05/06: image receptors and radiation

8/12/2019 05/06: Image Receptors and Radiation

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Transcribed by Eunsol Lee 7/15/14

Radiology Lecture 3

Image Receptors by Dr. Friedman

Slide 60: Image receptors

[Dr. Friedman] Ok. Lets get started. Todays lecture actually will be two lectures. One is on image

receptors and image receptor used in dentistry today, we have several image receptors. We have

dental film. Those of you who had preclinical laboratories we use intraoral films and we also have

other image receptors called film screen combinations, and that looks like something like this. For

those of you who are going to be working in a hospital, those of you who are oral surgeons or

orthodontist, you are going to take what is called extraoral film. Extraoral means the film is outside

of the patients mouth. Dont try to get this in the mouth, it will be very difficult. That is extraoral

film. The films that we put inside the patients mouth are called intraoral film. The intraoral films

include periapical films, bitewing films and occlusal films. You will see why we use each of those

films, what are the indications for those films. We will start with. And then one of the types of image

receptor are the digital sensors that are used for digital imaging, ortho-digital panoramic machines.They all use X-rays, but instead of having a film, you can actually have a computer printout, a

computer readout. So those are also a type of receptor. When you get a film of a CAT scan or MRI,

thats not actually a film. Thats a printout of an image thats done by a computer. Its computer

generated image. The intraoral films and the extraoral films use X-rays and you get a direct image

on those films. And you process them.

Slide 61: Intraoral film sizes

There are different film sizes. Depending upon what you want to use them for, size 0 film is

pediatric film. Size 1 film for patients who have narrow anterior arches and you cant get the film inthere. So we use size 1 film. Size number 2 film is the normal film that we use for all patients and

some of you who are thinking, well why dont we use size 1 film on all anterior film? The reason is,

you are exposing patient to radiation. So, you are exposing patient to radiation, you would like to

get the most information on the film. So the larger the film we use, the more advantageous it is to

the patient. So we use narrow anterior film for the patients who have very constricted arches, and

we cant get the film in the mouth. Number 2 is the standard film. Number 3 film, youll never see. I

actually was looking for one this morning to bring in. We have them hidden away, those are secret

films. They are actually not secret films, but they are long bitewing films. When we take bitewings

on patients, we do a premolar bitewing and a molar bitewing. But you know the dentists are saying,

well why should we do two separate films? Lets just stick one long film in there are get every toothin the arch on that film. And so thats where the number 3 film was. The reason we dont use it is

because you are never going to be able to see the interproximal spaces. The spaces between the

teeth on the long film, so thats why we break it up into two films. But you can still find that around.

Size number 4 film is called an occlusal film. An occlusal film looks like that. Ok. And there are

indications for these types of film which we will talk to you about in later lecture. But the reason its

called an occlusal film, when you place this in patients mouth, its placed on the occlusal surface of

the teeth. (bite) If you cant see up there. The old name for this by the way, you may see this in some


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textbooks. Its a sandwich film because thats the way you eat a sandwich, the same way. So the

occlusal film is the number 4 size film. What is the difference between each of these films? Only the

size. Inside the film packet, they are all exactly the same. They all have the same components as we

will see in few minutes. The back of the film has a piece of Lead in it. There is a piece of Lead behind

the film, so the X-rays come through the tooth, they hit the film and they form an image on the film.

This is what the film looks like. And we will see examples of that, but behind the film is a piece ofLead. Thats placed on by the manufacturer. And what is the purpose of the lead? Why do we put

the lead in the back of the film? Very good. If you said protect the patient, that is the correct answer.

Everything we do: collimation, filtration is to protect the patient. What it does is, any excess

radiation thatsnot needed is absorbed by the Lead. And by doing that on the side of the patient(?)

doesnt get hit by the radiation. Theres another reason for it. If you have any kind of scattered

radiation, scattered radiation is produced when X-rays hit an object. Well see examples of that in a

little while . The X-rays will bounce back on the film. They bounce back on the film, they will fog the

film. It will cause something called film fog. Film fog is when any form energy touches the film other

than the necessary radiation. So, we actually get fogging of the film if you have safelight thats not

working properly and well discuss that when we talk about processing. You can also get fogging inthe film if you are walking in a carpeted area in the office, and you know when you touch a

doorknob you get that shock from the static electricity? If you go into the dark room to process the

film, and you open it up, and you form static electricity when you pull it out very rapidly, you will

see a fogged, static electricity artifact on the film. Well show you examples of that in later lectures.

So those are some of the sizes of the films.

Slide 60: Image receptors

So what you have on the film well see in a moment in an outer plastic wrapper and thats to

prevent saliva from getting into the film. And the film itself is made out of plastic and it has an

emulsion. Its coded on both sides. Its called doubled emulsion film. Its coated on both sides with

something called Silver Halide in gelatin. Well talk about that in a little while. Theres also a piece of

black paper that is to protect the film from getting any light onto it. And the Lead Foil Backing. Now,

the lead foil backing is to do what? Is to protect the patient from excess radiation, absorbed excess

radiation and prevent back scattering onto the film. Uh if you place the film in the a ptients mouth

backwards. So think about this. You place a film in patients mouth backwards, so the X-rays first go

through the Lead. What kind of image would you expect to see on the film? If some of you said no

image, thats not correct. Youll actually see a very light image. Why? Because the Lead is thin. Its

not going to absorb all the radiation. So, the effect will be a light image with a geometric pattern. A

manufacture puts this geometric pattern on the film, so if you ever see a film in the clinic thats

extremely light, its possible that the film was placed backwards, and if you put your Sherlock

holmeshat on, and you look very carefully, you see the geometric pattern and you know thats alight film. Because there are many ways you can get a light film. Anybody know any ways you can

get a light film? One is underexposure. If the film is suppose to be taken at 12 impulses, and you

take it at 5, youll have a light film. If you collimator is far away from the patient, youwill get a light

film. If you are processing the films, and you dont keep them under the developing solution long

enough, they will be light. There are many ways you can get a light film. When you have a film

backwards, thats a reverse film with a geometric pattern on the film would be a light film. The old


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term is a herringbone effect because the pattern on the Lead used to be a herringbone pattern. We

dont have that any longer, but if you see herringbone effect, that means film was placed backwards.

The result would be a light film with a geometric pattern on the film. So, those are the different

sizes of the film.

Slide 62: Components of intraoral film packet

And if you look here, its hard to make out, but the plastic is waterproof packaging, and you have a

Lead foil. Thats the back part of the film. And you actually have a black paper protecting the film,

and you have the film itself. So if you open up one of those packets, you will see all of those features

in there.

Slide 63: Orientation dot on film packet

When you are taking a film in patients mouth, you dont know if its the right side or left side. There

has to be to orient you. So theres a little dot on the film that has a concave and a convex. The dot

that is sticking out is always a dot thats facing towards the source of radiation. So, when you mount

the film, you always mount them with the dot out, facing towards you. When you use extra-oral

films, we have lectures on that, there is no dot. So how do you know which is right or left side? You

actually have to put a little L or an R in here. Theres still L and R are actually a piece of Lead tape

thats shaped in the form of an L, so it gets imprinted on the film itself, and thats how you know the

difference. But in the intraoral film, with those receptors, you have to make sure that the dot is

always facing towards the source of radiation. If your dot is not facing towards the source of

radiation, you are going to get a light film with geometric pattern on it. Ok?

