0:02

Hello and welcome to Noon Conferences

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hosted by MRI Online. In response to

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5 00:00:07,380 --> 00:00:08,970 and the shutting down of in-person events,

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Conferences to all radiologists worldwide.

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And, uh, today we're joined by Dr. Nadine Mallek.

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She is an Assistant Professor of Diagnostic

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Radiology at Oregon Health and Science University,

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Division of Body Imaging and Nuclear Medicine.

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Her area of interest focuses on novel molecular

0:23

imaging tracers, and the combination

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of anatomic and functional imaging.

0:28

Reminder that there will be time at the

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end of this hour for a Q and A session.

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Please use the Q and A feature to ask

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all of your questions, and we'll get to

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as many as we can before our time is up.

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We're also using the polling feature

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today, so be on the lookout for that.

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That being said, thanks so much

0:40

for joining us today, Dr. Mallek.

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I will let you take it from here.

0:43

Thank you very much, Ashley.

0:44

Um, hello everyone, and thank you for

0:46

joining today to watch this talk.

0:48

So, our talk today is gonna be about some

0:50

of the bread-and-butter nuclear medicine

0:52

studies that we do for common GI pathologies.

0:55

So I think it's gonna be probably mostly helpful for

0:58

people who are in training or for people who are not,

1:02

uh, specialized in nuclear medicine, but they still

1:04

encounter nuclear medicine studies in their practice.

1:10

So the important role of nuclear medicine, what

1:13

it can really add to anatomic imaging, is

1:18

the added value of the ability to show physiology

1:21

and function more than anatomic imaging.

1:25

So you can actually see a physiologic or

1:27

pathologic process and a certain function of

1:30

certain organs as they are happening over time.

1:33

Um, so this is very important to understand what's

1:35

going on, but at the same time, the anatomic details

1:38

on the nuclear medicine studies are not great.

1:41

So that's why it's very important to remember

1:43

to look into the patient's charts.

1:45

So if they've had an ultrasound, a CT, or an MRI, it's

1:49

very important, um, to look at those and to compare.

1:52

So this sometimes can be very helpful

1:54

in problem solving in nuclear medicine.

1:57

So the studies that we're gonna be talking

1:59

about today are hepatobiliary scintigraphy, or

2:02

HIDA scan, GI bleed scan, and Meckel scan.

2:06

So to start with the hepatobiliary imaging.

2:09

So what does HIDA mean?

2:11

Where, what does the name come from?

2:14

So the H simply stands for hepa, and the IDA

2:18

stands for iminodiacetic acid, which is the

2:21

first molecule that was labeled with Technetium-99m

2:24

and used, um, to image the hepatobiliary tract.

2:28

So we do not really use this molecule anymore.

2:30

We use derivatives of this molecule, which

2:33

have been modified, um, to come up with

2:35

molecules that have better biochemical

2:37

profiles and better imaging characteristics.

2:40

Um, so experts in the field don't really

2:41

like the name HIDA because it's not very

2:44

accurate, but we're still holding to the name.

2:46

Um, although what we use today

2:48

are modifications of this molecule.

2:50

So these molecules that are labeled with Technetium-

2:52

99m and used to image the hepatobiliary tract,

2:56

they follow the bilirubin metabolic pathway.

2:58

So we inject them IV, they bind to albumin,

3:01

and then they're transported to the liver

3:02

and excreted into the biliary system.

3:05

The difference though, is that they're not conjugated.

3:09

So the molecules that we most commonly

3:11

use today are disofenin and mebrofenin.

3:14

So the mebrofenin has the advantage of a higher

3:17

hepatic uptake compared to the disofenin,

3:20

with 98% and a lower renal excretion.

3:24

So that's why it's preferred and it is

3:27

the most commonly, um, used molecule today.

3:32

So let's start with acute cholecystitis, which is,

3:35

uh, one of the most common indications for this study.

3:37

So 90 to 95% of acute cholecystitis are calculous,

3:41

which means that they are secondary to gallstones,

3:44

and they happen because of a sequence of events.

3:47

So the process will start with gallstones

3:50

in the gallbladder, and the gallstones get

3:52

impacted in the gallbladder neck or cystic duct.

3:55

And here we have an ultrasound

3:57

image of the gallbladder.

3:58

So we see the stone that's at the level of

4:00

the gallbladder neck, and we see the wall of

4:03

the gallbladder, which is not inflamed yet.

4:06

So at this point it's difficult to know.

4:08

So gallstones are very common, and

4:09

it's difficult to know at this point, is

4:11

this gallstone truly impacted or not?

4:13

So during the study, it's important to move the

4:15

patient to see if the gallstone will move, or is

4:19

it stuck in the gallbladder neck at this point?

4:22

So once we start with a gallstone that's stuck in the neck of

4:24

the gallbladder or in the cystic duct.

4:30

This is gonna lead to accumulation of bile

4:34

within the gallbladder, and it's gonna lead to

4:36

chemical injury of the mucosa by bile salts.

4:40

And because of the obstruction, we're gonna

4:41

have increased pressure and distension, which is

4:44

gonna lead to venous and lymphatic obstruction.

4:46

And at this point we're gonna have edema and

4:48

inflammation of the wall of the gallbladder.

4:50

And that's when we are gonna have that

4:52

typical, uh, findings of acute cholecystitis

4:55

on imaging, on ultrasound or CT.

4:58

So you're gonna have a gallbladder that's

4:59

distended because it's obstructed by the gallstone.

5:02

You're gonna have edema of the wall, which is

5:04

thickened, hyperemic, and you're gonna have a

5:07

little bit of free fluid next to the gallbladder.

5:09

So this is a typical acute

5:11

cholecystitis image on ultrasound.

5:13

And sometimes you can have complications.

5:15

Also, you can have secondary bacterial

5:17

infection, necrosis, gangrene, or perforation.

5:22

So when the patient comes to the ER with suspected

5:25

acute cholecystitis, usually they're gonna start

5:28

with ultrasound or CT, which totally makes sense

5:31

because they are quick to perform, they're very

5:33

quick to perform, very quick to have the results.

5:36

And a lot of time you can have

5:37

a confident, certain diagnosis.

5:40

So on ultrasound and on CT, you

5:43

can see the gallbladder wall edema.

5:45

You can see the inflammation, a little

5:46

bit of fluid around the gallbladder.

5:49

The added value of ultrasound is that

5:51

it can show you the gallstones, okay?

5:53

So remember that gallstones are often not

5:56

calcified, so they're often radiolucent,

5:59

not opaque, and you can miss them by CT.

6:02

So if you do not see gallstones on CT, it

6:04

doesn't mean that the patient doesn't have them.

6:06

It means that you probably are not seeing them.

6:08

So when you do ultrasound, you can see the gallstones.

6:11

The CT though might show you the inflammation around

6:13

the gallbladder a little better than ultrasound.

6:16

So when would you need a HIDA though?

6:19

So if you have a patient who's coming to the ER with

6:22

suspected acute cholecystitis and these findings

6:24

on imaging, you definitely do not need a HIDA scan.

6:27

So you have a quick imaging modality that you

6:29

are able to put the diagnosis and you're done.

6:32

But this is not always the case, and the

6:35

diagnosis is often not straightforward by imaging.

6:38

So remember that gallstones are

6:39

very common in the population.

6:42

Um, and most of the time they're not symptomatic.

6:45

And there are a lot of reasons

6:47

for gallbladder wall edema.

6:48

So to just name a few.

6:49

If you have liver disease, you can have

6:51

reactive edema of the gallbladder wall.

6:53

If you have cardiac disease, you might have

6:54

congestion and then edema of the gallbladder

6:56

wall and also some fluid around the gallbladder.

6:59

Um, and if you have hyperemia also, you

7:01

can have edema of the gallbladder wall.

7:02

So basically you have a lot of scenarios

7:04

when you're not sure, is this actually

7:07

starting acute cholecystitis or is it just

7:10

not, and the pain is due to something else.

7:12

And that's when a HIDA scan can

7:14

play a very important role.

7:17

So a HIDA scan is not gonna show you

7:19

the inflammation, so you do not see the

7:21

inflammation, um, in the gallbladder.

7:24

What you can see though is, is

7:26

the cystic duct patent or not?

7:29

So that's the question that the HIDA

7:30

scan is gonna answer, which is basically

7:32

the cause of the acute cholecystitis.

7:34

So that's a very nice HIDA scan.

7:37

You inject the tracer, it goes to the liver,

7:39

and then it'll be excreted into the CBD.

7:42

So you start seeing CBD,

7:43

you start seeing gallbladder.

7:44

The gallbladder will fill with time,

7:46

and basically you have your answer.

7:48

There is no acute cholecystitis, cystic duct is patent;

7:51

no acute cholecystitis, cystic duct is obstructed.

7:54

There is acute cholecystitis.

