This course introduces the beginning radiography student to the nature and properties of x-rays. Areas of focus include: radiographic image quality and the influencing factors of recorded detail, distortion, contrast and density, the construction of the x-ray tube and the production of x-rays, basic x-ray equipment, primary and secondary radiations, filtration and an analysis of the radiographic image.
Pre-requisite: Admission into Radiography Program
UNIT 1 - Radiation Concepts
- Points of Review - Powerpoint Presentation 1 - Bushong
Matter: anything that occupies space and has mass
- The fundamental building blocks of matter are atoms.
Mass: the quantity of matter contained in any physical object
- weight is the force exerted on a body under the influence of gravity
Mass is measured in kilograms.
Weight is measured using a unit called the Newton.
Weight is determined by the gravitational force exerted on a body.
As an example, a student having a mass of 75 kilograms would weight 735 Newtons on the Earth but weight only 120 Newtons on the moon.
Energy is the ability to do work.
In the International System of Measurement (SI), energy is measured in joules (J).
Potential Energy – the ability to do work by virtue of position
Kinetic Energy – the energy of motion
Chemical Energy – the energy released by a chemical reaction
Electrical Energy – the work that can be done when an electron moves through an electrical potential difference
Thermal Energy – the energy of motion at the atomic/molecular level – closely related to temperature
Nuclear Energy – energy contained in the nucleus of an atom
Electromagnetic Energy - includes cosmic rays, gamma rays, x-rays, ultraviolet light, visible light, infrared light, radar, microwaves, TV, radio, cell phones and all electronic transmission systems. Electromagnetic radiation is made up of electric and magnetic fields that move at right angles to each other at the speed of light.
Matter and energy are interchangable.
This fact was first introduced by the famous physicist, Albert Einstein.
Energy emitted and transferred through space is called radiation.
Ionizing radiation is any kind of radiation capable of removing an orbital electron from the atom with which it interacts.
The orbital electron and the atom from which it was separated are called an ion pair.
The x-ray was discovered (not invented) by Wilhelm Conrad Roentgen quite by accident.
highly penetrating, invisible rays which are a form of electromagnetic radiation.
electrically neutral and therefore not affected by either electric or magnetic fields.
polyenergetic and heterogeneous.
release small amounts of heat when passing through matter.
travel in straight lines.
travel at the speed of light.
can ionize matter.
can cause fluorescence of certain crystals.
cannot be focused by a lens.
affect photographic paper.
can produce chemical and biologic changes in matter through ionization and excitation
produce secondary and scatter radiation.
There are two general types of x-ray examinations - Radiography (static Images) and Fluoroscopy (Dynamic - Moving Images)
An X-Ray beam satisfactory for imaging requires:
1. Thousands of volts of electricity – kilovoltage
2. Thousandths of an ampere of electricity – milliamperage
Today, the hand can be imaged in milliseconds (thousandths of a second).
In the early days of radiography, it often took several minutes to image the hand!
Image blur, due to motion, was a huge problem in radiography’s early days.
Imaging times were shortened with the development of the intensifying screen and double-emulsion radiography.
The fluoroscope was developed in 1898, by the American inventor, Thomas Alva Edison. He eventually stopped his work in radiology after his assistant, Clarence Dally, became the first x-ray fatality in the United States.
-Collimation and filtration
- usually credited with being introduced by a Boston dentist, William Rollins, before the turn of the twentieth century.
1970’s – CT and PET
1980’s - MRI
1910 – biologic effects of x-rays began to be investigated
Years latter it was discovered that over exposure to x-radiation could lead to:
blood disorders including:
- aplastic anemia
Today we know low doses may result in a small incidence of latent harmful effects.
It is well established that a fetus is most sensitive to the effects of radiation exposure within the first trimester.
Although effective radiation safety practices make for a safe working environment today, never become complacent when working with radiation!
Always practice ALARA and utilize the cardinal principles of:
Radiography is the recording of images created by the use of x-ray energy.
Radiography is both an art and a science.
Science - the use of knowledge in an organized and classified manner.
Natural Science - the study of the universe and its contents.
- can be divided into two categories
1. physical science
2. biological science
Physics - a branch of physical science that studies matter and their interrelationships.
Matter - the substance that comprises all physical objects
- it has shape, form and occupies space
Mass - the quantity of matter contained in any physical object
- the unit of mass is the kilogram
Weight – the force that an object exerts under the influence of gravity
- the unit of weight is the Newton
Substance - a material that has definite and constant composition
Mixture - the combination of two or more substances
Substances may be either simple or complex.