Slide 64: Film sensitivity to radiation

Ok. Film sensitivity radiation. Different companies make different types of film. We use Kodak films

here. We use a very high speed film. Whats the advantage of a high speed film? Less radiation to the

patient. To protect the patient. Ok? So, what determines how fast the film is? What does the

manufacturer do to make faster films? There is an emulsion on the film which contains Silver Halide

crystals. Halide is a salt of a halogen. So, its usually bromide 80-90% of the time, its silver bromide.

They throw a little silver iodide in there to make it a little faster, but its mostly silver halide, silver

bromide. The larger the crystals, the larger the crystal, the faster the film. If you look it under a

microscope, and you look at F-speed film which is a fast film vs. D-speed film which is a little slower.

The only difference youre going to see is the faster films have larger silver halide crystals. Thoseare the determining factors. Also, the manufacturer puts the emulsion on both sides of the film. The

emulsion is on both sides. Thatscalled a double emulsion film. Whats the advantage of double

emulsion film? Less radiation to the patient. Since the emulsion is on both sides, silver halide

crystals are more concentrated and so if you open up any film packet, in here or the clinic, youllsee

that emulsion is on both sides of the film, and the way you can tell if a film is fast, many years ago,

there were many companies that made film. So, each company would give its film a name. So, one


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company would say, lightning fast film. Another one would say super-duper fast film. We have no

way of knowing which film was, the film that we needed. So, there is an institute called American

national standard institute (ANSI) which gives the film a letter. So the lower the letter, if you have

D-speed film, D like David, thats a very slow film. Requires more radiation to get the same image. E-

speed film is twice as fast as D-speed film. And then you have F-speed film. F-speed film is 20%

faster than E-speed film. Ok? So its a little faster and its about 70% faster than D-speed film. So,always try to use the fastest film possible. Theoretically, the larger the crystals are, the less

definition on the film. You know this from pixels, when you have more pixels, the sharper the image.

Thats a theoretical consideration. The human eye cant tell the difference. So, you always want to

have the fastest speed film to get the least amount of radiation to the patient. How do we achieve

the fast film? What is the manufacturer do? Uses large silver halide crystals, the larger the crystal,

the faster the film. And also puts a double emulsion on the film. That helps reduce the amount of

radiation to the patient. Ok? What is film fog? A film fog is when any light or any energy hits the film

so if you go into a dark room in the old days, we used to process a panoramic films. If you went in

there with a cell phone and started talking, the light of the cell phone would fog the film. So the

definition is, any unnecessary energy that hits the film in the form of light or static electricity willdarken the film. And when it darkens the film, it causes a loss of contrast on the film. So, you are

degrading the contrast. You want to try to avoid Film Fog. So youll have a lecture, next lecture is on

developing and processing your films. The safelight in the dark room has to be correct. There was a

case where a dental office in Manhattan that was sold to another dentist, and the new dentist was

using the same equipment, and the same processors and same dark room and same X-ray machine.

All of the new dentists films were coming out fogged. Every single film was dark. And they called

myself and Dr. Fromer to take a look and see whats going on. And we walked in there and the first

thing we did was, we closed the dark room door and we saw that there was a light leak. So, if theres

a light leak, youre fogging the film. Now, why werent the other dentists films fogged? Because the

person processing the film was a very large individual. They blocked the light. Now, the new dentist

hired someone a little slimmer, and so I dont know what the moral of that story is. The moral is, go

into the dark room, check the safelight. If theres a crack in the filter, you got a problem. Ifthe

safelight bulb has to be at a certain wattage. We had a situation a few years ago, where all our films

were fogged because the safelight burnt out. The safelight has to be 15 Watts and one of the supply

people came in and they put a 100 Watt bulb in there. They thought they were doing us a favor. Too

much light. Even though there was a filter, the wattage of the bulb was too high. So sometimes you

have to check into these things. If your films are fogged, theres a reason for it, and you try to

correct those reasons, those problems. Ok?

Slide 65: Duplicating film

Now if you want to have a duplicate, if you want to have a duplicate of your films you take a full set

of X-ray. What are some of the indications that insurance wants you to send them the X-rays before

you work on the patient, to see if the work is necessary. So we have to send them duplicate film. You

never send them the original film. You send the original film, youre setting yourself up for major

problem if those films get lost and the patient decides to bring a law suit. So you need to keep the

original films in there. There are two ways you can duplicate films. One way is to use a double film


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packet. Double film packet means there are two films in each packet. So, when you expose the film,

you process the film instead of one film coming out of the packet, two films come out of the packet.

So, some dental offices like to do that if they know the patient needs duplicates instead of going

through the duplication process. They just use double film. Ok. That doesnt mean double emulsion.

Both of those are double emulsion, but the difference is one has two packets in there. So thats one

way you can duplicate the film. There is another way you can duplicate the films by using aduplicator. We have one in the dark room in 1A, if anybodys interested in seeing it. Im just going to

go over couple of the steps. Its a very simple thing. It doesnt involve radiation. You just take the

films that you took on the patient, you place them on a machine, cover them with duplicating film,

and then turn the button, light will go through the film and will hit the duplicating film, and you

process the film just like you did. So, I will show you how thats done.

Slide 66: Radiographic duplicator

So this is the machine that we have. So you go ahead and you take the films out of the mouth, you

put h them on this device here, and then you take a piece of duplicating film which looks like this.The duplicating film has an emulsion only on one side. Thats the difference between duplicating

film and regular film. The emulsion is this side over here. When you are in the dark room, its the

dull side. And if anybody needs to duplicate film, just come down well show you how todo it.

Theres a little trick, and for those of you who cant see it there are little teeth on the side of the film

here, little indentation. When you duplicate film, always place the teeth on the lower left hand side

of the film, and youll always have the correct side. But we can demonstrate that to you. And you

shine the light through, and you take this and you put it through the processor, and you have your

duplicated films.

Slide 67: Duplication

Ok so this is a diagram showing your light source on the machine. Thats your radiograph,

remember theres double emulsion on the radiograph which contains silver halide crystals. Ok then

you have your duplicating film which has emulsion on one side. The light goes through and the

image is formed and then you process the film.

Slide 68: Film-screen combination

Ok just one difference. This is one difference you have to know and were done with duplicating film.

Lets say you duplicated a set of X-rays, and the duplication is dark. You have very dark films. You

cant read the duplication. Now, you have to go back and duplicate it again. So, heres the question.

Do we use more light? Or less light? Before you answer the question, think about radiographs, and

you do exact opposite. In radiographs, if your radiographs are too dark, what do you do? You

decrease the exposure time. With duplicating films, its the opposite. If youre dark, you would think

well ifits dark, I got to do the exact opposite, increase your time of duplicating light thats the

difference between the two. You do the opposite that you do for X-rays in the patients mouth.