7:55

So it's a binary study, um,

7:57

and very, uh, straightforward.

8:00

So if you're imaging for acute cholecystitis and at

8:03

this point you see gallbladder, should you just stop?

8:07

I mean, you've answered the question that

8:08

there is no acute cholecystitis, but at

8:10

this point you're not seeing small bowel.

8:12

So since the patient is there and they're on your

8:15

table, you better just continue imaging and

8:17

just make sure that the CBD is patent as well.

8:21

So do not stop the study really before you

8:23

see the small bowel and the gallbladder.

8:25

At this point, you have, you've

8:27

established that the cystic duct is patent

8:29

and CBD is patent, and you can send the

8:31

patient back with, um, an accurate diagnosis.

8:36

So let's look at how, uh, some of

8:39

the problems that might happen in an

8:40

everyday practice with HIDA scans.

8:42

So let's start with our first patient, an 80-year-old

8:45

male who's coming with right upper quadrant pain,

8:47

mildly elevated WBC, and ultrasound that's equivocal.

8:50

And so they referred for a HIDA scan.

8:53

So you learned that the patient

8:54

didn't eat for the last 32 hours.

8:56

What do you recommend?

8:58

Should you just go ahead and perform the scan?

9:00

No problem.

9:01

We'll just do it.

9:02

Would you pretreat with morphine and then

9:06

image 30 minutes later, would you pretreat

9:08

with sincalide and image 30 minutes later?

9:11

Or you just delay the study till after the next meal?

9:17

So what do you guys think?

9:18

It's very important before you bring the patient to

9:21

make sure that they're well prepped for the study.

9:23

So what do you think is, um,

9:26

a good prep for the study?

9:30

Okay, fantastic.

9:31

Great.

9:33

So yes, you need to prep with—

9:40

So for patient preparation for a HIDA

9:42

scan, you need the patient to be NPO for

9:44

four hours, but not more than 24 hours.

9:46

Why?

9:47

Because, um, any meal when the patient eats,

9:50

um, the meals that when they come to the

9:52

small bowel, they are gonna induce the production

9:55

of cholecystokinin, and cholecystokinin

9:57

is gonna induce gallbladder contraction.

10:00

And as long as the gallbladder is subject to

10:03

CCK and is contracting, it might not

10:05

take up the radiotracer because of that, because

10:08

it's just reacting to the fact that there

10:10

was a recent meal that went to the GI tract.

10:12

So you might have a false positive study.

10:15

And you want the patient to be NPO for not more than

10:17

24 hours because if it's been more than 24 hours, then

10:20

the gallbladder might be already full with viscous

10:23

bile and might not take the tracer because of that.

10:26

So if the patient did not eat in the last 24

10:29

hours, you would wanna pretreat with sincalide.

10:31

So what is sincalide?

10:32

Sincalide is a cholecystokinin analog.

10:35

It's gonna promote gallbladder contraction,

10:37

so it's gonna help the gallbladder empty.

10:39

And, um, so it can take the radiotracer that

10:42

you're gonna give. The dose is

10:45

important, especially for both purposes.

10:47

So also, remember, always remember 0.02

10:50

microgram per kilogram, so you can infuse it over

10:53

30 to 60 minutes and then give the gallbladder

10:55

30 minutes to relax before you start the study.

11:00

Morphine, on the other hand, is an opiate,

11:03

so it's gonna contract the sphincter of Oddi.

11:05

So when you have a sphincter of Oddi that's

11:07

contracted, this is gonna mimic biliary obstruction.

11:10

And so you don't wanna do a study and

11:12

then not see small bowel and not be

11:14

sure, is the CBD obstructed or not?

11:16

So that's why it's recommended to withhold the opiates

11:19

for at least, um, three half-lives before the study.

11:23

So morphine has a very important role later on.

11:25

Um, and we'll see that in a little bit.

11:28

So the patient comes to the ER, to

11:29

our department, they get imaged.

11:31

So here we have the first 60 minutes of imaging.

11:36

So we see the CBD, we see

11:38

tracer going to the small bowel.

11:40

So CBD is patent, great, but we're

11:41

still not seeing the gallbladder.

11:44

So what do we do at this point?

11:46

We have two options.

11:48

We can give morphine since we see small bowel,

11:50

so we're not worried that there might

11:51

be CBD obstruction, that if we give morphine, we might mask it.

11:55

So, uh, we can give the morphine and close

12:00

the sphincter of Oddi and try to push this

12:01

radiotracer into the gallbladder.

12:04

So the dose is also important for morphine,

12:06

0.04 milligram per kilogram over one minute.

12:10

And you might need a booster of radiotracer

12:12

because by the end of the one hour you might

12:14

have very, very little tracer left in the liver.

12:16

So you might wanna give a booster

12:18

dose to have more tracer on board.

12:20

And then you image for 30 more minutes.

12:22

And then at the end of the 30 minutes, if you

12:25

see gallbladder, then cystic duct is patent.

12:28

And you are done.

12:29

If you don't see gallbladder,

12:30

then there is acute cholecystitis.

12:33

So what's the alternative?

12:34

If you cannot give morphine for some reason, like

12:36

you don't see small bowel, or the patient just

12:38

cannot have morphine, you can always image, uh,

12:41

four hours after; you could do four-hour delayed.

12:43

And both techniques have the same

12:45

accuracy to detect acute cholecystitis.

12:48

So one important point here is the diagnosis.

12:52

If you don't see gallbladder by one hour,

12:55

if the patient is coming in acute setting,

12:56

you're worried about acute cholecystitis.

12:58

If the patient is coming in chronic

13:00

setting, then it's, it's clinically, you

13:03

know that it's not acute cholecystitis.

13:05

So then it's probably some chronic inflammation.

13:07

So we'll go over that, um, in a little bit.

13:11

So we give morphine in this case, and we are still

13:15

not seeing gallbladder by the end of the 30 minutes.

13:18

So we have our diagnosis, uh, our diagnosis

13:21

of acute cholecystitis, and this is

13:23

highly sensitive and highly specific.

13:27

So let's go for another case.

13:29

So this is a 70-year-old female who's coming for

13:32

right upper quadrant pain and equivocal ultrasound.

13:34

So she comes for a HIDA scan, and

13:37

we do the first 60 minutes.

13:39

So if by the end of the 60 minutes you're,

13:41

you're not sure whether you start to see

13:43

gallbladder or not, you can always give morphine.

13:45

Even if the gallbladder started to fill,

13:47

you can give morphine and just promote the

13:49

filling of the gallbladder to be certain.

13:51

So here we're not sure that

13:53

we're seeing gallbladder at all.

13:54

So we go ahead and give morphine, and at the end of

13:59

the 30 minutes we see these two foci of tracer here.

14:03

So the gallbladder here, not really certain.

14:06

It usually is a little bit higher than that.

14:08

So that's basically where the fossa is, inferior.

14:14

So remember, you always have problem-

14:16

solving tools in nuclear medicine.

14:18

So you could always start with lateral imaging.

14:21

So in lateral imaging, the gallbladder is supposed to

14:23

be anterior, while duo is a little bit more posterior.

14:27

So sometimes you can tell them apart.

14:28

Sometimes though, like in this

14:30

case, this wasn't very helpful.

14:31

So what you can do, you have a very good friend in

14:34

nuclear medicine, and this friend is called SPECT/CT.

14:37

So whenever you're not sure and you need more

14:39

anatomical details, you can go ahead and do SPECT/CT.

14:42

So we did a SPECT/CT here and we see that the

14:45

gallbladder did not fill with tracer at all,

14:48

and that the radiotracer that we saw is in

14:51

a duodenal diverticulum next to the gallbladder.

14:55

So remember to always, um, that you have your good

14:58

friend the SPECT/CT even for unusual indications.

15:01

So even if you've never done a SPECT/CT for

15:03

this indication before and you think it might

15:05

be helpful, you can always go ahead and do it.

15:07

Uh, and sometimes it's gonna be problem solving.

15:10

So there is a little bit of uptake that we see here

15:13

in the liver parenchyma just next to the gallbladder.

15:16

So we think it might be an early rim sign.

15:18

So what is the rim sign?

15:21

We see this in about 25 to 35% of acute

15:24

cholecystitis, where we have this radiotracer in

15:26

the liver parenchyma next to the gallbladder fossa.

15:29

So we see this as, as so.

15:32

So it basically reflects that there

15:33

is liver inflammation here, so there's

15:35

hyperemia, the tracer comes here at a higher

15:38

rate, and then it stays in this region.

15:40

So this is associated with more severe

15:42

disease when there's a high risk of

15:43

complication like perforation and gangrene.

15:48

So this is another case, um, of a

15:50

patient who came with right upper

15:51

quadrant pain and equivocal ultrasound.

15:53

So this is a nice example of an

15:54

equivocal ultrasound in any ER setting.

