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  • 8/12/2019 01/02: Ionizing Radiation

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    Transcribed by Christina Gory 7/1/2014

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    [Radiology] [1] Ionizing Radiation by Dr Friedman

    [1] [Radiology]

    [_________]Hello, welcome. This is your first day as a D2 student. You were D1s first.

    Now from today you are D2 students. And we are going to start with a radiology

    lecture. And this lecture is total 22 hours course and a 2 hours exam. And there aretwo exams in this course. One is a midterm and one is a final. And each exam will

    have around 30 questions. And the questions will be multiple choice with or without

    diagrams. And the course in the first exam will be covered only up to the lectures we

    give you til the first midterm exam. Then the second exam final exam that will cover

    only from the lectures after the midterm to the final exams. So you dont have to

    worry about comprehensive. And the points is both grades exam will have 50% and

    30 questions so in both you have to get 70% passing. And grades are given A, A+, A-,

    B+, B, B-, C+, and C. And passing and those who dont pas get D grades F grades. And

    of all the exams everybody has to be on time and those who miss the exams they will

    they may they go for uh the second chance okay make up exam. And the grades for

    the make up exam will be same okay but you cannot (something? Idk what he says?)Unless you have a genuine reason. So you have to come and tell me what is exam.

    Im _______ coordinator of your course and Dr Friedman will give you lectures today.

    And he has many lectures with you. And then the course lectures all faculty-

    radiology faculty will be giving you one or two lectures. So youve got familiar with

    the faculty also. Any questions? And I have a syllabus on the learn service okay and

    we have the slides there and you can check it. Any questions? And at the end of the

    class I would like to see your representatives and the class president in 1a radiology

    clinic. Now Dr Friedman will give you the course. And I didnt mention one of the

    books that everything is written on the syllabus.

    [2] Ionizing Radiation and Basic Principles of X-Ray generation.[Dr Friedman]-Okay let me just give you a little uh additional information about the

    course. -------- mentioned the exams. Uh multiple choice questions. The exam

    questions will come directly out of the lectures. Were not going to find some

    obscure place in the book that we didnt talk about. So its very important to come to

    lecture. Another thing about multiple choice exams in this course in particular. Dont

    memorize large list and numbers. Were not going to ask you to list 14 things related

    to radiology. All right most of the material we cover at least the material I cover I try

    to make it relevant to the clinic. Were not going to make anybody physicists or

    chemists were not trying to do that. Youregoing to be doctors youregoing to be

    working with the machine. You have to know how the machine works how the

    machine produces x-rays and the effects of those x-rays on the patient. So weregoing to keep it on that level. For those of you that have some time I know you have

    a long weekend. This is the textbook, this is one of the textbooks, uh Radiology for

    the Dental Professional. And youllnotice that most of the slides in the lectures come

    directly our of this textbook. So if you need any additional information do that. If

    anybody wants to go further and is interested in becoming an oral-maxillofacial

    radiologist there is another textbook that you can use. Thats the farrow and white

    textbook. Thats on your list there as well. Its also a very good book goes into a lot of

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    details if you want to learn about corks and physics be my guest. But for clinical

    radiology its not absolutely necessary. Okay so uh wheat I like do to when I give a

    lecture at least the last lecture before the exam, Ill have some information about the

    exam because I would have seen it. And I would encourage you to come to that

    lecture because we have something called the review sessi0on okay its a review

    session. Its a little more than a review session. It allows you to ask us any questionsif you have any questions. We are available at least Im available in the clinic

    Tuesday Thursday and Friday if anybody wants to come see me they have any

    particular question or you can email me please do so. Okay so thats important. Uh I

    apologize I dont have any pictures of teeth for you to look at. I know this is dental

    school. The teeth will come later in the course. Once we learn about production of x-

    rays and how to aim the x-rays and how to place the film then well actually show

    you the results So if youre looking for color slides you donthave any. In radiology

    everything is all black and white. This is not going to be like pathology where you

    see all the colors and stains and things like that. Okay so what were gonna do were

    gonna start with the basic principles and if anybody wants to go ahead and read the

    textbook you can go ahead and do that. The first thing were going to talk about isactually ionizing radiation and the basic principles of x-ray generation. Now were

    sitting in the room right now. Were being bombarded with radiation. Okay. The

    light thats hitting you is a form of radiation. Its a form of electromagnetic radiation.

    X-rays fall into that spectrum. One of the and were going to show you slides of that

    in a moment. So there is radiation in the room. If you were to open a radio youd

    have a radio signal. There is radiation uh radio waves. That is another form of

    radiation. So the definition of radiation is the emission and propagation of energy

    through space in the form of waves or particles. When we talk about x-rays were

    gonna some parts of the course will talk about waves with wavelengths or bundles

    of energy called photons. So those are synonymous- photons and energy waves. Uh

    energy waves have no mass. There is no mass in the energy wave. And radiology isbasically the study of radiation and the effects of radiation. Uh before we start on

    the actual radiology were gonna looka little bit about the history of x-rays. The x-

    rays were first found by Wilhelm C Roentgen, who was a German physicist. And he

    was a professor at the University of Wurzburg. And like many inventions or

    discoveries he was working in his laboratory late at night and what they were doing

    at the turn of the century is they were working with these glass tubes- vacuum

    tubes. A vacuum mean the air has been removed from the glass tubes and they had

    electrodes- positive and negative- anode and cathodes- hooked up and they shot

    electricity through these glass tubes and they were gases in the tubes and they

    noticed that when they shot electricity through the tubes certain lights were

    forming. Different form, different color lights were forming. Thats the concept ofneon lights if you go to Vegas or in New York you see that there are different colored

    lights. They were interested in the reaction of electricity and gases. And what was

    actually happening well see in a few minutes- is when the electricity hit the gas it

    caused ionization of the gas. Ionization of the gas, ionization is the loss of an electron

    when that electron is lost another electron when into that position and there was a

    loss of energy and that energy was in the form of light. He was working in the

    laboratory and he noticed on the other side of the laboratory opposite of his cathode

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    ray tube or crooks tube. That started glowing. There was a photographic plate there

    and it started glowing. And he said well something is coming out of here so he

    covered these tubes with black paper. Something was coming out the glass tube that

    was striking that and was causing it to glow. And as well see in a little while, one of

    the properties of radiation, it has the ability to cause glowing of certain types of

    chemicals, fluorescent chemicals. He then moved, he moved that plate closer to thetube and he noticed the glow was even stronger. It was glowing more. It was

    something coming out of the x-ray tube that was causing that to glow. He had no

    idea what it was and hence the name x-radiation. X is the symbol, the algebraic

    symbol, for I dont know. An unkown radiation. And for many years after his paper

    he actually won the Nobel prize for this. It was called the Roentgen ray. Named after

    him. So if you ever see an old textbook it says Roentgenology, that is radiology. It

    was named after him. Uh he then proceeded to call his wife down uh middle of the

    night. And his wifes name was Bertha. And he said Bertha, do me a favor, could you

    put your hand, he didnt put his hand for whatever reason I dont know. He said

    Bertha, do me a favor, put your hand over here next to the tube. And he noticed the

    fingers, the bones of her hand were on the photographic plate. Something wascoming out of that x-ray, well that wasntan x-ray tube. It was a glass tube called a

    crooks tube. Something was coming out of there that had the ability 1- to cause

    glowing, 2- it had the ability to penetrate an opaque object. It had enough energy

    and well talk about how x-rays modern day. It had enough energy to penetrate

    Berthas hand and she actually saw the fingers of her bones on the photographic

    plate and that laid the foundation for modern radiology. Okay then proceeded to uh

