RADT 086 Image Intensification Tube

Summary

This lecture delves into the workings of the Image Intensifier (II), a crucial component in fluoroscopic imaging. It explains how the II converts X-ray beams into visible light, overcoming limitations of conventional imaging. The device's structure, including its input phosphor, electrostatic lenses, accelerating anode, and output phosphor, is discussed. The process of photoelectric emission and the importance of maintaining a vacuum are highlighted. The lecture also touches on the amplification of light to improve visibility, with a focus on the second-generation intensifier screens containing cesium iodide, which enhance spatial resolution.

Takeaways

• 🌟 The lecture focuses on the image intensifier (II) and its role in fluoroscopy, explaining its function and the reasons behind its design.
• 🔬 The II is an electronic device that converts the image-forming X-ray beam into visible light, overcoming the limitations of conventional fluoroscopy.
• 🛡️ The II is housed within a metal container for protection against rough handling and to maintain the vacuum inside the glass tube.
• 💡 The vacuum tube contains four basic parts: the input phosphor, electrostatic focusing lenses, accelerating anode, and the output phosphor.
• 📽️ The input phosphor is the first component to intercept the X-ray photon, converting its energy into visible light through a process similar to intensifying screens.
• 📷 The photo cathode, closely bound to the input phosphor, emits electrons in proportion to the light intensity it receives, a process known as photoemission.
• ⚡ The accelerating anode applies a high voltage of 25,000 volts to speed up electrons towards the output phosphor, enhancing the light signal.
• 🔍 Electrostatic lenses focus the electrons into a fine beam, ensuring that the image at the output phosphor is a minified and brighter version of the input image.
• ✨ The output phosphor converts the energy from the electrons back into light photons, resulting in a significantly brighter image compared to the input phosphor.
• 🔑 The II design is crucial for producing a bright enough image for daylight vision, eliminating the need for radiologists to use dark rooms and special goggles.
• 📈 The lecture will continue to cover topics such as magnification, the impact of charge on the lenses, and the differences between first and second-generation intensifier screens in subsequent sessions.

Q & A

What is the main purpose of an image intensifier in fluoroscopy?

The main purpose of an image intensifier in fluoroscopy is to receive the image-forming x-ray beam and convert it into visible light, making the image bright enough for daylight vision without the need for a dark room or special goggles.

What are the two significant limitations of conventional fluoroscopy without image intensification?

The two significant limitations are that it produces a statistically inferior image and the light is too dim for daylight vision, requiring radiologists to adapt to low light conditions in a dark room.

What is the role of the input phosphor in the image intensifier?

The input phosphor is the first component that intercepts the x-ray photon in the remnant beam, converting the energy of the photon into visible light.

What is the material typically used in the input screen of second-generation image intensifying tubes?

Cesium iodide (CSI) is typically used in the input screens of second-generation image intensifying tubes.

What is the function of the photo cathode in the image intensifier?

The photo cathode receives light from the input phosphor and emits electrons in proportion to the intensity of the light it receives, a process known as photoemission.

Why is the vacuum tube important in the image intensifier design?

The vacuum tube is important as it provides structural support for the components inside, maintains the vacuum necessary for the operation of the image intensifier, and is mounted inside a metal housing for protection against rough handling or breakage.

What is the role of the electrostatic lenses in the image intensifier?

The electrostatic lenses are responsible for directing the electrons emitted by the photo cathode to a focal point, ensuring that they arrive at the output phosphor with the correct kinetic energy and in a fine beam, containing the image of the input phosphor in a minified form.

What is the potential difference applied across the image intensifier tube, and why is it significant?

The potential difference applied across the image intensifier tube is 25,000 volts, which is significant because it accelerates the electrons emitted by the photo cathode, allowing them to reach the output phosphor at a high rate of speed and with greater kinetic energy.

What happens when the accelerated electrons hit the output phosphor?

When the accelerated electrons hit the output phosphor, the energy is converted back into light photons, resulting in a much brighter image due to the minification and additional energy given to the electrons during acceleration.

What is the typical diameter of the output phosphor in modern image intensifiers?

The typical diameter of the output phosphor in modern image intensifiers is 1 inch (1 in).

What are the four basic parts contained within the vacuum tube of an image intensifier?

The four basic parts contained within the vacuum tube are the input phosphor, the photo cathode, the electrostatic focusing lenses, and the accelerating anode.