15:56

So the patient comes with pain, um, and then

15:59

you're imaging, you see gallstones in the,

16:00

in the gallbladder, but you're not clearly

16:02

seeing the gallbladder neck or the cystic

16:05

duct to make sure that there's no stone there.

16:08

And there's a tiny bit probably of

16:09

gallbladder edema, but it's not reaching

16:12

the threshold to call acute cholecystitis.

16:14

So this is a very good scenario

16:16

where HIDA scan might be helpful.

16:18

So you go ahead and you do the HIDA scan.

16:21

So by the end of the first 60 minutes,

16:23

we're still not seeing gallbladder.

16:26

We go ahead and give morphine, and we see this here.

16:31

So it's really important to recognize what this is.

16:35

So this is a cystic duct, right?

16:38

So this is tracer in the cystic duct.

16:40

The gallbladder is obstructed, and the

16:42

gallbladder, you'd expect it to be larger here.

16:44

This is just the first portion of

16:46

the cystic duct that's filling with

16:47

tracer, but not the whole gallbladder.

16:49

So if you see this, do not confuse it

16:51

with early filling of the gallbladder.

16:53

Okay?

16:54

So this is not early filling of the gallbladder.

16:56

This is cystic duct sign, and it is a common

17:01

sign in the setting of acute cholecystitis.

17:03

So this is another cystic duct sign.

17:05

This is a more prominent one.

17:08

So this is the CT of the same patient.

17:10

So you see the gallbladder is distended, and

17:12

there is edema of the wall of the gallbladder.

17:14

So this is like a way smaller, um, structure.

17:17

So this is not the whole gallbladder.

17:20

So the gallbladder is not filling.

17:22

Um, so this patient has ovarian cancer also, and

17:25

she has a large mucinous, um, tumor in her abdomen.

17:28

And that's why, um, we're seeing this neoplasm here.

17:31

And this is a scan diagnostic of, um, acute

17:34

cholecystitis and the cystic duct sign.

17:36

You're gonna see it most commonly after

17:38

you give morphine because basically

17:40

you restrict the sphincter of Oddi

17:43

and you're forcing the tracer to go back.

17:45

So it's gonna go back at a higher rate

17:46

and fill the cystic duct like this.

17:50

So this is a new case with right upper quadrant

17:52

pain, nausea, vomiting, and, uh, white blood counts.

17:56

So we image over the first 60 minutes.

18:00

What do you think we should do now?

18:03

So we're still not seeing gallbladder by

18:06

the end of the 60 minutes, what would you do?

18:13

Would you give morphine at this point,

18:15

image four hours after, give sincalide,

18:18

or would you do a SPECT/CT?

18:23

Okay, great.

18:24

Fantastic.

18:25

So remember, do not give morphine if

18:27

you're not seeing small bowel, right?

18:30

So by the end of the 60 minutes, if you're not seeing

18:33

small bowel, what's your differential at this point?

18:36

So we have delayed excretion from the liver.

18:40

The differential is either we have a

18:42

complete CBD obstruction, or we might

18:45

have hepatocellular dysfunction.

18:47

Okay?

18:47

So we really wanna image four hours after.

18:53

So this is the imaging after four hours, and we still

18:55

see a lot of radiotracer on board in the liver.

18:58

So this is, we have really delayed

19:00

pharmacokinetics here, right?

19:03

So the patient underwent an MRI, and we see the CBD.

19:06

The CBD is completely clear.

19:08

It's a very nice, non-dilated

19:10

CBD with no filling defects.

19:12

So there is no CBD obstruction here.

19:14

This patient had acute hepatitis, so if you

19:17

have hepatocellular dysfunction, you're gonna

19:19

have delayed pharmacokinetics and delayed

19:22

uptake and clearance of the radiotracer.

19:24

And the clearance is even more

19:25

important than the delayed uptake.

19:27

Sometimes the uptake of liver is not really

19:30

impaired, but you have, like, the clearance

19:33

just takes a very long time, so you're not

19:36

seeing the radiotracer leaving the liver.

19:37

So by four hours you should not see

19:39

radiotracer in the liver anymore.

19:41

It should be all excreted normally.

19:43

So here the liver is just retaining this tracer

19:46

because, um, it's just not functioning well.

19:50

And here you see there is edema of the

19:52

gallbladder, and this is, um, reactive

19:54

to the liver pathology, to the hepatitis.

19:57

So if you're not seeing small bowel, do four-

20:00

hour delayed, and this is gonna really help you.

20:03

And the anatomic imaging, of course, just making

20:06

sure that there is no biliary obstruction.

20:08

That's how we can be able to exclude a complete CBD.

20:14

Now let's talk a little bit about

20:15

acute acalculous cholecystitis.

20:18

So, although the vast majority of acute

20:20

cholecystitis are secondary to gallstones,

20:22

some of them rarely are not secondary

20:25

to gallstones, and they're acalculous.

20:28

So although they're uncommon, they're life-

20:30

threatening, and we often see them in ICU settings.

20:32

They have high mortality, high morbidity, and

20:35

the cause could be cystic duct obstruction

20:37

from another cause, like from some inflammation,

20:40

or debris, or inspissated bile, or could be

20:42

not secondary to cystic duct obstruction.

20:44

Could be secondary to inflammation of the

20:46

gallbladder wall because of other causes,

20:47

like systemic infection or ischemia.

20:50

So in this case, the imaging is the same.

20:52

So the findings on ultrasound and CT are

20:55

the same, without the gallstone, of course.

20:57

Um, and on HIDA scan we're looking for the same thing.

21:00

So the findings are the same.

21:01

We're looking for obstruction

21:02

of the, uh, cystic ducts.

21:05

But because they're acalculous,

21:07

they have lower sensitivity.

21:08

So the HIDA scan has lower sensitivity of about 80%.

21:11

So if the clinical scenario is really,

21:14

really suggestive of acute cholecystitis,

21:17

but the HIDA scan is normal, you could

21:19

consider doing an Indium-111 WBC.

21:23

And so if there is, um, infection or

21:25

inflammation of the gallbladder, you

21:26

might be able to see it on the WBC scan.

21:31

Now let's look at some of the chronic

21:33

pathologies of the gallbladder.

21:35

So the most common chronic pathologies, uh,

21:38

of the gallbladder are two entities — calculus,

21:41

chronic cholecystitis, and biliary dyskinesia.

21:44

And they're very similar to the clinician because they

21:46

have very similar symptoms of recurrent biliary colic.

21:49

And post-prandial pain treatment is the same —

21:52

cholecystectomy. Pathology is the same.

21:55

We have chronic inflammation of the gallbladder wall.

21:57

The difference though, is we can

21:59

tell the difference by imaging.

22:01

If the patient has gallstones, then it's

22:03

calculus, chronic cholecystitis. Or if there

22:05

are no gallstones, then it's biliary dyskinesia.

22:08

So that's really the main difference.

22:10

It's the presence of gallstones.

22:12

Now on HIDA scan, remember, like we said

22:15

initially, so if the patient is coming in an

22:17

acute setting and we image and we don't see

22:19

gallbladder by one hour, that's not normal.

22:22

Like usually you should see

22:23

gallbladder by the end of one hour.

22:25

So if the patient is coming in an acute setting,

22:28

we're worried about acute cholecystitis.

22:30

So then we give morphine or we do delayed imaging.

22:32

If the patient is coming in a non-acute setting, so

22:34

they're coming as outpatient to your department,

22:38

if you don't have gallbladder filling by

22:39

one hour, this is a very, very

22:42

reliable sign for chronic cholecystitis.

22:46

Now if the gallbladder fills

22:47

by one hour, this definitely

22:49

does not exclude the diagnosis.

22:51

Here,

22:51

you're gonna have to go ahead and do

22:53

the gallbladder ejection fraction.

22:55

So if you have poor gallbladder ejection fraction,

22:57

um, this is suggestive of chronic biliary pathologies,

23:00

and this can be seen with both entities.

23:02

So we're gonna talk about it a little bit.

23:04

So the clinical role of the HIDA scan — if you have

23:06

a normal HIDA scan, normal gallbladder ejection

23:08

fraction, then the pain is not due to the gallstones.

23:11

So gallstones are very common in the

23:13

population and they're not always causing problems.

23:15

So if you have a normal, uh, HIDA scan, then

23:19

the gallstones are not causing problems.

23:20

There's another cause for the pain.

23:23

Biliary dyskinesia —

23:24

also, if you have a normal gallbladder ejection

23:26

fraction, you're basically excluding the disease.

23:30

So this is a patient, a young patient,

23:33

who's coming for chronic abdominal pain.

23:35

So we start by doing the first 60 minutes, and

23:38

we see a really nice filling of the gallbladder.

23:43

We give sincalide.

23:44

So as a reminder, the sincalide

23:46

is a cholecystokinin analog, and it's

23:48

gonna promote gallbladder contraction.