    well when she saw that she said in German. Does anyone speak German here? She

    said [he says something in German but unfortunately I am monolingual soooooo

    sorry no clue what he said]. Which means uh Wilhem youre working hard, lets go

    upstairs. No, it doesnt mean that (students laugh). It means literally it means I have

    seen my death. She saw, ya know, skeleton, dead person. No meat on the body. Justbones. This was unbelievable. He then proceeded to take his shotgun, whatever he

    had around. Lets x-ray this. Took his shotgun- and that led to industrial use of the x-

    ray. In many industrial situations they take x-ray of steel beams, of concrete, to see if

    there are any breaks or fractures in there. He also then took a box, put something in

    the box. And he x-rayed the box and he was able to see what was inside the box. And

    that led to the modern, go to the airport, and you stand in there and you do all kinds

    of things and they were able to see what was on your body .So that was the

    beginning of uh modern radiology. He is called the father od radiology. He wrote his

    paper. He got a Nobel prize for it. And just to show you how dentists are very uh ya

    know, I say smart, okay. Somebody heard about it and the guys name was Otto

    Walkhoff, he was German dentist. Hes the person who actually took the first dentalradiograph. It was a lower premolar of his own mouth. He didnt call his wife. He

    laid down on the floor for 25 minutes and he blasted himself with radiation for 25

    minutes. Okay not good in todays uh but he is credited with doing the first

    radiograph. And then the next guy on the list is Dr Kells, he was a New Orleans

    dentist. He was the first one in the USA to take a radiograph. William Rollins is very

    very, a man after my own heart, he was the first person to notice, I dont know how

    he did that, but he surmised that something is dangerous is going on here.

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    Something is not right. And there may be harmful effects to this. So he is actually the

    father of radiation protection. What he said was lets take this glass tube, which was

    exposed to the air, and lets put some lead shielding around it. And lets make a little

    opening so the x-rays come out of that little opening instead of flying all over the

    room and radiating everything in the room. So he is the father of radiation

    protection. And he actually uh he actually suggested that if you take a radiograph ona patient put a lead apron on to protect the patient. He surmised that idea if you do a

    radiograph of the face you dont need to rest of the body radiated. So he is the father

    of radiation protection. And the last guy on the list. He is the guy that is credited

    with the prototype of the x-ray machine we use today. And many many respects, its

    almost exactly like we use today. Before there were this ionization of gases. We

    werent able to control the amount of electrons ionized. He was the first one who

    developed something called a hot filament tube. Hot filament tube. Uh Dr Cooliges

    coolige tube, hot filament tube, where instead of randomly hitting gases he put a

    piece of metal in there and he struck that with electrons and were going to go over

    that. That is basically the same design that we use now in our modern x-ray

    machines even today. So that is a little bit of a history.

    [3]- Wilhelm Conrad Roentgen

    [Dr Friedman]-Okay this is. I carry a picture of him in my wallet. No I dont. But that

    is the guy. He discovered x-rays.

    [4]- Atomic Structure and Ionization

    [Dr Friedman]- Okay now you have to understand that whatever happens in

    radiology happens at an atomic level. You cant see what is going on. There are

    electrons and atoms and protons and atoms of body tissue and atoms of metal that

    are involved. So were just going to basically cover a few topics in atomic structure

    and well talk about ionization in a moment. Atomic structure. What do we have? Wehave things called molecules. And what are molecules? Smallest particle of a

    substance that retains the property of the substance. So for example H2O is a

    molecule. Okay. Sodium chloride is a molecule. Smallest particle of a substance that

    retains the property of the substance. The atom is the basic unit of matter. Okay so

    each element has its own atom. And uh, the atom contains subatomic particles.

    Subatomic particles- you have a nucleus, which contains protons and neutrons. So

    protons are the positively charged subatomic particles. And neutrons have no

    charge. So a neutron walks into a bar and orders a drink. And he says to the

    bartender after he is done- how much do I owe you? And he says, no charge. Very

    good. Okay. How about two atoms walking down the street and one atom says to the

    other, I dont feel so good today, I think I lost an electron. He says, are you sure? Hesays, Im positive. Okay. So thats about it. Okay. How could you make a joke about

    atoms, I dont know. But I have a hundred of them. If youre interested come tothe

    clinic Ill let you have a couple of them. Okay. All right and then surrounding the

    positive, surrounding the nucleus, which is positively charged, we have the electrons

    which are rotating. And the electrons have specific shells. Therescertain numbers

    of electrons. I know this is all ya know so Im gonna go over this very quickly .Uh

    what keeps the electrons in the orbit. Because the electrons are spinning at very

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    high speeds. So there has to be a balance between the centrifugal force of the

    electron, the spinning of the electron, and the positive charge. The electrons are held

    onto the atom by the nucleus. The nucleus is positive so others an attraction and

    that keeps the atoms where theyre supposed to be.

    [5]- The Atom

    [Dr Friedman]-Okay so this is a diagram of the atom. Number one are the protons,

    which are positively charged. And then the electrons are rotating. And you have the

    uh positively charged, thats the nucleus. And then you have the electrons. Theres

    something called binding energy. The electrons, the amount of energy necessary to

    remove an electron is called a binding energy. The amount of energy. So where do

    you think, which one would have a higher binding energy? The inner shell or the

    outer shell? Inner shell. Because it is closer to the nucleus. As a matter of fact an

    inner shell electron, in order to remove an inner shell electron, requires 69000

    volts, energy volts, electron volts of energy. 69000. Thats gonna come up later when

    we talk about radiation. The outer shell of electrons, the further you get away fromthe nucleus, the less binding energy. So the K shell is the inner shell that has the

    most binding energy. As you go further away less and less binding energy. Which

    means you can ionize an atom, a large atom, with a lot of outside electrons, without

    radiation. You can do that with electricity. You can even do it with heat. You will see

    in a moment. If you heat a large atom like tungsten you will get boiling off of the

    electrons.

    [6]-Atomic Structure and Ionization

    [Dr Friedman]-Okay so just very quickly. So the atomic number is called Z. Thats

    the number of protons. The atomic mass is the protons and neutrons, thats the

    letter A. Electrons have very very little, very very little mass. Negligible amount ofmass. What is a neutral atom? A neutral atom is the one we just saw [he goes back a

    slide to show the image]. It has an equal number of protons in the nucleus as

    electrons. If we knock one of those electrons off we have caused ionization.

    Ionization. Ionizing energy is that energy that has enough energy to remove an

    electron. So if I hold my hand up to a light, light is not harmful. Its not ionizing. It

    doesnt have enough energy to cause damage. X-rays, however, will penetrate but

    they also cause ionization of the atoms of the body. And that ionization of the atoms

    of the body, youlllearn, causes harm. Potential harm to the patient .So the basic

    theme in the course is the least amount of radiation, the best possible film with the

    least amount of radiation to the patient. Okay so we got that. Ionization. The

    definition of ionization is loss of an electron causing the production of a positive ionand a negative ion. The negative ion is that electron that shoots off, itshanging out.

    the positive ion is the remainder of that atom and well see diagrams of that. There

    are different types of photons, or energy waves, or bundles of energy. Light. Radio

    waves are not ionizing. Radar is not ionizing. Well see a whole group of them and

    well discuss that in a moment.

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    unit of time. So which one do you think has higher frequency? Which one has more

    bumps? The top one. The shorter frequencies have higher wavelengths. They

    contain more energy and those are the one that can penetrate and cause harm.

    Longer wavelengths, less energy.

    [11]- Properties of Radiation[Dr Friedman] Okay so properties of radiation. Of all electromagnetic radiation

    including x-rays and light and well see the whole spectrum. No mass. Neutral

    polarity. Travel at the speed of light- 186,000 miles per second. Propagate an

    electric field at right angles to their path of travel.

