Basic X-Ray Overview
This course is divided into 12 parts. It is recommended that the student print out a copy of the course and read each part carefully before proceeding to the examination.
Objectives:
After completing this course the student should be able to:
1. Discuss the origins and properties of X-rays
2. Know the biological effects of radiation
3. Understand basic safe operation of basic x-ray equipment
4. Understand the safe handling of x-ray film
Part 1
Discovery of X-rays
Wilhelm Konrad Roentgen- Discovered X-Rays in 1895
- Won Nobel Prize in Physics in 1901
- Decided to call his new discovery "X-Rays ("Because "X" is the unknown in algebra)
- Also called "X-Rays" because he wasn't sure what they would do
Properties of X-rays
- X-rays are a form of electromagnetic radiation. This is similar to Gamma radiation. The differences being that x-rays have a higher energy photon and a much shorter wavelength.
*PHOTON - A very small bundle of electromagnetic energy
- other forms of electromagnetic radiation are radio waves and visible light waves.
X-rays have certain properties:
* Since they have very short wavelengths, they can penetrate most forms of matter (except LEAD)
* They travel at the speed of light - 186,000 Mi/Sec
* They only travel in a straight line
* They are neither Positive nor Negative (Neutral)
* They can make certain chemicals emit light
* They can ionize matter, including living tissue (Biological Damage)
* They obey the Inverse Square Law
* They cannot be reflected, but they can be deflected (ricochet like a bullet)
* Cannot be seen, heard, or felt. This is why radiation is so dangerous.
Ionizing Radiation
- Radiation is the emission of energy in the form of waves and particles.
· When radiation interacts with atoms, the atoms are transformed into electrically charged particles, called Ions.
· - this conversion is know as ionization
Sources of Ionizing Radiation
- There are two types of ionizing radiation: Natural and Man Made
- Natural sources are: - Cosmic Radiation from the sun, stars, moon
- Radioactive Materials (Uranium, Cesium) found in the earth
- Radionuclide
- Man Made sources are: - Radiographic and Nuclear Medicine procedures
- Fallout from atomic and nuclear testing
- Television
- high voltage electronic devices
Interaction of x-rays with matter
- X-rays can interact with matter in a number of ways:
- Photoelectric effect - when an x-ray photon interacts with an electron around an atom, and the x-ray photon transfers all of its energy into the electron.
-Compton Effect - when the x-ray photon transfers only part of its energy into an electron and the remaining energy of that photon known as a low energy photon. This travels in a different direction and causes scatter radiation.
-Pair production - when the photon changes its energy into an electron and a positron (positive electron).
X-ray Production
- X-rays are produced when fast moving electrons are accelerated towards a target (Anode). This target has a positive charge, and is made of a material called Tungsten. Tungsten has a very high melting point and very high heat conductivity. The electrons are produced when a filament inside the tube (Cathode) is heated. This filament is also made of tungsten. When a high voltage (60 - 110,000 Volts) is applied to the filament, the negatively charged electrons are emitted from the filament and are attracted to the positive charged target. As the high-speed electrons are rapidly decelerated by hitting the target, x-rays are produced.
MA
- MA (Milliamperes) controls the number of electrons produced, and the amount of heat produced. By varying the MA on the machine, we can control the Quantity of x-rays produced.
KVP
- KVP (Kilovoltage Peak) controls the speed of acceleration of the electrons. This acceleration controls the Quality of the x-ray beam. The higher the voltage, the greater the speed of the electrons, which increases the penetrating power of the x-ray beam.
Types of Radiation
- Photons (or x-rays) produced inside the tube have various energies and travel in various directions from the target. Photons that are directed at the object are known as the Primary radiation. Those photons that are not aimed at the object are know as leakage radiation.
-Primary radiation can be divided into two types: Remnant and Attenuated.
* Remnant is called the "useful" x-ray beam. This radiation goes through the patient/object and to the film to create an image.
* Attenuated radiation interacts with the object. This is known as the "unuseful" radiation. It can be grouped as two types: Scatter and Absorption. Scatter will interact with the object and change direction and not be absorbed. Absorption is when the x-ray photon is so weak that is absorbed into the object/patient. Too much absorption can cause damage to the human body.
Units of Quantity and Measurement
- The amount of ionization in a specific amount of air is known as the amount of exposure. The unit used to measure exposure is the Roentgen. This can be measured per second, minute, or hour.
-The exposure rate is the number of roentgens produced in a specific amount of time.
-A RAD (Absorbed dose) [D] - the amount of energy absorbed by any object.
-A REM (Roentgen Equivalent Man) [H] - known as the biological dose. This is used to measure the dose equivalent.
-The Quality Factor [Q] takes into account the different degrees of biological effect that can result from exposure to different types or radiation.
-The Modifying Factor [N] is the product of all other factors and external sources.
- H = D x Q x N is the formula for the Dose Equivalent. It will convert Rads to Rems.
Part 2
Biological Effects of Radiation
* Most Human Body cells can be damaged by ionizing radiation
- Different cell can receive different amounts of radiation before damage can occur
*Immature cells (cells that undergo rapid cell division) have a higher sensitivity to radiation than mature cells
- Lymphocytes (white blood cells) are the most radiosensitive
- Reproductive cells (sperm and ova) are highly sensitive
- Linings and covers of body organs are moderately sensitive
- Muscle and nerve cells are least sensitive
Three Levels of Biological Effects
1) Molecular
- effects the DNA of a cell. Two possible ways damage may occur: Direct hit and Indirect hit theory.
- Direct Hit: the x-ray photon directly hits the nucleus of the cell and destroys the DNA (brain) of the cell, thereby killing it.
- Indirect Hit: the x-ray photon hits the cytoplasm in the cell, surrounding the nucleus. This causes the water in the cytoplasm to chemically change from H2O to H2O2 (Hydrogen Peroxide) and literally "Bleaches" the cell to death.