23:50

So we cause the gallbladder to contract, and

23:53

we look at how it is contracting over time.

23:56

So here we see it emptying really well.

24:00

So we can compute that by putting a region

24:02

of interest and measuring the counts in

24:04

the gallbladder and how they're emptying.

24:06

So we see it emptying really well,

24:08

with an ejection fraction of 72%.

24:10

And this is the formula for the

24:12

ejection fraction, where you have the

24:15

maximum counts in the gallbladder minus

24:17

minimum counts over the maximum counts.

24:19

And so —

24:23

How do we calculate the gall-

24:24

bladder ejection fraction?

24:25

So how much sincalide should we give,

24:27

and how long should we image?

24:28

So there have been a lot of studies, um,

24:31

studying this with multiple methods of injecting

24:35

sincalide at different doses and different infusion times.

24:38

So the two techniques that have been shown to be the

24:40

most reproducible and most reliable are these two —

24:44

either giving, um, sincalide as 0.015 microgram per

24:50

kilogram and image over 45 minutes,

24:53

and with this technique, you want a gallbladder

24:55

ejection fraction higher than 40% to call the

24:58

study normal. Or you can give 0.02 microgram per

25:02

kilogram and image over an hour,

25:05

and for this technique, you need an

25:07

ejection fraction higher than 38%

25:09

to call it normal.

25:12

So these two are the most reliable techniques.

25:16

Some people still use

25:17

the 30-minute timeframe.

25:21

And then you're gonna have other thresholds.

25:25

So it's important to look at the threshold

25:27

for the technique that you're using.

25:29

So fatty meals have been used in the past

25:33

as an alternative to giving sincalide

25:35

because they're gonna promote gallbladder

25:36

contraction, but they are not as reproducible.

25:39

So basically, the response of the gallbladder

25:41

is gonna depend on the size and the type

25:44

of the fatty meal that we're giving,

25:46

and we don't have really normal values for that.

25:49

So we don't know what the normal

25:50

gallbladder ejection fraction is if

25:52

we give a certain amount of food.

25:54

So, um, this is really not

25:57

the best way of doing it.

26:01

So this is another example where we

26:04

image the gallbladder ejection fraction,

26:07

and here the gallbladder

26:09

ejection fraction is poor,

26:12

at only 20%.

26:14

So this patient has chronic gallbladder disease.

26:18

So there's a misconception that reproduction

26:20

of the patient's pain with sincalide

26:23

infusion is diagnostic of gallbladder disease.

26:26

So that's really not true because sincalide can cause

26:30

small bowel peristalsis, which can be painful.

26:34

So, um, if the patient is having pain, this is

26:37

not really diagnostic of gallbladder disease.

26:42

So now let's go to another set of

26:45

pathologies, especially after surgery.

26:49

So this is a patient who's coming, um,

26:51

after cholecystectomy, and they have

26:53

abdominal pain, severe nausea, and vomiting.

26:55

So we often get ultrasound or CT, and if you

26:58

have fluid in the abdomen after cholecystectomy,

27:01

then you know what you're suspecting, right?

27:03

You're suspecting a bile leak.

27:06

So we give the radiotracer, and

27:08

here we see a very nice leak.

27:10

So this is not going into the small bowel,

27:12

this is going into the peritoneal

27:14

cavity underneath the left diaphragm.

27:17

Um, so this is diagnostic of a —

27:21

so it doesn't always go under the left diaphragm.

27:24

It can go into the right pericolic gutter,

27:26

or it can diffuse in the peritoneum.

27:30

This is another case where after we give — so this

27:34

is also after cholecystectomy presenting with pain,

27:37

and after we start the HIDA scan, we see that the

27:40

radiotracer is going into the gallbladder fossa.

27:42

So normally, if the patient is after

27:44

cholecystectomy, the tracer should not

27:46

accumulate in the gallbladder fossa.

27:48

So here it comes to the fossa, and we see

27:51

that it accumulates around the liver.

27:55

And when you look at our anatomic imaging,

27:58

there is indeed fluid around the liver.

28:00

So this is also bile leak.

28:02

And you can also use this

28:04

to see if there is a biloma.

28:06

So sometimes you have bilomas in the liver,

28:08

and they're gonna retain tracer afterwards.

28:12

And always remember that if the patient

28:14

has a drain and the drain is working well,

28:16

then your bile leak is draining into the sac.

28:20

So if you have a drain in place, you

28:23

might see the leak going into the sac and not

28:25

actually diffusing into the peritoneal cavity.

28:28

So keep that in mind.

28:31

Now let's go to GI bleed scans.

28:36

So we have a patient who's coming

28:37

to the ER with active GI bleed.

28:41

Usually we start by doing a CTA, right?

28:44

So it's a very quick study, it's very easy to

28:46

perform, and you really want to do non-contrast,

28:49

arterial phase, and delayed phase. In the GI bleed,

28:53

you should see contrast extravasation that you

28:55

see on the arterial phase that was not present

28:58

on the non-contrast phase and that accumulates

29:02

further on the portal venous or delayed phase.

29:04

So this is a nice case of active

29:08

bleeding from a colonic diverticulum.

29:11

So why would you?

29:13

Um, so, and here it is on the coronal

29:15

view as well, and sometimes it can move

29:17

retrograde and not always antegrade.

29:20

So why then you might need to do

29:23

a nuclear medicine GI bleed scan.

29:27

Does it provide better anatomic localization

29:29

of the bleed, or you really shouldn't do it?

29:32

It shouldn't be done anymore.

29:33

It has no advantages over the CTA, or

29:36

is it more convenient to the patient,

29:38

or is it more sensitive than the CTA?

29:42

I hope no one answers B.

29:46

Okay.

29:49

So it is more sensitive than CTA.

29:51

Fantastic.

29:51

It is definitely way more sensitive than CTA.

29:56

So why then you might need to do a GI bleed scan?

30:00

So with GI bleed scans, you can image over 90 minutes.

30:03

So typically you image between 60 to 90 minutes.

30:06

So if you're not seeing a bleed over the first

30:08

60 minutes, you might wanna extend over 90

30:10

minutes, and you can even do longer imaging.

30:14

And also it can detect lower rates of bleeding.

30:17

So it is much more sensitive.

30:18

It's sensitive for as low as 0.05 to 0.1 milliliters

30:22

per minute versus 1 milliliter per minute rate

30:25

of bleeding for angiography to detect the GI bleed.

30:28

So it is tenfold more sensitive than angiography.

30:31

So the two scenarios when the GI bleed scan is

30:33

really helpful are the intermittent bleed

30:35

and the low-rate bleeds.

30:38

So that's when you really need the scan.

30:41

And it's very important to keep in mind that

30:43

we know that the patient has a GI bleed, right?

30:46

We just need to localize where the bleed is.

30:48

So if the patient is just coming — they need

30:50

to have blood per rectum in order to do the GI

30:54

bleed scan, because if we're just looking, there's

30:56

like a drop in hemoglobin, or we're suspecting

30:58

there's a bleed somewhere, then they should go

31:00

to CT, and they should not come to GI bleed scan.

31:03

Okay.

31:03

So this is just gonna diagnose if there is

31:05

an active bleeding occurring in the bowel.

31:10

So we give technetium-labeled RBC for the scan,

31:15

and the labeling issue is really important.

31:18

Um, so if we have poor labeling of the red

31:21

blood cells with technetium, then we're gonna

31:22

have a lot of tech-free pertechnetate on board.

31:25

And if you have a lot of free pertechnetate on board, this

31:28

is gonna degrade the quality of the images — we're gonna

31:30

have poor target-to-background, but also we are gonna

31:32

have uptake in salivary glands and gastric mucosa.

31:35

And subsequently, this tracer is gonna be

31:38

secreted into the GI tract and is

31:40

gonna decrease our accuracy for the study.

31:43

So here, bear with me over the next couple

31:46

of slides because I'm gonna go over the

31:48

labeling process, which is really important

31:50

to know, especially for board purposes.

31:53

So we need a good radiolabeling efficiency,

31:56

and here comes the tin process.

31:58

So what does that mean?

31:59

So you have the red blood cells,

32:01

and the red blood cell has the hemoglobin

32:04

within it, and we need the pertechnetate to come

32:07

and label the beta chain of the hemoglobin.

32:09

But in order to label the beta chain of

32:11

the hemoglobin, we need to reduce the pertechnetate.

32:14

So this has to happen within the red blood cell.

32:17

So we need to have protein

32:19

within the cell and stannous ion.

32:21

We give the stannous ion, and it needs to diffuse within

32:23

the cell and reduce the pertechnetate in the red blood cell.

32:26

And then we're gonna have reduced pertechnetate that's able

32:30

to bind to the beta chain of the hemoglobin.

32:34

So remember, this process has to

32:36

happen within the red blood cells.

