0:01

So I promised you in the cliffhanger, so why are we

0:04

as radiologists so important to ILD diagnosis?

0:09

It's because we don't really pursue lung biopsies anymore.

0:11

We just don't do it. And so why is that?

0:14

It's because even though surgical lung biopsy is the gold

0:17

standard for histological assessment,

0:19

not the gold standard overall gold standard for

0:23

diagnosis in ILD is really multidisciplinary diagnosis.

0:26

So you get the, the pulmonologist, you get the radiologist,

0:30

you get the pathologist if there are pathological slides

0:32

and sometimes the rheumatologist altogether either

0:35

synchronously or asynchronously

0:37

and try to figure out what the

0:38

best diagnosis for that patient.

0:39

That's really the gold standard way to do it.

0:41

But from a histological standpoint,

0:43

it's really surgical lung biopsy.

0:44

That's how we get the, the slides

0:46

that the pathologist needs.

0:48

It's not transbronchial biopsy, the amount

0:50

of tissue, it's too small.

0:51

There are some other methods out there which people are

0:53

experimenting with, but really the gold standard

0:55

is surgical lung biopsy.

0:57

However, we were finding anecdotally that a lot of patients

1:01

who were doing surgical lung biopsy

1:03

on, they weren't doing well.

1:04

In fact they were were causing some

1:06

of these acute exacerbations.

1:07

And now we have a lot of data that shows

1:09

that we were probably actually, um, killing people.

1:13

So these acute exacerbations in patients

1:15

with pulmonary fibrosis, it's no joke,

1:17

especially in the setting of idiopathic pulmonary fibrosis.

1:20

These patients can delve with acute exacerbation

1:23

and then reach their demise in a matter of sometimes days,

1:26

weeks, or even months.

1:28

But bottom line, it sets off this inflammatory casca in

1:30

their lungs and just can't calm it down.

1:33

And so after we figured that out, we stopped being

1:36

as aggressive with surgical lung biopsy.

1:38

So bottom line, what's the status quo right now?

1:41

We really don't do it. When I first got out of training,

1:44

wait, so it's goodness gracious now, uh,

1:46

16 years ago we did surgical lung biopsy.

1:49

I'd say at 15, maybe 20% of patients maybe

1:51

that's a bit high, but that's sort of my, my recollection.

1:54

Now I'd say it's well less than 5%, maybe 2%, maybe even 1%

2:00

in in certain quarters.

2:02

And it's because, because again of this, the fear

2:04

of causing acute exacerbations but also it's

2:06

because CT has gone so darn good.

2:08

And I'm not just talking about photon counting cts,

2:11

which are obviously quite impressive,

2:12

but even the previous generation of CT scans

2:16

so good in terms of the the spatial resolution

2:18

and just the sharpness and delineation of abnormalities.

2:22

And so CT has gotten much better.

2:24

We're scared of doing lung biopsies.

2:25

So now CT has sort of become both the imaging modality

2:30

to use and sort

2:31

of a pseudo pathological modality to use as well.

2:35

So bottom line, we are what the pulmonologist rheumatologist

2:38

and the other clinicians are relying on to try to figure out

2:42

what is the underlying histopathology

2:44

of interstitial lung disease.

2:47

So let's talk about what the heck an HRC CT is.

2:50

And so many people have asked me this

2:52

because it used to be that HR cts were those axial sort

2:56

of like skipping thin cuts through the thorax.

2:59

And you would do those both in inspiration,

3:01

exploration and prones.

3:03

Now it's sort of blurred HR CT with regular chest ct

3:08

'cause all chest CT at modern day centers

3:11

and even centers that maybe don't have the best technology

3:14

but any modern a CT scanner,

3:16

you're gonna do a volumetric acquisition.

3:18

It's pretty uncommon

3:19

to see people now do these axial sort of skip cuts.

3:22

We just don't do that as much anymore.

3:25

Some places still do it

3:26

'cause obviously there can be radiation dose savings.

3:29

But bottom line CT scans, again, again

3:31

so good there's not great reason to do it.

3:33

And so again, the line is blurring

3:37

but I still think there are some differences in terms

3:40

of the inspiratory series.

3:41

You want obviously someone to have be the patient

3:43

to be in full inspiration and inspiratory acquisition.

3:48

And then the most important part is

3:49

that when you reconstruct

3:50

those images, they have to be thin.

3:51

So I like 'em about one millimeter thin.

3:53

Other people use about 1.5 millimeter.

3:55

Other people get far thinner than one millimeter.

3:57

But bottom line around one millimeter

3:59

or thinner is probably the sweet spot you want to get.

4:02

So you have the best in plain resolution.