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This is the, this is the film-screen combination. Let me explain that to you. This is called a cassette. It

holds films. These white things here are called intensifying screens. Intensifying screens. You take

your film, you put it in here, its sandwiched between the intensifying screens. This is an extra-oral

film, called a film screen combination, screen for intensifying screen. And what is the purpose of the

intensifying films? Protect the patient, less radiation to the patient. Listen to what happens. When

the X-rays hit these devices, theres chemicals on here called Phosphors. And when the X-rays hitthe Phsophors, light is given off called Fluorescence. So, the light is what exposes the film not the X-

rays themselves. So, you need minute amount of radiation to cause the fluoresce and the advantage

to the patient then is very simple. The advantage is less radiation. We used to take an entire arch, a

panoramic film which showed us a condyle, the jaw bones. One of these, about the amount of

radiation you would use for 4 bitewing films. So we had an entire arch, including the bones. Why

were we able to do that with so little radiation? Because the film in here is extremely sensitive to

light. So, when small amount of radiation hits it, light is given off. Its actually exposed by the light,

and there are different types of intensifying screen. You have, well talk about this when we get to

extra-oral films in the later lecture. I dont want to give you too much information. y\You dont need

that right now. But this is a type of image receptor.

Slide 69: Extraoral cassette, film and intensifying screens

Ok so this is showing the placement of the film of course in the dark room. You dont do this outside

otherwise, you are going to expose the film. This is done in the dark room. Notice that L. That L is

important because this film does not have an orientation dot. So, when you place it in there and put

it in the machine, it tells you which is the right and left hand side of the patient. Ok but its called

intensifying screen. Those are the white objects there, and its the film-screen combination.

Slide 70: Effects of X-rays on intensifying screens

Ok, so what actually happens is the X-rays penetrate, they hit in this case calcium tungstate which is

a phosphor and light is given off. And it exposes the film

Slide 71: Lead markers

Thats a lead marker

Slide 72: Biologic effects of radiation

Ok so basically those are the different types of image receptors we use in dentistry. The last image

receptor that professor Stabulas will talk to you about that is digital sensors. A digital sensor or a

panoramic machine with digital sensors still use X-rays, but instead of having film to process, you

can get an automatic image on your computer screen. Its computer generated. Ok. What I want to

talk to you about now is some of the biological effects of radiation. The study of the biological

effects of radiation is called radiobiology. Thats a six month course, so were going to try to do that


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in about 45 minutes to an hour. Ok but well do the best we can. The fact is, well the radiation is all

over the place. We cant live in this world without radiation. The radiation from the sun causes

photosynthetic reaction in plants which produces all the food that we have. Ok, also the

combination photosynthesis of carbon dioxide and water produce oxygen that we breathe,

radiation is all around. But what we are concerned with are the harmful radiation itssomething

called ionizing radiation. Ionizing radiation is the type of radiation that has very, very shortwavelength, high energy wavelength, and because of that, they have the ability to cause ionization

in structures in the body. Ok and the cells of the body. Now, about 75% of the body is made up of

what? water. Ok so what happens is, when water is hit by X-rays, ionization occurs. And it breaks

the water into different ions. Now the water can recombine to form water, but they can also

recombine to form something called Hydrogen Peroxide which is toxic to the body. Hydrogen

peroxide. So one of your facts of ionizing radiation is the conversion of water through hydrolysis,

breaking up of the water and formation of H2O2. Another problem is the formation of free radicals.

When the radiation hits the cell, free radicals can form. The free radicals can combine with other

free radicals which are toxic to the body. So, those are some of the toxic effects of radiation. Ok an

ionization is when, this is a review.

Slide 73: Ionization

When you have photon of X-rays, light will not cause this ionization. It doesnt have enough energy.

When an X-ray photon hits an atom, and it has enough energy to knock out one of the electrons,

and thats called ionization. Now, the electron shelf thats closest to the nucleus has the highest

binding energy and requires lot of energy to knock that out. Well talk about that in alittle while.

Slide 74: Photon interactionOk. There are four possibilities for things that can happen when X-ray radiation hits an atom. Four

things that can happen. One of them is actually no interaction. The electron goes right through and

theres no alteration.

Slide 75: Interaction of X-rays with matter

So, if you look at the top diagram, you have a photon of energy. It goes right through, passes

through, theres no interaction. And that happens probably about 7-8% of the time. So, its not a

very , its not very important in our imaging of films because what we want to happens is, we want

the x-ray to go through and then cause an image to be placed on the film. The next thing that could

happen is

Slide 74: Photon interaction

Something called Thompson Scatter. Thompson scatter. Now what happens in Thompson scatter?


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Lets go on here. Is we have, thats the top one on the left hand side. The photon enters the, enters

the atom. And it has very long wavelengths. Its not a very high energy type of a photon. And it

interacts with the electrons. It just gets knocked out. So what is the difference between the first andthe second? In the first one, you get no scatter radiation. Zero scatter radiation because it doesnt

hit anything. It just passes through. With Thompson scatter, hence the name scatter, you get a small

amount of scatter radiation. But the photon is not affected. This is called un-modified scatter

because the entry photon leaves with the same energy as came in. ok? So thats called Thompson

scatter and the effect is, all you et is scatter radiation, you d dontget any ionization. No ionization

what so ever. Ok.

Slide 74: Photon interaction

The next one is called photoelectric effect.


What happens there? Thats a very high energy photon. It comes in, it knocks out the electron of the

inner shell, so its got to have at least 69,000 Volts of energy to knock out this high binding energy

electron here. The electron comes out, all of the energy is used up. All of the energy is used up. Ill

try to simplify this. So, we dont get any scatter radiation out of that reaction. There is no scatter

radiation. What you do get is ionization. You do get ionization and this happens about 30% of the

time. Ok. So to repeat, in this reaction, the photoelectric effect, what happens is, you have high

energy photon. It has to be high energy because it has to knock out an inner shell electron, and thatcauses ionization, but there is no scatter. Its a complete loss, the energy is transferred to knock the

electron out. And this happens about 30% of the time. The last reaction is where the energy photon

is also a high energy photon, but it knocks out an outer shell electron. It knocks out an outer shell

electron. So if it does that, theresexcess energy, and that energy is in the form of scatter. So in this

reaction, not only do you have scatter, you also have ionization. Because it knocked out an outer

shell electron which requires less energy. So, those are the different reactions that we have in

respect to formation of ionization. Ionization occurs in these two here Compton and photoelectric,

but Compton also has some scatter and Thompson has only scatter radiation. It doesnt have

enough energy to cause ionization. Ok they give this on the boards a lot. Its not on our exam, but I

needed to show you that in case you see that, you dont go.