Simple substances = elements
Complex substances = compounds
An element is a substance that cannot be broken down into any simpler substance by ordinary means. There are 92 naturally occurring elements.
When two or more elements are chemically united in definite proportion, compounds are formed.
An atom is the smallest particle of an element.
A molecule is formed by two or more atoms which are chemically united. A molecule is the smallest component of a compound.
The degree of attraction between atoms and molecules determines if the substance is a solid, liquid or gas.
Weak attraction = gas
Strong attraction = solid
Energy is the ability to do work.
Energy emitted and transferred through matter is called radiation.
Albert Einstein, in 1905, described the unique relationship between matter and energy. According to Einstein, matter and energy are interchangeable.
The basis of Einstein’s work is the Law of Conservation of Energy - matter and energy cannot be created or destroyed but can be converted from one form to another
Atoms can be divided into three basic subatomic particles.
Protons – positively charged and located in the atom’s nucleus
Neutrons – no charge and located in the atom’s nucleus
Electrons – negatively charged and located in shells surrounding the nucleus
In 1913, Neils Bohr, a Danish physicist, proposed a model of the atom which is likened to the solar system.
Center = nucleus (Sun)
Orbits = electrons (planets)
This model is still widely used today.
Protons and neutrons together are called nucleons. They are located in the atom’s nucleus.
Electrons are located outside of the nucleus and have a relatively insignificant mass compared to the nucleons.
Electrons cannot be divided into smaller parts, but protons and neutrons can be divided into subnuclear structures called quarks.
The number of protons in the nucleus is known as the atomic number or Z number.
The atomic number gives an atom its identity (the type of element it is an atom of).
If an atom gains or loses a proton, it becomes an atom of a different element!
The number of both protons and neutrons in the nucleus determine an atom’s mass number or A number.
The mass of the particles of an atom is sometimes described in atomic mass units. In science this is more exact than simply stating the mass number.
An atom that loses or gains a neutron is called an isotope.
An atom that gains or loses an electron is called an ion.
The distance from the nucleus determines the energy level or shell the electon occupies.
Each shell has a certain amount of binding energy (measured in eV) which holds it in its orbit around the nucleus. The closer an electron is to the nucleus, the greater is its binding energy.
The shell closest to the atom’s nucleus is the K shell, next is the L shell, then the M shell.
The shell number is referred to as the principle quantum number.
K shell = 1 L shell = 2 etc.
In a neutral atom, the number of electrons equals the number of protons.
The maximum number of electrons that can occupy a given shell is defined by the formula:
The Octet Rule – The number of electrons in the outermost shell never exceeds eight electrons. Atoms are most stable if they have a filled outer shell. Atoms may gain or lose (ionic compounds) or share (covalent compounds) electrons to achieve this stability.
The noble gases are found in group 18 of the periodic table. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable. The noble gasses are described as being inert.
The periodic "law" of chemistry recognizes that properties of the chemical elements are periodic functions of their atomic number (that is, the number of protons within the element's atomic nucleus). The periodic table is an arrangement of the chemical elements ordered by atomic number in columns (groups) and rows (periods) presented so as to emphasize their periodic properties.
During the mid-1800’s, a Russian scientist Dmitri Mendeleev (1834 – 1907), developed the first periodic table of the elements.
- The Periodic Table of the Elements
The elements are arranged in increasing order of atomic number(Z) as you go from left to right accross the table. The horizontal rows a called periods and the vertical rows, groups.
A noble gas is found at the right hand side of each period. There is a progression from metals to non-metals across each period. Elements found in groups (e.g. alkali, halogens) have a similar electronic configuration. The number of electrons in outer shell is the same as the number of the group (e.g. lithium 2·1).
The block of elements between groups II and III are called transition metals. These are similar in many ways; they produce colored compounds, have variable valency and are often used as catalysts. Elements 58 to 71 are known as lanthanide or rare earth elements. These elements are found on earth in only very small amounts.
Elements 90 to 103 are known as the actinide elements. They include most of the well known elements which are found in nuclear reactions. The elements with larger atomic numbers than 92 do not occur naturally. They have all been produced artificially by bombarding other elements with particles.
The number of electrons in the outermost shell determines the chemical combining characteristics or valence of the element.
Energy is the ability to do work
Work = Force x Distance
Electromagnetic radiation (EM) spans a continuum of wide ranges of magnitudes of energy.
All waves of energy encompassed in the electromagnetic spectrum travel at the speed of light.