    [12]-Electromagnetic Spectrum

    [Dr Friedman]-And here is our electromagnetic spectrum. On this side we have very

    very long long wavelengths. These are measured in meters. On this side, we have

    short wavelengths such as x0rays, gamma rays. This is the guy were going to be

    looking at. Dont memorize any of these numbers here. You dont need to know that.

    You just need to know these are all electromagnetic radiations. They havesimilarities. The differences between each one have to do with he wavelength.

    Shorter wavelengths are damaging and have the ability to penetrate. Longer

    wavelengths will not penetrate. SO we have television and radio and radar on this

    side. Then we have microwaves, which really are not ionizing. When you put

    something in there it causes heating of the water molecules, but its not really

    ionization. The ionizing radiations are the gamma rays and the x-rays. Okay. And in

    that group are ultraviolet rays as well.

    [13]- Properties of Radiation.

    [Dr Friedman]-Properties of radiation. X-rays specifically. Theyre odorless. So if you

    come down basically you can see all of these things if you come into 1A and youwatch us take x-rays. Uh theyre odorless. If you smell anything its not the x-rays. I

    would look at maybe the patient. Tasteless. Whoever tasted these things. Theyre

    invisible. We had students today coming down to the clinic from upstairs. Uh Dr.

    Friedman I want you to look at my x-rays. You see I cant look at your x-rays. The x-

    rays are invisible. There an invisible form of electromagnetic radiation. After having

    said that everybody in the clinic upstairs is gonna say put your x-rays on the view

    box let me see, go develop your x-rays. The correct term is radiographs or films. But

    everyonesgonna say x-ray- go take an x-ray. Its invisible where I cant see it, what

    do I do? Okay so thats invisible. How do I know that? Because if Im in the cubicle in

    1A I dont see anything coming out of the machine. Imaiming at the patient and I

    dont see anything. Its invisible. So some of these things you can see just by lookinginto the room. Uh travel in straight lines .Why do I know they travel in straight lines?

    Because if this is the tooth that I want to take a picture of I take my collimator,

    which I have a whole collection of here, and I aim it straight at the patient. I dont uh

    I dont do something like that. I aim it straight. So they travel in straight lines. Travel

    the speed of light. They have the ability to ionize atoms. Why do they have the ability

    to ionize atoms? They have very short wavelength. Short wavelengths contain a lot

    of energy.

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    [14]- Proper of Radiation

    [Dr. Friedman]- Uh produced by an electrical current. Electric current. How do we

    know x-rays are produced by an electrical current? Because theyre plugged into the

    wall. The machine is plugged into the wall. So the electrical energy somehow when

    you push these buttons is converted to x-rays. And were gonna show you how thatactually works. But it is produced by an electric current that penetrates opaque

    tissue. How do I know? I put a film behind the tooth. I send the x-rays through.

    Process the film and I see the tooth. I see an image of the tooth. So it has the ability

    to penetrate opaque tissues and structures. Now of course in a tooth, there are

    different densities of the material. You have the enamel, which is very dense, you

    have the dentin, you have the pulp So x-rays will go through, and some of them will

    go through further than others. For example, the pulp tissue, which is soft tissue,

    will appear black on an x-ray because the x-rays penetrate. The enamel or if the

    patient has a crown, ever see a picture of a crown? A radiograph of a crown? Itll be

    white because the x-rays have not penetrated. They have been absorbed by the

    crown metal. And well see that later on when we talk about formation of the image.Right now were talking about the x-rays coming out of the x-ray tube. How do we

    produce them? And how do we control the penetrating ability? Can affect

    photographic emulsion. The film that is in the patients mouth is a photographic

    emulsion. The x-rays penetrate, theres an image, a latent image that is produced on

    the film, when you process it you can see that. That is going to be covered in the

    lecture of processing film. It is given by Dr Jane. Good luck.

    [15]- Uses of X-rays in Dentistry

    [Dr Friedman]- Okay uh very nice. Okay uses of x-rays in dentistry. Okay. One of the

    uses, the main use of radiographs is for diagnosis obviously. The patient comes in-

    doc Im having pain when I have something cold. So the patient has pain whentheyre having something cold, what would you suspect? Anybody? You didnt learn

    this yet? Okay. Uh they may have a cavity. A cavity is a hole in the tooth. So when the

    cold goes into that cavity it goes into the dentin and nerve and I feel it .okay what

    else could be? Well if the patient has a large amalgam filling, a silver filling, and they

    have something cold, guess what happens? The cold is conducted by the metal right

    into the tooth and theyll feel a momentary sensitivity. Okay. Another way patients

    can have sensitivity to cold? They have gum recession. So the gum is covering the

    root surface which has nerve endings in them and if the gum recedes guess what

    happens? The cold goes right there and they feel the pain. Now youre going to

    diagnose that how do you know what to do? Do I drill the tooth? Do I change the

    filling? Do I send the patient to a periodontist? Anything like that. So youll need afilm to diagnose that. If the patient says I feel sensitivity to cold but then it goes right

    away. It only lasts for a few seconds. Do you know what that means? That means its

    a healthy tooth. Its a hypersensitive tooth but the tooth has a nerve. its responding

    to the stimulus, the cold, the tooth says oh. But then a few seconds later it doesnt

    hurt. So what does that mean? It means that the nerve has the ability to shut off the

    response. Now if the patient walks in and says doc Im having pain for two days and

    its not stopping- that nerve is bad. Youre gonna have to do something like root

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    canal therapy. But in order to know all of this information you cant tell by looking at

    the tooth. Diagnosis ya know. Theres a thousand different things you can do with

    that. Legal evidence? You have to have appropriate radiographs in the patients

    chart. And they have to be good quality radiographs. If youre ever summoned to

    court, god forbid, and you have lousy films, you probably lost the case right there. So

    its very important to have good radiographs. Also, theresa situation where a fellowcame down came up from Florida to a dentist in New York, this was written in the

    journal. And they had a bad toothache and they went to the dentist. The dentist said

    that tooth has to be extracted. Oh but doc I dont want any x-rays I just had x-rays,

    can you just extract the tooth? The tooth was broken down from decay to the gum

    line the dentist took the tooth out without a radiograph. Patient healed there were

    no problems, no post-operative complications and then a month or two later gets a

    letter from an attorney that the patient is sewing the dentist. Why is the patient

    sewing the dentist? Because that tooth couldve been saved. Okay whats the

    defense? You have no defense. So before you do anything take a radiograph. Very

    important. Itscalled the CYA principle. Cover Your. Im not gonna say because.

    Okay so you always need to have good radiographs in case of something like hatoccurring. Therapy well radiation therapy, god forbid the patient has some type of

    cancer in the mouth or in the head, they use radiation therapy. What does that have

    to do with radiology? Well patients who undergo radiation therapy what happens

    to their teeth? Anybody know? They have severe caries in their teeth. Anybody

    know why? Any guesses as to why a patient undergoing radiation therapy will have

    severe caries especially near the roots? Near circumferential caries. Anybody?

    Because the radiation kills the tumor but it also destroys the salivary gland tissue

    and theres no production of saliva. No production of saliva caries. Xerostomia. Dry

    mouth. Okay and the last one is forensic use. I was here in the school 911. And uh it

    was a horrible situation. People were running uptown and we were called in at the

    time. Dr. Fromer, who was the author r that textbook, and myself to the morguetotake radiographs of the body parts and the teeth and see if we could identify

    patients that way. You may get a call in your office. Did you have a patient named so

    and so? Do you have their radiographs? We need to see them so we can match the

    body to that. Okay a little morose but that is what uh another use of dental

    radiographs are. Okay. Lets go to the next one.