Slide 76: Units of radiation measurement

Ok. So, now were going to talk about the units of radiation measure. In order to talk about how

radiation a patient got from this, and how much a patient got from this. We have to break it up into

different form of measuring these things. The first unit of radiation measure is the exposure. The

exposure is the measure of ionization in air produced by x-radiation or gamma radiation. So, what


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we do is, we take the light, put it up against the patients face, we aim an x-ray machine at it, and it

reads out the ionization of air at the patients face. So thats called Roentgen or R. Roentgen. A

Roentgen is a measure of exposure at the patients face. It doesnt go into the patient yet. Its

measured before it goes into the patient. And thats called R. and thats the conventional way. We

dont have to, well, this is millirads can be converted to Roentgen. This is milli-Roentgen. The newer

term for Roentgen is Coulomb per kilogram. Ok? So if you see the word coulomb, thats the same asRoentgen. Ok, its the measurement of exposure at patients face. Now, what I like to do for exam

purposes, is I make a column of the old terms on one side and I make a column of new terms. Im

going to show you those other terms, and you can play around with it because itsvery simples

Slide 77: Ionizing chamber measuring X-ray exposure (machine output)

So this is a nice ionizing chamber. If you want to figure out how much output this machine is, how

much, how many Roentgen a machine is putting gout, we can measure it with that chamber. Just

like if you put it up against patients face. So again, exposure is the amount of radiation in the air

Slide 78: Units of radiation measurement

Now, the next thing you can measure is the dose. The amount of energy absorbed into the patient,

amount of energy absorbed per unit mass of tissue. And what is that terminology? Thatsa Rad.

R.A.D. absorbed dose of radiation. Radiation absorbed dose. Ok? You dont need to do these

conversions here by the way. The new term for the Rad is the Gray. Ok? So Rad is the Gray. Thats

the amount of exposure inside the patient, you absorb dose in the patient. As opposed to the

Roentgen which was the exposure outside the patient. Now, every type of radiation has a different

quality factor, and this is where were lucky as dentist. This is a lucky day. That the exposure factor

for dentist and x-radiation is the same Roentgen, Rad, and Rem are exactly the same. What is theRem? The Rem is Radiation Equivalent Men which means you take the absorbed dose and you

multiply it by a quality factor of radiation. So, certain types of radiation are more harmful.

Particulate radiation which were not involved more harmful will have high quality factor. So,

radiation equivalent men would be a higher number. For our purposes, to make it simple, very very

simple, theyre all the same. If you have one Roentgen, its one rad, and its one rem. So, theres no

conversion. So If you see in a textbook theyretalking about 1 rad of radiation, its same as 1

Roentgen or 1 Rem or millirem and millRoentgen. Theyreall the same. So if you make a column and

you do this alphabetically, the top of your column should have a big R, right here. And right here,

would be Coulomb right? So you put R here, coulomb here. Notice here, alphabetically R is first,

then Rad and then Rem. And on this side, Coulomb, gray and Sievert. So for exam purposes, I mayask you what is the conversion to the new system for Rem. So you just make your columns and

alphabetically, R, Rad and Rem for the old conventional, and this is for scientific: Column Gray and

Sievert (CGS). So, make your columns and when you get to eh exam, you may have to use that.


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Slide 79: Localized radiation and total body exposure

Ok, there is a big difference between a localized dose of radiation vs. a total body exposure. If youre

in a nuclear accident, you get a total body exposure of radiation. What were giving our patient is a

localized dose, just right up against the face, a localized dose of radiation. So, we go into the

operatory, we aim, were giving a patient a localized dose. Now, what is the total body radiation

given from that small dose? Its a lot less. Its a lot less. Its actually 1/10,000thof that. So, whenpatients come into you and they say I read that, yourenot supposed to have more than 300

milliRad of radiation, thats actually a whole body dose of radiation. You cannot give the patient

whole body dose of radiation with an X-ray machine. And were going to talk about some of these

number in a while. The differences, when yourewalking around, theressomething called

background radiation. The average American, depending upon where they live, gets 360 milliRads

of background radiation a year. What does that mean? Well, when you take X-rays on a patient, each

film that you take is about 150 milliRads. Do the calculation. Doing 20 films. The patient gets 3000

milliRads of radiation, correct? 150 times 20, 3000, right? So, how could you give the patient 3000

milliRads of radiation when in the entire year, theyre getting 360 milliRads of radiation? The

differences are apples and oranges. The patient is getting 3000 milliRads of a localized dose ofradiation. To convert that to a full body dose, youd have to multiply, youd have to divide by 10,000.

So, what is the patient actually getting in relation to background radiation? Well, 3000 divided by

10,000 is probably .003 something like that. Someone do the math. So, when the patient runs in and

says, doc, how much radiation am I getting? you explain to them, that each film is 150 milliRads.

And then they start going bananas. And you have to explain to hem the difference between localized

dose of radiation and a full body dose of radiation.

Slide 80: Localized/Total body exposure

And this is just a diagram showing a dental radiograph, localized dose vs. a total body exposure ofradiation. Theres no way that we can give the patient anything close to a total body exposure of

radiation. But when you walking around in the street, and youre getting cars grazed, and theres

ray going, well talk about that. The average American youll see the break down gets to about 360

milliRads of total body radiation. Yes, you have a question? (how much radiation is in the airport?)

very good question. You go to airport, they put you into the machine, they tell you to do this and

everybody is afraid that theres radiation. The exact amount, i dontknow, but I can tell you that

when you get upon that plane and youre flying, in two minutesyou get more radiation than uh,

than this thing. So if your flight is four hours, dont worry about that. Ok, it just doesnt, people get

upset about these things, its so minor about of radiation compared to the radiation that you get

when on an airplane. The higher you are, the more effective the cosmic radiation. so theyve done

studies on that. For example, I spoke to students today in the lab. Where do you think is more

radiation? In the grand central station or in a nuclear power plant? If you said grand central station,

youre correct. Its a thousand, they make more than thousand times more radiation. So, dont

worry about nuclear power plant. It is regulated, and theres all kinds of shielding. What is

radioactive in Grand Central Station? Someone said granate? Granate, very good. Granate marble.

Thats the stuff thats dug up from the ground, and it contains very high amounts of radioactive

materials. So, you go in there with a Geiger counter, its going to go off the scale, but nobody knows


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because they dont see any nuclear bombs, so they think its okay. If youre smoking a cigarette,

theresradiation coming out of that because it goes in the ground and the heat will liberate some of

the radiation from a cigarette. If you live in a brick house versus a wood house, you have about 10

times the amount of radiation coming from the brick than you have form the wood. So all of these

things, if youre sitting next to somebody, theres radiation being emitted from that person as well.

So, you could stay there, dont worry.

