to leave artifacts on the, um, 3D views—

16:40

these bathtub rings at that three-material interfaces

16:43

between the contrast, the gas, and the bowel wall.

16:46

So I, I don't tend to like

16:48

to use that on the 3D views.

16:51

So continuing through there, I think

16:53

there's, um, this was the major finding.

16:56

Um, I do the same thing and I just keep, I

17:00

continue going through the remainder of the colon

17:03

on the 2Ds and looking at any interesting

17:06

findings on 3D just to make sure that, um—

17:12

Anything that I do see does not represent

17:14

a haustral fold and looks like a real polyp.

17:17

And then you confirm the, um, the attenuation

17:19

of that polyp on the, um, the 2D views.

17:23

And here where we've reached the, the cecum

17:25

here, this is our ileocecal valve, our

17:29

typical appearance with the ileocecal valve.

17:30

It looks like a, um, pair of lips here,

17:34

and between the, the lips, you can see

17:36

the hole going into the terminal ileum.

17:38

And then right next door to it here,

17:40

this is your appendiceal orifice.

17:44

So there's a little bit of a, a tiny little hole,

17:47

which represents the orifice of the appendix.

17:49

You can see on the 2D views here,

17:51

where the appendix is coming off.

17:53

And then there's contrast in the

17:54

remainder of the appendix here.

17:56

And then if you keep scrolling through,

17:58

you'll see that it should be a blind

18:00

ending, defining it as the appendix.

18:02

So that's the appendiceal orifice.

18:05

The typical appearance for the ileocecal valve.

18:08

And there's a wide, uh, variety of

18:10

appearances for the ileocecal valve.

18:12

They can be varying degrees of, um, thinness

18:15

or, or, you know, plumpness and, uh, but

18:19

for the most part, uh, as long as it's, um—

18:23

Typical in appearance or fat in attenuation.

18:26

'Cause oftentimes the, a bulky part and a

18:28

bulky ileocecal valve may look very, um, um,

18:32

will show fat attenuation in the inside of it.

18:35

But, um, but that's your typical

18:36

appearance for the ileocecal valve.

18:38

And sometimes you can fly through

18:39

into the ileocecal valve as well.

18:42

So I'll look at as much of the, um, termin—

18:44

um, as I can if, if the fly-through includes it.

18:47

And then I do this exact same

18:48

thing with the, the prone images.

18:50

And I'm not gonna take you through the exact

18:51

same process, but basically I do the same

18:53

thing in this position, scrolling through

18:57

from anal verge all the way back to cecum.

19:01

With a, a window wide enough to look at the, the

19:04

wall, looking for any bumps, as well as to look through

19:06

the contrast to look for any submerged polyps.

19:10

And that's the, um, the 3D fly-through.

19:13

And again, on the, uh, on the prone images, you can

19:15

see what the typical appearance of the ileocecal valve

19:18

is, uh, as well as the appendiceal orifice over here.

19:24

All right, so that is our first case.

19:27

I think there may have been one

19:29

other smaller polyp in this case.

19:30

Let's see if I can show you an even more subtle one.

19:38

Right here.

19:39

So this is an example of kind of the, um,

19:41

the lower limit of what we would be confident

19:43

in calling a polyp on, uh, CT colonography.

19:46

You can see this one does not have a stalk

19:48

in it, and, uh, it looks a little more sessile.

19:51

It's also, uh, located on a

19:53

haustral fold in the sigmoid colon.

19:56

And just to confirm that, that's not a—

19:59

An untagged piece of stool.

20:02

You can look for the same finding in

20:04

the same location on the prone images.

20:08

And right there you can see the same

20:13

similar-looking structure there, which if

20:17

you measure the long axis is probably going

20:20

to barely meet the six-millimeter cutoff.

20:24

May or may not even meet that six-millimeter cutoff.

20:27

I think at the time that I read this originally, I

20:29

called it six millimeters and both of these were

20:32

confirmed at the time of, uh, of colonoscopy.

20:36

All right, so that is basically the, the

20:40

primary 2D read for, um, CT colonography.

20:45

In the next case, I'll show you

20:46

how, uh, how I like to read.

20:48

I actually prefer reading that with

20:49

a primary 3D read in the beginning.

20:52

It takes at least 20, 30 minutes sometimes

20:55

to, to, to read one of these cases,

20:57

uh, when you're first starting out, but

20:58

then you get much quicker at doing this.

21:01

And, um, in the best of hands, oftentimes

21:03

you can, you can finish reading a

21:06

CT colonography within 10 minutes.

21:08

Um, the, either the better distended and the

21:10

better prepped the colon is, the easier they

21:12

are to read and the faster they are to read.

21:15

But, uh, just to, to change up the pace,

21:18

I often prefer reading in the primary

21:20

3D mode, which I'll show you next.

21:23

So for a second case, I've loaded up a,

21:26

another case with the, uh, the primary 3D

21:29

workflow here, and I'm gonna show you how I

21:31

like to read, uh, with a primary 3D setup.

21:34

So, uh—

21:35

Basically I have the three, uh, multiplanar reformats

21:38

set up here on the left side: your axial image, a

21:40

coronal reformat, and a sagittal reformat, again starting

21:44

at the anus and flying through to the cecum.

21:47

And then we're gonna turn around and fly back.

21:49

So the primary 3D read, instead of looking at the 2D

21:52

images and scrolling through the 2D images, looking

21:54

for a, uh, polyp, we're gonna do the same thing,

21:57

but with a fly-through on the 3D fly-through here.

22:00

Um, there's a colon map here in the corner

22:03

here, which you can, uh, use as your roadmap to

22:05

try to figure out where you are in the colon.

22:08

Uh, we're better able than the gastroenterologists

22:10

are in figuring out where we are and in which

22:13

segment of the colon we are, because oftentimes

22:15

when the endoscope is inside the colon, they

22:18

don't know which segment they're exactly in,

22:20

especially, uh, the more tortuous the colon is.

22:23

They don't know which flexure is the splenic

22:25

flexure and which flexure is the, the hepatic

22:28

flexure. With our colon map here, we're much

22:31

better able to tell where we are in the colon.

22:35

And the colon map—

22:35

When you make any findings and you tag

22:37

any findings, they show up as a, as a,

22:40

a nice annotation on this image as well.

22:42

So I like to save these images to PACS to show

22:44

the endoscopist where a finding that we make is.

22:49

So that's our map.

22:50

And then our primary 3D area is here.

22:53

Some packages will also have other

22:55

alternate 3D views of the colon.