32:38

So if you have pertechnetate that gets reduced

32:42

outside the red blood cells, this is

32:44

just gonna give you more free pertechnetate,

32:46

and it's gonna reduce your labeling efficiency

32:50

and degrade the quality of your images.

32:53

So there are several ways of labeling.

32:55

We have first the in vivo labeling,

32:58

where you just give the IV stannous ion,

33:00

you wait 10 to 30 minutes, and you give them the pertechnetate.

33:03

So the efficiency is in the order of 75 to 80%.

33:06

So you still have quite a bit of,

33:08

um, tracer that's outside the cell.

33:12

A little better method is the modified

33:14

in vivo, where you give the IV stannous ion,

33:18

and then you wait 10 to 30 minutes.

33:20

You take some blood into a syringe

33:21

that contains pertechnetate and anticoagulant,

33:24

you mix it, and then at this point, you expect

33:26

that the pertechnetate had diffused into the cells and was

33:29

reduced and is labeled to the hemoglobin chain,

33:33

and then you re-inject.

33:35

So this has a higher labeling efficiency,

33:37

but still, like, not the greatest.

33:39

So in vitro is the best method

33:41

for labeling efficiency.

33:43

You can take out blood from the patient,

33:45

centrifuge and separate the red blood cells

33:48

from the serum, and then you radiolabel

33:50

the red blood cells, and you re-inject.

33:52

So it has a very high labeling

33:54

efficiency, but it's a very involved process.

33:57

So an easier process with almost the same labeling

34:01

efficiency is the in vitro with a commercial kit.

34:04

So you have a commercial kit, you withdraw blood,

34:07

you add it to a reaction vial that contains

34:09

stannous ion, and then you add sodium hypochlorite

34:12

to wash out whatever, uh, whatever you have,

34:14

like stannous ion that's outside the cell.

34:17

And then you add the pertechnetate, which is gonna

34:19

go into the red blood cells and get reduced

34:21

and label the, um, beta hemoglobin.

34:25

You incubate for 20 minutes and then you inject.

34:28

So with this process — this process is less subject

34:31

to drug-to-drug labeling interference and to

34:34

problems of excessive, um, or deficient stannous ion.

34:39

So it is very simple for technologists to perform, and

34:42

so that's why this is the most preferred method today.

34:46

So let's look at some cases.

34:48

So in order to diagnose a GI bleed, we

34:52

need a radiotracer activity that — first, it must

34:54

appear where there was no radioactivity before.

34:57

It must increase over time, and it must move

35:00

in a pattern consistent with bowel anatomy.

35:02

So these are the three conditions

35:05

to diagnose GI bleeds on the scan.

35:08

So remember, it can move in the bowel

35:10

anatomy antegrade or retrograde.

35:12

So let's look at our first case.

35:14

So first we do our angio images,

35:17

where you give the tracer and then you

35:20

image with just two seconds per frame.

35:22

So basically this is, um, very low counts

35:25

per frame, so that's why they're so noisy.

35:27

But they're gonna help you to see if

35:28

there's any, um, like, the vascular anatomy,

35:31

and if there are hyperemic lesions.

35:33

And then later on you start imaging

35:34

with, um, one minute per frame.

35:38

So here you have better quality,

35:40

higher counts per frame.

35:43

So we're gonna look for a tracer that's gonna

35:45

appear where there was no tracer before.

35:47

So we started to see something here in the

35:49

mid-abdomen, and then it's increasing over

35:51

time and it's moving in a bowel anatomy.

35:54

So that is a typical GI bleed.

35:57

And this is originating from the ileum. So

35:59

remember, we need to localize where the bleed

36:01

is because that's where, like, this is

36:04

gonna help IR to go and target the vessels that

36:08

they think are responsible for the bleeding.

36:10

So this is a nice example of ileal bleed, and

36:15

if you start seeing a bleed by the end of

36:17

your imaging time — there is no solid rule

36:19

that you can image only for 90 minutes.

36:21

You can keep on imaging to make

36:23

sure how this tracer is gonna move.

36:25

So it's gonna help you localize the bleed better.

36:29

So this is the second case.

36:31

Also, the patient is coming with GI bleed.

36:34

So we start the angio phase and then our imaging.

36:41

And I hope you can see that there's

36:43

something in the left upper quadrant.

36:45

So we need to see how this tracer is moving.

36:49

Is it like in the stomach, or is it in the jejunum?

36:52

And here it moves nicely in the jejunal

36:54

pattern at the end, and it comes inferiorly.

36:58

So this is a nice case of active jejunal bleed.

37:01

If you're not sure, you can keep on imaging

37:02

and see how it's gonna move, and make sure that

37:04

it is actually jejunum instead of stomach.

37:08

So this study is not indicated for upper GI bleeds.

37:11

So if you're suspecting esophageal or

37:13

gastric bleed, this is not the study to do.

37:15

But sometimes the patient can be sent — they're

37:18

having melena, and we're not sure, is it, like,

37:20

upper or lower GI bleed, and they get a GI bleed scan.

37:23

So at this point, um, you might

37:25

encounter an upper GI bleed.

37:27

So if you're not sure — remember,

37:28

like we talked about, um, poor labeling.

37:32

So if you have poor labeling and free pertechnetate on board,

37:35

um, you might have uptake in the stomach.

37:37

So how can you make sure that there's

37:39

actually gastric bleed or free pertechnetate?

37:43

So you could do images of the neck.

37:45

So if you have thyroid and salivary gland uptake,

37:47

this means that you have free pertechnetate on board.

37:50

Um, and probably the uptake in the stomach

37:52

could be secondary to free pertechnetate.

37:54

And you could use this also to see if you're

37:57

suspecting that you have poor labeling.

37:59

So if you're suspecting free pertechnetate,

38:01

remember — take images of the neck.

38:06

Okay, so this is a patient

38:07

who's coming with blood per rectum.

38:10

So I'm gonna show you the case, and

38:12

then there's a question after that.

38:16

So the angio phase looks okay, and

38:20

then, oh, we're seeing something.

38:25

So what do you think of this uptake pattern?

38:33

What's your impression on this scan?

38:39

Is it a normal scan?

38:41

Just physiologic?

38:43

You think there's an active rectal bleed?

38:45

Are you concerned for hyperemic mass in the

38:47

pelvis — you would evaluate a CT — or this is likely

38:52

urinary contamination due to incontinence?

39:01

So these are your images.

39:07

So remember, we need a tracer that

39:09

appears where there was no tracer before,

39:12

that's increasing over time, and

39:14

that's moving in a bowel pattern.

39:21

There's active activity.

39:22

So this is a very — this is a very confusing

39:28

uptake pattern, and that's why I wanted to

39:31

show this case, because this is typical uptake

39:36

of penile blood pool.

39:39

So what might help you in this

39:41

case is to get lateral images.

39:43

So you have the bladder here, and you have — so

39:47

this is anterior, this is posterior, and this

39:49

uptake is anterior where the vessels are, right?

39:53

So if you wanna go back, so you have the

39:54

femoral vessels and this uptake here, and

39:57

they're basically at the same location.

40:00

And also one other thing — if you look at the last

40:02

images here, where you see the urinary bladder,

40:05

so the rectum can be a little bit lower, can extend

40:08

lower than the urinary bladder, but not that low.

40:11

So this is very low for the rectum, right?

40:13

So you look at where the bladder

40:15

is, look at where this uptake is.

40:18

So this is very low for, um, for rectal bleeds.

40:21

And this is a typical, uh,

40:23

pattern of penile blood pool.

40:25

And this is very commonly seen.

40:27

So other

40:29

findings in the pelvis that might be confusing

40:31

is if we have activity in the bladder, if the

40:33

bladder shape is not typical, or if we have some

40:36

uptake in the uterus, especially with menses.

40:38

And in these cases also, laterals might

40:41

help because if you have rectal uptake, you

40:43

would expect rectal uptake to be posterior,

40:45

but also you could do a SPECT/CT as well.

40:49

So this is another case.

40:51

I'm gonna show you the video here.

40:53

So I am not showing the angio phase,

40:55

I'm just showing the uptake after that.

40:57

So now I think we all know

40:59

that this is penile blood pool.

41:00

The patient is a little bit, um, so they're

41:03

not straight AP, they're a little bit oblique.

41:07

And I wanna draw your attention to this here.

41:14

So by the end of the study, we

41:16

start seeing bladder accumulation.

41:18

So —

41:19

we see, like, this tracer that's

41:21

moving at this location, right?

41:24

So if you are not sure, as we said, you

41:27

could do laterals, you could also do a SPECT/

41:30

CT, and here we did a SPECT/CT, and this shows

41:33

really nicely the uptake in the rectum.

41:35

So you see where the penile activity

41:36

is and where the rectal bleed is.

41:39

So we have the penile activity here, rectal bleed.

41:42

So the rectal bleed could extend a little

41:44

bit more inferior into the bladder.