Electromagnetic energy travels through space in the form of waves.
The distance between any two successive points on a wave is termed wavelength. It is represented by the Greek letter lambda.
Wavelengths vary from kilometers to angstroms (A)
1 angstrom = 1.0 × 10-10 meters .
radiowaves = meters/kilometers
X-rays = .1 to .5 angstroms
The frequency is the number of waves that passes a particular point in a given time frame. It is represented by the Greek letter nu.
Wave/particle duality is the possession by physical entities (such as light, x-rays and electrons) of both wavelike and particle-like characteristics. On the basis of experimental evidence, the German physicist Albert Einstein first showed (1905) that light, which had been considered a form of electromagnetic waves, must also be thought of as particle-like, or localized packets of discrete energy (photons).
Photon energy and frequency are directly related.
Increase Frequency Increase Energy
Examination Review - Unit 1
- There are 92 naturally occurrring elements.
- Oxygen, helium, and nitrogen are all examples of elements.
- Physics is a branch of science which studies matter and energy.
- Weight is dependent on the physical force of gravity.
- Mass is the quantity of matter contained in an object.
- Atom = nucleus (protons and neutrons) + shells (electrons)
- Salt is an example of a compound.
- smallest particle of an element is an atom
- smallest particle of a compound is a molecule
- radiation = energy transmitted and transferred through matter.
- Protons = positive charge
- Neutrons = no charge
- electrons = negative charge
- atoms = no charge
- ions = positive or negative charge
- energy = mass multiplied by the speed of light squared
- Niels Bohr likened the atom to a miniture solar system
- Mendeleev developed the first periodic table of the elements
- Quarks = smallest divisions of protons and neutrons
- Periodic table: periods - horizontal rows groups - verticle columns
- Z# (Atomic Number) = number of protons in an atom, gives the atom it's identity (i.e. Z# of barium = 56)
- A# (Atomic Mass Number) = number of both protons and neutrons in an atom's nucleus
- to find the number of neutrons in an atom - subtract the Z# from the A#
- electrons are held in their shells via binding energy
- to find the maximum number of electrons that can be in a given shell, use the formula 2(N)^2
- Octet rule - outer shell never exceeds 8 electrons
- Wavelength - distance from crest to crest (lambda)
- Valence - chemical combining characteristic determined by the number of electrons in outer shell
- Frequency - number of cycles per second (Nu)
- Wavelength and frequency are inversely proportional.
- Photon energy and frequency are directly proportional.
- Be sure to review the X-Ray Properties on pg. 36 (Carlton).
Unit 2 - X-Ray Equipment
Medical X-Ray units can be described as being either diagnostic or therapeutic.
Diagnostic units operate between:
The tabletop is designed to support the patient in a position that will enhance the radiographic examination.
Characteristics of the tabletop:
The grid within the “Bucky” moves during an exposure to blur out the thin lead lines incorporated in the grid’s construction. This is termed a reciprocating or oscillating grid.
Also incorporated into the tray, of many pieces of equipment, are sensors for automatic exposure control.
Some table tops do not move (stationary) and others move when an electromagnetic lock is released via a hand, knee or foot switch.
Table-tops that move are termed floating table-tops.
Tables are available in fixed or tilting models.
Fixed tables do not permit tilting the patient’s head or feet down.
Tilting tables are utilized in R & F (radiography and fluoroscopy) rooms.
Tilting tables are sometimes described by their tilting capabilities.
Example – a 90 -15 indicates a table that tilts 90 degrees in one direction and 15 degrees in the other.
The table is usually at a height that reduces physical strain on the radiographer, who has to bend and stretch in maneuvering both the patient and the equipment.
Many tables can be lowered to assist the patient in getting on and off safely.
Remember, the patient must always be assisted when he/she is getting on or off the radiographic table!
Footboard - used on tilting tables to give the patient a platform to stand on when the table is being tilted upright
Remember, it is critical that the footboard always be checked/tested to see if it is securely attached to the table!
Shoulder Supports – necessary when patients are being tilted Trendelenberg (head down). This will prevent the patient from sliding off the table.
Handgrips – attached to the sides of the table, give the patient an added feeling of security when table is being raised or lowered.
Compression Bands – restrain the uncooperative patient and compress the abdominal tissue for more even subject density.
Tube suspensions are available in numerous configurations.