2) Cellular
- Instant Death: when a dose of about 100,000 RADS is absorbed within a few minutes
- Reproductive Death: when the cell loses its ability to reproduce. A dose of about 100 to 1000 RADS.
- Genetic Death: The cell dies after a few divisions (also known as MITOTIC death.
3) Organic
- The cellular effects of radiation can cause organic damage. The degree of this damage depends on:
- the quantity of radiation
- the ionizing ability of radiation
- the body part exposed
- the amount of body area exposed
Two categories of Biological Effect
Genetic Effects -
- Molecular damage to DNA in reproductive cells can cause biological damage in offspring. Damage may not show up for generations. GSD - Genetically Significant Dose : Dose to the gonads. Symptoms of GSD are called genetic dose indicators.
Somatic Effects -
- Biological damage that happens to the individual and not passed on to the offspring. Somatic effects are either Short term or Long term. Symptoms are called somatic dose indicators.
Short Term Somatic Effects:
- Severe and begin a short time after a large dose of radiation.
this is also known as Acute Radiation Syndrome.
1) Initial Stage - Begins within 48 hours after exposure. Flu like symptoms set in (i.e. nausea, fatigue, loss of appetite, etc.)
2) Latent Stage - Lasts about a week. During this time, the initial symptoms disappear, and the person feels better. At the same time, changes are taking place internally.
3) Manifest Illness Stage - the person show signs of fever, infection, hemorrhage, nausea, vomiting, shock, and Death may follow.
4) Recovery Stage - if the dose was not lethal enough, the body starts to heal. This healing may take weeks.
There are 3 types of Acute Radiation Syndrome: Central nervous System (CNS), Gastrointestinal (GI), and Hematopoietic (Blood forming organs).
Long Term Somatic Effects:
Cataractogenesis - the formation of cataracts due to large doses of radiation
Life - span Shortening - when the average life span of a person is shortened due to large doses of radiation
Carcinogenesis - the formation of tumors (cancer) due to large doses of radiation
Embryological Effects - the effects on a fetus/embryo form exposure to radiation. The first trimester is the most sensitive to radiation. Sensitivity decreases in the 2nd and 3rd trimesters.
Dose Response Curves:
Linear - The longer someone is exposed, the more damage that person receives.
Sigmoid - when a person is first exposed, there is a threshold (tolerance), and then the damage increases as the exposure does. Then as the damage increases, it reaches a plateau at which the effects level off.
Protection of the X-ray Machine Operator
There are many different sources that the operator may receive an exposure from:
- Accidental exposure to the primary beam
- Scatter radiation from patients
- Scatter from other surfaces (table, walls, floor)
- Leakage radiation from tube
Adjusting the following can reduce occupational exposure:
Time: Keep your exposure as short as possible. Quantity is controlled by time.
Distance: Keep a good distance between yourself and the x-ray tube. A safe distance is 6 feet. At this distance, when radiation travels this far, it is so weak by the time it gets 6 feet. Then it will cause little or no damage.
The Inverse Square Law can also control distance. This states that the intensity of radiation is inversely proportional to the square of the distance. (The closer to the source, the stronger the intensity. The farther away, the weaker.)
I1 = D2
I2= D1 Inverse Square Law Formula
I1 - Original /Old Intensity (Exposure)
I2 - New Intensity (Exposure)
D1 - Old Distance
D2 - New Distance
The Inverse Square Law theory is just like a garden hose and water. Instead of water, we use radiation. The closer we get to the hose, or source, the wetter we get. The farther away we get from the hose, or source, the less wet we get.
Shielding Accessories
- Shielding should be used every time an x-ray is taken. Both for the patient and the operator.
NCRP thickness recommendations for shielding accessories:
Lead gloves: .25 mm Lead/Pb
Bucky slot cover: .25 mm Lead/Pb
Lead Apron: .50 mm Lead/Pb
The X-ray room itself has built in shielding to protect the operator and the areas surrounding the x-ray room.
Primary barriers - Barriers that the primary beam will be aimed at.
Secondary barriers - Barriers that will be exposed to radiation (scatter), but not the primary beam.
NCRP thickness recommendations for room barriers:
Primary Barrier: 1.5 mm Lead/Pb
Control Panel: 1.5 mm Lead/Pb
Lead Glass in Control Booth Window: 1.5 mm Lead/Pb
Secondary Barrier: .75 mm Lead/Pb
Part 4
Patient Protection
There are several ways to reduce the chances of overexposure to the patient: - position the patient properly
- restrict the primary beam
- using a filter
- use proper exposure factors
A NEEDLESS REPEAT EXPOSURE GIVES THE PATIENT AN ADDITIONAL 100% MORE
RADIATION!!!!!!
Beam Restriction - the primary beam should be limited to the body part being x-rayed
- the smaller the field of exposure, the smaller the amount of scatter there will be.
Diaphragms, Cylinders, and Cones - non-adjustable devices of this kind are no longer used in the state of Florida.
Collimators - this is the best device for restricting the primary beam. It is composed of two sets of shutters, which can be adjusted to control the size of the area being exposed. The bottom of the collimator must be at least 15 CM from the surface of the patients skin.
- collimators are considered a Positive Beam Limitation (PBL) device. Every x-ray machine in Florida MUST have a PBL. Each collimator has a light localizer to show where the field of exposure will be. Every film must show evidence of collimation by creating a clear border on the film. This shows that precautions were taken as to make sure the field of exposure was not larger that the film size used or the size of the body part.
Filtration - reduces the exposure to the patients skin by absorbing low (weak) x-ray photons. Aluminum is usually used. NCRP recommends 2.5 mm Al equivalent.
Week 1, Day 3
Shielding - there are many different types of shields used to protect the patient:
Gonadal shield - most common. placed directly on the patient's pelvis. Used to protect the gonads (male or female).
Shadow shield - shield that is suspended from the tube. A radiopaque, triangular shaped material casts a shadow when the light is turned on. Where the shadow is cast on the patient is the area being protected, usually the gonads.