    [16]- The Dental X-ray and Its Components

    [Dr. Friedman]-Now were actually going to talk about whats in the x-ray machine

    that you hanging in all the clinics. When you look at he x-ray machine youre going

    to see something like this sticking out of it connected to a machine. Thats called the

    tube head. Part of the machine that you see is called the tube head. Inside the tubehead is a little glass tube, remember Roentgen with the glass tube and Coolige. Glass

    tube. And were gonna talk about that. And there are different components to the

    glass tube. Im gonna give you some terms and then were going to show you

    diagrams and were going to relate the term to the diagrams. There are two parts to

    the x-ray tube. The x-ray tube is about 6 inches long, its wired up with electrical

    wires and well talk about the wiring system. And thats where the x-rays are

    produced. They come out of the x-ray tube and they go through the position and

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    something? (43:29 not sure what he said) and they hit the patient. Okay, the first

    component of the x-ray tube is the anode. Which is the positive part of the x-ray

    tube. The anode is the positive part. And I actually have a piece of anode here for

    display purposes but were gonna see that in a minute. What the anode contains is a

    stem or a sleeve, this copper device, its made out of copper. And Ill show you

    diagrams of that. It has a little piece of tungsten. White metal, right here on thesleeve, tungsten. So what happens well see in a moment. Electrons will strike the

    tungsten. Focal spot. This tungsten is called the target or the focal area. So the target

    or the focal area is synonymous, same thing, but theres one sport right in the center

    where the x-rays are focused to. That is called the focal spot. So the focal spot is a

    small part on here the entire is called the focal area or target. Primary radiation.

    What is primary? There is primary and secondary radiation. Primary radiation is

    defined as the radiation in the air before hitting the patient. So when you aim that

    collimator the x-rays coming out of the collimator, or position-indicating device, is

    called primary radiation. When that primary radiation hits the patient or hits an

    object itsconverted to secondary radiation. Thats for a later lecture. Uh then you

    have the negative part of the x-ray tube, the glass tube. The negative part is calledthe cathode and the cathode contains a little tungsten filament. So tungsten is in

    anode and in the cathode. Its a little thin wire like in a light bulb. And then theres

    something called the focusing cup, which is made out of molybdenum. Its hard to

    say but thats what it is. Its molybdenum. And that focuses the electrons from the

    cathode over to the anode. Remember electricity flows from the negative to the

    positive so well see that in a moment. Well see in a diagram. Well put all of this

    together in a second.

    [17]- The Dental X-ray and Its Components

    [Dr Friedman]-Uh then you have the glass envelope, which is the glass tube, and a

    little opening in the glass tube where the x-rays come out of is called the porte. Theporte is the opening in the glass tube. Then we have an aluminum filter. Well look at

    that and well talk about that in a minute. And then you have a diaphragm okay. The

    aluminum filter I can show you. So remember this is screwed into the tube head.

    Theres a little glass x-ray tube, the x-rays come out, the first thing that theyre going

    to encounter is a piece of aluminum, a very thing strip of aluminum. And then when

    you go past the aluminum youll actually see something made out of lead. This

    particular one, Im sorry, I wont show you pictures of that. Anyone is welcome to

    see that later. Then you have lead. The purpose of the lead is to collimate the x-rays.

    We dont want the x-rays hitting the entire patients face. So theres a little hole

    where the x-rays come through so all the other x-rays are stopped by the lead. Okay

    so were gonna talk about what the purpose is. Why do we put these things in here?And the answer is to protect the patient. And youll see how these devices protect

    the patient.

    [18]- The Dental X-ray Tube

    [Dr. Friedman]-Okay so this is just a diagram of the x-ray, dental x-ray tube, which is

    in the tube head. There is no air. Its a vacuum tube. The air has been removed. Why

    do we remove the air? Two reasons. 1- we want electrons to shoot across to form

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    radiation. We dont want any air to prevent the movement. Theres no air? We have

    freer movement of electrons. The faster the electrons move, the more kinetic energy

    they have, and the more radiation, the better quality x-rays are produced. The low

    wavelengths. (2) The air is also removed because also you dont want oxidation of

    the tungsten filament and well see that in a moment. So the air is removed for those

    two reasons.

    [19]- X-ray Production

    [Dr. Friedman]Okay heres a few terms. Were gonna talk about all of these things

    when I show you a diagram. Thermionic Emission Effect. Okay now I dont know

    how we can do this. I can try my best but uh what happens is is heat generated in

    the x-ray machine when you turn the x-ray machine on and it heats a little filament

    and the filament by being heated produces electrons. The electrons are needed for

    production of radiation. Theres an Electron Cloud, which hangs out at the cathode

    by the filament. The cathode rayis When the x-ray, the electrons shoot across the

    tube. Kilovoltagecontrols the amount of voltage in the circuit. And Head Leakage

    just means when x-rays are coming out of the tube head thatsa dangerous situationand you want to avoid it.

    [20]- The Dental X-ray Tube

    [Dr Friedman]-Aha finally a picture and now lets put all these terms together for

    you. There is a negative end called a cathode, which contains a little filament of

    tungsten, a thing filament of tungsten. Surrounding that is a focusing cup made out

    of molybdenum. Okay so that is the negative end. This is the positive end, which has

    a little piece of tungsten, called a tungsten target, which is embedded in copper.

    Why? A lot of heat is produced and tungsten is not a good dissipater of heat. So we

    cant to remove the heat so we dont burn out the tube so we put it into a copper

    sleeve that is going into a cooling mechanism outside. Well talk about that. This isthe anode, the positive end, again, contains the sleeve, a copper stem, and a tungsten

    target. Notice the tungsten target is angled, it has an angulation. Well talk about that

    in a little while. The x-rays are produced and they come out through a little opening

    called a porte. Just get the terms down because were going to go step by step. Thats

    called the porte. And of course you have the aluminum filter and the diaphragm The

    aluminum filter and the diaphragm. Again, the aluminum filter well discuss. Purpose

    is the diaphragm is used to collimate to aim the x-rays at the most pin point area.

    Okay so.

    [21]- Rotating Anode

    [Dr. Friedman]-Okay so. Okay this is a machine that has a rotating anode instead of afixed anode. In large machines, panoramic machines, they will have a rotating anode

    so that it doesnt burn out the tube.

    [22]- Activated Filament Circuit

    [Dr Friedman]-Okay so lets start. And the way were going to start is you walk into

    your office in the morning and youre ready to work. The first thing you do is turn on

    your x-ray machine. Its on. Are x-rays being produced? No. What happens when you

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    turn your x-ray machine on? What happens is there are two circuits in there. In the

    tube. One is called the filament circuit that goes to the filament, or the cathode. And

    the other one is the high-tension circuit which goes to the anode. Okay so this is

    what happens. You turn your machine on, that causes heating of the tungsten

    filament. Youreheating the tungsten filament. When you heat the tungsten filament

    what happens? Electrons are boiled off. Theyre ionized from the heat. The tungstenyou look has a lot of electrons. The outer electrons can be boiled off. We need those

    electrons. Theyre just hanging out right there minding their own business and

    thats an electron cloud at that point. Theyre not going anywhere because theresno

    positive charge. Okay so then when you go ahead and put the film in the patients

    mouth and aim and then you walk out of the room and press the exposure switch,

    that is when you are setting up the positive charge. The electrons will then shoot

    across, hit the tungsten target, and that is how x-rays are produced. So you come in

    the morning, what you are doing is you are opening your machine; you are heating

    the filament circuit. How much voltage is necessary to heat the filament circuit? 2-5

    Volts. But we just said that the x-ray machine is plugged into the wall. How many

    volts of electricity are in the wall circuit? About 120 something like that 110. Okayhow do we get 2-5 volts into that circuit? Theres something called a transformer.