Slide 81: Dose-Response curve

So its all relative, the fact is you have to be able to explain to a patient without getting. You know,

the patient will always ask you. doc, are X-rays, are X-rays dangerous. And you say nah, theyre

not dangerous, dont worry about it. Then they see you runningout of the room. What are you

running out of the room for? Why dont you stayhere with me. And you into a whole big things

about. Well, Imhere all day long. You dont have to, you dont have to. X-rays will cause problems,

certain problems. The fact is they havent been able to pinpoint. They have been trying to for many,

many years. They havent been able to pinpoint any type of disease caused by radiation. Low dosesof radiation. Not high doses of radiation. Were going to look at that in a minute. Low doses of

radiation. First they were talking about induction of cancer-like leukemia. But the problem is, thats

very long term, and if youre in the environment, and you have genetic disposition or if youre living

in an area with a lot of nuclear lab, and things like that, your chances of getting a Leukemia are very

high has nothing to do with the radiation. So they were not able to pinpoint it. But you still, there is

ionization, there are changes. Well talk about some of the changes that occur when radiation hits

the cell. So you have to be able to explain that to a patient. Everything is risk vs. benefit. Whatsthe

risk? Some minor ionization. Remember theres repair of the cells even if your cells get hit with low

dose radiation, within a few seconds, theyre completely repaired and theres no sign of anydamage.

So whats therisk? Very low. What is the benefit? Well, you can have an infection that you didnt see,and that infection could spread to the rest of your body. So the risk versus benefit is weighed on

that respect. Ok, so if youre going to put this on curves, scientists like to look at curves. So theres

different curves, a relationship of X-rays to the response and to the damage. There are, um

illustrates the possible biologic response to a harmful radiation such as ionization. Theres linear

and non-linear. Ill show you that where one is a straight line and one curves off when the effect is

gone. Theres threshold, non-threshold. Its believed that low does ionizing radiation is a linear,

non-threshold relationship. And Ill show you the graphs and youllunderstand what Im talking

about

Slide 82: Linear/non-linear, thresnold/non-threshold dose-response curve

Ok, so what you have on the bottom here is what they feel, the scientists feel you have a linear type

of relationship. So as you increase the dose, the response is a linear response. Ok? In this type of

non-linear response, as you increase the dose, it levels off. But in most in most situations, it levels

off because the subject is probably dead at that point. Thats why theres no response. So if you

didnt give a mouse some arsenic, and you give him some more arsenic, and give him a little more

arsenic, youre not going to have a linear response. Because when they get enough arsenic, it levels


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off. Ok, but in low dose radiation, at least in low dose radiation, given over periods of time, youre

not going to get that. So, you have, its whats called, a non-threshold. What that means is that, a

smallest amount of radiation will cause a response. There are certain chemicals and things that are

harmful that have a threshold. You know you give a mouse a little arsenic, and it keeps running

around. Theres no response yet. So you have to reach a threshold, but in our case, in lose dose

radiation they consider a linear, non-threshold relationship. Ok. So you saw a graph

Slide 83: Basic concepts

Ok. Some of the responses, basic concept. You have somatic and genetic effects. All the cells in the

body except the reproductive cells in the body are called somatic cell. What are some of the

response in somatic cell? Well, if you have enough radiation, obviously, you can cause a burning of

the cell, we dont deal with that in dental radiology. And genetic effects if the radiation can hit some

of the Gonads, some of the Testes and Ova, then you can actually get a genetic effect. The difference

is somatic effect doesnt get transferred to the next generation. Youre not going to get any of those

genetic effects or somatic effects with low dose radiation, dental radiation. Acute and chronic

effects. Acute effect would be a high dose of radiation, will cause burning of the skin will cause

nausea, vomiting and all kinds of problems. Again, we dont deal with that. Theres a latent period

and latent period is the time that it takes for the dose of radiation to the response. Thats a period of

time, and you can have cell recovery. Low dose radiation, all the cells will recover. Theresreally no

problem with that. The dose rate, well, if youre giving a patient with certain dose of radiation over

a short period of time versus. a prolonged period time, there are more harmful facts with the rate

and short period of time. Theresmore chance of damage, and the risk estimates, forget about.

Slide 84: Tissue sensitivity

Ok, therescertain types of cells in the body that are highly sensitive cells to radiation, and some of

those cells can be classified as Young Rapidly dividing non-differentiatedcells. Again, young

rapidly dividing non-differentiated cell. You can think of something right away, like an embryo. Ok.

Thats why we used Lead aprons. The Lead apron protects, theres 0 radiation to the patient. Now

when it comes to taking radiograph on pregnant patients, it has to do with scientific versus

psychological. Scientifically, theres no contraindication. Now if the patient comes in, and you want

to do full series of X-ray, but nothings in the mouth, you shouldnt do that. But if the patient comes

in and they have a swelling, theyre pregnant, and theres infection in the mouth. You better treat

that infection. Otherwise, itll spread to the fetus, so you need to take radiographs. And you can take

any radiograph that are necessary on a pregnant patient without any problem because you have the

Lead apron and were going to talk about protection, the lead apron in a while. There are othertissues and organs in the body which fall into that category. You have lymphoid organs, by the way,

this is in the textbook, you can check this out. Testing skin, skin peels off and gets repaired

constantly. Bone marrow it the big one. Bone marrow rapidly dividing cells, and they are constantly

forming new cells to replace the other cells. And the effect they thought the effect of radiation on

bone marrow is leukemia formation. That was the old theory. They have no evidence for that.

Because as Ive said before, you dontget leukemia after you have a bitewing x-ray. Its a long period


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of time, and there could be other factors involved. So theres no scientific way of pinning to that. So

those are some of the cells that are highly sensitive. Then you have cells with intermediate

sensitivity. They divide occasionally in response to demand for more cells. Those are growing

cartilage, fine vasculature in growing bone. Ok. Again, this list is in the book. If you want to write it

down. Growing cartilage, fine vasculature and growing bone. There is certain tissues and organs,

very low sensitivity. Those are highly differentiated and mature. They are incapable of cell division.So theres no cell division. Theyre no sensitive to any kind of genetic changes. And some of those

are neurons, striated muscles, and salivary glands. Those are mature. They dont divide, and so

theyre not as highly sensitive to any kind of damage.

As far as critical organs, whatever we consider critical organs? When we take X-rays, what are the

X-rays going through? Theyre going through patients face, theyre going through the eyes

sometimes, they go through the bone if youre taking a radiograph, youregoing to see the

trabeculation of the bone. That means the X-rays have to go through there. And so, there are specific,

specific responses which they believe have to do with these risks. It hasnt been proven. Carcinoma,

skin carcinoma. Well, the fact of the matter is that there are more than 2 million cases of skin cancer

in united states every year. And not everyone is getting that from dental X-rays. Its actually more

than all of the cancers combined. So I suspect that its probably the sun, UV-light, and other types of

factors. But those are some of the critical organs.

Slide 85: Background radiation

Ok. Lets talk about background radiation, something thatsin the environment all over. Its a form

of ionizing radiation and Im going to show you a list of things. All of these things have the ability to

cause ionization. So, youre not going to see light on there, youre not going to see radio waves

which dont have ability to do that. You can have natural and artificial. Artificial, the major source of

artificial background radiation is dental X-rays, medical X-rays, especially now with CAT scan. Every

patient walks into hospital, they get CAT scans, excessive amount of radiation. Other artificial types

of radiation is nuclear fallout, nuclear waste that gets thrown into the soil. Its present in the

environment either in the air, in the soil, in the water and weregoing to see some examples in

moment. What is ALARA principle. It stands for As Low As Reasonably Achievable. This has nothing

to do with background radiation, but when youre taking a film on a patient, you do everything you

possibly can to get the least amount of radiation for the patient and what are some of the things?