Contact shield - placed directly over the gonads
Three Primary Exposure Factors
- There are three primary exposure factors used to control the quality and quantity of x-rays in an exposure:
KVP - (Kilovoltage Peak) The higher the KVP, the higher the quality of the x-ray beam. KVP is also the penetrating power of the beam, the speed of the electrons traveling across the tube from the filament to the target, and also the energy of the x-ray beam.
MA - (Milliamperage) MA controls the rate at which the electrons are emitted from the heated filament {Cathode}. The higher the MA the higher the temperature of the filament, the higher the number of electrons emitted.
Time - the length of the exposure time affects the quantity of radiation. The combination (multiplication) of milliamperes and time factors will produce milliamperes per second [mAs].
A combination of Higher KVP and Lower mAs will reduce your patients'
radiation dose!!!!
Selection of Exposure Factors
All exposure factors should be chosen from a technique chart located near the control panel.
KVP - KVP should be adjusted according to the thickness (density) of the body part. The thicker the body part, the more KVP needed.
The thinner the body part, the less KVP needed. {Quality}
MA - should be chosen from the technique chart {Quantity}
Time - should be chosen from the technique chart {Quantity}
X-ray Accessories
X-ray Film - X-ray film is composed of two parts:
Base - a blue-tinted polyester plastic that provides support for handling
Emulsion - consists of a mixture of gelatin and silver halide crystals. When x-rays and light interact with these crystals, the crystals are converted into clumps and strands of black metallic silver, which is the blackness on the developed film.
- The Latent image is that image on the film after it has been exposed, but before it has been developed.
- The Manifest image is the image that can be seen after the film has been developed.
Types of Film
- Just like any film bought in a store, x-ray film has many different speeds of films. The faster the film speed, the less exposure required. The slower the speed, the more exposure required.
There are two types of film that are used:
Non-screen film - very sensitive to direct exposure to x-rays. This
film requires a larger exposure. It also requires the use of a cardboard film
holder. The use of non-screen film and cardboard film holders is not
recommended for use in the State of Florida.
Screen Film - sensitive to fluorescent light produced by an intensifying screen.
- Film also comes in a variety of sizes. Some of them are:
14 X 17", 11 X 14", 10 X 12", 8 X 10", 9 ½ X 9 ½",
5 X 7", AND 7 X 17".
Cassettes
- A cassette is a light tight film holder that contains one piece of film and two intensifying screens.
- the front of the cassette is constructed of a radiolucent material such as plastic or Bakelite.
Intensifying screens
- intensifying screen are thin sheets of plastic or cardboard coated with chemicals that will emit fluorescent light when exposed to x-rays.
- the screens are composed of the following: a protective coating,
an active layer, a reflective layer, and a base.
- the protective coating protects the active layer from being damaged when the film is being removed from the cassette or inserted into the cassette.
- the screen's active layer is coated on one side with phosphor crystals. Every time one of these crystals absorb an x-ray, it emits a flash of light. These crystals are responsible for 99% of the Latent image on the undeveloped film.
- the reflective layer receives the light emitted from the phosphors and reflects it towards the film. The useful light is known as fluorescence. The continued emission of light from the screen after the exposure is know as phosphorescence.
- the base is made from plastic or cardboard and acts as a support for the other layers.
- there are two types of screens: Rare Earth and Calcium Tungstate. Rare earth screens emit a green light when exposed to x-rays. Calcium Tungstate emits a blue light. Film is designed to be sensitive to a certain color, depending on which screen is being used. Blue sensitive film must be used with calcium Tungstate screens. Green sensitive film must be used with the rare earth screens.
- Screens also come in different speeds, just like film. The slower the screen, the more exposure it takes to create the proper amount of light to create an image on the film. The faster the screen, the quicker it will make the image, and will require less exposure to make the proper amount of light.
- the combination of high-speed film and high-speed screens will reduce the patients' exposure.
Grids
- Grids are a device used to reduce the amount of scatter radiation to the film. It is made of strips of lead that are separated by pieces of plastic, wood, or aluminum. The use of a grid requires more patient exposure. Grids are only to be used on very dense body parts ( those parts measuring 12 CM or more ).
- The strength of a grid is expressed by it grid ratio. The grid ratio is the ratio of the height of the lead strips to the measurement of space between two strips. The ratio's are: 6:1,
8:1, 10:1, 12:1, 16:1. The higher the ratio, the stronger or more effective the grid is at absorbing scatter radiation.
- The grid frequency or strip density is the number of lead strips per inch.
- Dr. Gustav Bucky invented the grid. Every time he made an exposure, lines would show up on his films. A friend his, Dr Potter, figured a way to move the grid during an exposure to blur out the lines and still remove scatter radiation.
- There are two types of grids: Linear and Crossed. A linear grid has the lead strips parallel to each other. This is the simplest , most often used, and least expensive. The crossed grid has two sets of lead strips that intersect with each other. This grid can remove scatter from many directions. It is more expensive, and must be perfectly lined up with the tube or the primary beam will be cut off. This blocking of the primary beam is called grid cutoff.
- A focused grid is the same as a linear grid except it's lead strips are arranged to be used at a specific distance from the tube.
Reducing Scatter
Automatic Photo timer - this device measures the amount of radiation that passes through the patient and stops the exposure when enough radiation reaches the film to make a proper image. It will keep the exposure time down to a reasonable amount. The less time, the less scatter.
Immobilization Devices - These devices, such as sandbags, special sponges, and tape, will help reduce patient movement, and therefore will reduce scatter.
X-ray Table - the x-ray table is made from radiolucent materials that must be free from flaws or imperfections that would absorb radiation or cause scatter.
Part 6
Patient Protection
Pediatric Patients - extra precautions must be taken with pediatric patients because:
- Cells in cartilage and bones are more radiosensitive
- Children's bone marrow that is overexposed to radiation can cause a drop in certain blood counts
- Children under the age of two years old have very highly sensitive nervous systems
- Gonadal shielding is REQUIRED on all pediatric patients ( as well as all other patients ).