    There are two transformers in the x-ray machine. One is a step down transformer

    and Im not going to talk about how the wires are. Step down transformer. So when

    you turn your machine on you are activating the step down transformers taking 110

    volts of electricity and stepping it down to 2-5. What happens if you use more than

    2-5? You burn it out. So you need. Thats called the filament circuit orlong-voltage

    circuit. Itssynonymous. A filament circuit, a low voltage circuit, or low-tension

    circuit. Those are all synonymous. Okay so you have that electron cloud, you turned

    your machine on, 2-5 volts of electricity are heating the filament, electrons boil off,

    what do you think that effect is called? When the electrons are boiling off?

    Thermionic Emission Effect. Why? Therm means heat, producing ions, emission ofelectrons. So you have a bunch of electrons hanging out there ready. How do we

    control the number of electrons? Milliamperage. Well talk about that in a little while.

    So you got the picture? So you have the electrons hanging out there. You then go and

    put the film in the patients mouth, take your collimator and aim it at the patient,

    what do you then do? Youve activated the high-tension circuit. This circuit is now

    closed. And so doing that becomes positive. The anode becomes positive and only

    when you press the exposure switch, that causes the anode to become positive.

    When the anode becomes positive what happens to the electrons that were hanging

    out there? They shoot across the tube at very, very high speeds. Now how many

    volts of electricity are in the high tension or high voltage circuit? Anywhere from 50-

    100 kilovolts. Kilovolts. 70,000. The machines we have run at 70,000 volts ofelectricity. 70,000. Ill explain why you need that much. But thats 70,000 kilovolts.

    How do we get 70,000 kilovolts, which is 110 volts? Transformer. A step up

    transformer. Step up transformer. The more kilovolts you have, the higher the

    kilovolts, think about this. The higher the kilovolts, the higher the kinetic energy, the

    energy of those electrons shoot across. The higher the kinetic energy, the shorter

    the wavelengths are going to be. So if you have a patient who has a large skeletal

    build. Thats a patient for a guy with a big head. Okay large skeletal build. Youwant

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    to increase the kilovoltage to get more penetration. Because the kilovoltage controls

    the penetrating ability of the x-rays. So 70,000 volts you press the button, the

    electrons shoot across from the cathode to the anode and you get in a moment you

    see this is called the cathode ray. The electrons shooting across is called the cathode

    ray.

    [23]- X-ray Production

    [Dr Friedman]-Okay this is x-ray production. You press the exposure switch you

    close the switch here, the circuit is now closed the electricity flows through there

    causes that target area to become positive. The electrons strike, they strike at very

    very high force. So what do you need to produce x radiation? You need a source of

    electrons, which we have over here. Thermionic emission effect. We have to

    accelerate the electrons by using a very high kilovolt potential or peak and you have

    to have a target to stop the electrons. When the electrons strike the target, radiation

    is produced. And well show you how in a minute Okay. Anybody have nay questions

    about that?

    [24]- Types of X-rays Produced At The Tungsten target

    [Dr. Friedman]-Okay So when the electrons come across and they strike the target,

    three things can happen. 1- the electron can go into the tungsten target. Were gonna

    pick out one atom of tungsten. This happens millions of times. Were gonna pick out

    one atom of tungsten. One of the things that can happen is the electron can shoot

    right through and hit the nucleus and give up all of its energy and then no radiation

    is produced. Another thing that can happen is called Bremsstrahlung- that is the

    major source of radiation coming out of the tube. Caused by Bremsstrahlung,

    literally meaning breaking radiation. And then we have something called

    characteristic x-ray. So these are the two forms of x-rays coming out of the x-ray

    tube- Bremsstrahlung and characteristic. And both of them combined are used toproduce the image. Most of them will be the Bremsstrahlung.

    [25]- Bremsstrahlung and Characteristic X-rays

    [Dr. Friedman]-Okay so we have an atom this is an atom of tungsten. Remember we

    shot the electrons across, they hit the tungsten target, this is one atom of the

    tungsten target. So. You have two different electrons lets say this is electron A, this is

    electron B. The electron goes into the target, into the tungsten atom, and gets close

    to the nucleus. What happens when it gets close to the nucleus? It gets ejected

    because the nucleus is positive and this electron gets positive and you end up with A

    prime. The energy that slows down the electron and causesdoes anybody drive a

    racecar? When youre going very fast and then you get to a curve you have to slowdown, there is a loss of energy. This is almost like a racecar. When the electron is

    coming at very high speeds it comes into the tungsten and strikes the tungsten atom

    and it gets close to the nucleus. When it gets to the nucleus actually the electrons, I

    misspoke before. And then electrons, you can correct me if Im, and the electrons

    will actually eject because the negative chargers the similar charges. So as if gets

    close to the nucleus, the inner shell electrons will repel that. And the slowing down

    and the veering off course, the change in direction, the breaking, produces energy in

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    the form of Bremsstrahlung radiation. Okay. Now what do you think happens to that

    A prime? The A prime goes its a million atoms. That A prime goes into the next

    atom. And the same reaction occurs. But what do you think happened? Which one

    will have more energy? This one of the second one where the electron has been

    slowed down? This one will have more energy. The other one the electron is already

    slowed down. It goes into another atom, more bremsstrahlung radiation isproduced. So in effect what do we have? We have a heterogeneous formation of x-

    rays and some of the radiation will have short wavelengths and longer wavelengths,

    longer are whole different group of wavelengths. Which of the wavelengths that we

    need for our patients to get the best possible image? Short wavelengths, those are

    the ones that penetrate. What would happen if the long wavelengths hit the patient?

    Its gonna bombard them with radiation, cause damage, ionization. But theyrenot

    useful. Theyrenot going to form an image so we dont want those there. How do we

    get rid of the Aluminum filtration? What the aluminum filter does, it removes the

    long wavelengths that are non-penetrating. Those will be harmful to the patient. The

    short wavelengths will penetrate the aluminum. Okay that is one way of forming

    radiation. The other way is the electron goes into the atom, strikes the inner shellelectrons, and actually knocks it out of its orbit. Remember we said what the binding

    energy of an inner shell electron is? 69,000 volts. 69,000 volts or 69 kilovolts. The

    only way we can get a high-speed electron to be able to do that is if we use our x-ray

    machines from 70-90 kilovolts of energy. Done by the step-up transformer. So the

    high-speed electron hits the inner shell, it knocks out that k shell electrons, which

    requires 69000 volts of energy, and what happens? The other electrons cascade into

    the inner shell. And when an outer shell electron goes into an inner shell electron,

    into the inner shell, theresa formation of energy. Energy is given off just like when

    there is ionization, light is given off. This is in the form of something called

    characteristic radiation. Without getting into detail its characteristic to the atom

    used. Tungsten we have characteristic radiation. Very small amount of the radiationhowever is in this form. But those are the two ways that radiation are formed.

    Bremsstrahlung , high speed electron veers off course loses energy. The other way is

    it knocks out the inner shell electron, the electron from the outer shell coming in has

    to give up a lot of energy to give up the inner shell and that is given off in the form of

    characteristic radiation.

    [26]- The Dental X-Ray Machine and X-ray Production

    [Dr Friedman]- Okay uh you guys mind if we take a five minute break? Okay. Im

    sorry for these two hour lectures. I dontknow how. [5 minute break] Attention.