How do we protect the patient? One is the Lead apron that goes on. What else do we use?

Rectangular collimator, high speed films, aluminum filtration. The list goes on and on. Even the size

of the collimator matter. If you have long collimator, you have less divergence of the beam, less

facial tissue is exposed. Ok?

Slide 86: Specific effects to tissues from exposure to dental X-rays

These are. Ok. We spoke about skin carcinoma. Formation of cataracts in the eyes. These are all

hypothetical. Thyroid exposure. Thyroid gland, when patient is less than 16 years old, very highly

differentiating, rapidly cells are being formed. So, for children, we always use thyroid collar. Weve


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gotten to a point, where we use it for everybody now. So, theres really no scientific reason to use it,

but well be using it. Pregnancy we spoke about. The fact that you can scientifically take any

radiographs necessary for pregnant patient. If someone is coming in for a checkup, and they want

bitewings and they are 8 months pregnant, Tell them, you know what? Well clean your teeth today.

And after the baby is born, come in. why? It has nothing to do with any harm to the fetus because

theres lead apron. Its a psychological thing. Patient will go back and say wow, that dentist is sothoughtful. Theyre trying to protect the baby. Didnt take any X-ray. Whats radiation caries? Well,

one of the uses of ionization radiation is actually in therapy. It does shrink tumors and if its

pinpointed at the right place, you can have radiation therapy along with chemotherapy for certain

types of tumors. And when that happens, youll notice that the patient will have rampant caries in

the mouth. The reason for that has to do with the destruction of the salivary gland. Salivary glands

in the head and neck are destroyed by the radiation. Theresno saliva, when theresno saliva, you

have an increase in caries. And its very, pathognomonic for patients who had radiation therapy.

The caries are not going to be interproximal. Caries ,theyre going to be around the necks of the

teeth, circumferential caries. Youre going to see that in a bit.

Slide 87: Annual exposure of US population

Ok, these are some of the sources. Dont memorize the numbers. Nobodies going to ask you how

much get, but this gives you an idea of some of the natural source. Radon which is a gas. Radon is

produced from the breakdown of Radium, and we were talking about this before. You have to have

certain parts of the country have a lot of Radium, a lot of Radon gas. So before you buy a house, have

it checked out. What happens is, theres lot of Radon in the water supply aswell. So when you take a

hot shower, youll get more Radon because it evaporates from the water, and youll get Radon

shower as well. But these are average numbers. Cosmic radiation from the sun, from the stars, soil

and building materials, internal radioactivity, occupational. Depends if you work at a plant that cutsgranate, youre going to get a lot more. It all depends on consumer products, miscellaneous. Always

a miscellaneous. How they got that 0.06, I dont know. And if youre ever making your form, you

know we have a new dental form and radiology for looking at radiographs, and this 18,000 things

you can see on the radiograph, and theres box that says other. I think I told you about this. Always,

if you are making a form, put other at the bottom. Otherwise, youre going to get someone from

upstairs coming down, what kind of crazy form is this? You donthave blah blah blah on it. ok put a

other, check it and put that over there. So, you wont have. If they say its not all in there, check the

otheritem over there. But anywhere, theres always some miscellaneous. What that is? I dont

know. Ok, medical and dental. But if you look at this, you can see very clearly, the main source of

background radiation is Radon. Ok, now dental radiographs and you have cosmic radiation which

increases when youre flying in a plane. Youre going to have a lot more radiation, cosmic radiation

based on that. And of course, if you got to grand central station, youre going to have a lot of

radiation internal radio activity. And certain types of food. Its very interesting. The most

radioactive food. Does anybody know? I dont know why, but its the brazil nuts. Just, in case youre

in jeopardy once and they ask you that. Brazil nuts.


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Slide 88: Radiation protection

Ok. What Im going todo now, were going to take 5 minute break. And then were going to talk

about radiation protection. Its basically a review of what we had because every time I spoke about

a feature of X-ray tube or anything, the point was to protect the patient from radiation. So, thats

going to be easy and well get you out a little early today. Ok.

-Break-

Slide 88: Radiation protection

Ok just a few notes about the upcoming exam, I just want to give you some information about the

upcoming exam. Itsgoing to be multiple choice questions no fill in and no listing of 14 different

things. Ok? Its going to be in the form of multiple choice and I would say that every lecture we had

4, 5 questions would come out of that particulate lecture. So its based on each lecture. The material

is directly out of the lecture notes, what we talk about in the lecture. Werenot going to pick out

anything youve never heard or seen. So my suggestion is, when you get a chance, look at Dr.

Frommerstextbook and read, see if you can do the reading on that. The last lecture before the

exam, well have whats called a review session. What the purpose of review session is, you can askany questions that you want. I will give you the basic materials that will be on the examination. But

if you come to lecture, read textbook, youllhave no problems what so ever. Ok? I do have, where

did that film go? I have one mystery film for you. Guys in the back cantsee this. This is mystery film.

Anybody know what this is used for? So far, Ive been giving this course for about 20 years and not

person got it. I dont expect you to get it. If you do, itll be a first. Yes. (student: overhead projection?)

Ok, thatsgood, Ive never thought of that. They used to write on these things, right? But its not, its

not. This is actually what the film would look like if it hasnt been exposed and youve processed it.

Itll be completely clear. This is actually used in the dark room. As you learn, they go through roller.

Rollers collect all kinds of schmutz. You know what schmutz is? Did you have Dr. Vernillo yet? no?

Antony Vernillo? Did he mention schmutz? No? schmutz is dirt. Ok, just for you. What this is usedfor, you put it through the rollers and it cleans the rollers. Ok? Big deal. If you see something like

that, youll know what it is. Youll be the first in the neighbor to know what that is. Its to clean the

rollers.

So we have patient protection we need to speak about. Next time, well talk about operator

protection. Operator protection is us. Operator protection is going to be a very short lecture.

Basically, run out of the room and stand behind the wall. Thats the whole lec.. no there are other

things. Thats going to be pretty short lecture. Radiation protection for thepatient. What type of

radiation are we most concerned with to protect the patient from? Primary radiation. Theyre

getting showered with that stuff. So we have to do everything we can to reduce primary radiation.

As operators, what are we concerned with? Secondary radiation. Because the X-rays have alreadyhit the patient. Remember and youre going to get scattered radiation via Comptonand Thomspon

scatter and all that kind of stuff. So theres scattered radiation involved. We have to protect

ourselves from scattered radiation. Primary radiation is the radiation coming out of the X-ray tube

before striking anything. Ok, and some of the equipment. The tubehead and arm should not be

drifting, thats the second thingon the list, drifting. Because If you put it next to patient and it drifts

away. You walk out of the room and you press the button. Guess what? youre going to have to


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retake the film. So if you have any kind of drift, how do you protect the patient? Call someone in to

stop the drifting. Usually, that requires tightening of a couple of screws with allen wrench in there

to get it tighten. Killovoltage and milliamperage seconds. Ok, we dont really have to concerned with

that because our machines are pre-set. But if you are selecting a machine, you probably want a

machine with a lowest. We have 65 kVP machine. That will give us in between contrast that we are

looking for. Filtration. Thats very important. Aluminum filtration. What is aluminum filtration?There is a certain thickness of aluminum necessary to remove the long wavelength of radiation.