22:58

In this case, this is a, uh, a filet view.

23:01

Um, when we get further up in the colon, I'll show

23:03

you what the typical appearance of the filet view

23:06

is, but there's quite a bit of, um, image distortion

23:08

inherent in this method of looking at the colon.

23:11

But it can potentially, um, accelerate your read,

23:17

your primary 3D read, if you know how to read through

23:19

the, um, image distortion inherent in this image.

23:23

So I start here and I fly through from the anus.

23:30

And then initially you fly retrograde through

23:32

the colon, and then we're flying along

23:34

the barrel of our rectal catheter here.

23:36

If you wanna see the rectal catheter, I'm—

23:39

showing you, this is the rectal catheter.

23:41

Um, and this is the anal verge looking back

23:46

at the back of the colon in the anal verge.

23:48

This is the, the, the tip of

23:50

the, um, the catheter here.

23:55

And on the fly-through, we're looking for any bumps.

23:58

And so here it's, I think I find it less fatiguing

24:01

looking at these images than the 2D images because

24:04

it's a lot easier to tell what a fold looks like.

24:08

And, uh, it's easier to differentiate

24:10

a, a polyp from these folds.

24:12

But you do have the 2D views here to, um, correlate

24:15

a finding that you make on the 3D views, just to make

24:18

sure that what you're seeing is not, uh, not a polyp.

24:22

For example, this little—

24:23

Here, it's smaller than six millimeters, so I

24:25

wouldn't have even bothered with looking at it.

24:28

But you can tell here on the, on the 2D

24:29

views that it's denser than soft tissue.

24:32

It's, uh, it's, um, contrast attenuation.

24:35

So that's just a little tagged piece

24:37

of stool and I keep going through in

24:39

this direction until I reach the cecum.

24:42

And then the goal is to fly, to turn

24:44

around and fly back towards the anus.

24:47

So usually we set up 120-degree field of view on the,

24:52

on the endoluminal camera here, and you can set that

24:55

in your options, depending on your software package.

24:59

You can set the angle viewing angle here.

25:01

The, the wider the angle, the more of the, um, mucosa

25:04

you're going to be able to see on each fly-through.

25:07

And you, you can see on this particular

25:08

package, you can go all the way to 360

25:11

degrees and have a 360-degree field of view.

25:13

But again, there, there can be quite

25:16

a bit of distortion inherent in that.

25:17

For example, here, this is what a 360

25:19

degree camera looks like, not, um—

25:23

Physically possible, but through the

25:25

magic of software, you can do it.

25:27

And you can see backwards over here, but you can

25:29

see how the image gets, uh, very fisheye distorted.

25:33

So our recommended field of view is 120 degrees for

25:36

the most comfort in terms of the fly-through, but

25:38

it does require flying through in both directions

25:41

to be able to see both sides of a haustral fold.

25:43

'Cause, uh, for example, if you're flying through,

25:45

you may not be seeing the backside of each haustral

25:47

fold quite as well, uh, as if you fly both

25:51

fly forward and backward in both directions.

25:54

So right now we're in the transverse colon.

25:55

You can appreciate also the, the, the typical

25:57

architecture of the colon with our three haustral

26:00

folds, these three arcades of haustral folds.

26:03

And in some cases, you can even see the tenia coli

26:05

between the, the haustral folds here. For example,

26:08

here's a nice tenia coli, um, between each

26:12

of the three sets of the haustral folds and the—

26:17

The colon map is showing you, with that

26:20

purple arrow here, where the camera is

26:22

and where we are in the transverse colon.

26:26

So we're getting towards the ascending colon, where you

26:29

can already see that I marked a finding in advance.

26:37

So here's our hepatic flexure.

26:38

You can still see our gas-fluid level here.

26:41

And then we're seeing something that doesn't

26:43

look like a haustral fold in the ascending colon.

26:49

And I'm gonna delete the measurement here

26:50

because it's obviously an undermeasurement.

26:54

You see this mass here.

26:56

And then the question, I guess, is in the

26:58

ascending colon cecal area, is it an ileocecal

27:02

valve or is it not an ileocecal valve?

27:05

And there are multiple of these, um,

27:08

abnormal-looking haustral folds here.

27:10

So once we've found this area, and then

27:12

here's our, our appendiceal orifice.

27:14

Again, we know we're in the cecum.

27:18

This is what the appendiceal

27:19

orifice looks like on the 2D views.

27:21

So you're confirming that that's the appendix here.

27:25

We're also looking at what the rest of

27:27

the ascending colon looks like here.

27:28

Let's go into soft tissue windows, and you

27:30

can see what these folds look like on 2D and

27:37

widening the window to see through the contrast.

27:40

You can see there's definitely some, some

27:42

masses and haustral fold thickening and luminal

27:44

narrowing in the ascending colon here.

27:48

Uh, another plane that appreciate that

27:50

on would be the coronal images here.

27:52

So you can see if this is your appendiceal orifice.

27:57

We can see where the ileocecal valve is.

27:59

It's actually this fold right here, and on the

28:03

3D view, you can see the typical appearance.

28:05

This is a, a fairly classic appearance of the I valve.

28:09

Which tells me that nobody has

28:11

more than one ileocecal valve.

28:13

So everything else out here is not ileocecal valve.

28:15

It's this annular constricting mass in the ascending

28:19

colon just above the level of the ileocecal valve.

28:22

And remi—remember that the ileocecal valve

28:24

divides the cecum from the ascending colon.

28:27

So this, if this is located antegrade,

28:31

uh, downstream from the ileocecal valve,

28:33

it's located in the ascending colon.

28:35

So we've got a, an ugly looking

28:37

mass here in the ascending colon.

28:41

Another way to look at this is, um, you can

28:45

go to something called a Q view, which kind

28:47

of renders the, the mass, uh, in a cube.

28:53

And you can even go outside the mass to see what it

28:56

looks like from outside the, um, the colonic lumen.

29:04

Actually not quite, quite

29:06

working the way I want it here.

29:08

Gimme one second.

29:15

Okay, so on the outside view here, you can see the,

29:19

what the, um, the outside of the colon looks like.

29:22

You can see that annular constriction

29:23

here in the outside wall, the colon.

29:25

So this is the view that then

29:26

endoscopically definitely cannot get.

29:30

And then again, the view from

29:32

inside the colonic lumen there.

29:34

So we've got a mass here that's clearly

29:36

measuring more than 10 millimeters.

29:37

In fact, it's probably measuring more than, than, uh—

29:40

than four, three or four centimeters in size even.