    Alright lets get back to this so we can get ya out of here. Okay. Uh do we have any

    anybody from Canada here? All right! Okay you guys have a 4thof July in Canada?You dont have a 4thof July right? Today is the 4th. Okay so you dont have a 4thof

    July. You have one day less than we do in the year? No but you find that clinic 1A is a

    very Canadian friendly clinic. Ya know why? We named it 1A. So explain that to a

    whatsthat? No? Alright. [laughing] Okay. So we were talking about we were talking

    about the different electrical components in the x-ray tube. We were talking about

    he low voltage and the low voltage circuit and the high voltage or high tension

    circuit. But basically electrical current is the flow of electrons and there the current

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    that we use here uh is called an alternating current. Alternating current. And what

    does that mean? It means the current flow from one direction and it changes and

    goes to the opposite direction. Well show you examples of that. Then is goes back,

    the flow. So in the x-ray tube there is some ramifications of the use of alternating

    current. And youll see some of that in a moment. There is also something called

    direct current. The x-ray machines we have on the 11th

    floor. If you havent had yourpreclinical radiology, our direct current units. The ones we have in most dental

    offices are alternating currents. Okay so were gonna talk a little bit about that.

    [27]- Wavelength image

    [Dr Friedman]-Okay this is what alternating current means. When you press the

    exposure switch, the current starts to flow and you have the peak of electrical

    current at the top, 90 KVP. KVP. P is the peak potential or the greatest amount of

    current that can flow at 90. Okay so what happens is as the current goes up, you

    start out with 20 40 60 80 you get a peak of 90 and then it comes back down again

    btu it reaches this point. The cathode is the anode is no longer positive its anode.

    And the cathode is positive. So what happens to the electrons at that point? Theydont go anywhere. At that point, whereyou have the reversal of the current. So at

    this point, from here to here, since you have a reversal, alternating current, there are

    no x-rays produced at that point. So when you press your exposure switch, and

    youreusing alternating current, are you getting a flow of electrons or are you

    getting impulses of electrons? The answer is pulses or impulses. So if I press the

    button one second, for one second there are 60 of these reversals. So in a cycle of

    alternating current, you have 60 reversals. So theres only radiation produced at this

    point and then when it gets here and then so on and so forth. So in one second you

    are going to get 60 impulses of radiation. In one second. Okay because of the

    reversal of the alternating current. Direct current doesnt work that way. Direct

    current gives you continuous peaks and so theres a continuous flow of radiation. Soif you look up in the clinic well show you a picture of that. Thats measured on the

    11thfloor. We measure it in seconds. In fractions of seconds- .5 second, .32 seconds,

    .16 seconds. When we measure the x-ray, the time of exposure here, in clinic 1a,

    were measuring it in impulses. How many impulses of radiation is the patient

    getting for that film? Well if I were to tell you that the patient is getting 30 impulses

    of radiation, for this film, how many second of radiation is that? Just divide by 60. So

    the answer is a half. Patients getting 10 impulses how many seconds is that? 1/6 of a

    second. Remember I told you you dont have to memorize numbers? But these

    numbers are the ones that they give you on board exams of conversion of impulses

    to seconds. So again if they give you impulses how many seconds? Knowing that

    there are 60 pulses per second due to the reversal of the current, the conversion isvery simple. Just divide by 60. So 20 impulses, 1/3 of a second. Those are the

    numbers that you are going to encounter. Sometimes on our exam Ill give you more

    information when it comes to that. But understand that you are getting pulses of

    radiation. Oh with direct current, now how do we get direct current from an

    alternating current plug? Theres a device in there called a rectifier. A rectifier. All

    you need to know about rectification, were not electrical engineers. A rectifier

    converts alternating current to direct current. That is a rectifier. Uh these machines

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    are self-rectified. The alternating current machines are self-rectified because there

    is a conversion to direct current by itself. Another term for this is halfwave

    rectification. Those are synonymous- self rectify because you produce it without

    anything, without any rectifier in there, and also halfwave rectification. Dont go into

    more detail than that. Okay.

    [28]- Comonents and Functions of the Dental X-ray Machine

    [Dr Friedman]- Okay we spoke about some of the components of the dental x-ray

    machine. This is just a review. Voltage, there are two voltages in the x-ray tube. This

    is gonna be a little bit of a review. We have the low voltage circuit, thats the filament

    circuit. When you turn your x-ray machine on, what you are doing is 2-5 volts of

    electricity being converted by a step down transformer. That heats the tungsten

    filament .What is the effects of the heated tungsten filament? Thermionic emission

    effect. The electrons are boiled off. Theyrejust hanging out there minding their own

    business. Theyrenot doing anything . Then theres a high voltage circuit, 70,000-

    90,000 kilovolts of electricity. And that is converted to high voltage by a step up

    transformer. Autotransformers are something in there to keep the line currentssteady. Yourenot responsible for that. And there are certain meters when the old

    machines you were able to set their kilovolts. I want 90 kilovolts, this is a large

    patient. And then the next patient I had in the chair was a pediatric patient who was

    5 years old. If I use the same kilovolts, kilovolts control the penetrating power, uses

    the same kilovolts, what kind of film do you think I would get on a pediatric patient?

    Very dark film. Unreadable because theres too much penetration. So we were able

    to change the kilovolts. Yourelucky. You dont have to worry about changing

    kilovoltage or milliamperage. Milliamperage as you see over here is by a step down

    transformer. We want to control the heating of the filament. We want to control the

    heating of the filament you change the milliamperage. The higher the milliamperage

    the more electrons boil off. So you have more electrons, are those electrons going toproduce higher, greater penetrating ability? No. That is the function of the kilovolts.

    So to get it straight kilovoltage controls the kinetic energy. Milliamperage then

    controls the quantity of x-rays produced. The higher the milliamps, the more

    electrons are boiled off. More electrons are boiled off, the more radiation you will

    have. You will not give you higher quality penetrating radiation but it will give you

    more radiation. And in so doing, you can cut down on the exposure time. That is

    important if you are taking ct scans, the patient has to be standing there, sitting in

    the machine for longer period of times. You want to have the highest milliamps.

    Some of the ct scan operate at 50-100 milliamps. Our machines cant take more than

    5-7. Some machines 10. Otherwise if you have so many electrons boiled off , they

    will burn out the target. There will be so many electrons bombarding the target.Thats why on those extra-oral machines, ct scans, you have a rotating anode. So the

    electrons shoot across and they hit a different part of the anode in the cycle. Okay?

    [29] Basic Electric Circuits of the Dental X-ray Machine

    [Dr Friedman]-Uh this is just the diagram of the. Heresyour x-ray tube. You have a

    step down transformer, which goes into the cathode area to crank down the

    kilovoltage. The voltage, the 2-5 volts. Not kilovolts, 2-5 VOLTS of electricity. And

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    you have the step up transformer. Dont memorize this. Okay this is for someone

    who is opening up the machine and wants to see all the uh schematics.

    [30] Other Parts of the Control Panel

    [Dr Friedman]- So what are the other parts of the control panel? Well what we spoke

    about previously was the x-ray tube itself. And the tube head. Theresparts of thecontrol panel- the on/off switch. What does that do? When you press the on switch

    what are you doing? Heating the filament. Thermionic emission effect. Thatsall

    youredoing. Then you have the electronic timer, you set the exposure that is the

    only thing that we have. Now if you are taking a full set of x-rays on a patient, do we

    use the same exposure time for every tooth? Centrals, premolars and molars? What

    do you think? The answer is no. Because the anterior teeth will be light. Okay the

    anterior teeth, excuse me. Youre using a pre-set exposure that is good for the

    anterior teeth, and you get the proper film. When you get to the posterior teeth,

    those teeth are thickest, the bone is thicker, youre not going to get as much

    penetration so those will come out light. So the anteriors are the correct exposure.

    So what do we do to compensate for that? We only have one thing we can do. Wecantchange the KVP, we cant change the milliamps. That is preset for you. Well

    letschange the exposure times. And youll see when you go to the clinics. Come visit

    us, Youll see a chart. Anterior, upper anterior- 10 impulses. Im just making these

    numbers up. Uh premolars- 14 impulses. Molars- 18 impulses. You have to increase

    the numbers of impulses so you get the proper penetration so you get a film that has

    the proper density, darkness, and contrast. Well talk about that in a later lecture.