41:45

So we have the tracer of the bladder here.

41:47

Rectum can extend a little bit

41:49

inferiorly, but not that inferior, right?

41:52

So this is the penile blood pool, the tracer

41:55

in the rectum, and the bladder right here.

41:58

So this shows really nicely that tracer

42:02

in the rectum and confirms that GI bleed.

42:07

So this is a case of a young patient

42:10

who's coming also with blood per rectum.

42:13

So we do our imaging, and I wanna draw

42:17

your attention to this uptake here.

42:21

So you remember the three rules?

42:23

We need to see uptake where

42:24

there was no uptake before.

42:26

So this is, um, an uptake

42:29

that wasn't present initially.

42:30

It's increasing over time also.

42:32

That's true.

42:33

It's increasing over time.

42:34

But is it moving in a bowel pattern?

42:39

It is not.

42:39

Right?

42:40

So it's not moving in a bowel pattern.

42:42

What is this?

42:44

So you remember, if you have, like, correlation

42:46

to anatomic imaging, if you have anatomic

42:48

imaging, it is extremely helpful, right?

42:51

So the patient did have a CT.

42:55

The patient — the right kidney is where it should

42:58

be, but the left kidney is ectopic in the pelvis.

43:01

So this was uptake in the left kidney,

43:05

um, collecting system at pelvis.

43:08

So it's really important, when you're not seeing

43:10

an uptake pattern that's typical of bowel,

43:12

you could always either, like, look at the

43:16

imaging, if the patient had other imaging,

43:18

there's something to explain this uptake or not.

43:20

And if there's nothing to explain the

43:22

uptake, you can always do a SPECT/CT.

43:24

So it's your friend in nuclear

43:25

medicine — SPECT/CT is really your friend.

43:27

You can use it whenever there's a need to.

43:33

So I'm gonna show you this case as well.

43:37

We see this here and this uptake here.

43:41

And now we all know that this is penile blush, and we

43:44

see the bladder accumulating by the end of the study.

43:47

So are we seeing anything moving in a bowel pattern?

43:51

Not really.

43:52

Nothing moving in a bowel pattern here.

43:55

But what is this?

43:59

So the patient happened to have renal cell carcinoma

44:02

and metastasis to the right pelvic bones.

44:05

So hyperemic lesions will show uptake with

44:08

red blood cells, and they will look like this.

44:11

So, and I'm mentioning this specifically because if you

44:14

have a colon cancer — so patients who are presenting

44:16

with bleeding — colon cancer is in the differential.

44:18

And if you have a colon cancer,

44:20

it might look exactly like that.

44:22

So this is not a bleed — active bleed —

44:25

if it's not moving in the bowels.

44:27

So, but it is a hyperemic lesion

44:29

that is an abnormal finding.

44:33

If you have inflammation, like, for example, Crohn's

44:35

disease or ulcerative colitis, you might see

44:38

hyperemia that's in the pattern of the inflamed bowel.

44:41

But also, you're not gonna see — if it's not

44:43

actively bleeding, you're not gonna see a tracer

44:46

that's moving in the pattern of the bowel.

44:48

Okay.

44:49

So pay attention to the pitfalls on this imaging.

44:52

Um.

44:53

So they're not uncommon, and anatomy is gonna help

44:57

you, like, if they have a CT; if not, do a SPECT/CT.

45:03

Now let's go to Meckel scan.

45:06

So when kids come with GI bleeds, um, if the patient

45:12

is actively bleeding, we should consider getting a GI

45:15

bleed scan to see where the bleeding is coming from.

45:17

But if they're not actively bleeding right

45:19

now, but they have history of melena or blood

45:22

per rectum, then we could consider Meckel scan to

45:25

see if this is the cause of the bleeding.

45:27

So this is the most common

45:28

congenital anomaly of the GI tract.

45:30

It arises from the antimesenteric side of the small bowel.

45:35

And a rule that's very helpful to remember

45:38

is the rule of twos for Meckel scan.

45:41

So it affects 2% of the

45:42

population, two feet approximately

45:44

from the ileocecal valve, two inches of length —

45:47

can be a little larger, but typically

45:49

two inches of length — and half of patients

45:52

are symptomatic before the age of two.

45:55

We have two types of mucosa, which

45:56

typically is pancreatic and gastric, and

45:59

the male predominance is two over one.

46:01

And in adults, it is symptomatic in only 2% of cases.

46:06

So we have two types of mucosa, right?

46:09

So gastric mucosa — heterotopic gastric

46:12

mucosa — can be present in 30 to 50%

46:15

of patients with Meckel diverticulum.

46:16

So it's basically, like, best

46:18

case scenario in 50% of cases.

46:20

So why do we do the scan when

46:21

the patient's having a GI bleed?

46:23

Because the heterotopic gastric mucosa is

46:26

present in 98% of diverticula that are bleeding.

46:32

So when you have bleeding, most likely it is secondary

46:34

to the presence of heterotopic gastric mucosa.

46:36

So that's why we do the Meckel scan.

46:40

We use technetium pertechnetate, and the pertechnetate is

46:43

gonna be taken up by the gastric mucosa.

46:46

Right?

46:46

And so, and since the bleeding Meckel's

46:49

diverticulum usually has gastric

46:51

mucosa, that's what we're looking for.

46:54

We need to prep the patient beforehand.

46:56

And most commonly, we prep them with H₂ blockers.

46:59

So H₂ blockers are just gonna inhibit

47:01

the pertechnetate release from the gastric mucosa.

47:04

So they're gonna stick there,

47:07

so you're gonna be able to see them.

47:09

Either PPIs, if you don't have H₂

47:11

blockers, but H₂ blockers are preferred;

47:14

glucagon in non-diabetic patients.

47:16

Um, it reduces the peristalsis.

47:17

So if you have pertechnetate that's secreted by the

47:21

Meckel's diverticulum, this is gonna reduce

47:22

the peristalsis and the transit of secretate.

47:25

So you'd be able to see it easier.

47:31

So this is a 4-year-old male

47:33

with history of blood in stool.

47:35

So the patient comes for Meckel scan.

47:37

So you see, with pertechnetate, this is

47:40

gonna accumulate in the stomach.

47:42

So we start seeing stomach that accumulates the

47:45

tracer, and then, with time, we gonna start seeing

47:48

tracer accumulating in the urinary bladder.

47:50

So we gonna look for some

47:52

ectopic gastric mucosa, right?

47:53

And it's very important not to confuse

47:55

urinary activity with Meckel's diverticulum.

47:58

This is the most important pitfall to avoid.

48:02

So we start looking here, and we're seeing stomach.

48:06

We're seeing bladder, and here we start seeing

48:10

some activity in the right lower quadrant, right?

48:13

So we need to follow the activity, and then it's gone.

48:17

We're not seeing it anymore.

48:18

So this is most probably a little

48:20

bit of urine in the ureter here.

48:23

So it's important not to confuse that with a Meckel scan

48:25

if it's not sticking till the end of the study.

48:28

It's not a Meckel's diverticulum.

48:31

Okay?

48:32

And it's very important to avoid having a full stomach

48:35

or a full bladder because, as you can see, there is

48:38

a lot of uptake in the stomach and the bladder.

48:40

And if they're full, and if they're

48:41

distended, they might mask lesions, okay?

48:44

Especially the bladder.

48:45

If it's full, like usually Meckel's diverticulum

48:47

is in the pelvis, and if we have a

48:48

full bladder, it might mask that.

48:50

So have the patient void before the study

48:53

and fast for the last two to four hours.

48:59

Now this is another case.

49:01

The patient comes, we inject the tracer.

49:03

So initially, we see blood pool with the

49:04

heart, and then the heart's gonna start

49:06

clearing, and we'll start to see stomach.

49:10

And at the same time as the stomach, we start

49:12

seeing some uptake in the right lower quadrant.

49:15

So you see the uptake is accumulating.

49:17

We start seeing it at the same time

49:19

as the stomach as it accumulates.

49:22

With time.

49:23

So, and it persists till the end of the study.

49:26

And this is diagnostic of Meckel's diverticulum.

49:28

Now, on the other hand, we have this

49:29

uptake in the right upper quadrant.

49:32

So it's very important to remember that this

49:34

is the location of the kidney, and if you see

49:36

accumulation here, it's probably the renal pelvis.

49:38

So not to confuse this with an abnormal uptake, right?

49:42

And here you have this linear uptake that's

49:45

in the ureter, and if you follow it at the

49:47

end of the scan, it's gonna empty from the

49:49

ureter, and you see the bladder getting larger.

49:52

So it's very important not to confuse, um, urinary

49:56

activity with Meckel scan with Meckel's diverticulum.

50:04

So the particular uptake — always remember —

50:07

we should start seeing it five to 10 minutes

50:08

after injection, and it increases over time

50:11

at a rate similar to normal gastric uptake.

