0:01

So having understood some of the fluoroscopic imaging

0:04

configuration, the physics principle behind these system

0:08

are pretty much the same common. So we're going to examine what is called

0:12

a fluoroscopy X-ray generator.

0:16

So fluoroscopy X-ray generator, what we try to understand is

0:20

how does this X-ray generator works,

0:23

especially when it is operating on a fluoroscopy mode

0:27

that has both a continuous fluoro

0:31

mode and also pulsed fluoro mode. We're going to discuss it more

0:35

detail in the pulsed fluoroscopy later.

0:38

When you say continuous fluoro mode means moment

0:42

you put the foot on the pedal, that's how the fluoroscopy is operated, where

0:46

there is a foot pedal where the operator such as the

0:50

radiologist or cardiologist will put pressure on the foot to

0:54

keep the X-ray on.

0:56

In the continuous fluoroscopy mode, there is a steady low

1:00

mA exposure continuously, which is

1:03

automatically able to see the image continuously.

1:07

Most of the fluoroscopy system these days are pulsed

1:10

fluoroscopy. When you say pulsed fluoro, they can

1:14

operate in different pulses, 3 to 10 millisecond

1:18

pulses at 30 pulses per second. And this

1:22

is done in order to reduce the radiation dose.

1:25

And I'm going to discuss about fluoroscopy more later.

1:28

One of the major advantage of doing pulsed fluoroscopy is it

1:31

improves the temporal resolution and also reduces the

1:35

radiation dose to the patient.

1:38

Another feature of X-ray generator is the

1:41

capability of the fluoroscopy system to have what is called

1:45

as automatic brightness control, ABC,

1:49

or automatic exposure control, also called as

1:52

AEC.

1:54

Which basically the function of this one is to keep the image

1:58

brightness constant

2:00

as system is panned over body parts of different

2:04

thickness and attenuation. You may have observed in a

2:07

fluoroscopy suite, the images changes as

2:11

brightness change. When you move a fluoroscopy system from a

2:15

thick portion area to the thinner portion, it automatically

2:19

adjusts the brightness so that it is not delivering the same

2:23

radiation dose on all area of the body

2:27

depending on the thickness. So the way the physics works behind

2:30

is, it adjusts the tube voltage and the tube current

2:34

setting as needed. The automatic brightness

2:37

control, which keeps the image brightness constant as the

2:41

system is panned over body parts of different thickness and attenuation,

2:45

is a true advantages of this particular imaging

2:49

mode. The way it does this, it varies from system to

2:53

system, but generally, it adjusts the tube current

2:57

first up to certain level, and then it adjusts the

3:01

kV to maintain the same brightness.

3:04

This is a typical diagram of an X-ray tube,

3:08

which is very useful for fluoroscopy application.

3:11

Typically, for radiography or fluoroscopy application, these

3:15

X-ray tube have bifocal focus. Means

3:20

basically it has two types of X-ray filament, which is

3:24

called bifocal system, which when it's turned on,

3:28

generates the electrons, which are then when interact with the X-ray

3:32

tube, the anode create the X-rays.

3:36

For typically for fluoroscopy, there is a small

3:40

focal spot, which is a .3 to .6 millimeter in

3:44

size, and there is also large focal spot,

3:48

1 to 1.2 millimeter for recording.

3:51

So as we discussed earlier, the focal spot makes the

3:55

determination on what's the impacts the spatial resolution.

4:00

It also impacts on heating the X-ray tube and the

4:04

life of the X-ray tube, everything.

4:06

So for fluoroscopy, small focus spot of .3 to

4:10

.6 millimeter is quite sufficient.

4:13

For a small and large focus spot when it's 1 to 1.2 is typically

4:17

used for fluoroscopy and also for recording modes.

4:22

For radiography, angiography, or interventional application,

4:26

you need very large heat capacity because you are continuously

4:30

operating the X-ray machine. And even though it's a low tube current,

4:34

but you are continuously operating, there's lot of heat generated.

4:37

Therefore, you want the system to have a X-ray tube which has a

4:41

large heat capacity,

4:43

and that's only achieved by high-speed anode rotation

4:47

and also by circulating water or oil heat exchanger with

4:51

the fan inside the X-ray tube to take the excess heat out.

4:56

There is also grid control exposure pulsing for

5:00

cine and pulse fluoroscopy, which can limit heat

5:03

capacity for smallest focal spot.

5:07

This is a schematic diagram of a collimator housing,

5:11

which sits next to the X-ray tube out of the X-ray portal

5:16

of the X-ray tube outlet where the X-rays are coming out, the

5:19

collimator housing is packed in.

5:22

And you can see here, this particular collimator housing has a

5:26

variety of material to harden the X-ray beam,

5:30

remove soft X-ray, which basically contribute to the

5:34

increased patient skin dose. And that's done, and

5:38

typically it's done either aluminum material or tungsten material or copper

5:42

material, and these are inside this one, which can be

5:45

inserted depending on the choice.