Female Patients - women in there childbearing age should take great precautions when being x-rayed.
- 10-day rule - women within childbearing age should be exposed to radiation within the first 10 days after the beginning of menstruation.
- All females should be asked if there is any chance of pregnancy. If the answer is anything except " NO ", the ordering doctor should be notified, and he will make the decision to continue or postpone.
- a consent form should be used if at all possible. This is the only legal way of documenting that the patient is stating that she is not pregnant.
Radiation Monitoring
Maximum Permissible Dose ( MPD )
- the dose of ionizing radiation that a person can absorb without having any biological damage.
- to determine the MPD, we have to determine what kind of radiation we have received, and also how much we received in RADS. To convert RADS to REMS, we use the following conversion formula :
QF X RADS = REMS
Q - Quality Factor - depending on the type of radiation you are exposed to determines the quality factor. X - Rays have a QF of 1,
Neutron Radiation has a QF of 10, and Alpha Radiation has a QF of 20. If you multiply the amount of RADS by the appropriate QF, you will figure out the amount of REMS received.
Recommended Annual Dose Limits
Occupational Dose - The annual MPD for a radiation worker is 5 REMS per year.
Nonoccupational Dose - ( general public ) - the annual dose for nonoccupational persons is .5 REMS per year.
Cumulative MPD - this is known as the retrospective annual dose equivalent. The formula to figure out the cumulative MPD is :
(N - 18 ).5
N-Your current age. The result from this formula will give you your unused cumulative MPD since the age of 18.
Special situations of MPD
- emergency life - saving situations at nuclear power plants, a one time accidental exposure of 100 REMS is allowed.
- Students under the age of 18 in a radiology program are allowed an annual MPD of .1 REMS.
- Pregnant x-ray machine operators should wear two monitoring devices. One should be worn at the collar level, the other at the waist level ( for the fetus ). The device worn at the waist level should not receive any more than .5 REMS per PREGNANCY.
ALARA
- As Low As Reasonably Achievable - radiation dosed should be kept
to a minimum for both patients and personnel.
Monitoring Devices
Film Monitors -
- contains two small pieces of x - ray film sealed in a light tight, waterproof package. this is place in a special holder
( either a badge, ring, or bracelet ). Each of these has a metal filter used to determine what kind of radiation the individual was exposed to. This device is very inexpensive, very accurate, and is changed every four weeks.
Pocket Dosimeters -
- This device is about the size of a fountain pen. There are two types of this device: the Pocket chamber, and the Self-reading pocket chamber. The pocket chamber requires a special charger - reader. the Self-reading pocket chamber can be read by holding it up to the light and looking through it. One advantage is that it can be read immediately, one disadvantage is that it is very sensitive to shock.
Thermoluminescent Dosimeters - This is very similar to a film monitor, but instead of a piece of film, a crystal is used that will undergo changes if exposed to ionizing radiation. This also is changed about every four weeks.
If you leave your employer and go to another office that has an x -ray
machine, YOU MUST TAKE A COPY OF THE LAST DOSIMETRY REPORT WITH YOU FOR
YOUR NEW EMPLOYER.
Please leave your dosimeter at the office, do not take it home. They are very sensitive to outside sources of radiation or interference : Monitor on Dashboard ( Sun ), Television or Microwave or any electronic device, or accidental washing and drying in laundry will give a false reading.
Part 8
Control Panel -
- The control panel has the three main exposure factors : KVP, MA, and Time. It also has a few additional switches and buttons : Main power switch ( on/off switch ), the prep/rotor switch, and the exposure switch. There may also be buttons that control which grid is operating during an exposure, and the line compensation button.
KVP - controls the penetrating power of the x-ray beam ( quality ). There may be two KVP settings: Major KVP and Minor KVP. Major KVP will adjust he KVP setting by increments of 10, either increasing or decreasing. The minor KVP will adjust the KVP by increments of 2.
MA - controls the amount ( quantity ) of radiation. The higher the higher the MA, the more heat and the higher the amount of radiation produced.
Time - also controls the amount ( quantity ) of radiation produced.
this setting will control the rate at which he radiation is emitted from the tube.
Main Power Switch - Turns the x-ray machine on/off
Exposure Switch - this is where the exposure starts and stops.
Electrical Circuits - There are many different circuits in the
x-ray machine. The four basic circuits are : the autotransformer circuit, the filament circuit, the high - voltage circuit, and the timing circuit.
Autotransformer Circuit - this circuit will either increase ( high - voltage circuit) or decrease ( filament circuit, timing circuit ) the voltage coming from the outside power supply, depending on what the electricity will be used for.
This circuit also has an adjustment device attached to it. The button labeled " Line compensation " will adjust the voltage coming in fro outside to make sure the voltage you set on the machine
( KVP ) is actually what you are using. Use this device as follows:
1) Increase KVP until the indicator/needle on the KVP meter reaches the voltage position that says " LINE ".
2) Press the button labeled " Line Compensation " and watch the
needle/indicator to se if it moves.
3) If it does not move, your line voltage matches the KVP you are setting when you make an exposure. If it increases or decreases, then the voltage you are setting with your KVP is not actually what you are using. If it goes up, you are using more than you are setting. If it goes down, then you are not using as much as you
think you are. If it is off, please turn the " Line Compensator"
knob until the reading matches the amount indicated for checking the line voltage.
Filament Circuit - this circuit controls the MA of the tube until the filament glows. It will also control the quantity of radiation produced. It requires a step - down transformer.
High - Voltage Circuit - this circuit controls KVP. It requires a step - up transformer to go from 220 Volts from the outside source to 60 - 120,000 volts needed for KVP. there are two sides to the high - voltage circuit : a primary circuit and a secondary circuit.
High Voltage Circuit / Primary - Includes KVP selectors, exposure switch, and the KVP meter.