29:43

So this would be something that we would, um, clearly

29:46

be very suspicious about a malignancy and, and we

29:49

would call this a C4 finding for a colonic mass.

29:54

This patient ended up go—getting

29:55

sent to a colonoscopic biopsy,

29:59

where it was confirmed that

30:00

we were dealing with a cancer.

30:01

And in fact, the, uh, a management option

30:04

that's acceptable for a C4 is a direct,

30:07

um, uh, direct referral to a colorectal surgeon.

30:12

Um, because our confidence is pretty

30:14

high that you are dealing with a neoplasm,

30:15

here, regardless of what the histology is.

30:18

More often than not, they want the histology

30:20

prior to planning for a right hemicolectomy.

30:22

But at the time of a hemicolectomy, this ended

30:25

up being a T3 N1b, uh, adenocarcinoma.

30:30

So this is an example of a, of a colon cancer on 3D.

30:34

But just to finish the, the, the 3D approach,

30:38

basically, once we reach the cecum, we turn

30:39

around and we fly back towards the anus.

30:44

And this gives you a chance to look at the

30:45

backside of all the haustral folds, uh,

30:48

on the way back to the, uh, anal verge and—

30:53

Once I do that for the supine views, then I switch to

30:55

the prone images and do the exact same thing from anal

31:01

verge to cecum, starting at the anus, flying through.

31:06

And I'll do this in a much

31:07

faster than I usually would,

31:09

just, uh, in the interest of time to show you

31:12

the, the primary 3D method from start to finish.

31:16

And again, you can see that mass

31:17

in the ascending colon there.

31:19

And then it—you turn around in the cecum and you

31:21

fly back and you can control the speed of how quickly

31:26

you're flying back through, through the colon.

31:30

And then when you reach the anus, then the one last

31:32

thing that I do do on, uh, with a primary 3D method,

31:35

is since I'm not electronically subtracting any fluid

31:39

present—

31:40

I'll look one last time on the 2D views,

31:42

just mainly focusing on the, the contrast levels

31:46

to make sure that I'm not missing a polyp that's

31:49

submerged on one view or the other view, or rarely—

31:53

It can be submerged on both views,

31:54

if there's an up of a twist of the colon between

31:57

the supine and the prone in, uh, positions where the

32:00

polyp could theoretically still be, um, submerged.

32:03

Um, and gravity dependent in both locations,

32:06

especially if it's a polyp on a long stalk that tends

32:08

to flop around, uh, where the head of the stalk may

32:11

flop around dependently, uh, in, in both positions.

32:16

And then I'm done with the, uh, looking at the colon.

32:20

Keep in mind the, the, you have the rest of

32:22

the, um, the abdomen on these images as well.

32:25

So one thing I do like to do, you, you want to

32:28

also make sure that you're not finding any, um—

32:32

Clinically relevant extracolonic findings.

32:35

So the other half of the C-RADS, uh, system

32:37

includes, uh, an E-score for extracolonic findings.

32:41

Um, again, E1 would be normal.

32:45

E2 is what we call a finding that's

32:49

clearly benign or not worth working

32:51

up, for example, like a renal cyst.

32:53

And then the next C-RADS, um, version that's

32:57

coming out imminently, we're combining C

32:59

1 and CT together into the same category.

33:01

In effect.

33:02

A C3 would be a finding that's incompletely

33:05

characterized and may require workup.

33:07

For example, a hyperdense renal cyst or

33:10

something that's, uh, not clearly defined,

33:13

but, um, but could be further evaluated with a

33:15

contrast-enhanced study, for example, CT or MRI.

33:19

And then an E4 is a, a, a clinically relevant, uh,

33:22

potentially urgent finding like a, uh, AAA or, um, uh—

33:28

Something that looks much more, um, uh, worrisome

33:32

for malignancy, like liver metastases, for example.

33:36

So that's the, the E portion of the, uh, C-RADS system.

33:39

So that's the primary 3D read.

33:42

Okay, for our third case, I'm gonna

33:44

show you a few more polypoid findings.

33:47

Um, in this partic—particular case, we have

33:49

multiple findings here in the right colon.

33:52

Um, we're here in the ascending colon here.

33:54

You can see on the 2D views here that

33:56

there are multiple findings that don't,

33:59

that look different from the haustral folds.

34:01

And, um, the largest one is located right here.

34:05

I'm showing it to you on the 3D image right here.

34:08

And you can see it looks polypoid.

34:11

There may or may not be a stalk associated

34:13

with it, but the key finding here is that

34:15

on the soft tissue windows, it does not

34:19

look like it's soft tissue attenuation.

34:21

It looks like it's similar in

34:22

attenuation to adjacent fat.

34:24

So that makes this a lipoma.

34:27

There are some tools in our toolbox for some of these

34:30

3D workstations that help you, uh, look inside a

34:33

polyp without necessarily looking at the 2D views.

34:36

But I find the 2D views to, to still be ground truth.

34:39

That's the one I trust the most, but there are some,

34:42

some of them have this kind of an x-ray view to it.

34:45

Um, try to get it centered over the polyp here,

34:50

where it'll kind of allow you to look inside

34:53

the polyp here and scroll through the inside

34:55

of a polyp and render the attenuation of the

34:58

material, uh, along the Hounsfield unit scale here.

35:01

And what you're really looking for here is

35:03

something that's kind of mostly green-colored,

35:06

whereas in this case, we're seeing things that

35:07

are kind of closer to blue or purple, representing

35:10

fat attenuation, negative Hounsfield unit numbers.

35:13

So this x-ray view, this, this spot NPR

35:17

view is, um, is telling us that we're

35:19

dealing with a lipoma in this case.

35:22

So it doesn't matter what the size of this is.

35:24

You can try to measure it here just for

35:26

reporting purposes, but, um, the size doesn't

35:29

judge the, um, management of a lipoma.

35:32

Uh, generally, um, nothing is necessary in these

35:35

cases unless it happens to be so large that it

35:38

ends up being symptomatic or causes some issues

35:40

with, um, with luminal narrowing, for example.

35:45

Uh, there are other findings though in the ascending

35:47

colon that don't look clearly fat attenuation.

35:50

And you can see there's other—this one

35:52

looks like more of a billowy-looking, um,

35:55

polypoid mass located on an adjacent haustral

35:59

fold or further down the haustral fold here.

36:02

And this, uh, is, uh, consistent with a,

36:04

a polyp—soft tissue attenuation polyp.

36:08

You can either measure it as two separate

36:09

ones or one large one, but basically it

36:12

measures greater than one centimeter in size.

