0:01

So from our list of, uh, anonymized cases,

0:04

I'm gonna be choosing the case with the supine

0:08

and the prone dataset.

0:09

So usually CT colonography,

0:11

we get at least two data sets in two different positions

0:14

at our institution.

0:15

We usually will scan the patient once on their

0:18

back and once on their belly.

0:19

But you can choose any two different, um,

0:21

uh, positions you like.

0:23

Uh, as long as you give the tag fluid

0:26

and the tag stool a chance to redistribute on the two views

0:30

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

0:32

the entire circumference of the colonic mucosa, uh,

0:36

in air relief on one of the two positions.

0:39

So we choose supine and prone,

0:41

but it can be any tooth that you'd like.

0:44

I make sure I'm choosing the thin cuts, the ones

0:46

that are 1.25 millimeters thin.

0:48

And basically we recommend scanning with, uh, thin cuts at,

0:52

uh, no greater than 1.25 millimeters,

0:55

I would say can be thinner than that.

0:57

And then I load it up in the colonography, fly

1:01

through package here,

1:02

and it will choose the, um, center line.

1:06

The package is gonna try

1:08

to automatically select out the gas field colon

1:11

and render a camera line through the center

1:14

of the lumen in both the supine and the prone dataset.

1:17

So on the left we have the supine images

1:19

and it's automatically picked the,

1:21

the colon out in green here,

1:22

and you can turn the three D model around

1:24

and make sure that the segments that are selected are colon

1:28

and not anything else.

1:29

And then here we've got most of the colon selected except

1:32

for the, uh, the rectosigmoid.

1:34

And now I've added that back in.

1:37

If there's a fluid-filled segment of the bowel,

1:39

it may not note how to trace the center line

1:42

through the lumen quite as well.

1:44

So you have to manually select that.

1:46

But these look like they're both appropriate.

1:48

Then hit the, the next step button

1:51

and it'll try to render the, the center line through.

1:54

So basically this part is just a game of connect the dots.

1:58

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

2:00

in the right place and ending in the right place

2:02

and going through the segments in the right order.

2:04

So this looks like it's doing a pretty good job of that,

2:07

although in the beginning it looks like it's going right

2:09

down the barrel of our rectal catheter, which is fine.

2:13

You're not gonna find polyps inside the rectal catheter.

2:15

But, but we will get into the, uh, the rest of the colon

2:19

and then I hit okay.

2:20

And then we should be ready to do our,

2:22

our three D fly-throughs.

2:25

But for the time being, I think we will start

2:27

with the two d, um, evaluation,

2:29

because that's probably the, the easiest way to, uh,

2:33

pick up CT colonography.

2:36

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

2:39

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

2:42

to minimize the amount of noise on the, um, on the, um,

2:45

the wall of the structures.

2:49

And given that we are using a very, uh,

2:52

low radiation dose protocol, I tend to have

2:55

to adjust this just a little bit

2:56

to make it a little bit less noisy. So

2:58

These are our three D settings.

3:00

Basically the, um, the rendering thresholds

3:03

for the surface render.

3:05

And I do that for both positions here.

3:10

So basically you can see how there's a little bit of, um,

3:13

noise along the wall of the colon here,

3:15

and I'm just adjusting the, um, the threshold

3:18

to make it a little bit smoother.

3:21

All right, so that's basically that.

3:23

And then you can choose on this package, you can choose a,

3:25

a variety of different workflows and different layouts.

3:29

Uh, for a primary two D read, you can either use the three d

3:34

read here or you, we can try the primary two D, which does,

3:37

which aligns both the supine

3:39

and the prone together at the same time.

3:41

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

3:44

because, uh, I like to look at each side individually.

3:48

The first step is just to judge the quality

3:50

of the distension and the quality of the valve prep.

3:53

So I'm looking through, uh, on small field

3:56

of view windows through the colon.

3:58

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

4:02

to assess the entire colonic lumen from the a**l verge all

4:07

the way to the cecum on both positions.

4:10

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

4:13

that you can see through the tag fluid.

4:16

'cause here you can see the oral contrast tagging any

4:19

residual fluid in stool in the colon,

4:22

while still being able to differentiate, uh,

4:26

a soft tissue density polyp from, from the adjacent fat

4:29

or from my lipoma, for example.

