0:00

Because we do a series, for example, here in this case, one

0:04

might wonder, we are doing so many of these scans, will it have any

0:08

radiation worries?

0:11

In fact, this is exactly one example which caused a lot of

0:14

stir and put some brake to the whole procedure of perfusion

0:18

CT.

0:19

Unfortunately, this was incorrectly done.

0:23

This is a series of images showing a radiation injury

0:27

from CT perfusion studies. These images were all

0:31

about the patient who had gone through perfusion CT at a particular

0:35

center in the West Coast Hospital and who experienced hair loss.

0:39

You can see this hair loss is part of the deterministic

0:43

effect or a tissue effect because the radiation

0:47

dose to the same area exceeded the threshold to

0:51

cause these skin injuries.

0:53

In another lecture on radiation protection and tissue reaction,

0:58

I'm going to be talking more detail about the deterministic effect.

1:02

But it is suffice to say here,

1:04

these patients who underwent brain perfusion scans

1:08

experienced this type of a hair loss.

1:10

The band of hair loss kind of tell us it was a

1:14

64-slice CT scanner with a 40 millimeter of

1:18

maximum beam width.

1:20

And again, because of that, there are a lot of new requirements installed

1:25

or required on how we do the brain CT and dose

1:28

recording and so forth. But this is an example, an extreme

1:32

case, which has happened back in 2010.

1:36

What I want to show here is this is the screen of a CT

1:40

perfusion dose data.

1:42

As I mentioned in the radiation dose part of the lecture,

1:46

the radiation dose from CT can be

1:50

a lot of detail in the image. Usually, every CT

1:54

exam at the end, there is one screenshot showing the technique

1:58

used for that particular scan.

2:01

And if you want to go more detail, there is always what we call a

2:04

radiation dose structure report, which has all the details of

2:08

each series.

2:10

What I'm trying to show here is a typical

2:13

example of a perfusion dose data.

2:18

This is a particular protocol where the subjects are

2:21

getting a topogram, having a head routine.

2:25

Then you have this pre-monitoring before you inject the contrast.

2:29

There is a dual energy angiography is done.

2:32

But more importantly, what I want to draw here is this is the dynamic CT, the

2:36

perfusion CT done, which is acquired at

2:40

80 kV. This is the one which is really important to watch out,

2:44

because if it was done at 120 or 140 kV, the

2:48

dose delivered will be very higher, which has caused this radiation

2:52

injury. For example, the CTDI volume here is

2:56

about 258 milligray, and if it exceeds

3:00

more than 3,000 milligray, that's when you see the

3:04

onset of the early hair loss or erythema.

3:08

In this case, it is suffice to say a series of images were done.

3:12

Acquisition was done with the 80 kV and 200 mA,

3:16

but the result is less than the

3:19

needed threshold. But this is the acquisition which now

3:23

results in this type of acquisition at different time point.

3:27

So you can actually quantify the uptake at a particular

3:31

point over a period of time, a short period of window, and thereby

3:35

you can quantify the vascularity or the stroke

3:38

evaluation or the movement of the contrast to the area.

3:42

That is the main function of the CT perfusion.

3:46

So let's examine the radiation dose for a typical

3:50

perfusion CT.

3:51

Here is an example of an effective dose obtained for a

3:55

brain perfusion CT,

3:58

published in this particular publication.

4:00

They have shown here using phantoms, both male and female, for

4:04

all the radiation dose calculated for all the different phases,

4:08

the approximate effective dose for a brain CT can be

4:12

anywhere from four to six millisievert.

4:15

But if you are doing a perfusion body CT protocol, that can range

4:18

between 23 to 26 millisievert.

4:22

One needs to also keep in mind that this dose can vary from

4:25

protocol to protocol and how many acquisition you're acquiring

4:29

at the same location.

4:31

More than the effective dose, the caution is on the

4:35

tissue or the organ doses that can show an

4:39

indication whether that can result in any type of a hair loss or

4:43

a skin erythema. So we need to watch out.

4:46

The techniques are done at 80 kV in order to keep it

4:50

safe.

4:52

The application in oncology is an example shown here,

4:56

a conventional CT before therapy.

4:59

You can see there's lot of interesting objects,

5:03

the tumors in the liver, and the next slide in the

5:07

center is called the pre-hepatic perfusion before radiation

5:11

therapy, and four hours after therapy, the

5:15

hepatic perfusion has shown quite remarkably what

5:19

things have changed. So CT perfusion has a good

5:22

application for following up a patient to evaluate

5:26

their treatment pre and post after the radiation treatment or

5:30

chemotherapy. So this is another example or functions of CT

5:34

perfusion.

5:36

Here is another example, the perfusion CT of liver metastasis

5:40

from colon cancer. The metastasis, you can see in the liver, is a

5:43

large tumor area of a low contrast object here in the liver.

5:48

And as you can see here, this is on the first top left is

5:52

the without contrast, and as the contrast is injected and

5:55

follow up, you are able to see the uptake of

5:59

the contrast agent in the tumor area.

6:02

The perfusion CT will enable early treatment response

6:06

after chemotherapy for liver metastasis from colon

6:10

cancer. This is another application which is now been considered.

6:15

Having said that, I want to close this aspect discussion,

6:19

short discussion, on CT perfusion.

6:21

One

6:23

of the aspect of CT perfusion is it is done, CT

6:27

acquisition is acquired at the same location

6:30

repeatedly for a number of times after injecting a

6:33

contrast in order to see how the contrast agent flows through the tissue

6:37

area. A good example of application is brain

6:41

perfusion, which is heavily used.

6:43

One has to be caution on how the protocols are set,

6:46

especially for perfusion protocol.

6:49

The kV or the tube voltage should be set

6:53

at 80 or less in order to avoid delivering

6:57

very high dose for the same surface that can lead

7:01

into radiation injury. So this is the aspect about

7:05

perfusion CT.