36:14

So this is something that we already know is gonna

36:16

be sent on to colonoscopy as a C3 lesion—C3 finding.

36:23

Um, let's see what else.

36:25

There are a few other findings in this case.

36:29

Right down here, you can see there's, there's a third

36:32

polypoid finding in the end colon on the 2D views.

36:36

You can see that the core of it is soft

36:39

tissue in attenuation, although there is a

36:41

coating of, of contrast around that polyp.

36:46

As long as it's on the surface and

36:47

not on the inside of it, that is fine.

36:50

Uh, as if the core of it looks like it's

36:52

soft tissue, then it counts as a polyp.

36:55

And this one looks a little more, um, like it could

36:57

be a, could have a little bit of a stalk to it.

37:01

So that one's more of a pedunculated

37:03

polyp and its size also.

37:06

Let's see what its size is.

37:08

It's, it's probably also big

37:10

enough to, to represent a C3.

37:15

Yeah, so we have some multiple sizable polyps

37:20

in the ascending colon in this particular case.

37:23

Um, let's see, what else is there to see here?

37:28

I think there was a fourth polyp in here somewhere.

37:31

Let's take a look and see if we can find it.

37:41

This one may have been easier

37:42

to appreciate on the 2D views.

37:48

There's a little bit of thickening and a lot

37:50

of contrast along this haustral fold here, but

37:55

one lipoma and multiple polyps

37:58

meeting size criteria for C3.

38:06

Okay.

38:08

Uh, one last thing I'll show you here is the, um.

38:11

This is the file view.

38:12

So basically the file view is, uh, analogous

38:15

to gross anatomy specimen of the colon.

38:18

Basically it's a, the colon stretched out,

38:20

straightened out, cut on one side and opened

38:23

up, fillet open like a, like a, a canvas.

38:27

And basically you're looking at the full

38:29

360-degree, um, circumference of the colon.

38:33

And, uh, this is the, um, the, the

38:35

luminal direction of the colon here.

38:37

The area that's grayed out here is basically

38:39

your area of overlap, so it's a little

38:41

bit more than 360 degrees, uh, wraparound.

38:44

And you can see your three haustral folds

38:47

here with the three taenia coli between them.

38:49

And basically you're looking for something

38:51

that looks different from these haustral folds.

38:54

For example, these, these, um,

38:56

lesions here in the ascending colon.

38:57

So this is what a mass would look like

38:59

on the, on the, um, on the fillet view.

39:02

Multiple of them here.

39:03

And you can just click your mouse on each one of

39:05

these and find them on the 3D and luminal view here,

39:09

as well as on the 2D images.

39:12

So this is how you can use this.

39:13

And if you page through this, you can

39:15

basically go down the length of the entire

39:17

colon very quickly in just a couple pictures.

39:20

Um, as long as you can read through the

39:23

image distortion that's particularly, um,

39:25

prominent at the, um, colonic flexures.

39:30

You can see there's other findings in here

39:31

that don't look like haustral folds either.

39:33

Um, and if you click on them, you can

39:35

see that they actually are outies, not

39:38

innies, so they're holes in the colon.

39:40

These are diverticula.

39:42

So this is your typical appearance

39:43

of the, the diverticulum.

39:45

And they differ in appearance from the haustral, from

39:48

the polyps in that, uh, when you rotate your camera,

39:51

you can see that it's, it's projecting outward

39:54

rather than inward into the lumen of the colon.

39:56

But you can also see that oftentimes you'll have

39:58

an incomplete ring of, um, of this, uh, dark, um,

40:04

dark rendering around the, the rim of the

40:06

finding because, uh, you're seeing some mucosal

40:10

continuity with the diverticulum on the other side.

40:12

So they tend to look a little different on the

40:14

3D views and usually are not a, uh, a difficult,

40:18

um, diagnosis to make on the 2D images.

40:20

As you can see that they, they look like they're

40:22

projecting out from the wall rather than, uh,

40:25

soft tissue attenuation projecting into the lumen.

40:28

Okay, for our fourth case, I'm showing you,

40:31

uh, another case here of a patient with, uh,

40:36

bilateral hip prosthesis.

40:37

So you can see there's a lot of artifact, streak

40:39

artifact, uh, beam hardening artifact, uh, between

40:42

these, uh, metallic prostheses in the bilateral hips.

40:46

You wanna widen your windows to be able to

40:47

see through that, you know, just like any

40:49

other, um, CT image you're looking through.

40:52

Um.

40:53

You have to deal with artifacts that

40:54

you have, uh, at the time of the scan.

40:57

There are metal artifact reduction algorithms

40:59

on many of these scanners that can help, uh,

41:01

alleviate some of the artifact associated with this.

41:04

You can see, interestingly, there's some

41:05

cement, um, leakage here medial to the,

41:08

uh, to the right acetabulum as well.

41:09

But when you fly through on the 2D images, when

41:12

we, when you scroll through on the 2D images, you

41:14

can see our first finding is in the sigmoid colon.

41:19

And this is the reason for the CT

41:21

colonography in this particular case.

41:23

So they, in addition to having an extremely tortuous

41:26

sigmoid colon here with a lot of diverticulosis,

41:30

there is a stricture in the sigmoid colon.

41:33

Uh, you could see some luminal narrowing here, uh, and

41:40

parts of it, you can see it on the 2D images as well.

41:45

This, uh, area of luminal narrowing and eccentric

41:48

wall thickening, um, soft tissue windows.

41:51

You can really see that there's some

41:52

bulky soft tissue in this suspected, uh,

41:55

malignant stricture in the sigmoid colon.

41:57

And this is what the, um, the,

41:59

the colonoscope could not pass.

42:01

So, you know, usually in these cases, the colonoscope

42:05

will get far enough that if there's a stricture

42:07

that's worrisome on endoscopy, they're gonna

42:09

auto, they're going to still be able to biopsy it.

42:12

But just as importantly, in a patient with a

42:15

suspected colon cancer, is to determine what the

42:19

status of their remainder, remainder of the colon is.

42:21

Because if there are other masses or polyps

42:24

elsewhere in the colon, they want to be

42:26

able to deal with it at the time of surgery.

42:29

Um.

42:31

To be able to tell whether this patient is just

42:33

gonna get a partial colectomy or if they're gonna

42:35

need something more than just a partial colectomy.

42:37

Are there other lesions to worry

42:39

about in the remainder of the colon?