Outlines

00:00

🌟 Introduction to Image Intensifier and Its Role

This paragraph introduces the topic of the image intensifier (II) and its function in medical imaging. It sets the stage for a two-week lecture series covering various objectives related to the II. The script describes the layout of a typical fluoroscopic room, including the table, tube, floating tube, and monitors. It emphasizes the importance of the II as an electronic device that converts the image-forming x-ray beam into visible light, overcoming limitations of conventional fluoroscopy such as poor image quality and the need for low light conditions. The paragraph also outlines the basic components of the II, including the input phosphor and photo cathode, electrostatic focusing lenses, accelerating anode, and output phosphor. It provides a historical context, mentioning the transition from television cameras to digital imaging and the use of different phosphor materials like silver-activated zinc cadmium sulfide and cesium iodide in the input screens.

05:02

🔬 Components and Functioning of the Image Intensifier

This paragraph delves deeper into the components of the image intensifier, explaining the role of each part in the process of converting x-ray photons into visible light. It discusses the input phosphor's role in intercepting x-ray photons and converting them into visible light, the photo cathode's function in emitting electrons in response to light intensity, and the electrostatic lenses' job in focusing the electrons to a focal point. The accelerating anode is highlighted for its role in speeding up electrons with a high potential difference, which is crucial for the amplification process. The paragraph also describes the output phosphor's task of converting the energy from the electrons back into light photons, resulting in a significantly brighter image due to the minification and amplification of the electron beam. The importance of the 25,000-volt potential difference in the acceleration process is reiterated, and the paragraph concludes with a brief mention of upcoming topics on magnification and the effects on the focal point.

10:02

💡 Conclusion on Image Intensifier's Output Phosphor and Anticipated Topics

The final paragraph wraps up the discussion on the output phosphor of the image intensifier, which is responsible for converting the energy from accelerated electrons back into light, resulting in a much brighter image compared to the input phosphor. It emphasizes the modern construction of most intensifiers with a 1-inch output phosphor and the process of minification and amplification that leads to the brightening of the image. The paragraph also previews the next lecture, which will cover topics such as flex gain and the mathematical aspects of using magnification in image intensification. The summary provided in this paragraph ensures that the audience has a clear understanding of the basic functioning of the II and sets expectations for the more advanced topics to be discussed in subsequent lectures.

Keywords

💡Image Intensifier (II)

An image intensifier is an electronic device used in fluoroscopy to convert the image-forming X-ray beam into visible light. It plays a central role in the video's theme by enhancing the visibility of the X-ray image, making it bright enough for daylight vision. The script mentions that older units had television cameras, but modern systems have transitioned to digital imaging, emphasizing the evolution of II technology.

💡Fluoroscopy

Fluoroscopy is a medical imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. It is the main subject of the video, as the script discusses the components and functions of the image intensifier within a fluoroscopic setup, highlighting its importance in medical diagnostics.

💡Phosphor

In the context of the video, phosphors are materials that emit light when struck by electrons or other particles. The input phosphor is the first component that interacts with the X-ray photon, converting its energy into visible light. The output phosphor, on the other hand, converts the energy from electrons back into light photons, resulting in a significantly brighter image.

💡Photocathode

The photocathode is a component of the image intensifier that emits electrons in response to light. It is made of a combination of antimony and cesium compounds and is crucial for the photoelectric effect, where light from the input phosphor is converted into electrons that are then accelerated towards the output phosphor.

💡Electrostatic Lenses

Electrostatic lenses are used within the image intensifier to focus the electron beam to a fine point. The script explains that these lenses help direct the electrons to the focal point, maintaining the image's integrity while it is being amplified and miniaturized before striking the output phosphor.

💡Accelerating Anode

The accelerating anode is a part of the image intensifier that applies a high voltage to accelerate electrons emitted from the photocathode. It is responsible for the significant increase in brightness of the final image by speeding up the electrons towards the output phosphor, as mentioned in the script with the use of 25,000 volts.

💡Focal Point

The focal point in the script refers to the location within the image intensifier where the electron beam converges after being focused by the electrostatic lenses. It is where the electrons strike the output phosphor, resulting in the production of a bright, miniaturized image.

💡Spatial Resolution

Spatial resolution is the ability to distinguish between closely spaced objects in an image. The script mentions that the design of the output phosphor, with its tightly packed cesium iodide crystals, is ideal for improving spatial resolution, thus enhancing the clarity and detail of the final image.

💡Cesium Iodide (CsI)

Cesium iodide is a material used in the input screens of modern image intensifiers, as discussed in the script. It is known for its high light amplification properties, which are essential for producing a bright and clear image from the X-ray source.

💡Digital Imaging

Digital imaging refers to the representation of visual information using digital technology, as opposed to traditional analog methods. The script mentions the transition from television cameras to digital imaging in modern fluoroscopic systems, indicating a shift towards more advanced and efficient imaging techniques.

💡Minification

Minification in the context of the video is the process of reducing the size of the image while maintaining its content. The script explains that the image formed on the input phosphor is miniaturized and amplified, resulting in a brighter and more detailed output image at the output phosphor.