4:06

I talked about the volumetric heel acquisition already.

4:09

In terms of field of view,

4:10

you can't have a big field of view.

4:11

I've seen this as probably the biggest air in some

4:14

of the HRCT series that I've seen from outside hospitals

4:17

where they think, oh well you know, we're doing thin cuts

4:20

but they forget about the field of view.

4:21

So instead of sort of focusing on the lungs,

4:23

they have this big field of view that includes a lot

4:26

of the overlying gas and air around the patient.

4:30

You know, you see sometimes you see

4:31

the blankets and things like that.

4:33

That is not great because again you're losing the in

4:35

plain resolution, aren't you?

4:37

Right? Because now you have a lot of wasted matrix.

4:40

So we wanna have a a cone down field of view into the lungs

4:44

so we can delineate those really subtle abnormalities,

4:48

especially within the lung periphery.

4:51

In addition to those inspiratory acquisitions,

4:54

we also do these other supplemental series as well.

4:58

And there are some places that actually amid some of these,

5:00

for example the prone inspiratory phase.

5:02

And so why do we do the prone imaging?

5:03

Really it's for one reason, it's

5:05

because the posterior aspect of lungs,

5:07

they have some aleiss when you're lying in your back when

5:10

you're in a supine position.

5:11

So the lungs are mostly filled with gas

5:14

but they still have some weight to them.

5:16

So if you're lying on your back in a supine position

5:18

in the posterior aspect of lungs,

5:20

you can develop a little bit of alais, sometimes nodule

5:23

and certainly that can mimic interstitial lung disease

5:26

or interstitial lung abnormality.

5:28

So to open those areas up

5:31

to exclude underlying interstitial lung disease

5:34

or interstitial lung abnormality,

5:35

just flip the patient over onto the belly

5:37

and then opens up the posterior aspect of lungs

5:39

and we can delineate those areas in much better detail.

5:42

I'll say in my experience, the prone inspiratory series,

5:46

it helps me very seldom, maybe one out

5:49

of 50 times does it help me.

5:51

But what does that imply? It means one out of 50 times.

5:54

Um, it's actually clinically useful.

5:56

The problem is you don't know which one outta 50 those are.

5:59

So I know some places that will admit these,

6:01

but a purist will say that

6:02

with an HR ct you're gonna include these prone inspiratory

6:05

images as well, at least on the first ct.

6:08

And we, we tend

6:09

to do these at on every H-R-C-T-I-L-D CT that we acquire.

6:14

The end expiratory series really is gonna be something

6:17

that you, you also want to do.

6:19

And this is probably more important than

6:21

the prone inspiratory imaging.

6:22

The only reason we do the end expiratory imaging in the

6:25

setting of interstitial lung disease is to look

6:28

for air trapping or small airway disease.

6:30

'cause if you have significant air trapping,

6:33

it really draws you away from the more common

6:36

types of lung disease.

6:37

And really right now I'm talking about pulmonary fibrosis.

6:40

So, so we have this sort of 800 pound gorilla subtype

6:43

of pulmonary fibrosis called UIP

6:46

usual interstitial pneumonia.

6:47

We'll talk about that in our fibrotic lung disease session.

6:51

But bottom line, that is the main pattern

6:53

that we're sort of working off of.

6:55

So even before you get a CT scan,

6:57

if you know someone has pulmonary fibrosis,

6:59

if you're just a betting person,

7:02

UIP is gonna be the most common pattern

7:04

that you're gonna see in most clinical settings.

7:06

Most hospitals depends on your patient population,

7:09

but again, I'd say 90% of hospitals out there,

7:12

medical centers, UIP, is gonna be the most common pattern.

7:16

And so if you have associated air traffic

7:19

or small airway disease, that draws you away from

7:22

that UIP diagnosis and more toward alternative diagnosis.

7:27

And the thing that's high on the differential diagnosis

7:29

would be that of hypersensitivity pneumonitis.

7:33

Uh, sometimes you could also see in

7:34

connective tissue disease.

7:35

Okay, we talked about before the volumetric acquisition.

7:40

So that's through the whole thorax versus these

7:42

axial targeted levels.

7:44

I think most people are just using volumetric acquisitions.

7:47

I think with the expiratory imaging,

7:49

I guess you could use these osteo targeted levels

7:52

because again, you're just sort

7:54

of sampling for air trapping.

7:55

But I strongly prefer volumetric expiration.

7:58

And I think that's really where the field is going.

8:02

The QR codes at the bottom here, these are examples

8:06

of various CT protocols that are supported

8:09

by these different societies or groups.

8:11

So on the left hand side we have the,

8:13

the Pulmonary Fibrosis Foundation.