42:40

So this is where we can be particularly helpful to

42:44

complete the, um, screening of their remainder of the

42:47

colon, uh, in somebody that's, um, likely going to go

42:51

on to, uh, a partial colectomy at, of some sort, uh,

42:56

to get the status of the rest of the colon, to find

42:58

if there are any, uh, synchronous lesions elsewhere

43:00

in the colon, in the non-visualized part of the colon.

43:03

And in this case here, the first finding

43:04

you can see just upstream from the

43:07

sigmoid mass here is a submerged polyp.

43:10

Here you're not seeing it on the 3D views

43:12

because it's submerged within contrast.

43:15

But you can see on the 2D images here, that

43:17

similar appearance of a pedunculated polyp on a

43:20

stalk arising from the proximal sigmoid colon.

43:24

Actually, the stalk is on this side

43:25

here, and then it's falling dependently.

43:30

Into the, uh, the pool of contrast

43:31

on this particular prone image.

43:33

You can take a quick look at the supine image

43:35

in that same location to see, um, how well

43:39

the sigmoid mass, the stricture, uh, opens up.

43:44

And you can see it.

43:45

It's pretty fixed and, uh, narrowed in this location.

43:48

And on the supine images, you can see that polyp

43:52

is obeying the force of gravity and it's kind of,

43:55

uh, lying dependently on the, um, the, uh, the

43:58

supine side of that, of that proximal sigmoid colon.

44:01

And we've got a chance to be able to

44:04

see it on the 3D view here as well.

44:06

So on the 3D image, it kind of looks like that lipoma

44:10

I showed you on the other case, uh, in terms of the,

44:13

uh, shape of it, uh, the, uh, the polyp on the stalk.

44:16

But in this case, it is not fat attenuation,

44:19

it's soft tissue attenuation,

44:23

confirmed on the soft tissue windows here.

44:26

Remember, contrast coating is okay as long

44:29

as there's not contrast or bubbles of gas

44:31

within it to tell you that you're dealing

44:33

with a stool ball rather than a polyp.

44:36

Um, I think there was one other

44:38

finding in this particular case,

44:46

and it was actually in the right colon here,

44:48

so you can see there was a, a more proximal

44:52

lesion in the, in the ascending colon here.

44:54

This is located, I think it was, it

44:58

was located above the ileocecal valve.

45:00

So that would place this in

45:01

the, uh, in the ascending colon.

45:04

You can see it here on the coronal recons here again

45:07

with a little bit of a contrast coating around it.

45:10

Another pedunculated-looking

45:13

polyp with, on, on a haustral fold,

45:17

superior to the ileocecal valve in the

45:19

right colon at the time of resection.

45:22

Uh, this was a colon cancer.

45:26

And both those polyps were, were

45:27

confirmed to be tubular adenomas.

45:30

Okay, for our next case, I'm gonna show

45:32

you a, a case where they already knew that

45:34

there was a cancer, uh, in this patient.

45:37

You can see here in the descending colon and

45:42

on the colon map, I'll show you the image

45:44

right here where the, um, the purple arrow is.

45:47

You can see there's an area of

45:48

luminal narrowing on the coronal NPR.

45:51

You can see that there's already a stent

45:52

placed through this, this colonic mass.

45:55

So we know that there is a, a mass here in the colon.

45:58

They had to put a stent in to decompress

46:00

the, the, um, the colon because it was an

46:02

obstructing mass at the time of presentation.

46:05

And for one reason or other, they couldn't get the

46:08

scope all around to the, uh, to the remainder of the

46:10

colon to see if there were any synchronous lesions.

46:13

So this was our opportunity to complete

46:15

the, um, the, the workup looking for

46:19

synchronous lesions in the colon.

46:20

Similar history to the prior one.

46:22

Except in this case I get to show you a, a stent and

46:26

on the fillet views you can sort of see the, the mesh

46:28

of the stent here on the 3D, um, fillet view here.

46:33

And then we can also fly

46:35

through the stent on 3D views.

46:38

So you can see the, the mesh here again.

46:42

And in this case we're able to get through the

46:44

stent and look at the remainder of the colon.

46:50

And I believe there were findings in the

46:52

remainder of the colon in this particular case.

46:54

One thing to note is with the appearance of

46:57

motion artifact on, uh, CT colonography, sometimes

47:00

you'll see these little, uh, jagged edges.

47:03

Uh, and if you look on the coronal images

47:05

in particular, you can see they correlate,

47:08

they're in the plane of the axial, uh, slices.

47:12

And you can see there's motion artifact in this

47:14

particular scan here, and that's what the motion

47:16

artifact ends up looking like on the 3D fly-throughs.

47:19

These little kind of straight

47:21

cuts through the, uh, the lumen and it's

47:24

important to just realize that that's

47:25

artifactual related to, um, respiratory motion.

47:28

Usually

47:31

the, uh, in the proximal colon,

47:35

there are other findings here.

47:40

Uh, get to the cecum.

47:42

I think that's where the main mass

47:43

was, as well as ascending colon.

47:48

So here we're flying through the transverse

47:49

colon and you, again, you can use your, your

47:53

colon map here to, to show you where you are.

47:55

There's a very, very tortuous

47:58

transverse colon in this case.

48:01

And again, appearance of motion artifact here,

48:07

as fluid level.

48:10

And here we are in the ascending colon.

48:12

We can see some, uh, other abnormal findings here.

48:15

There's definitely a thickened

48:16

SSL fold here with a mass on it.

48:21

And, uh, there are also other findings here,

48:25

which we can look at on the 2D images to

48:27

see whether these represent real polyps.

48:31

And there's, there's multiple of these,

48:32

so that, that probably is a real polyp,

48:35

although it may not meet our size criteria.

48:38

One way I, the only time I ever mention

48:43

polyps that are five millimeters or smaller

48:44

in size is if I know that somebody's going

48:46

to be going on to colonoscopy or surgery.

48:50

Um, and, um, and that area is going

48:53

to be seen, going to be looked at.

48:55

If the five millimeter polyp is the

48:57

only finding, then, uh, gen, generally

49:00

it doesn't meet our size criteria to be

49:01

specific enough by CTC to call it a polyp.

49:05

And those polyps, even if they're

49:06

below five millimeters, the so-called,

49:09

uh, diminutive size category.

49:11

Uh, they will get picked up if you follow

49:14

a regular, um, screening interval.

49:17

So usually for CT colonography, the recommendation's

49:19

been every five years to get a CTC. For colonoscopies,

49:23

it's every 10 years, but usually you'll pick up

49:25

a, a tiny polyp if it grows in that interval.

49:29

Uh, it's important to note that, uh, uh, polyps,

49:32

abnormal polyps are a waxing and waning phenomenon.