Highlights

Introduction to the image intensifier (II) and its role in medical imaging.

Explanation of the limitations of conventional fluoroscopy without image intensification.

Description of the II's design, including its evacuated glass tube and metal housing for protection.

Importance of maintaining a vacuum within the II for proper functioning.

Overview of the four basic components of the II: input phosphor, electrostatic focusing lenses, accelerating anode, and output phosphor.

Historical development from first to second generation image intensifying tubes.

Use of cesium iodide in modern II for improved image quality.

Function of the input phosphor in converting X-ray photons to visible light.

Role of the photo cathode in emitting electrons in response to light intensity.

Process of photoelectric emission and its significance in II operation.

Explanation of electrostatic lenses and their role in focusing electrons to a fine beam.

Details on the accelerating anode's function in speeding up electrons with a high potential difference.

Conversion of electron energy back to light photons at the output phosphor.

Advantages of the 1-in output phosphor in modern intensifiers for brightness and spatial resolution.

Discussion on the amplification process of the II, increasing light brightness for visibility.

Overview of the upcoming lecture's content, including Flex gain and magnification.

Final summary of the II's operation, from X-ray photon to light conversion and electron acceleration.

Transcripts

hello students today we're going to be

talking about the image

intensifier and what it does and the

reason why it does what it does so

here's just a little something fun for

you on

floro there's a lot of objectives that

we're going to be covering over the next

probably two weeks um and we'll be

covering these in lab in addition so it

won't just be here in this lecture in

all of these

objectives so so here is your basic

floral room um when we look at this uh

layout we see that we have a table this

is the under the table uh tube you see

your I I up here we have a floating tube

up top and we have the monitors um these

are nice flat panel monitors we're going

to be talking about monitors in the

weeks to

come so here's a picture from buang you

probably recognize him here on the table

so here is your X-ray Source within the

table we like this model because it has

the metal that's um part of the table

that helps a shielding to protect you

the occupational worker and the

radiologist so your patient lies here

here's your image receptor um here it's

called the image intensifier or your II

um the older units had television

cameras um there are some units still

out there um it's some very old old

facilities um it's gone to Digital

Imaging now like our um room that we

have so we will talk about um the TV

cameras not in this lecture but I

believe next week so you'll learn all

about what happens after the II So today

we're just going to talk about the

II so the image intensifier it's an

electronic device that receives the

image forming x-ray beam and converts it

to visible light um

so in conventional floral without image

intensification there are two big huge

limitations so one um it produces a

statistically inferior image and the

light is too dim for our daylight Vision

so historically Radiologists had to go

in a dark room where special goggles to

adapt to the low light of the image

intensifiers so the whole reason that we

have these image intensifiers is to make

the image bright

enough so when we look at the Image

intensifier

Design it is an evacuated glass tube or

envelope um it provides structural

support for the objects inside of it

which we'll be talking about and the

glass tube maintains the vacuum and is

mounted inside of a metal housing or

container to protect it from rough

handling or breakage of the TU tube so

very important for you to remember these

next four things um the vacuum tube and

contains four basic parts and these are

what we're going to be studying in this

lecture so number one is the input input

phosphor phosphor and the photo cathode

they're um two separate things but

they're stuck together so um they

consider it just one item uh number two

is the electrostatic focusing lenses

three is your accelerating anode and

four is your output

phosphor the first generation image

intensifying tubes had silver activated

and zinc cadium sulfide crystals in the

input screen they didn't amplify the

light like our new generation the second

generation and this is typical for what

we're using today um some of the flat

panels are a little bit different in the

Dr but we'll cover that later on so

typically most systems in the hospitals

have the second generation intensifi

screens that contain cesium iodide so um

CSI input screens are usually used like

we have that in our lab currently so

we're going to talk about the input

phosphor the in input phosphor is the

first thing that intercepts the X-ray

Photon in the remnant beam so it

transmits through the glass envelope and

interacts with the input phosphor the

energy of the photon is converted to

visible light so this process is just

like our intensifying screens um same

idea so how does it do this the

fluorescent material is deposited on a

thin substrate of on the glass envelope

it hits the X-ray the x-rays hit it and

it gives off light the purpose of uh

converting incident photons into light

is so that we can

amplify the signal so amplify the light

so it's easier for us to

see so so cium iodide crystals on the

output phosphor are approximately 5

micrometers in diameter and are packed

tightly together as you can see here you

can see how tight these are um they

result in a microlite pipes with little

um dispersion so it's this design is um

ideal for improving spatial

resolution so the photo cathode so the

distance between the input phosphor and

the photo cathode um is minuscule so

they are there's just adhesive and the

