0:00

There are two major advances in CT tube current modulation.

0:05

One is called the tube current modulation.

0:08

What it basically says,

0:11

the tube current when you're acquiring an image can be changed based

0:15

on different factors.

0:17

There are two type of dose modulation.

0:19

One is called the spatial dose modulation, which is mostly

0:23

used in body protocol. The second one is the temporal dose

0:27

modulation, predominantly used in cardiac CT protocol.

0:31

The way it works is as follows.

0:34

If you examine here, as the gantry goes around the

0:37

patient,

0:38

X-rays pass through the object. And since we are not

0:42

circular in nature, the number of X-rays

0:45

required to penetrate this portion of the body is different

0:49

from the amount of X-ray photon required to penetrate this

0:53

body in the XY direction.

0:56

This is exploited in what is called as the tube current modulation by

1:00

varying the tube current when acquiring around the region

1:04

of thin region, thereby, we can actually reduce the radiation dose

1:08

to the patient.

1:09

There are two type of tube current modulation.

1:12

The most commonly known tube current modulation is spatial dose

1:16

modulation,

1:17

which is based on modulating tube current at different

1:21

spatial projections.

1:23

And this is utilized in most routine body CT

1:27

protocol, and the second type of modulation is

1:31

called the temporal modulation.

1:33

The temporal modulation is based on modulating tube current at a

1:37

specified time points of a ECG signal.

1:42

Demonstrate further what is dose modulation here in a protocol.

1:46

The tube current required to create the same image quality in the shoulder

1:50

blade area was higher compared to this region where

1:54

it is full of gas and chest area. Therefore, you did not

1:58

require the same amount of tube current.

2:01

In the absence of tube current modulation, we were acquiring data

2:05

all at the same higher level. So the CT dose

2:09

modulation has indeed impacted on

2:12

understanding and also lowering some of the patient doses.

2:17

Here is an example of different vendors and their

2:21

technique used for dose modulation.

2:24

For any users, I would recommend you to read these things before

2:28

we start practicing because at one junction, one

2:32

hospital, somebody had not checked and the automated dose

2:35

modulation took over to the higher dose, resulting in a lot of

2:39

hair loss in the patient and so forth.

2:43

So here are two scans, post-scan display of the CT scan.

2:47

Here is one without dose modulation.

2:49

You can see here they are pretty much the same technique.

2:53

Whereas with the dose modulation, it automatically went

2:57

down because it is now the scanner is acquiring data

3:01

based on the level of interest. Therefore, in this one,

3:05

you can see here there are two numbers in the MA, which means it

3:09

has a dose modulation.

3:12

This is the impact of temporal dose modulation.

3:15

What I'm trying to show here is with this retrospective ECG gating

3:19

signal where we were acquiring with multiple heartbeats

3:23

until the heart is covered, resulting in lot of radiation

3:27

dose misused.

3:29

With the retrospective gated helical modulation, you can see that

3:33

the tube current is decreased around the systolic area

3:37

and increased around the diastolic area because in reality,

3:41

we only require image in this particular area.

3:45

With the prospective triggering method, there are a variety of ways.

3:48

One is we have a very thin window to acquire the data

3:53

or slightly larger window to acquire the same data,

3:56

but there'll be a lot more information on either side of

4:00

the image.

4:02

With the wide detector module, which is 360 to

4:06

320 degree slices, in one rotation, it will cover the entire heart.

4:10

If that becomes effective, then the radiation dose from

4:14

that particular study is only this much.

4:17

So for someone in the cardiac CT field, you can see how

4:21

rapidly the movement of the technology is delivering

4:25

the radiation dose to the patient far lesser than what it

4:28

started.

4:30

But when you're doing cardiac dose modulation, it also becomes very important

4:34

how the patient is positioned. And this is what a

4:38

good technologist does, is to make sure the area of interest

4:42

is at the isocenter because if it is too high

4:46

or too low, that can cause a lot of unnecessary

4:50

radiation and so forth.

4:52

There are a variety of dose modulation technique.

4:55

Among them, you have to minimize the scan range.

4:59

If you're asked to scan a neck region, you need to make sure you're only

5:02

scanning the neck region, not all the way to upper lobe of the heart or

5:06

all the way to the naval cavity and so forth.

5:09

The second modulation strategy is the tube current modulation.

5:13

Now, it is by de facto, all these vendors are

5:17

indeed using tube current modulation.

5:20

There is also reduced tube voltage in suitable patient.

5:23

Therefore, you can actually benefit in not only

5:27

reducing the patient dose, but also increasing the

5:30

image on the contrast resolution.