Why do we have long wavelengths of radiation? It has to do with multiple Bremsstrahlung. When

the electron goes from one atom to another, and the second and third, you have longer wavelength.

The initial bremsstrahlung gives shorter wavelengths. You need to remove that. Also, because the

electrical currents that we use alternating current, it has to build up to a peak like 70 KVP is the

peak potential as its building up, all the electrons at that point will have slower, less kinetic energy

and so we have to remove the long wavelengths. Protect the patient. Long wavelengths are not

useful. All theyre going to do is give the patient a higher dose of radiation without getting the

proper image. So that has to do with ALARA. Do anything you can to get the proper image by

putting Aluminum filter in there, we remove the long wavelengths. How thick does the aluminumfilter have to be? Depending upon the kVp of your machine. If you have red pen, or something you

can underline with. Federal regulations require that if your machine is operating below 70 KVP, 55,

60 or 65, you need 1.5mm of aluminum. Not inches, ok. 1.5mm of aluminum. If your machine is

operating at high kVp, you need thicker aluminum filter, thats 2.5mm of aluminum. Ok. Obviously

the higher kVps will produce a lot more long wavelengths that has to be removed. Thats why you

need thicker aluminum filtration. What is the term collimation? Collimation is restriction of the size

of the X-ray beam. I mean, we can give the patient a shower of radiation. Well still get the film, but

well be exposing the patient to unnecessary radiation. How do we collimate the x-ray beam in our

machine? There are two things. Position indicating device which is made of Lead. And the lead ones,

rectangular ones are much better. They reduce the patient radiation dose by 55-60% because the

beam is collimated to be the same exact size as the film. The circular collimator will give the patient

a higher dose of radiation. And the federal government is looking out for patients so the federal

government came out and they said the maximum diameter that youre circular collimator can be,

2.75 inches. 2.75 inches. Thats a good number to remember as well. 2.75 inches of diameter is the

maximum. Any more than that, they feel the patient is getting an excessive dose of radiation. The

timing device has to be electronic and when they come to inspect your office, theyre going to take a

machine and theyre going to set your X-ray machine, look at your timer and see if the read out I

correct. If your timer is off, the patient will be getting too much or too little radiation. Both of those

are harmful. Too little, films will be light and youre going to need to retake. Too much, theyrenot

going to be readable. Again, if you come into dentist office and he has a pointy plastic cone, run out.

If he has a timing device that he cranks with his hands and it goes (ka-z-z), run out. You need anelectronic timer, its necessarybecause were dealing with a fraction of a second. With impulse of

radiation. You should know the conversion of impulses to seconds. There are 60 impulses per

second, so half a second will give you 30 pulses or impulses. Ok. And position indicating device,

what are they used for? For those of you who had pre-clinical laboratory know that you have to aim

your collimator on these position indicating devices. Theyrecalled XCP device. Youllsee examples

of that in a minute.


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Slide 89: Production of scatter radiation by interaction w/ patients face

Ok, so the production of scatter radiation by interaction with the patients face. The radiation up to

here, this is called primary radiation. After it hits the patient, due to the Compton and Thompson,

you get scatter radiation. Actually, I think I have another slide of that, but Illshow it to you in a

minute.

Slide 90: Tubehead drift

This is what you see in clinic sometimes when youre walking by. The collimator has to be here and

that moved away. Thats not patient protection. See, youve got to makes sure you dont have that

drifting collimator.

Slide 91: Protective equipment

Film holders, you want to have a film holder so that you can send to the film on the radiation. How

do we protect the patient with film? We use the fastest films possible. And how do we know which

is the fastest film? You have the ANSI rating, you have F-speed, you have E-speed, you have D-speed.

Whats the difference between F-speed and D-speed film chemically? One difference. Larger silver

halide crystals, very good. The larger the crystals, the faster the film. How do intensifying screens

protect the patient? Well, less radiation is necessary because when the radiation hits those white

devices that the film is sandwiching between, they call it intensifying screen for a simple reason.

They intensify the effect of the radiation. So, a small amount of radiation gives off a lot of

fluorescence. And thats how the film is exposed. Not directly. If you had to take a skull film on a

patient, without intensifying screen, they probably have to be in machine for 3-4 minutes. This way,

itll be couple of seconds, tenths of a second. And digital sensors. Digital sensors are twice as fast as

a film. So if you have, theyll talk about why that is. They are very, very sensitive to radiation. So afast film is sensitive to radiation. When you hear the term sensitivity radiationthe faster the

radiation is, the more sensitive the film is to the radiation. Lead aprons and thyroid collars is to

protect the patient. We see lead aprons in the clinic. What youre supposed to do with lead apron is

hang them up. If you dont hang up a lead apron and you crumple it up on the chair, what do you

think happens? The lead is going to crack. And this is going to crease, youll have creases in the lead

and X-rays will go right through there. So be very, very careful about that.

Slide 92: Film-holding devices

Ok. These are some of the film holding devices that we use. Thats a localized radiation. Those are

called XCPs. These are some of the tabs and these are called Stabes. Actually the stabe is a

Styrofoam device and its named after professor Stabulas grandfather who invented it. No, thats

not true, I just made that up. Its not, dont tell her I told you.


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Slide 93: Fast speed film

Heres more graph. Theres no graphs on the exam, but what this is showing youis that when you

have high speed film like E-speed or F-speed film at different kVp, theres less radiation necessary

to get the same density on the film. This is slow speed, slow-film, so that 60 kVp you need 450-500

of the miilli-Roentgen. Here down here, you need about a half. Whats the advantage? Less radiation

to the patient. One of them is a faster film with larger silver halide crystals. All of these films by theway do have double emulsion and the purpose of the double emulsion is to protect the patient. And

have a high, a faster film on the film.

Slide 94: Intensifying screens

These are the intensifying screens that we spoke about. How does this protect the patient? Well,

less radiation because the film is not exposed by radiation. Its exposed by light and extremely

sensitive. These are called screen films. Theyre differentthan intraoral films because they are very

sensitive to light. So when you have lectures on safelites, youll find that a safelite thatsgood for

intraoral film is going to expose these. So what do we do in the dark room? We use a safelite thatsgood for these films. Well, not expose films. And youlllearn about safelites when Dr. Jain comes to

talk to you.

Slide 95: Digital sensors

And digital sensors. Two different types. You have lecture specifically on the digital sensor. Those

are image receptors, they receive the image, but it goes into a computer. There are two types of

digital sensor. The one that goes directly into the computer. These are called direct digital sensors.

Some of them have wires, you trip over them. You got to be careful and some of them dont have

wires. They go remotely into the computer. And you place them in the patients mouth exactly theway you do with regular film, and you get an image on the computer. Whatsthe advantage? Less

radiation to the patient. Instantaneous image. You can alter the image, you can enlarge it, magnify it.