49:35

Clearly not all polyps become cancer.

49:37

Only a tiny subset do.

49:39

Uh, some of them will actually stay stable

49:41

or even, uh, get smaller or completely

49:43

disappear between, um, follow-up studies.

49:46

So, so some polyps can be safely watched.

49:50

Many of them can be.

49:51

The smaller they are, the more

49:52

safe they are to, to watch.

49:54

But in this case, we have a synchronous

49:56

mass in the ascending colon.

49:59

On the 2D images, you can confirm that

50:01

it's soft tissue attenuation here.

50:05

A lot of it is, is mostly soft tissue.

50:07

There's some contrast outlining

50:09

the submerged portions here.

50:11

The 2D images, you can see how grainy our images are

50:14

here because we're using a very low radiation dose

50:16

study analogous to lung cancer screening, right?

50:20

And lung nodule screening.

50:24

So in this case, this is important to note that

50:26

there were, um, both polyps and masses seen in the

50:30

right colon, um, much more, uh, proximal to the known

50:36

annular constricting mass in the descending colon.

50:39

And we were able to get this patient

50:41

set up for, uh, a subtotal colectomy

50:44

rather than just a left hemicolectomy.

50:46

So this is very important for,

50:48

um, for the surgical planning.

50:51

Uh, other things that I should point out here,

50:53

the low dose images, um, they can look a little

50:56

grainy because you don't need much radiation

50:58

to render a, a polyp in a gas-filled loop of

51:01

bowel, just like you don't need much radiation

51:04

to, to render a pulmonary nodule in the lung.

51:08

Uh, we aim with our radiation doses

51:10

to be lower than that of a barium enema.

51:13

So even with both supine and prone images

51:15

combined together, usually our radiation dose

51:17

ends up being less than five millisieverts.

51:20

Sometimes, um, even two or three millisieverts.

51:23

And I've seen some groups get it to even closer,

51:26

close to one millisievert depending on, uh, what kind

51:28

of, um, iterative reconstruction or deep learning

51:32

image reconstruction, uh, algorithms you use to,

51:35

to aggressively get that, uh, radiation dose down.

51:39

Um, when you are reading extra colonic findings,

51:43

sometimes the image noise can really get in the way.

51:45

Um, but, uh, one thing that you can do to,

51:49

to reduce the, uh, that appearance is you

51:51

can, you can read with a, a thicker cut.

51:54

So you, instead of looking at the thin cuts

51:56

here, the 1.25 millimeter cuts, you can

52:03

set the slice thickness a little bit thicker.

52:07

That will, that will reduce

52:08

your image noise quite a bit.

52:12

And then this way you can look for any adjacent

52:15

adenopathy next to these masses as well as,

52:18

uh, any incidental liver mets that you might be

52:20

able to pick up on a, um, non-contrast study.

52:24

And then you can get a sneak

52:26

peek at the lung bases as well.

52:28

So you can do some of the, um, M staging, although

52:33

this is not a, uh, contrast-enhanced study.

52:35

One other thing I would probably bring

52:37

up here in this case, the one thing that

52:39

could have made this study even better.

52:41

Than it was and even more helpful than this

52:43

was, is performing it with IV contrast.

52:46

So if you know that the reason the patient is

52:49

coming to you is for a known obstructing colon

52:52

cancer and it hasn't been fully staged yet with

52:55

a, um, CT abdomen, pelvis, or CT chest, abdomen,

52:58

pelvis, you can combine the staging CT with IV

53:03

contrast with the CT colonography at the same time.

53:05

So what we would usually do then is what we would,

53:08

we would inflate the colon and probably scan

53:11

a non-contrast in the prone position and then

53:13

flip the patient's supine and set them up with

53:16

a higher radiation dose, uh, routine contrast

53:19

enhanced CT with the colon still distended.

53:23

And then we would scan through the, uh, the

53:24

relevant body parts with the IV contrast onboard

53:27

with the usual routine, uh, contrast timing

53:30

and be able to stage all the solid organs,

53:32

uh, at the same time as doing the, um, the CT

53:35

colonography to look at the rest of the colon.

53:39

So keep in mind that that is an option, but

53:41

that you don't want to use low radiation dose

53:43

for the IV contrast portion of that study.

53:46

Thank you for sharing your lecture today, Dr. Chang.

53:48

At this time, we'll open the floor for any

53:51

questions from our audience and you can submit

53:54

those questions through the Q and A feature.

53:56

Dr. Chang, we have quite a few in that

53:58

Q and A box, and I can kick us off. When

54:01

the colon isn't perfectly distended,

54:03

how do you differentiate a fold and flat

54:05

polyp mass if it's both sides of the bowel?

54:07

That looks bunched up also.

54:10

What are your tips for the assessment of flat polyps?

54:14

Yeah, those are excellent questions.

54:16

So, ob obviously the, the better distended

54:18

the colon is, the, uh, better quality the,

54:21

the read you're gonna be able to impart.

54:22

So the, the first tip there is to try to,

54:25

to, to distend the colon as best you can.

54:27

If it's not fully distended, if a specific

54:30

segment is not fully distended on the two

54:32

initial views you get, then you can get, though

54:35

I would recommend a, a third scan in maybe a

54:38

different position such as the right lateral

54:39

decubitus position to try to give that segment,

54:42

uh, one more chance at, uh, fully distending,

54:44

making sure that the CO₂ distension is running

54:47

the entire time to try to open that up.

54:49

But we all will encounter, uh, times where there are

54:52

certain parts of the colon that don't fully distend.

54:55

And the way to determine whether you can clear

54:58

that segment or not when it's not fully distended,

55:02

is to look at the architecture of the haustral folds.

55:04

So I still look at whether the folds are in the,

55:08

in the usual locations, whether the, the, uh, the,

55:11

the arcades of the haustral folds are still preserved.

55:13

'Cause in most cases, even when the colon is not

55:16

fully distended, or in cases where you have, uh,

55:19

patients that have chronic diverticulosis, for

55:21

example, and myosis coli with the, um, the muscular

55:24

hypertrophy or the muscular thickening, uh,

55:26

associated with that, you still have the preserved,

55:29

uh, haustral architecture of the colon in those cases.

55:31

So, so usually, uh,

55:33

we look at the, the shape of the folds and

55:35

determine whether there's any, anything that

55:37

looks a little more irregular or, or more

55:39

mass-like or polyp-like to differentiate that

55:41

in the, in the setting of under-distension.