4:32

Uh, basically the definition

4:33

of your target lesion on CT colonography is a either

4:37

a polyp or a mass.

4:38

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

4:42

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

4:45

If you see something that has gas bubbles inside it

4:48

or contrast inside of it,

4:50

or fat attenuation inside of it, then you're dealing

4:53

with either a tagged, um, stool

4:56

or bubbles, uh, or fecal material,

5:00

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

5:03

So it needs to be soft. Have a soft tissue core.

5:06

So here you can see the rectal catheter here.

5:08

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

5:12

with air, and you could see that better if you go

5:15

to a long window, you'll see the,

5:16

the wall or the balloon there.

5:19

And then I basically, this is the tip

5:21

of the rectal catheter here, and I'm just scrolling through

5:24

and bringing up the field of view here so that you can look

5:28

for any bumps along the wall of, uh, the colon, either the,

5:32

the lateral walls, or you have to also scroll

5:34

through the top and the bottom of each turn, looking

5:37

for any polyps on the top

5:39

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

5:42

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

5:47

And basically we're scrolling through looking for any bumps,

5:51

anything that doesn't look like a house to fold

5:55

that might be soft tissue in attenuation.

5:58

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

6:01

of the sigmoid colon here through the

6:06

proximal sigmoid colon here.

6:09

And then now we're in the descending colon,

6:12

scrolling all the way up.

6:14

And the, the more experience you have with this,

6:16

the faster you can do this.

6:18

Looking through the contrast, making sure

6:20

that there's no submerged polyps

6:22

that you may not necessarily be able

6:24

to see on the three D view.

6:27

And then going all the way up

6:28

through the splenic flexor here,

6:34

scrolling through the transverse colon now,

6:40

and then this is your transverse colon.

6:41

I'm gonna scroll through the bottom

6:44

and the top of each turn.

6:46

And then you see our first finding here.

6:48

So right there

6:52

to confirm that finding.

6:54

So, so you can see there's something here

6:55

that looks a little bit different from the adjacent folds.

6:58

You can go to our soft tissue windows.

7:00

You can see that the center

7:02

of it does look like it's soft tissue

7:03

and attenuation similar to, uh, muscle or,

7:06

or liver, for example, different from the adjacent fat, uh,

7:11

outside of the clo wall.

7:13

There's a little bit of contrast between the, this polyp

7:16

and the adjacent fold here.

7:18

And that's fine. Contrast on the surface of a polyp is,

7:21

is, uh, acceptable.

7:22

In fact, sometimes it's the best way to see a polyp,

7:25

especially on these two D views, is if it's, um,

7:28

coated with contrast.

7:29

But the center of the, um, of the finding needs

7:31

to be soft tissue and attenuation.

7:34

And if you look at that same area on the three D images,

7:39

so if you set up the three D images here, you can see

7:41

what this, uh, polyp looks like in three D.

7:44

And this is probably the best way you can appreciate the

7:46

morphology of a finding.

7:48

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

7:51

and it looks like the stock is arising from a,

7:55

a house drill fold,

7:58

just like you can see it on the two Ds.

8:02

So there's a couple different ways of, uh, figuring out what

8:05

to do with this polyp.

8:06

Basically, a lot of our management is based off polyp size.

8:10

The larger the polyp is, the higher the likelihood

8:13

that it's going to represent a high grade adenoma.

8:16

The larger it is, the more precancerous

8:18

or the potentially cancerous a polyp may be.

8:21

The best way to measure it is actually off the three D

8:23

images because you can get the maximal dimension

8:25

of the polyp excluding the stock.

8:28

And that's how a polyp is classified

8:30

by the gastroenterologist at the time of a colonoscopy.

8:33

The best way to figure out what the long axis the, the,

8:36

the maximal dimension of a polyp is, is

8:39

by looking at it on the three D views.

8:41

'cause there's no guarantee that the two D views is gonna be

8:43

the maximal dimension.

8:45

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

8:47

You wanna measure from edge to edge without shooting

8:50

off the edge of the polyp.