50:14

If it clears, then it's not Meckel's

50:16

diverticulum — it's probably urinary activity.

50:19

So you could always do lateral or

50:21

oblique if you need to, or you could

50:23

do upright and post-void imaging.

50:25

So usually, on the lateral or oblique imaging, the

50:28

kidneys and the ureteral activity are more posterior,

50:31

while the Meckel, you would expect it

50:33

to be in a more anterior location.

50:36

If you do upright or post-void imaging,

50:38

this is gonna help void the renal or ureteral

50:41

activity, and it's gonna help you visualize

50:45

areas outside of the GI tract better.

50:50

So it is a highly sensitive and specific

50:52

study for heterotopic gastric mucosa.

50:54

The false negatives usually are

50:57

secondary to either a small diverticulum or

51:00

to the lack of sufficient gastric mucosa.

51:01

If we don't have enough heterotopic gastric

51:03

mucosa in the diverticulum, the false positive

51:07

most commonly is activity in the GU tract.

51:10

A common

51:12

pitfall also is a duplication cyst.

51:14

So duplication cysts of the GI tract can have ectopic

51:17

gastric mucosa in 30 to 50% of cases, and these

51:20

will label as well. Tumors and inflammation,

51:23

similar to the cases we showed with GI bleed —

51:25

if you have a tumor or inflammation, they're

51:28

gonna show uptake as well because of the hyperemia.

51:34

So my take-home messages are the day.

51:36

So nuclear imaging, imaging is functional and dynamic,

51:40

and it's very important to understand the process.

51:42

With imaging, um, it is very important

51:44

to pay attention to pitfalls.

51:46

And don't forget your problem-solving tools.

51:48

Delayed imaging, additional views.

51:50

You could do, um, lateral, uh, you could do obliques.

51:54

SPECT/CT is always your friend as well as the

51:57

anatomic imaging that you may have to compare to.

52:04

Thank you very much, and, um, I'm ready

52:09

for your questions if there are any.

52:12

Perfect.

52:12

I see one in the Q and A feature, and if there's

52:14

any more, feel free to throw those in there as well.

52:17

Okay, so the normal gallbladder ejection fraction

52:19

is gonna depend on what protocol you're using.

52:24

So, um, if you are using the protocol over 45

52:29

minutes, then you need it to be more than 40%.

52:31

If you are using the protocol over 60

52:33

minutes, um, you need it to be more than 38%.

52:36

So, um, and there is, um, a nice, nice — there are

52:40

nice guidelines by the Society of Nuclear Medicine

52:43

that — where they put the different protocols and

52:46

the different normal values for each protocol.

52:49

So, would SPECT/CT help in Meckel? Um, definitely.

52:52

So if there's, like, any doubt, if there's any

52:54

doubt, you could do a SPECT/CT and this, this will

52:58

help you — like if you have, like, a case of ectopic

53:01

kidney like that we showed with GI bleed — the scan

53:03

easily occur with, with a Meckel scan as well.

53:06

Um, and so, so it's, it's definitely

53:09

gonna help you if you're not sure.

53:13

How long the dynamic imaging for GI bleed?

53:16

So typically you wanna image over 60 to 90 minutes.

53:20

Some institutions do 60, some institutions do 90.

53:23

So the longer you image, the higher the likelihood

53:27

that you're gonna detect a bleed, right?

53:29

So if you image for 90 minutes, um, that's,

53:33

that's basically, that's, that's good enough.

53:36

And you can bring the patient for delayed always.

53:38

Um, and if you start seeing bleeding by, let's say,

53:42

80 minutes, and then you start seeing accumulation

53:44

of the tracer, you can image even longer to see

53:47

how it's gonna move to be able to locate it better.

53:50

So, so it's a dynamic process and you can

53:52

get more delayed images as you need to.

53:54

Um, so at least 60 minutes.

53:56

At least 60 minutes, ideally 90,

53:58

and you can image even longer.

54:03

Um, is calculous cholecystitis entity still

54:07

considered that chronic? So, uh, so, so if it's

54:12

acute cystitis, it's most commonly calculous because

54:15

of an obstructing stone, um, if it's chronic.

54:18

So yes, it is considered — like, so basically there

54:22

are two scenarios when you would wanna consider that

54:26

you have chronic calculous cystitis. First,

54:28

if, if the patient is coming as an outpatient

54:31

and they're not having acute pain, and you image

54:34

and you're not seeing gallbladder by the one-hour

54:37

mark, then probably it is chronic cholecystitis.

54:40

And then if the gallbladder fills, you wanna give them

54:43

CCK and calculate the gallbladder ejection fraction.

54:45

If it's slow, then probably it is, um, chronic cystitis.

54:50

So yeah, it is, it is a common entity,

54:51

and, um, for chronic, uh, pain.

54:54

And when they take the out, the patient gets better.

55:00

So there is no gallbladder ejection fraction

55:02

for a fatty meal because, so that's why

55:04

it's not, um, so that's why it's, it's

55:07

recommended to use CCK instead of fatty meal.

55:10

So some people use fatty meal

55:11

if, if CCK is not available.

55:13

But basically you don't have normal values.

55:15

We, we, we don't have studies that tell us

55:17

exactly how much to give to the patient,

55:20

um, what meal to give, and what's the fat

55:23

content of the meal, and then what's the

55:25

normal gallbladder ejection fraction for that.

55:27

So, um, so, so we don't have normal values.

55:30

That's, that's why it's recommended not to do a fatty

55:32

meal and to give, uh, CCK instead. Why to do HIDA

55:37

scan for leak, which can be seen faster and easier.

55:40

So if you have fluid — so if you wanna confirm

55:44

that it is bile leak, you would wanna do a HIDA scan.

55:48

So if you do ultrasound or CT with a patient — ha,

55:53

in a patient who has had, um, cholecystectomy

55:56

or recent surgery, and you're suspecting bile.

56:00

So if you're sure, then you're sure — definitely,

56:02

you don't need a HIDA scan, but if there is

56:03

a little bit of fluid and you're not sure,

56:05

is this, like, just, um, just fluid in the

56:08

pelvis that's not bile, or is it truly bile?

56:11

Then you can confirm by doing a HIDA scan, right?

56:15

Because what you can see on ultrasound or

56:16

CT is that there's fluid in the abdomen.

56:18

So you can be suspicious, but you

56:19

can confirm it with a HIDA scan.

56:22

Would you explain the patient

56:24

preparation in acute cholecystitis?

56:26

Of course.

56:27

So, uh, for acute cholecystitis, you need the patient

56:30

to be NPO for four hours, but not more than 24 hours.

56:35

So if the patient, let's say, ate

56:39

an hour ago,

56:41

so we just wait three more

56:42

hours before doing the scan.

56:43

Okay.

56:44

So wait till the patient ha—

56:45

is at least four hours NPO.

56:47

But if they have been NPO for more than 24 hours,

56:51

then probably the gallbladder is full and it's not

56:53

gonna take radiotracer because it's full already.

56:55

So that's when you're gonna need

56:56

to prep the patient with CCK.

56:58

So we give CCK over 30 to 60 minutes, and

57:01

then you give 30 minutes to the gallbladder

57:03

to contract, uh, to, to, to relax.

57:05

So, so basically you give it CCK, it contracts,

57:08

it empties its content, and then you give it 30

57:10

more minutes to relax and then you perform the scan.

57:13

Morphine, although it's not gonna really,

57:15

really affect visualization of the gallbladder,

57:18

morphine is gonna close the sphincter of Oddi.

57:20

So if the patient has morphine on board and you

57:23

do the scan and you don't see CBD — uh, you don't

57:26

see, uh, CBD emptying into the small bowel — then

57:29

basically you're not sure, is this CBD obstruction,

57:33

or is this just because the patient is on morphine?

57:35

So that's why it's recommended to stop opiates,

57:38

uh, for at least three half-lives before the scan.

57:43

What is the role of tin colloid in GI

57:46

bleed study and when should that be done?

57:48

So, um, so the sulfur colloid in GI bleed, um, I, I

57:54

think, like, you mean probably sulfur colloid, right?

57:57

So the sulfur colloid used to be used before

58:00

the labeled red blood cells for GI bleed scan.

58:03

So it used to be used before the red blood cells.

58:07

The problem with it, though, is first,

58:10

the quality of the images is poorer

58:12

compared to the red blood cell scan.

58:14

But also when you do the sulfur colloid,

58:17

um, scan, you need to have the bleeding

58:19

happening at the time of injection.

58:21

So it's, it's somehow similar to the CTA.

58:24

So if the bleeding is not happening shortly,

58:27

like during the injection time and during the

58:30

first pass of the sulfur colloid, you might miss it.

58:32

And then over time the sulfur colloid is

58:34

gonna be taken up by the liver and spleen.

58:37

So you're gonna have a lot of background activity.