    Okay and then you have the exposure switch. You place the film in the patients

    mouth, you aim your collimating device at the patient, you run out of the room and

    the patient says to you- are x-rays dangerous? No theyre not dangerous. So what

    are you running out of the room for? Why dont you stay in here? Because Ive got to

    press the button. So theres a button on the outside, a retractable cord, when youpress that buttons, two things happen. One thing, thats mandated by the federal

    government, is that you need a light that goes off to show that theres an x-ray in uh

    being taken at the time. Theres also an audible sound, youll here a beep as well. But

    what happens inside the machine itself? You have the high tension circuit is closed.

    When the high-tension circuit is closed what happens? The anode becomes positive.

    The electrons shoot across. What controls the speed of the electrons shooting

    across? The kilovoltage. The higher the kilovoltage, the faster the electrons shoot

    across. The faster they shoot across, the more energy, the lower wavelengths they

    will have. What do we do with the long wavelengths? We dont want those.

    Filtration. Well talk about that in a minute. Okay.

    [31]- Dental Control Panel

    [Dr Friedman]-and this is the exact machine they have upstairs. Notice is says 765

    DC. What do you think DC stands for? Direct Current. This machine has a rectifier in

    it which convers the alternating current to direct current and so when you make the

    exposure it is done in fractions of seconds. .32 seconds. Okay and we can control. We

    can use the setting for adult, we can sue the setting for pediatric, we can use the

    setting for film, for digital x-rays. And these are the differences. The anterior,

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    premolars, bitewings, and different molars. When you press those buttons you

    change the exposure time. Thats the only thing we have under out control.

    [32] The X-ray beam

    [Dr Friedman]-Okay again we used some of these terms. What is primary radiation?

    Thats the radiation coming out of the x-ray machine. Before hitting the patient.Once it hits the patient it becomes secondary radiation. Whats the useful beam?

    Well the x-rays coming out of the tube have all different wavelengths in them. Why

    do they have all different wavelengths? For two reasons. Number one is the multiple

    bremsstrahlungs. Okay when the initial electron goes in it produces short

    wavelengths, then it goes into another one and it gets longer and longer and longer.

    So theresa whole, its a heterogeneous group of radiation that is produced. Another

    way you can get a heterogeneous, a production of radiation, is remember the KVP. A

    t the top of that peak those electrons will shot across at the highest speed.

    Everywhere up the hill and down the hill you are getting less energy. So we have a

    combination of long wavelengths and short wavelengths. What is the, what are the

    wavelengths we want to use for the patient? SHORT wavelengths, those arepenetration. What do we want to do with the long wavelengths? We dont want to

    shower the patient with unnecessary radiation. We have to remove them and those

    are removed by some process called filtration. Use aluminum filters. Well talk about

    that in a little while. What is the useful beam? Its actually the beam that after it has

    been filtered. And after it has been uh collimated by the diaphragm. The PID is the

    position indicating device. They come in all sizes. We have 8, 16. Okay and youll

    learn that the loner the collimating devices the better the image. Well talk about hat

    when we talk about image formation. What they have in common is that they are all

    lead lined. So the x-rays dont fly out all over the room. And you have circular

    collimators which give the patient an extreme amount of radiation and you have

    little tiny rectangular collimators, which are exactly the size of the film. That is lessradiation. This is a 60% reduction of radiation to the patient as opposed to this one.

    Okay uh as this is what we used to use many years ago, if you walk into a dental

    office and the dentist has one of these pointy plastic cones, my suggestion is get out.

    Get out. Because what does this do? It doesnt collimate. The x-rays are aimed this

    ray. It shoots through the plastic and hits your entire face with radiation, no

    filtration, no collimation, plastic cone. Okay remember the x-rays that come out of

    the x-ray machine are called primary radiation. What happens when the x-rays

    strike an object? That is called secondary radiation. The x-rays strike the plastic

    before hitting the patient. High production of secondary or scatter radiation, which

    is very harmful to the patient .So this is the plastic pointy cone, run away. Okay?

    And again, secondary or scatter a radiation is defined as the radiation after hittingthe patient. Were not getting into that today. We have enough trouble with the

    radiation coming out of the x-ray tube. Well talk about what happens when it strikes

    an object or the patient.

    [33]- The Divergent X-ray Beam

    [Dr Friedman]-Uh remember that the x-ray beam coming out of the collimator

    diverges. Its a divergent beam. Just like the flashlight. If I had a flashlight here and I

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    stood next to the wall and I shined it on the wall youd have a circle. As I walk away

    the circle gets larger. And that happens with x-rays, and light, and all forms of

    energy. Theres a divergence of the x-ray beam. Okay so what does that mean? That

    means if you have a short collimator, the x-rays are not collimated for a long period

    of time, theres more divergence of the x-ray beam with a short collimator. The long

    collimator, well the x0rays will travel through the center. the ones coming out aremore parallel. Whatsthe problem of divergence of the x-ray beam? Well we want to

    take a picture of a small film. We dont want the x-rays to diverge. So which patient

    is safer? This patient thats getting x-rays from here or here? Right over here (long

    collimator). Okay so because of divergence, the surface area of the patient, and the

    theme of this course is protect the patient. And youll see, everything I talk about I

    dont know about the other lecturer, protect the patient. So because of the

    divergence f the x=ray beam, the longer the collimator, the safer it is for the patient.

    Were gonna talk about that when we talk about patient protection and the operator

    protection in one of the later lectures. Okay and we have again, the central ray, okay

    here is your anode, the electrons shoot across, the radiation is produced. Whats the

    central ray? Its invisible. Its an imaginary line with the center of the x-ray. We usedto use that. We aimed the central ray and this and this and this. Its jut a term

    meaning the central point of the radiation. And if you notice there are two devices

    here. Theresa diaphragm. What is the diaphragm? Its either a circular piece of lead

    if you are using a circular collimator. Or a rectangular piece of lead with a little hole.

    And all the s-rays are blocked except those center x-rays. The enter x-rays are the

    ones that are focused on the film. And after the diaphragm there is another device

    that protects the patient .so how does the diaphragm protect the patient? By

    collimating the beam. The diaphragms a collimating device. How does the aluminum

    filter protect the patient? The long wavelengths are absorbed, they dont come

    through that. So we are eliminating the long, non useful wavelengths, which are

    harmful to the patient, and will not form an image, So speaking about collimating,another term for these, these are called collimating devices. Theyre collimators. So

    if you see aim the collimator at the patient, thatsanother device that collimates the

    x-ray beam. So there are two collimators, one is a lead diaphragm, which youre

    welcome to see if you come up her a little later. Theres a piece of lead with a little

    tiny circle in there. X-rays just go through the center here. Okay and uh lets see what

    else we got.

    [34]- Secondary Radiation/Scatter Radiation

    [Dr Friedman]- Okay we spoke about this plastic cone thats that pointy cone I spoke

    about. Same thing happened but theres no collimation whatsoever. It goes all over

    the patient . and another problem besides the fact that theres no collimation, werenot dealing with primary radiation anymore. Were dealing with secondary radiation

    , which are longer wavelengths and they harm the patient. So if you see one of those

    plastic cones, get out. Okay.

    [35] Filtration and Collimation

    [Dr Friedman]-okay a little bit of a review. Filtration and collimation. What is the

    purpose and function of filtration? Very simple. Its an aluminum disk that is placed

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    after the x-ray tube in the collimator that absorbs the long wavelengths of radiation,

    the unnecessary, harmful radiation. What are the federal regulations? Remember I

    told you about numbers, you dont memorize numbers and things like that. If you

    got a red pen, underline this because they have this all the time. The federal

    regulation is, if your x-ray machine is operating at less than 70 KVP, from 50-70

    KVP, theres a preset machine with the KVP, you need 1.5 millimeters of aluminumfiltration. 1.5 mm. On some exams theyll put 1.5 inches. MILLIMETERS. Very thin

    disk of aluminum. And that will provide the proper filtration for that type of KVP.