8:52

And this is, you have to be a little bit

8:53

careful of where you put the,

8:55

Put the caliper because, um,

8:56

if you place the caliper a little too far off the edge

9:00

of the polyp, you can over measure

9:02

because the, uh, three D workstation thinks

9:04

that you're measuring from this point

9:06

to a point on the far wall of the colon, for example.

9:09

So when you place this caliper, i I rotate

9:11

around the polyp just to make sure

9:13

that I'm staying on the polyp

9:14

and I'm not putting the, the, um, the marker down, uh,

9:18

on the far wall of the colon.

9:20

'cause for example, if I move it to over here, you can see

9:24

that, uh, it may not necessarily be measuring, uh,

9:28

the polyp itself anymore.

9:30

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

9:32

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

9:35

So we've got something that's over a

9:37

centimeter in size here.

9:39

If we try to measure it off the two Ds, uh,

9:41

usually you may end up underestimating the

9:43

size of the polyp.

9:45

See for example here, if you measured off

9:46

of just the two Ds, you could potentially get a, a number

9:49

that's less than a a centimeter.

9:52

And that one centimeter, um,

9:54

size threshold is an important one in the Crad S system.

9:58

So crad s is how we manage polyps

10:01

of different size and number.

10:02

So basically, um, C one would be, uh, a normal colonography

10:07

or benign findings like lipomas, for example.

10:11

Uh, AC two would be if you have one

10:13

or two sub centimeter polyps

10:16

and polyps, we define as being, uh, six millimeters

10:19

or larger in size.

10:21

So if you have one

10:22

or two polyps that are six to nine millimeters in size,

10:25

rounding to the closest millimeter, then uh,

10:28

we give the patient two options.

10:30

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

10:33

within three years, which is a perfectly acceptable

10:36

and safe, uh, option for,

10:38

for following up these low risk polyps

10:41

or in the, uh, refer

10:43

or the patient's, um,

10:44

preference if they prefer a colonoscopy, uh,

10:47

for a polypectomy, that's also an appropriate, uh,

10:50

management option.

10:52

And then at the one centimeter size threshold,

10:55

the 10 millimeter size threshold,

10:56

we start putting the patients into AC three category.

11:00

So if you have one polyp that's 10 millimeters

11:02

or larger in size, or you have three sub centimeter polyps

11:06

or more, then uh, generally the recommendation

11:10

for C three is to go onto the, uh,

11:13

colonoscopy for polypectomy.

11:15

And then we use the C four category for, uh, masses.

11:19

And these are our classic, uh, colon cancers

11:22

that I will show you a little bit later.

11:24

The, um, the large annular, uh, apple core lesions or,

11:28

or saddle lesions, big, big masses.

11:31

Alright, so this is our first finding here.

11:34

And the other thing that you want

11:35

to do once you find a finding is to confirm

11:37

that you're also seeing it on the other butte

11:39

because you have two chances to see this same polyp.

11:42

Uh, another way to differentiate a a polyp from a stool ball

11:46

is to show that it's in the same general location

11:49

on both positions.

11:50

So basically a polyp should have a pretty

11:52

Fixed location relative to the colon

11:55

and the adjacent house drill fields, uh,

11:57

despite changes in patient position,

11:59

whereas a stool ball may fall dependently, uh,

12:02

without an a stock

12:04

or without an attachment to the colonic wall.

12:06

So in this case, in this same location here, you're seeing

12:09

that there is a filling the effect within this pool

12:12

of contrast in the same location in

12:14

the mid transverse colon.

12:15

And you're able to see the stock connecting it to the, um,

12:19

to that house drill fold in the mid transverse colon.

12:22

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

12:24

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

12:27

And if we had not used our fluid tagging material,

12:30

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

12:33

on the two D images either

12:34

because there's not enough of an attenuation differential

12:37

between, um, untagged fluid and a polyp.

12:42

Although depending on your software package,

12:45

you could see the, the gas fluid level here is being

12:48

rendered as a solid in appearance.

12:50

But occasionally you can do a remove stool function to try

12:54

to subtract out electronically, subtract out fluid

12:58

above a certain threshold.

13:00

Uh, but you need to have enough, uh,

13:02

contrast hagging to be able to do that.

13:03

And it tends to leave artifacts on the, um, three D views.