58:39

So this is gonna — might mask GI bleeds, so it might

58:42

mask bleed, especially at the hepatic-splenic flexure.

58:45

So that's why the red blood cell, um,

58:48

labeled scan is better than sulfur colloid.

58:50

So we're, we're not using sulfur colloid anymore,

58:53

because the red blood cell is, is, is better imaging.

58:59

So recap the indication for

59:00

HIDA in acute, um, cystitis.

59:04

So basically there's no, like, clear, um—

59:07

it's, it's just, like, when you're not

59:08

sure on, on ultrasound or CT, right?

59:11

So if you are sure on ultrasound or CT, you have

59:13

your diagnosis, then, then, then you have it, right?

59:16

So you have a quicker scan and you

59:18

have a confident diagnosis.

59:20

You don't have to do, um, a 60- or 90-

59:23

minute scan additionally and, and waste

59:25

time while the patient is in acute setting.

59:27

So if you have your diagnosis on ultrasound

59:29

or CT, you don't need the HIDA scan.

59:32

You need the HIDA scan, um,

59:33

if you're not sure, right?

59:35

Because in a lot of cases, um, either you can have

59:38

equivocal findings on ultrasound where you have,

59:41

um, you have gallstones, you have a little bit of

59:43

pain, but you don't have your classic findings.

59:46

And you want to make sure that it is actually

59:50

acute cholecystitis or if you have gallbladder

59:52

wall edema that you think it might be

59:53

secondary to other causes — might be psuedocholecystitis,

59:56

the patient has underlying cirrhosis,

59:58

or if the patient is, um, in heart failure, then

60:00

you might have edema of the gallbladder wall.

60:03

That's not secondary to cystitis.

60:05

And in these cases, HIDA scan is very helpful,

60:07

because it's basically a binary study.

60:09

Um, and there is not a lot of, um, wiggle room.

60:14

Are there any instances where

60:16

CCK cannot be used in HIDA scan?

60:18

Um, not to my knowledge,

60:19

honestly, not to my knowledge.

60:23

So the two indications are if you wanna prep the

60:26

patient before a HIDA scan, and that's typically

60:29

if you're worried for acute cholecystitis, um,

60:32

or to calculate a gallbladder ejection fraction.

60:35

I am not aware of contraindication for CCK. They're

60:40

all of using PYP instead of labeled red blood cells.

60:44

Um, so the, the really, the gold

60:46

standard is the red blood cells.

60:47

It gives you the best.

60:48

Um, so there are, like, other

60:49

tracers that have been used before.

60:51

Um, not really PYP, but sulfur colloid and,

60:53

um, the red blood cells images are, are better.

60:56

So they are the gold standard for this.

60:59

And there's really no contraindication to do them.

61:01

So, um, so there are no scenarios where

61:04

you cannot actually do labeled red blood cells,

61:06

and you're gonna need PYP. Is sphincter of Oddi

61:09

dysfunction the same as biliary dyskinesia?

61:12

So, no, this is a little bit different.

61:14

Um, it's not very common, so that's

61:15

why I did not discuss it in depth.

61:18

And also because, like, I — there's no time in

61:20

the lecture to go in depth into the sphincter

61:22

of Oddi dysfunction, but there is — the,

61:23

the protocol is a little bit different.

61:25

So sphincter of Oddi dysfunction — you suspect that

61:27

if the gallbladder is out, so if the patient has the

61:30

gallbladder out and they're still having pain, then

61:33

you think that it might be sphincter of Oddi dysfunction.

61:35

And the protocol for that — you would do a HIDA

61:38

scan and then you calculate the regions of

61:40

interest, like in the CBD, um, and in liver.

61:44

So the protocol is a little bit different.

61:46

It's, it's specific for Oddi dysfunction.

61:49

So we don't do it that commonly, that’s

61:51

why I didn't discuss it in depth.

61:53

But it's different, and it is

61:55

like an absent gallbladder.

61:58

Since you give morphine to induce gallbladder filling,

62:04

I do not understand why it needs to be stopped.

62:06

Yeah.

62:06

So the — it's not for the gallbladder, really.

62:08

It's for the CBD. And so you do not, um, you

62:11

don't wanna end up in, um, in a scenario where

62:15

you're not seeing the bowel and you're not sure,

62:18

like, is it because the patient already has, um,

62:23

has opiates on board, or is it CBD obstruction?

62:27

Not really for the gallbladder, no.

62:28

You, you're right, it's not for the gallbladder,

62:30

but it's just, like, to optimize the study — to

62:32

have an optimal study where you can actually

62:34

see the gallbladder is filling and the

62:35

CBD is emptying into the, into the bowel.

62:37

The — go into the bowel.

62:39

Then you better have it, uh, stopped.

62:44

Can we differentiate between biliary

62:46

dyskinesia and partial biliary obstruction?

62:50

So...

62:54

So for partial biliary obstruction, um, so bi— so,

63:00

so, so they're really, like, very different entities.

63:03

So with partial biliary obstruction, you're

63:05

gonna see delayed emptying from the CBD.

63:08

Um, you're gonna have delayed emptying

63:10

from the CBD into the small bowel.

63:12

So you're gonna see it emptying, but it's delayed.

63:14

Um, for biliary dyskinesia, it's really

63:16

the contraction of the gallbladder that’s,

63:19

um, that's, uh, is gonna be impaired.

63:24

So the gallbladder ejection

63:25

fraction is gonna be impaired.

63:26

And what's gonna help you

63:28

here is the anatomic imaging.

63:29

So with partial biliary obstruction,

63:31

like, basically you should have, um, some—

63:35

degree of biliary dilatation.

63:37

That's, like, sometimes you might have

63:38

similar findings, like if the gallbladder

63:40

is not emptying appropriately because

63:42

of the partial biliary obstruction.

63:44

But that's, like, the presentation is, is also very

63:47

different — also when the patient's coming for biliary

63:50

obstruction, it's most commonly in a more acute setting.

63:54

So I think I, I missed the question.

63:55

What is the radiation dose of a HIDA scan?

63:57

So it is a — it is low, I think.

63:59

I'm not completely sure.

64:00

Um, but it is, like, I think about, like, four

64:03

or five millisieverts, if I'm not mistaken,

64:05

but I'm not completely sure about that.

64:07

Um, how frequently were you getting

64:11

the referrals for HIDA scan and/or GI

64:13

bleed before the COVID-19 pandemic?

64:16

Hmm.

64:16

So there are — there are very frequent studies to do.

64:20

Um.

64:22

So they're very frequent

64:23

studies to do — the GI bleed scan.

64:25

So initially, like, we start with CTAs, and

64:28

if they're different, we get GI bleed scans.

64:30

Um, so probably, like, I don't know,

64:32

um, like one a week for HIDA scans.

64:36

Like, it's, it's daily.

64:37

We do them daily either for acute or chronic settings.

64:43

So HIDA scan in biliary atresia.

64:45

So yeah, so it's basically when you have a

64:47

newborn, uh, and they have, um, they have jaundice.

64:52

So you would do the scan and if — so,

64:56

basically in hepatocellular dysfunction.

64:58

So your diagnosis is hepatocellular

65:00

dysfunction versus biliary atresia.

65:02

And in both, you can have very delayed

65:04

excretion of the, uh, bile from the liver.

65:08

So what you wanna do — you wanna do four-

65:09

hours imaging and 24-hours imaging.

65:11

So basically, if you see any bowel at four or 24

65:14

hours, you're excluding, um, biliary atresia.

65:17

Um, if you're not seeing any bowel, then

65:20

there is, um, most common — most likely atresia.

65:25

Is bleeding scan more sensitive than DSA — DSA?

65:29

Like, I'm sorry, what is exactly the DSA?

65:34

The angio.

65:34

Yes.

65:35

So it's 10 times more sensitive.

65:37

It's 10 — 10 times more sensitive

65:39

than the angio for low-rate bleeds.

65:41

Yes, yes.

65:44

It's 10 times more sensitive.

65:47

Yes.

65:48

So that's why sometimes, like, um, they can go

65:50

and, and — like, if you have a positive bleed at a

65:52

certain segment of the bowel, like, you can do, like,

65:55

empiric embolization to the artery that's

65:57

suspected to, um, uh, to be the source of bleeding.

66:04

Okay.

66:05

Well, I—

66:05

think that's it.

66:08

Perfect.

66:08

And right on time, uh, so that brings to close.

66:10

Thank you, Dr. Mallak, for your time.

66:12

Jay, we really appreciate this, and thanks all

66:14

of you participating in this noon conference.

66:16

A reminder, it will be made

66:17

available on demand at mrionline.com.

66:19

In addition to all previous noon conferences,

66:21

these are made available complimentary.

66:23

And Monday we'll be joined by Dr. Scott

66:24

Schiffman for a noon conference on bone tumors.

66:27

Thank you, and have a wonderful day.

66:29

Thank you very much.