If the contrast is too dark, you could make it light. There are many different advantages. You can

store this, theres no need for paper. The school is going towards that. When? I dont know. And

then you actually. And I told you all the good things about this, but theres also bad things. You trip

over the wires, so be careful about that. But if any one of you have had radiographs in the mouth

using sensors, it hurts like hell. Those things are not flexible. And one of the advantages of intraoral

film is that theres some flexibility in there. With these things, try to take a picture of a lower

anterior, good luck. But well try to show you how to do it. Now, if you want a digital system that

doesnt have that rigidity, theres another system over here called Indirect. These are calledphosphor plates. And what you do with these is, these go into patients mouth. And it doesnt go

directly into computer. You have to place it into a machine that scans it and then it goes into the

computer. What is the advantage? One of these sensors cost about 9000 dollars. So if you drop it

and step on it, 9000 dollars. These are about 200 dollars apiece. This is also a lot more flexible.

These actually bend a little bit. So there are different types of system which youll see. But I put it up

there because these are ways of protecting the patient. Less radiation to the patient.


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Slide 96: Lead apron/Thyroid collar

Its necessary with digital sensors, Lead apron/thyroid collar on the patient. Be careful about the

lead apron and the thyroid collar. Many times, what happens when you start your films in the clinic,

the patient is awake, theyre very you know very happy to be there or maybe not. And as you take

the films, they start to (strange noise). And then the thyroid collar is now above the lower border of

the mandible. And you merely take pictures and you have collimated cutoff on every lower filmbecause the lead, if this is sliding up here and you shoot the x-ray, youre going to have collimator

cutoff. Very common. Now whatsthe difference between the lead cutoff and collimator cutoff. If

you look at a film, again, you have to put your Sherlock holms hat. A collimator cutoff would be a

straight line because the collimator is a straight line. Rectangular collimator. The lead apron will

have a little wavy-ness to it. Also sometimes, youll see little black dots in that white area. Why

would you have black dots? Well, when they sewed the thyroid collar to the lead apron, the needle

goes through and makes a little hole. When the x-rays come through, they penetrate those little

holes. And youllsee that when we do Sherlock holm investigation about different errors that could

occur on film. But that again is to protect the patient. The fact of the matter is, no scientific need for

that thyroid collar in patients who are older than 16. But its a matter of psychology. So were goingto do that. Despite what Dr. Oz said. Dr. Oz said you need a thyroid collar. There is really no

scientific evidence. But you know what, it doesnt hurt. Just be careful that the thyroid collar doesnt

form.

Slide 97: Technique

How do we protect the patient with our technique? Limit the amount of retakes that we have. Youll

find that in the clinic, if one of the films is not exactly correct, but you see the tooth on another film,

were not going to have you retake the film. Up in the pre-clinical laboratory, well say retake the

film. Because those patients up there are not concerned with radiation, they are, some of them areskulls, real skulls. Their bigger problem is that they are dead. Theyre not really concerned with

radiation. So those patients were going to have you zap even if theres a little error. Because the

more films you take, the more practice you get, the better youre going to be. But we need to limit

the amount of retakes on patient. And your technique is very important. Also whats important is

when you take your film. I have the operatory, make sure that you dont mix them up with

unexposed film. You have exposed films and your unexposed films. And if you put them in the

wrong cup, you pick up a film to retake to take a picture that youve already taken. And youre going

to have whatscalled double exposed film. Double exposed film is useless and youre going to have

to take two films. So be careful about that. Avoid over exposure. What some dentists do, I hate to rat

them out. But what some dentists do is when their developing solutions are weak, instead of

changing the developing, refreshing the developing solution. Remember thats a chemical solution.

If they overexpose the patient, then its going to be fine. Dont do that. Change your developing

solutions when you see it. And you dont want to wait until your first patient in the morning and

take a full series and see that your solutions are weak and the films are completely light. Youre

going to need to have something in your office with quality assurance. Theres a way of testing the

solutions. Youll have lectures on that. Paralleling technique. Why does paralleling technique

protect the patient over the bisecting technique. The reason has to do with the angulations. When


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you use the bisecting technique, you steep the angulation. Patientseyes and thyroid glands receive

a lot more radiation using the bisecting technique. The paralleling technique usually come in

straight like this or with slight angulation. So paralleling technique is better because image

formation is better, you get more parallel rays without penumbra and without the magnification

and also theres less facial exposure to the patient. And certain critical organs are not affected as

much. Critical organ being the skin, the eyes, the thyroid gland and so on. Focal-film distance, veryimportant. You want to make sure that your machine is calibrated. So youre right up against the

patients face. If you move the collimator too far away, youre going to have a light film. Patient will

receive x-rays, but you wonthave an image to look at. Dark room procedures. Ok, Dark room

procedures. Make sure your safelite is correct. Youll have a whole lecture on that. The funniest

thing I ever saw, I walked into someones dark room and I tripped on a brick and I almost got killed.

I said what is a brick doing on a floor? Anybody? No, youre not even going to guess this I gotto tell

you. He said, when my. We used to do hand processing, you know dip the films in the developer. He

said when my developing solutions get low, I put the brick in and it raises the level of the

developing solution. Alright, change the solution. Ok. And viewing condition. Dont, and youre going

to see this all the time. I tell you not to do it. But all the faculty members upstairs, first they say letssee your x-rays. You cant see x-rays, theyre invisible. But given that, lets see your radiographs

and they hold it up to the light. And youre losing so much valuable information. You did everything

to get the proper film, you used the correct kVp and the exposure time, and you processed with

meticulously. Use the viewing conditions that are correct. Viewing light and darken the room.

Because if theres any extraneous light hitting it, youre going to cause, youre going to be missing

things especially small cavity or early changes in bone.

Slide 98: Paralleling vs. Bisecting methods

This was what we were talking about before. Look at the difference in radiation to the thyroid gland.Here, theres lot less radiation to the thyroid than with the bisecting technique. Notice in the

paralleling technique, the tooth is parallel to the long axis of the tooth hence the name paralleling

technique here is the bisecting technique where the tooth is very close to the film, and you have to

bisect the angle between the long axis of the tooth and the film. And come in perpendicular to the

bisected line.

Slide 99: Focal-film distance

Focal-film distance. We mentioned that before. The further you are away, the more radiation the

patient will get. Why? The dose of radiation, the size of radiation will be increased as you increasethe focal film distance. But that has nothing to do with collimator. Were talking about the end of the

collimator to the patient. Because you get a lot more divergence. The further you are away, the

more divergence of the x-ray beam the more divergence, the more surface area the patient is

exposed to.

And well take this up next time. So again, the exam will be 30 multiple choice question. Directly out

of the notes were not going to look for anything in some book and zap you with that. So read the


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notes, if you have any questions about any of the material, you can come see me, you can see Dr.

Jain, you can see professor Stabulas. Were always here to help you out if you need any.

05/06: image receptors and radiation

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