High Voltage Circuit / Secondary - Includes Step up transformer, rectifier, the x-ray tube, and the MA meter.
Rectifier - This device converts the alternating current ( AC ) from the outside power source to direct current ( DC ), which the x-ray machine must use.
Timing Circuit - This circuit controls the length of time of the exposure. It therefore controls the amount / quantity of x-rays produced.
Single phase and Three phase Machines
There are two types of generators for x-ray machines: single phase and three phase. Single-phase generators have a 1 or 2 pulse voltage pattern. Three phase generators have either a 6 or 12 pulse voltage pattern. Using a single phase, the generator produces one or two pulses of electricity in 1/60 of a second. Using a three-phase generator, it will produce either 6 or 12 single-phase pulses that overlap each other so that when the peak of one pulse begins to drop, the next pulse starts to pick up where the pulse before it left off.
Operating the machine
- 1) Turn on the main power switch
- 2) Check the KVP meter and line voltage. If voltage is off, adjust with the Line Compensation knob until corrected.
- 3) Select the proper exposure factors
- 4) Position your patient properly and give instructions clearly
- 5) Press the exposure switch
- 6) Listen or watch for indicator ( buzzer, bell, light ) to let you know the exposure is done and let go of the button.
The Radiographic Tube
- the x-ray tube consists of three main parts: the Cathode, the Anode, and the Glass Envelope.
Glass Envelope
- When the tube is constructed, the anode and cathode are placed inside the glass envelope and sealed. Once it is sealed, the air inside is removed and a vacuum is created. This tube is then placed in a metal tube housing and the housing is then filled with an insulating oil. This oil is used to absorb the heat created in the tube during an exposure.
Cathode
- The cathode is the negatively (-) charged electrode in the x-ray tube. It consists of two tungsten filaments, one large and one small. This filament is just like that in a light bulb. It also contains a focusing cup, which help direct the electrons emitted from the filament during an exposure towards the anode. The electrons are emitted in a fan - like direction. The focusing cup acts like a funnel, concentrating the electrons into one fine beam aimed at the anode.
Anode
- The anode is the positive electrode of the tube that includes the target. This is the object the electrons from the cathode strike in order to produce x-rays. The anode is made of tungsten and copper. Of all the energy used to make x-rays, 99% of the energy is converted into heat in the tube. The other 1% is converted into x-rays. Tungsten is used because it has a high melting point and high heat conductivity. The temperature in the tube can get up to almost 3400 degrees C.
- There are two types of anodes: stationary and rotating. The stationary anode is embedded in copper to assist in heat dissipation. The rotating anode spins up to 10,000 RPM in order to dissipate the heat produced.( Just like the paint used in SPIN ART: the paper spins under the paint, and as the paint lands on the moving paper, it spreads out from the center)
- The area on the anode where the electrons hit is called the focal spot. On the stationary anode, the focal spot remains in one place, where as with the rotating anode, the focal spot is constantly changing.
Tube Rating Charts and Cooling Charts
- Tube rating charts help to figure out the maximum exposure factors on a specific x-ray machine. Cooling charts are used to figure out a minimum cooling period for the x-ray tube.
Calculating Heat Units
- In order to calculate heat units on any type of machine, you need to know the three main exposure factors: KVP, MA, and TIME.
The formulas for determining heat units are:
Single Phase : KVP X MA X TIME = Heat units
Three Phase, Six Pulse : KVP X MA X TIME X 1.35 = Heat units
Three Phase, Twelve Pulse : KVP X MA X TIME X 1.41 = Heat units
Tube Rating Charts
- To use the tube rating charts, you need to know two of the three exposure factors ( KVP, MA, TIME ).
1) Determine if you are using a small or large focal spot
2) Find the two graphs you will be using and look in the upper right corner. There should be a marking of " 2F7" and "1F7". The "2F7" is the large focal spot, where as the "1F7" is the small focal spot ( 1 is smaller than 2 ).
3) On the chart, the MA will be on the left of the chart, the time one the bottom, and the KVP in the chart. Locate the two factors given to you on the chart. Find which line that the number is next to and follow it until it intersects ( Meets ) the line from the other factor. Wherever the two lines meet, that is your missing maximum exposure factor.
Heat Dissipation and Cooling Charts
- These charts are used to figure out the time it will take for the tube to cool down in between exposures so that the tube does not overheat and crack.
1) Determine the maximum amount of heat units the tube can handle ( this should be on the top of the column on the left of the chart).
2) Add the number of heat units from the first and second exposures. If the amount of heat units DOES NOT exceed the maximum amount of heat units, you do not have to wait in between exposures ( the answer will be 0 minutes ). If it DOES exceed the maximum, then you have to figure out how long to wait between exposures.
3) Take the amount of the second exposure and subtract it from the maximum amount. This will give you a difference. On the chart, there is a line from the upper left corner to the lower right, labeled " Cooling ". This is the only line to be used on the chart.
Look up the times on the chart for the amounts of the second exposure and the difference.
4) Once you have the times for the two amounts, subtract the two times and you will get a number. This number is the time you have to wait in between the first and second exposures in order to let the tube cool down. Once the tube is cooled down and you add on the second exposure, the heat units will only go up to the maximum and not over.
Warm Up Procedures
- The x - ray machine must be warmed up after lack of use to prevent the breakdown of the tube. First thing in the morning and after the tube has not been used for a while are the most common times to use the warm up procedure. Each tube has a recommended warm up technique.
Part 10
Identifying Equipment Failures
- The three main reasons for repeat x-rays are: operator error, patient movement, and equipment failure. The first two causes can be prevented.
- Some of the more common operator errors are:
* failure to set the exposure factors properly ( i.e., setting ½ sec instead of 1/20 sec.)