55:44

Uh, the flat polyp question is

55:45

kind of a separate question.

55:47

Usually flat polyps are more often

55:49

seen in the right colon than the left.

55:50

Uh, and in those cases we, we can see the flat

55:53

polyps, the flat lesions if you know what to look for.

55:56

So usually there are, there is some soft

55:59

tissue component associated with a flat lesion.

56:02

Uh, for the most part, most of them tend to

56:04

be a little raised from the adjacent mucosa.

56:06

So you have a little bit of a plateau or a mesa, uh,

56:09

in comparison to the remainder of the, of the bowel.

56:13

But, um, but yeah, you do need some

56:15

sufficient, sufficient distension to

56:16

be able to appreciate that appearance.

56:18

In addition, if you use contrast tagging, uh, either

56:22

barium or iodine, uh, or both, uh, many of these flat

56:26

lesions will, will have contrast adherence to it.

56:29

So it's important to note that when you have a kind

56:32

of a plaque-like look of contrast adhered to the

56:35

wall of the colon that's not falling dependently

56:38

with, uh, changes in the patient position, to take

56:41

a look at the wall undermining the, the contrast

56:45

area and not to just, uh, automatically dis, dis—

56:49

uh, discount it as, uh, adherent, uh, contrast.

56:52

Because oftentimes if you can demonstrate any

56:54

kind of a wall thickening underneath the tagged,

56:58

um, area, uh, oftentimes you'll—that that's one

57:01

of the best ways to, to pick up a flat lesion.

57:04

And I think that answers that question.

57:07

Yeah.

57:07

And there's a couple questions, um, that

57:09

ask, what's your procedure for CTC prep?

57:13

Okay, so that's a good question.

57:15

Uh, that was covered in, uh, Judy's, um, talk, uh,

57:18

the didactic lecture portion of the CT colonography.

57:22

But for that, there's a bunch of

57:23

different bowel preps you can use.

57:24

I, I'm not particularly, uh, uh, married to one

57:28

particular prep or the other, although the one

57:30

that I tend to use most often is magnesium citrate.

57:33

So you can use anywhere between one

57:35

and three bottles of magnesium citrate.

57:37

I usually, I use two bottles of

57:38

magnesium citrate the night before.

57:40

These are 10-ounce bottles.

57:42

Kind of separate them out.

57:43

Start like at five o'clock and eight o'clock,

57:45

for example, or even earlier if you want.

57:48

Uh, in addition, it's important to be, uh—

57:50

To, to have a clearly good

57:51

diet the day before as well.

57:53

Um, and then you can use an adjunct, uh, like,

57:56

um, like Culex to, to help with the bowel prep.

58:00

But there are other bowel preps that

58:01

you can use—MiraLAX, HalfLytely.

58:03

There's, there's a whole bunch of different,

58:05

uh, polyethylene glycol-based preps as well.

58:07

Some, uh, some newer, uh, preps like Plenvu as well.

58:11

So any bowel prep that works

58:13

should be, should be fine.

58:14

I know there's one question that asks

58:15

about, um, what to do in patients that have—

58:19

That have had a history of difficulty with bowel

58:21

preparation, especially, for example, they're

58:23

presenting after an incomplete colonoscopy

58:25

because of too much or a poorly prepped colon.

58:30

And in those particular cases, it's probably important

58:32

to change up that bowel prep, try something else, or,

58:36

or in terms of magnesium citrate, you can increase the

58:38

volume, uh, add an additional bottle, for example, find

58:41

a prep that works for that patient, uh, because it's

58:44

just as important to have a, a properly prepped colon

58:47

for CT colonography as it is for optical colonoscopy.

58:52

But the question: can stool or fecal

58:54

residue have soft tissue density?

58:56

And if yes, any tips to differentiate stool

58:58

from polyp besides air in the suspected focus?

59:02

I mean, theoretically, stool

59:03

could have any attenuation in it.

59:05

Uh, what part was particularly helpful, especially

59:08

when you're using contrast tagging, is if the contrast

59:10

can tag the interior of a, of a stool ball, that

59:14

definitely, uh, helps you differentiate it from a polyp.

59:16

Uh, and more often than not, you'll have some bubbles

59:20

of gas within some of these, uh, stool balls as well.

59:22

But theoretically, you know, the—if the, so—

59:25

if the stool, uh, poop ball, uh, theoretically

59:31

could be soft tissue attenuation, so there,

59:34

there can be some, uh, a few false positives.

59:37

But, but generally speaking, most stool balls are,

59:39

are pretty well differentiated from, from, uh—

59:43

from true polyps in that, uh, a true polyp tends

59:46

to be homogeneous and soft tissue attenuation and

59:48

be shaped differently from the, uh, haustral folds.

59:51

Dr. Chang, how much time do you

59:53

use approximately for one reading?

59:57

So I cover this during the, uh, the, the video—

60:00

usually in—when, when you have your learning curve

60:05

under you and you, if you figured out the interface

60:07

and you're very familiar with the 3D software

60:09

package that you're using, you could probably do

60:11

these—usually, even for me, about 10 to 15 minutes.

60:14

Uh, in general, depending on the complexity of the

60:16

case. Uh, if it's a negative, it definitely on the

60:19

shorter side—5 to 10 minutes even sometimes.

60:21

Uh, but you know, there, there are problem

60:23

cases where there's a lot of tortuosity,

60:26

under distension, uh, poor bowel prep.

60:29

In those cases, those can certainly

60:30

take longer, uh, on the order of 20 minutes.

60:33

But usually I would say I try to aim for 10

60:35

to 15 minutes, but it's gonna take longer.

60:37

In the beginning, I would probably

60:39

budget at least a half hour for a case.

60:41

When you're first starting out and getting

60:43

familiar with the, um, the 3D interface,

60:47

and in patients with an iodine allergy,

60:49

what oral contrast would you use?

60:52

So it's a good question.

60:53

Um, there's a couple different answers for that.

60:55

Uh, the practical answer, I guess, is that, uh,

60:59

it's very rare for, uh, an iodinated IV contrast

61:03

allergy to cross over, uh, to oral administration.

61:08

The, um, the risk of, uh, of, uh, contrast

61:11

reaction to orally administered iodinated

61:13

contrast is exceedingly low, very, very low.

61:16

So it's, it, the likelihood is very

61:18

low that you will have any kind of a

61:19

contrast reaction with just ingestion.

61:22

But, um, you know, some, there's certainly

61:24

some hospital policies that still would,

61:25

uh, would not recommend giving, um, the

61:28

iodinated oral contrast agents in that setting.