13:07

These bathtub rings at that three material interfaces

13:10

between the contrast, the gas and the bowel wall.

13:13

So I, I don't tend to like to use that on the three D views.

13:18

So continuing through there,

13:20

I think this was the major finding.

13:22

I do the same thing and I just keep, I continue going

13:25

through the remainder of the colon on the two Ds

13:29

and looking at any interesting findings on three D just

13:32

to make sure that anything

13:34

that I do see does not represent a house to fold

13:37

and looks like a real polyp.

13:39

And then you confirm the, um, the atte, the attenuation of

13:41

that polyp on the, um, the two D views.

13:45

And here where we've reached the, the cecum here,

13:47

this is our ileocecal valve, our typical appearance

13:51

with the ileocecal valve.

13:52

It looks like a, um, pair of lips here

13:55

and between the,

13:56

the lips you can see the hole going into the terminal ileum.

14:00

And then right next door to it here, this is your

14:02

appendiceal orifice.

14:06

So there's a little bit of a,

14:08

a tiny little hole which represents

14:10

the orifice of the appendix.

14:11

You can see on the two D views here

14:12

where the appendix is coming off.

14:14

And then there's contrast in the

14:16

remainder of the appendix here.

14:18

And then if you keep scrolling through, you'll see

14:20

that it should be a blind ending,

14:22

defining it as the appendix.

14:24

So that's the appendiceal orifice

14:26

and the typical appearance for the ileocecal valve.

14:29

And there's a wide, uh, variety of appearances

14:32

for the ileocecal valve.

14:33

They can be varying degrees of, uh, thinness or,

14:37

or, you know, plumpness.

14:39

But for the most part, uh, as long

14:40

as it's typical in appearance or fat and attenuation,

14:44

'cause oftentimes a bulky ileocecal valve will show fat

14:47

attenuation in the inside of it.

14:49

But that's your typical appearance for the ileocecal valve.

14:51

And sometimes you can fly

14:52

through into the ileocecal valve as well.

14:55

So I'll look at it as much of the, um, terminal, um,

14:57

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

15:00

And then I do this exact same thing

15:02

with the, the prone images.

15:03

And I'm not gonna take you through the exact same process,

15:05

but basically I do the same thing in this position,

15:09

scrolling through from a**l verge all the way back to cecum

15:14

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

15:16

the wall looking for any bumps as well as to look

15:19

through the contrast to look for any submerged polyps.

15:23

And that's the, um, the three D fly through.

15:25

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

15:29

what the typical appearance of the ileocecal valve is, uh,

15:32

as well as the appendiceal orifice over here.

15:35

So that is our first case.

15:36

I think there may have been one other

15:39

smaller polyp in this case.

15:40

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

15:43

one right here.

15:44

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

15:48

what we would be confident in calling a polyp on,

15:51

uh, CT colonography.

15:52

You can see this one does not have a stock in it

15:55

and uh, it looks a little more Cecile.

15:57

It's also a, uh,

15:58

located on a house tro fold in the sigmoid colon.

16:02

And just to confirm that that's not a, uh, an untagged piece

16:07

of stool, you can look

16:08

for the same finding in the same location on the prone

16:11

images and right there

16:15

similar looking structure there,

16:17

which if you measure the long axis may

16:20

or may not even meet that six millimeter cutoff.

16:22

I think at the time that I read this originally I called it

16:25

six millimeters, and both

16:27

of these were confirmed at the time of colonoscopy.

16:31

So that is basically the, the primary two D read for,

16:34

um, CT colonography.

16:37

In the next case, I'll show you how, uh, how I like to read.

16:40

I actually prefer reading the,

16:41

with a primary three D read in the beginning, it takes

16:45

at least 20, 30 minutes sometimes to, to, to read one

16:48

of these cases, uh, when you're first starting out.

16:50

But then you get much quicker at doing this.

16:53

And, um, in the best of hands, oftentimes you can,

16:56

you can finish reading a CT colonography within 10 minutes.

16:59

The better distended and the better prepped the colon is,

17:02

the easier they are to read and the faster they are to read.

17:05

But, uh, just to change up the pace,

17:07

I often prefer reading in the primary three D mode,

17:10

which I'll show you next.