* failure to position the patient correctly
* failure to observe the patient for movement
* failure to process the film correctly
Equipment Failure Indicators
- There are two types of equipment failures: electrical and mechanical
Electrical Failures
- When an exposure is made, the MA meter needle should only move up to the MA that was selected. If there is abnormal MA meter fluctuation, the x - ray tube may have lost its vacuum.
- If the technique that is normally used produces a very dark film and the MA meter fluctuates abnormally, the timer may be defective.
- If the technique that is normally used produces a film that is too light and there is abnormal meter fluctuation, either the rectifier or the timer may be defective.
Testing for Electrical Failures
- there are three main tests used to check for electrical system failures: spinning top test, mAs reciprocity, and KVP stability.
Spinning Top Test
- The spinning top test is used to check both the rectifier and the timer in single-phase machines only.
- This test uses a flat disc top with a hole in it. Single-phase machines produce 120 pulses or 60 cycles/Hertz per second. Each pulse will send a pulse of x - rays through the hole in the top and create a black dot on the film. If we make an exposure of 1/10 sec,
there should be 12 dots on the film if everything is working properly ( 120 divided by 10 = 12 ).
- If there are exactly 12 dots on the film, the timer and rectifier are fine.
- If there are exactly 6 dots on the film, the rectifier has gone bad.
- If there are more or fewer then 12 dots on the film, the timer may need to be adjusted.
mAs Reciprocity Test
- The mAs reciprocity test uses a penetrometer to compare the function of different MA settings and the timer.
- Two exposures will be made with the penetrometer on the film, both of which will have the same KVP and mAs, but the MA and Time will be different on each exposure. One exposure will be made at 100 MA @ ½ sec, and the other 200 MA @ ¼ sec. The densities on each film will be measured with a sensitometer. If the densities are the same, the machine is working fine. If the densities are different, the MA or time timer is defective.
KVP Stability Test
- The KVP Stability test is very similar to the mAs Reciprocity test in that they both use the penetrometer. The mAs is kept constant and the KVP is varied ( 50 and 60 KVP ). Make two exposures of the penetrometer using different KVP. then measure the density of each film. If the densities are progressive, then the machine is working fine. If the density decreases or jumps dramatically, the machine is not working properly.
Mechanical Failures
- Mechanical failures will include: beam restriction devices, grids, and cassettes.
Checking for Mechanical Failures
Beam Restriction
- If the patient is positioned properly, and the tube is in alignment with the film and a clear streak is down one side of the film, the actual radiation field and the light field are out of alignment. Call the maintenance company to repair the alignment of the collimator.
Grids
- Grids do not make mistakes, operators using them make the mistakes. If a focus grid is being used at the wrong distance, the lateral borders will be very light or clear, and the middle section will be very dark. This is due to Grid Cutoff. The lead strips towards the sides of the grid are angled to match the angle of the x - rays coming out of the tube at a specific distance . The center strips at vertical with no angle. If the distance is not what the grid is designed for, the outside strips will absorb the primary beam and the center strips will let the primary beam pass through because they have no angle.
- If the grid ratio is changed ( grid to non-grid or lower ratio to higher ratio or opposite ) the film will be too light or too dark.
Cassettes
- If an x - ray has an unwanted mark on it, this is known as an artifact. Artifacts can black or white. If they are black, this means that the cause of the artifact was outside of the cassette. Static electricity, film fog due to light of radiation, crease marks, and fingernail marks will create black artifacts. If they are white, this means the accuse of the artifact is inside the cassette, blocking the light from the screens to the film. Paper clips, staples, hair, dust, and anything else that comes between the film and screen will cause a white artifact.
- To remove any artifacts inside the cassette, use a camel's hair brush. Then use screen cleaner and a 4x4 gauze to wipe down the screen. Please allow it to air dry after this. Record the date at which the cassette was cleaned for future reference.
High quality Radiographs
- Each radiograph should have the following: Adequate density, good contrast, clear detail and sharpness, and no distortion of size/ shape.
Density
- Density is the amount of black, metallic silver on the film after development. It is also the measurement of the quantity of radiation absorbed by the film.
- Density is controlled by: mA, time and distance
- Density is influenced by: KVP, film-screen combination, grids, filtration, tissue thickness (density), anode heel effect, processing, film fog, and artifacts.
Controlling Factors:
- mA controls density by controlling the quantity of radiation that the film absorbs. The higher the mA, the higher the density.
- Time controls density the same way mA does. It controls the amount of radiation the film receives. The higher the mAs, the higher the density.
- Distance controls density by way of the inverse square law. Target Film Distance ( TFD ) is the same as Source Image Distance ( SID ), Focal Film Distance ( FFD ), and Target Image Distance ( TID ). The closer the tube is to the film without changing the techniques, the darker the film. The farther away, the lighter the film.
Influencing Factors:
- KVP influences density by regulating the average energy of the
x - ray beam. Therefore, if you increase the KVP by 15%, it has the same effect as if you had increased the mAs by twice as much [ or doubled the mAs ]. Also, if you decrease the KVP by 15%, you have the same effect as if you had cut the mAs in half.
- Film-screen combinations can influence density on a film. Depending on what type of screen you have in your cassette, depends on the color of light that will be emitted from that screen. Film is designed to be sensitive to certain colors of light. Orthochromatic film is sensitive to the green light of the rare-earth screens. Blue - sensitive film is designed to be used with calcium - tungstate screens, which give off a blue light. The combination of the rare - earth screens and the orthochromatic film will result in a short exposure time , and is best used in chest
x - rays.
- Grid ratios will also influence density depending on the actual ratio. The higher the ratio { 16:1 }, the more scatter radiation is absorbed by the grid, and less scatter to the film.
- Filtration influences density by removing the weak ( low energy ) x - rays from the primary beam before if leaves the tube.
- The patient themselves will influence the density. Tissue thickness and pathology will influence density the most. Tissue thickness is also known as density. Please do not confuse the two definitions for density: 1) thickness of a body part, 2) the amount of black, metallic silver on the film.