    The higher the KVP the more filtration you are going to need. So any machine thats

    operating from 70 KVP and above, if you buy a 90 KVP machine, its more expensive,

    you dont need to do that, because the human eye sees the best image around70

    KVP. Well talk about that when we talk about image formation. 2.5 mm. 2.5 mm of

    aluminum filtration is necessary in order to have the proper filtration in your x-ray

    machine. What are collimation? Collimation is restricting the size of the beam. Why

    do we want to restrict the size of the beam? Were aiming at a little piece of film. We

    dont need the entire patients head hit with radiation. So how do we collimate the

    beam? With collimating devices. What are the two collimating devices? We spokeabout the lead diaphragm. Okay which is a lead block of lead, a thin piece. There is

    no federal mandate for that. You can have it as thick or as thin as you want because

    the lead will absorb all of the radiation except in that little center area. That circular

    or rectangular. And another collimating device is the position indicating device. Uh

    its another collimator. And rectangular collimation is what you will see in every

    machine in the office. If you go outside to private practices you wont see many

    rectangular collimators. Anybody know why? Because when you have rectangular

    collimator you have to be very precise when you take your films, otherwise you

    msiss part of the film. Thats called collimated cutoff. And so part of the film will not

    be diagnostic. The larger collimator, you never can miss. So when you are going into

    private practice, you have to weigh patient protection vs collimated cutoff. Youllmake those decisions when you et out there. What I can tell you as the research

    shows, if you use rectangular collimation, remember you are getting the same

    amount of radiation coming out of the machine, the same exposure time, nothing

    changes. But what you have is about a 55-60% reduction in radiation to the patient.

    Okay quality and quantity and x-rays. What controls the quality of the x-rays? Which

    uh which control factor controls the quality of the x-rays? So the penetrating power?

    KVP. The higher the KVP, the better the quality of the x-ray, more penetrating

    power. And what controls the quantity of the x-ray? Milliamperage. The higher the

    milliamps, the more electrons are there and so therefore you can reduce your

    exposure time, if you have a patient thats moving around a lot you want to reduce

    your exposure time. If theyre moving around youre gonna get a blurry film eitherway you do it so. And the last thing I need to tell you about very quickly, on this. This

    is something called half-value layer (HVL). Im just piling on but okay. Half value

    layer is how we actually measure the penetrating power of the x-ray beam coming

    out of the tube. Now KVP will control. KVP is an electrical term, but the actual

    penetrating power has to do with the HVL. And what HVL stands for is how much

    thickness of aluminum is necessary to reduce the radiation by half/ How much

    radiation, how much thickness of the aluminum filter is necessary to reduce the

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    radiation by half? Im gonna tell you that in our x-ray machine, we have a half value

    layer of 2.75. How do we get that? 2.5 is the actual uh is the actual aluminum filter.

    Remember 2.5? Were using 70 KVP. 2.5. And theres also inherent filtration in the

    machine. Whats the inherent filtration? Something else is filtering the x-ray. One of

    those is the glass porte. Its not an opening but theres a little thin piece of glass the

    x-rays have to go through. And also theres oil surrounding the x-ray tube. Theresoil the x-rays have to go through this oil .So those are the inherent filtration. So if an

    inspector comes to your office and you have an HVL of four that is a problem.

    Patient is getting too much radiation. They should have 2.5-2.75 in that range there.

    But hats the way of measuring the penetrating power. What controls the penetrating

    power is the KVP.

    [36] Position Indicating Device

    [Dr Friedman]- These are some of the position indicating devices or collimating

    devices.

    [37]- Rectangular Collimation[Dr Friedman]-Rectangular collimation.

    [38]- Film Packet and Collimation

    [Dr Friedman]-forget that one.

    [39]- Collimation and Filtration

    [Dr Friedman]-Collimation and filtration again. Just a repeat you have the lead

    diaphragm and then you have the aluminum filter.

    [40]- Half-Value Layer

    [Dr Friedman]- Half value layer. We take a disk of aluminum and what is thethickness of this disk of aluminum to reduce the radiation by half. Thats the half

    value layer .So youregoing to see on your machines when you buy them, its gonna

    have the KVP setting, its gonna have the milliamps setting, the standard setting, and

    its gonna have HVL, the half value layer. And what does that mean? It has to do with

    the penetration of the x-ray tube coming out. And sometimes the inspector will say

    to you. Your HVL is 4 and thats a fine. Theyre gonna give you a fine for that. But you

    can correct it and then you get your money back. If you take another piece of

    aluminum filter and you put it in there, certain thickness of aluminum filter, you can

    add that, then when he tests it the HVL is 2.5-2.7, youre in business. Okay so you

    dont have to get a new machine.

    [41]- Milliamperage Seconds/Quantity

    [Dr Friedman]-Okay and this is the last thing I want to show you very quickly only

    because it shows up on exams. When we talk about exposure to the patient, we dont

    talk about milliamps or exposure in seconds. We talk about milliamp seconds.

    Milliamps second. So what that is is the milliamps times the exposure time is

    milliamp second. That will control the total density of the film. How dark the film is.

    The more milliamps, the more seconds, the denser the film is going to be. So heres

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    an example, a radiograph is exposure to milliamps of 12 and a KVP of 90 and the

    exposure time is 1 second. So thats the first film. Your given is 12 x the exposure

    time is 1, the milliamps seconds in that case is 12! Okay a second radiograph is

    exposed with a new exposure time of 2 seconds but the density remains the same.

    So what is the milliamps setting? Anybody?

    [41]- mAs CALCULATION

    [Dr Friedman]-There it is. So its six. Because 6 x 2 is12. You have the same density.

    So when when talking about calculations of density of darkness on the film, they

    usually talk about milliamps second. So those are separate entities but you can

    combine them into milliamps second. Uh I just want to tell you one more thing and

    Ill let you go, youve had enough. Uh this process of x-ray production is very very

    inefficient. For the electrons shoot across and x-ray energy is produced, 1% of the

    energy, of the kinetic energy of the electron, is converted to x-rays, x-radiation. 99%

    of the energy is in the form of heat. Heat energy. And that heat has to be dissipated.

    So do you know what in the device, what in the x-ray tube, will dissipate the heat?

    The copper stem. That little target is embedded in the copper so that when theelectrons bombard, a lot of heat is given off, the copper stem removes the heat, and

    theressomething else in the x-ray machine, in the tube head. Its surrounded with

    oil. If youre ever working on an x-ray machine and you see oil dripping out. Call

    something .The oil is an insulating material, its supposed to dissipate some 0f the

    heat that he target, the tungsten, the copper sleeve cannot dissipate. Okay. What I

    suggest you do, okay, for exam purposes, uh dont wait for a day or two because

    these things are going to pile up on you. And uh Its going to be too much. What you

    want to do, I know you guys are going to the beach and all that on the weekend, I

    would uh I would take a look at the textbook and just read it. I dont want you to

    memorize anything as far as diagrams. Just have a basic information what is

    filtration, what it is, how does x-rays produced, what happens in the anode, at thecathode, what controls these factors? So I through a lot out at you and if anybody

    has any questions please come forward and ask me, Ill be more than happy to

    answer you. But the way to do well in this course is to come to lecture, listen, and

    then you youre gonna leave with a foggy head and the best way is to just get that

    little textbook there. If you understand this, you dont need to textbook. If you want

    to put everything together in understandable terms take a look at the textbook.

    Okay? I think well see you Thursday. Okayyyy.