61:30

And, and, and instead you can give barium as well.

61:33

That's a good alternative.

61:35

Uh, and you could potentially do this without,

61:37

uh, oral tagging, although certainly oral

61:39

tagging makes the reads a lot easier than,

61:42

uh, than not using an oral tagging agent.

61:44

And that should—

61:46

That probably answers another question.

61:47

Somebody's asking why we were using a positive

61:49

oral contrast for CT colonography, and that's

61:52

in particular to be able to see through any

61:54

residual fluid that may still be in the colon.

61:57

So, you know, you don't, we, we rarely have a perfect

62:00

bowel prep where there's no fluid left in the colon.

62:03

The, the difference between a virtual colonoscopy

62:06

or CT colonography and optical colonoscopies

62:08

is that we can't suck out the fluid through

62:10

the endoscope at the time of the procedure.

62:12

So you have to deal with any fluid

62:13

that is still present in the colon.

62:16

And the best way to do that is to, to tag that

62:18

fluid hyperdense so that any submerged polyps

62:21

that are hiding beneath the fluid are visible,

62:24

uh, even when it's submerged under the fluid.

62:27

And that gives us a chance to look at the full

62:28

circumference, uh, and the full volume of the, of

62:31

the colon on either, uh, supine or prone image or

62:35

whatever, um, uh, position you have the patient in.

62:37

So it, it improves our, our sensitivity for polyps

62:41

and our confidence in, uh, calling the polyp,

62:43

especially when you can see it in both positions.

62:45

Despite the, uh, submerged, uh, location.

62:50

Software options, can you comment on, on that?

62:54

So, I've used a bunch of different,

62:56

uh, 3D software packages.

62:57

I would say the best one is the

62:58

one you're most comfortable using.

63:00

Uh, I don't think I've seen any specific packages

63:03

that are not appropriate for, for colonography.

63:06

I've used TeraRecon, I've

63:08

used Philips IntelliSpace.

63:09

I've used GE Advantage Workstation.

63:12

Um, others have used, uh, older

63:14

packages as well that they prefer.

63:15

I mean, I, I would just say whichever one you

63:17

feel most comfortable using, uh, uh, is, is the

63:21

one that's gonna be sufficient for reading

63:22

CT colonography.

63:24

I'm not going to, uh, uh, pick a, a winner here.

63:29

Okay.

63:30

Why can't we go inside distended

63:31

small bowel loops like colon?

63:34

You can, there's no reason why you can't.

63:36

Uh, so oftentimes if you have

63:38

an incompetent ileocecal valve,

63:40

you'll see CO₂, carbon dioxide, getting

63:42

into the distal small bowel as well.

63:45

And oftentimes you can fly

63:46

through that small bowel too.

63:47

But, uh, uh, for the most part, you know, you

63:50

don't know what the, um, the, the competence

63:53

of the ileocecal valve is going to be.

63:54

So our goal in, uh, colonic distension for CT

63:58

colonography is not so much to look at small

64:00

bowel as much as colon, but certainly if you

64:01

see a, a finding in small bowel and you're

64:04

pretty confident that it's real, uh, it's

64:07

definitely something that you can call on a

64:09

CT colonography—at least I have in the past.

64:13

Finally, for our last question, do you perform same

64:15

day CTC after a failed conventional colonoscopy?

64:18

Also, do you perform stoma CTC?

64:23

So the answer to the first question is yes.

64:24

In fact, that's the majority of

64:26

my current, uh, referral base.

64:28

Um, because that's the easiest time

64:30

you can sell CT colonography, right?

64:32

Uh.

64:34

Especially if you have a, a, a gastroenterology

64:37

group that might be skeptical of the role

64:39

of, uh, CT colonography, especially how

64:41

it impact—how it may potentially impact

64:43

their, uh, optical colonoscopy, um, volume.

64:47

They're going, they're going to encounter cases

64:49

where they can't complete the colonoscopy, where

64:51

they can't, uh, get into the, uh, the proximal colon.

64:54

And in those cases, you're actually helping

64:55

them out by offering them a same-day, uh,

64:57

alternative to complete the screening,

65:00

uh, when they can't get the scope passed.

65:01

So, um, oftentimes your first bunch of cases that

65:05

you're going to be referred for CT colonography

65:07

are gonna be your incomplete colonoscopy cases.

65:10

And in that—in that setting—their bowel's

65:12

already prepped, so you don't have to re-prep the bowel.

65:15

Uh, the, the colonoscopy prep is sufficient.

65:17

Is—is more than sufficient for CT colonography,

65:20

although they may have more fluid than we tend to

65:23

have with some of our drier or lower-volume, uh,

65:25

bowel prep, uh, regimens that I've been recommending.

65:28

But even in that case—

65:30

You know, if you give something like,

65:32

um, uh, Gastrografin, it'll get into the

65:36

colon pretty quickly, and I would say most

65:39

of the colon gets tagged within two hours.

65:41

So if you give oral contrast to these patients

65:44

after the colonoscopy and give them about two

65:47

hours before they come down for the CT scan, uh,

65:50

most of the right colon and especially the colon—

65:52

the, the, the proximal colon that's not visualized

65:55

at the time of colonoscopy—will have sufficient

65:58

contrast material in it to, uh, to evaluate.

66:00

So even a same-day colon CT—a same-day CTC—

66:04

does not, uh, preclude bowel, uh, fluid tagging.

66:08

You can do, uh, you can insufflate through a

66:10

stoma, um, as long as you can, uh, get a, uh, uh,

66:14

enough of a seal for the CO₂ to inflate the colon.

66:17

So in that case, two different ways of doing it: you

66:19

can—you can inflate the balloon tip of the catheter

66:22

and either push it up against the stoma or have the

66:24

patient hold it against the stoma, or gently put it

66:27

inside the stoma and gently inflate the balloon.

66:30

Um, uh, as long as it's sufficient to—to create

66:32

an airtight seal for the carbon dioxide.

66:35

But it is doable.

66:37

Thank you, Dr. Chang, for your case review today and

66:40

for answering all those questions and for everybody

66:42

for participating in our Noon Conference and asking

66:44

such great questions. You can access the recording

66:47

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66:49

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66:52

And be sure to join us next week on Thursday,

66:54

November 9th at 12:00 PM Eastern for a Noon

66:57

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67:00

Radiologist Essentials with Dr. Ella Kazerooni.

67:03

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67:06

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updates on future Noon conferences.

67:10

Thank you so much,

67:11

Dr. Chang, and thank you everyone else.

67:13

Have a great day.