- The anode heel effect is used on only two body parts: the AP thoracic spine, and the AP and Lateral femur. If the anode heel effect is used properly, it will produce a film with very uniform densities. Place the Cathode end of the tube over the thinner (less dense) area of the part, and the Anode end of the tube over the thicker ( more dense ) area of the part. As the x - rays come off of the cathode, they vary in strength. The x - rays that emit towards the cathode end of the tube are weaker than the x - rays that are emitted towards the anode end of the tube.
- Film fog is unwanted density on the film produced by radiation, light, or improper film development.
- As mentioned before, artifacts can either reduce density ( white artifacts ), or increase density ( black artifacts )
Contrast
- Contrast is the distribution of the black, metallic silver on the film. In order to have contrast on an x - ray , you must have at least two densities. There are two types of contrast: Short scale and long scale.
- Short scale contrast is many black and whites on the film, but very few shades of gray. This would be found on extremity films ( small body parts ).
- Long scale contrast is many shades of gray on the film and very few black and whites. This would be found on larger, thicker body parts ( CXR, KUB ).
- Long scale is also known as low contrast ( few differences between shades of grays ).
- Short scale is known as high contrast ( extreme difference between black and white ).
Controlling Factors of Contrast
- KVP is the controlling factor of contrast. The higher the KVP, the lower the scale of contrast. High KVP, low mAs produces a long scale contrast film ( CXR ). Low KVP, high mAs produces a high scale contrast film ( extremity ).
Influencing Factors of Contrast
- Density ( thickness of body part ) will influence contrast. Differences in densities will produce different shades of grays, black, and white.
- Intensifying screens in the cassettes will help create the image on the film and influence contrast because less radiation is required to produce an image with intensifying screens than without them.
- Collimation, grids, and filtration all help reduce the amount of scatter radiation, and therefore influence contrast.
GEOMETRIC PROPERTIES
- DISTORTION AND MAGNIFICATION MUST BE AVOIDED AT ALL TIMES. A FEW WAYS TO REDUCE THESE FACTORS ARE:
- REDUCE OFD ( OBJECT FILM DISTANCE ) AS MUCH AS POSSIBLE. OFD IS THE DISTANCE FROM THE OBJECT YOU ARE RADIOGRAPHING TO THE TABLE OR FILM. IF YOU CANNOT REMOVE OFD, MEASURE THE AMOUNT OF OFD AND INCREASE THE TFD BY THE SAME AMOUNT.
- ANGLING THE TUBE, PATIENT OR THE FILM CAN CAUSE DISTORTION ON THE FILM.
- USING A SMALL FOCAL SPOT ON THE TARGET WILL HELP INCREASE THE DETAIL OF THE IMAGE ON THE FILM . THIS IS DUE TO THE ANGLE OF THE ANODE ( TARGET ). THE SMALLER THE ANGLE, THE SMALLER THE FOCAL SPOT.
- USE 40" FOR ALL RADIOGRAPHS BEING TAKEN ACCEPT THE CHEST. THE CHEST REQUIRES THE USE OF 72" TO REDUCE THE MAGNIFICATION OF THE SIZE OF THE HEART ON THE FILM. IF LESS IS USED, CHF OR CARDIOMEGALY MAY BE INTERPRETED.
- PENUMBRA IF THE FUZZINESS AT THE EDGE OF A RADIOGRAPH DUE TO MOTION. WAYS TO REDUCE THE CHANCES OF MOTION ARE: SHORT EXPOSURE TIME, RESTRAINING DEVICES (TAPE, SANDBAGS, FAST FILM/SCREEN COMBINATION).
- POOR SCREEN - FILM CONTACT WILL RESULT IN POOR DETAIL
SELECTION OF EXPOSURE FACTORS
- THE MOST COMMON REASONS FOR REPEAT RADIOGRAPHS ARE: INCORRECT POSITIONING AND INCORRECT EXPOSURE FACTORS.
- ONE WAY TO REDUCE THE CHANCES OF A REPEAT RADIOGRAPH IS THE USE OF A PHOTOTIMER - A DEVICE USED TO MEASURE THE AMOUNT OF RADIATION THAT HAS PASSED THROUGH A PATIENT TO THE FILM. ONCE A PREDETERMINED AMOUNT HAS REACHED THIS SENSOR, IT WILL AUTOMATICALLY TERMINATE THE EXPOSURE. THIS IS ALSO KNOWN AS AN AEC (AUTOMATIC EXPOSURE CONTROL). THE LONGEST EXPOSURE WITH THIS DEVICE IS HALF (1/2) OF A SECOND.
- ANOTHER DEVICE USED IS AN IONIZATION CHAMBER. IT FUNCTIONS THE SAME EXACT WAY AS A PHOTOTIMER DOES, BUT IS IN A DIFFERENT LOCATION WITHIN THE X-RAY TABLE. THE PHOTOTIMER IS LOCATED UNDERNEATH THE FILM. THE IONIZATION CHAMBER IS LOCATED ABOVE THE FILM.
- NO MATTER WHICH DEVICE IS USED, A BACK UP TIMER MUST BE MANUALLY SET FOR HALF (1/2) A SECOND. THIS USED IN CASE OF FAILURE OF THE PHOTOTIMER OR IONIZATION CHAMBER, OR IF THE DEVICE IS NOT TURNED ON. THIS WAS NO EXPOSURE IS OVER HALF (1/2) OF A SECOND.
- BOTH DEVICES ARE DEPENDANT ON THE OPERATOR TO USE THE FIXED KVP TECHNIQUE. THIS TECHNIQUE IS BASED ON GROUPING ALL PATIENTS INTO SMALL, MEDIUM, AND LARGE. THE KVP IS SELECTED (60 - 110) AND NOT ADJUSTED DURING THE EXAM. THE MAS IS ADJUSTED ACCORDING TO THE FOLLOWING: IF THE PATIENT IS OF SMALL STATURE, USE HALF (1/2) THE RECOMMEND MAS ON THE TECHNIQUE CHART. IF THE PATIENT IS OF MEDIUM STATURE, USE THE MAS RECOMMEND ON THE TECHNIQUE CHART. IF THE PATIENT IS LARGE, USE TWICE (2X) THE RECOMMEND MAS ON THE TECHNIQUE CHART.