two are bound together so um the

adhesive is transparent it's important

to know that so the photocathode is made

up of a combination of um antimony and

cesium compounds so what it does is it

receives the light from the input

phosphor and it emits

electrons out so photo electrons is

another name that we may use so it emits

the electrons in proportion to the

intensity of the light that it receives

this process is called photo emissions

or photoelectric

emissions so here's an example of um

your intensifying tube with its

components as you can see here the input

phosphor is right so the you can see

here the photon comes up and in to the

input phosphor so we'll start off with

this one here so the input phosphor is

the yellow the Orange is the

photocathode and then you can see the

electrons this would be electrons coming

through to a focal point these little

lines here are electrostatic lenses

we're going to talk about those we're

going to talk about the focal point and

the anode with the output phosphor so

here's just a picture from bong and a

picture from Carlton to give you kind of

the idea we'll talk about the

amplification uh later so here is your

input phosphor with your photo cathode

here they have them in just set reset a

little bit with which is fine coming

through these are photo electrons and

they go to the focus focal point and

here's your anode and we're going to

talk about how it has a hole in the

middle um that's so that the electrons

can come through at the focal point and

here is your output

phosphor the idea is to take one photo

um

uh one electron and amplify it so you

get a lot of light coming out of the

output phosphor we do do that by

accelerating the

electrons so the photoc cathode um is

also the cathode of the image

intensifier so it's kept at Ground

potential so electrons are sped up by

accelerating anode giving a very high

potential difference so they apply

25,000 volts and that pulls the

electrons at a very very rapid rate so

the voltage or difference in the

electrical potential between the cathode

and the accelerating anode the electron

transverse the tube towards the output

screen at a high rate of speed than they

would have um when they

entered so these lenses the lenses

responsibility um it's located after the

photo cathode and they're along the

length of the image intensifier which is

50 cm long so um as we increase the

voltage the lenses will um direct the

electrons to the focal SC focal point

which which is a very fine beam so it

comes in nice and wide and these um

electrostatic lenses push the electrons

to a focal point so they arrive at the

output phosphor with the kinetic energy

and contains uh the image of the input

phosphor okay so in a minified form so

what happens is the image that is on the

output phos or on the input phosphor is

accelerated and minified so when it hit

hits the output phosphor it is a lot

brighter so the the accelerating anode

it's located at the neck of the image

intensifier it's a circular plate with a

hole in the middle so electrons can pass

through um to the output phosphor

without interacting with it it

accelerates um and draws electrons from

the photocathode and accelerates them

towards the output phosphor so the here

it is again the potential difference is

25,000 Vols very

important and here's a diagram again in

case you forgot so we're going to come

into the input phosphor so it's going to

take the photon change it to a light

Photon it's going to hit the photo

cathode and be converted to an electron

it's going to come out and be pulled by

the anode at 25,000 volts so it's going

to pull the electrons across these

electrostatic lenses are going to focus

it into a fine beam to the focal point

and then it's going to hit the output f

phosphor U so we're going to talk a

little bit about magnification and how

the focal point will change based on the

charge of the lenses that's in our uh

next lecture so this is your basic I I

there the output phosphor so when the

electrons strike the output phosphor the

energy is converted back to light

photons so it goes um x-ray to light

photons light photons to electrons

electrons back to light photons so um

thousands of times brighter than the

input phosphor due to its smaller size

that minification that I talked about in

the last slide and um the additional

energy given to electrons as they're

accelerated to the image intensifier so

that's that 25,000 volts usually made of

cesium C caum sulfide most modern

intensifiers are constructed with a 1 in

out outut phosphor so um all the current

um output phosphors are 1

in so that is all I want to cover for

the um II in this lecture our next

lecture I'm going to go into the

different um Flex gain and what happens

when we start using magnification so

there'll be some math involved so we're

going to end here on the output phosphor

so the basics of the uh two here so

we've got the the um x-ray Photon coming

in to the input phosphor the input

phosphor is going to convert the X-ray

to light it's going to hit the photo

cathode the photoc cathode is going to

take that light and convert it to

electrons the electrons are going to

come out of the photo cathode they're

going to be accelerated by the anode

with 25,000 volts across the tube which

is 50 cm long you have these

electrostatic lenses which are applying

a charge that's going to take this beam

and make it narrow to come to a focal

point and it's going to once it hits

that focal point it'll hit the output

phosphor and once it hits the output

phosphor they're going to be accelerated

due to the anode and the 25,000 volts

it's going to hit the output phosphor at

a minute at a smaller image so the light

is going to be brighter the output

phosphor is 1 in in diameter and it's

going to take the electrons and convert

it to light okay okay so that's the

basics of the input phosphor I hope all

of that helps and makes sense as we move

forward