8:15

In the middle you have radio pedia.

8:16

On the right hand side you have

8:17

the American College of Radiology.

8:19

So all three of these organizations have similar protocols.

8:23

But again, if you don't have one

8:25

and you're trying to build one,

8:26

these might be nice resources to look into.

8:30

All right, let's talk about indications.

8:32

So indications

8:33

for HRCT really is anytime you really wanna do a robust

8:37

evaluation of the lung parenchyma,

8:39

you're gonna get the inspiratory view.

8:41

The expiratory view, obviously the prone views as well.

8:44

And so this will make sure

8:45

that you've looked at under every stone,

8:46

you've figured out every sort of angle in terms

8:49

of possible lung diseases that are there.

8:51

Whether it's gonna be an infiltrated process,

8:53

whether it's gonna be an airways related process.

8:56

You have the tool to exclude it to the best of your ability.

9:00

If you look at this list,

9:01

this list is from the American College of Radiology.

9:03

And so it's nice to define things.

9:05

So I think that it's important to know these things as well.

9:07

And so according to the the college you use HRCT

9:11

or an ILG protocol,

9:12

if someone has a suspected diffuse lung disease,

9:15

if you're looking for some small airways disease,

9:18

so usually air trapping

9:20

or if you wanna look at the extent of diffuse lung disease,

9:23

this is helpful as well, which goes hand in hand

9:25

with diagnostics and for guidance for lung biopsy.

9:29

But again, as I alluded to

9:30

before, we

9:31

as a community in interstitial lung disease have really

9:34

moved away from leveraging surgical lung biopsy.

9:38

In most cases, if you are gonna pursue lung biopsy in these

9:42

patients with pulmonary fibrosis in

9:44

particular, CT can be quite helpful.

9:47

You actually don't want biopsy the areas

9:49

that have like the most dense fibrosis.

9:52

'cause if you biopsy dense fibrosis,

9:54

you almost will always just get back end stage

9:57

fibrosis on pathology, which usually is gonna look like UIP.

10:01

So usual interstitial pneumonia,

10:03

that doesn't help you from a diagnostic standpoint.

10:06

You actually want to get the areas

10:07

that are maybe less fibrotic,

10:09

have maybe more ground glass in them.

10:11

'cause there the fibrosis hasn't really progressed enough

10:15

and there may be some indications

10:17

of other underlying abnormalities.

10:19

So CT can be quite helpful in that setting.

10:21

But again, um, we just don't do it as much.

10:24

So some diseases, sub diseases, I think we'd be,

10:27

I'd be remiss if I didn't at least mention some

10:29

of these things that we typically will see

10:31

or are valuable on HRCT.

10:33

Uh, we'll start with diffuse parenchymal lung disease

10:36

or pulmonary fibrosis.

10:38

This includes those alphabet soups, things

10:40

that like UIPI talked about,

10:42

non-specific interstitial pneumonitis, NSIP,

10:45

HP hypersensitivity,

10:46

pneumonitis connected tissue disease related ILDs.

10:49

We'll be looking at these on HRCT.

10:52

And again, we'll be looking for the extent of disease,

10:55

how coarse the fibrosis or diffuse lung disease is

10:58

because this can help us predict prognosis in many patients.

11:04

The other disease

11:05

that we commonly see are the airways disease.

11:08

So large airways and small airways disease.

11:10

So HRCT is quite helpful

11:13

for looking at bronchiectasis though you could probably

11:15

evaluate bronchiectasis on a regular chest ct.

11:17

What it's really good for is to look

11:19

for concomitant air trapping.

11:20

And so when you see concomitant air trapping even without

11:23

bronchiectasis or a large air disease,

11:25

we're thinking about things like asthma, ablative,

11:27

bronchiolitis, and then other causes of bronchiolitis,

11:30

whether it's from post-infection or post lung transplant

11:33

or post stem cell transplant.

11:36

The expiratory imaging are obviously gonna be quite helpful

11:39

in terms of defining ear trapping within

11:41

this disease setting.

11:44

And then finally we have our cystic

11:46

and nodule lung disease as well as our rare lung disease.

11:49

And so bottom line, if someone comes in, a patient

11:52

Comes in and they have a disease where it's confused.

11:56

Other people at other hospitals, they say, oh,

11:59

this person has some sort of diffused lung disease

12:01

that no one has been able to diagnoses.

12:03

I make sure that patients get an HRCT

12:05

'cause we wanna kind, we wanna do the full court press

12:07

and our full court press modality

12:10

in chest CT is gonna be HRCT, that's gonna be the protocol.

12:14

So Inspiratory, expiratory, prones.