- ANOTHER GUIDE TO CALCULATING THE APPROPRIATE EXPOSURE FACTORS IS THE USE OF THE VARIABLE KVP TECHNIQUE. WHEN USING THIS TECHNIQUE, THE MAS IS NOT ADJUSTED, AND THE KVP IS ADJUSTED ACCORDING TO THE MEASUREMENT OF THE BODY PART IN THE POSITION BEING RADIOGRAPHED.
WITH THE USE OF CALIPERS, THE PART IS MEASURED IN CENTIMETERS AND THEN USED IN THE FOLLOWING FORMULA: (CM X 2)+30. THIS FORMULA WILL CALCULATE THE BASE (MINIMUM) KVP APPROPRIATE FOR THIS BODY PART.
- EXPOSURE FACTORS CAN ALSO BE ADJUSTED FOR THE CONDITION OF THE PATIENT. IN CASES OF PNEUMONIA, CASTS, TUMORS, OR ANY DENSE MASS, THE TECHNIQUE (KVP OR MAS) WILL HAVE TO BE INCREASED TO PENETRATE THIS DENSE MATERIAL. IN CASES OF OSTEOARTHRITIS, BONE (LYTIC) TUMORS, OR ANY DEGENERATIVE CONDITION, THE TECHNIQUE (KVP OR MAS) WILL HAVE TO BE DECREASED DUE TO THE REDUCTION IN DENSITY OF THE PART BEING RADIOGRAPHED. OTHER REASONS FOR TECHNIQUE ADJUSTMENT WOULD BE: CHANGE IN GRID RATIO, CHANGE IN SCREEN/FILM SPEED, AND PEDIATRICS.
Part 12
FILM HANDLING AND MANUAL PROCESSING
- All film handling and processing must be done in the darkroom. This is where radiography begins and ends. This is where film is place in cassettes and later removed for development.
- The darkroom is divided into two stations: a wet station and a dry station. The wet station consists of a sink, manual processing tanks (if used), and/or an automatic processor. The dry station consists of the film bin for storage of opened boxes of unused film, and a transfer cabinet. A film bin is a leaded, lightproof cabinet, which is divided in compartments for different sizes of film. This bin must be closed after EVERY use to avoid accidental exposure to the white light.
- There are two types of light in the darkroom: a white light and a red/amber light. The white light should only be used when maintenance is being performed on the processor. The red/amber light (also known as the safelight) is to be used when a film is being removed from a cassette, processed, and added to a cassette. This light is actually a white light bulb (15 watts) with a special filter (Wratten 6B). Although film is not exposed right away, it can still be ruined by the safelight. The safest time and distance the film should be from the safelight is 1 minute at a distance of 3 feet.
Film Storage
- Film needs to be stored at certain temperatures and humidity to extend the life of the unexposed film. The ideal storage conditions are 60 - 75 Deg. F. and 50 - 60% humidity. Film must also be protected from radiation to avoid film fog. Film should be stored upright to avoid mottle (wrinkling effect on film) and should always be used by the expiration date on the box.
Radiographic Identification
- Radiographs are considered legal documents, and therefore are required to have specific information on each film: Patients name, DOB, date of exam, Doctor's name, SS/Patient number, name and address of institution. It is also required by law to have a border on the film as evidence of collimation. This is the only way to prove that the operator used the collimator properly.
Manual Processing
- There are five basic steps in manual processing: Developer, stop bath, fixer, water wash, drying rack.
- Developer: an alkaline solution that converts the latent image to a manifest image. Ideal temperature and time are: 5 minutes at 68 deg.F. The higher the temperature, the shorter the developing time, but there is a loss in detail if time is shortened.
- Stop Bath: a mixture of clean water and acetic acid (1-5%). This is used to stop the action of the developer. Ideal time: 30 sec.
- Fixer: composed of a mixing agent, acidifier, hardener, preserver, and water. This solution makes the manifest image permanent. Ideal time: 10 minutes (longer will dissolve silver on film).
- Water wash: used to remove all chemicals from the film. Ideal time and temperature: 20 minutes at 68 deg.F.
- Drying rack: film is placed on a special hanger and placed to dry. Ideal time: approx. 60 min.
Automatic Processing
- Automatic processing has many advantages over manual processing:
shorter processing time (90 sec. vs. 90 minutes), films are more uniform, smoother workflow, improves patient care.
- An automatic processor has six systems working at the same time:
1) Transport system: this helps move the film throughout the processor and agitate the film in each solution.
2) Replenishment system: when a film is put into the processor, a pair of sensors measures the film and calculates how much developer and fixer is required to properly develop that film. It then will remove the same amount of chemicals from the storage tanks and refill the tanks within the processor. This assures that the levels in the processor never drop.
3) Temperature regulation system: this makes sure that all of the solutions being used in development are at the proper temperature to ensure premium results.
4) Recirculation system: helps keep the solutions moving to prevent breakdown of each solution.
5) Water system: helps replace the water in the wash tank to make sure the chemicals being washed off of the film are not redeposited on the film currently being processed.
6) Dryer system: helps dry the film as it exits the processor. Air temperature approx. 120 - 130 deg. F.
The Test you are about to take consists of 100 questions. You MUST provide an answer to every question (no blank answers) for your test to be valid. Failing to do so will require that you take the entire course over . Using the back button will not allow you to fill in any answers after you have submitted your test. At the end of the test, before clicking next, please take a few minutes to scroll through your test and ensure that you have answered each and every question. You may print out the questions as a reference while studying the text by clicking on take test and printing normally from your browser.
MEDCEU Continuing Education Courses CEU for Nurses and Healthcare Professional