Overhead Suspension System
Floor-to-Ceiling Suspension Systems
- Tube suspension is based on the floor suspension model
C-Arm Suspension System
Other Specialized Diagnostic Equipment
- Radiation Therapy Simulator
- Tomography Unit
- Mammography Unit
- Computerized Tomography Unit
Unit 3 - The X-Ray Tube
- negative side of the x-ray tube
- produces thermionic cloud
- contains the filament - thoriated tungsten
- most units contain two filaments - dual focus arrangement
- arcing may destroy tube when electrons stray from intended path towards anode and strike vaporized tungsten coated glass envelope
- a major cause of tube failure is breaking of the filament
- when tube is first turned on, a small amount of current keeps the filament in a "pre-heated" mode until the exposure is taken
- most tube manufacturers recommend that two-step exposure switches be fully depressed in one motion
- Focusing cup narrows the thermionic cloud as it is driven towards the anode
- charge on focusing cup is negative
- space charge effect limits x-ray tubes to maximum mA ranges of 1,000 to 1,200 mA
- grid biased tubes allow the quick regulation of electrons producing x-ray photons
- used with capacitor discharge generators and digital angiography
- in grid biased tubes, the focusing cup acts as a switch to accomplish the rapid production of exposures
- the positive side of the x-ray tube
- three functions: serves as the target for electron stream, conducts electrons back into x-ray system circuitry, and serves as a thermal conductor
- two types: stationary (used primarily in dental offices) and rotating (allows for greater heat dissipation/higher techniques)
- anode disc is composed of graphite, molybdenum and a tungsten-rhenium face
- tungsten has a high atomic number (74), a high melting point and high heat conducting ability
- pitting of the anode may occur if the rotating anode is not spun at sufficient/correct speed
- manufacturer warm-up procedures should be performed to prevent cracking the anode disc
- the target on the anode is considered to be a point source of x-ray photons
- tape measures on tubes take into account the distance from the collimator to the focal spot on the anode and thus may begin at 12 cm.
- rotating anodes have greater heat dissipating properties compared to stationary anodes
- actual focal spot - area on anode face actually struck by electrons
- effective focal spot - area of focal spot projected down towards patient
- line focus principle - the effective focal spot is controlled by the size of the filament and the angle of the anode's face
- the same actual focal spot size may be used in two tubes each with varying anode face angles
- allows for greater heat dissipation (larger area bombarded by electrons) with the advantage of a smaller effective focal spot (better radiographic detail)
- steeper anode angles = smaller effective focal spots
- the most common diagnostic radiography anode target angle is 12 degrees but may range from 7 to 17 degrees
- anode heel effect - anode material itself absorbs some of the radiation produced, and therefore the beam is more intense under the cathode side of the tube
- most dramatically demonstrated when large IRs are used at short SIDs
- classic example: AP T-Spine: neck area (thinner part) under anode and midchest (thicker part) under the cathode
- anode spins via an induction motor
- two parts of an induction motor: stator (outside glass envelope) and rotor (inside glass envelope)
- anodes may rotate as quickly as 10,000 rpm (faster rotation = greater heat dissipation)
- provides vacuum necessary for the production of x-rays
- pyrex glass is used to withstand large amount of heat produced during exposures
- window - thinned area on glass envelope where primary beam exits (allows for less absorption of primary beam photons by glass)
- metal is often incorporated in today's tubes to reduce arcing that can cause tube failure
- supports the x-ray tube
- lined with lead
- controls leakage and scatter radiation, isolates high voltages and providesa means to cool the tube
- contains dielectric oil: to help dissipate heat and act as an insulator
- must limit leakage radiation to less than 100 mR/hr at a distance of 1 meter
- many tube housings include a small fan to remove heat from the housing itself
Off Focus Radiation
- composed of photons produced on the anode other than at the focal spot area
- off focus radiation produces a "ghosting" effect of the anatomy on the radiographic image
Tube Rating Charts and Cooling Curves
- help radiographers to avoid thermal damage to x-ray tubes
- safe techniques are "under the curve"
- heat units = kVp x mA x rectification constant
- rectification constant - single phase = 1 3 phase, 6 pulse = 1.35 3 phase, 6 pulse = 1.41
- To extend tube life: warm up cold tubes, do not hold down rotor button unnecessarily, use lower mA stations
- Greater than 99% of the kinetic energy of the projectile electrons is converted into heat. Less than 1% of the kinetic energy is converted into x-radiation.
2 means by which x-rays are produced:
- Characteristic Radiation Production
- projectile electron dislodges an inner shell electron, thus ionizing the atom.
- outer shell electrons transition to fill in the vacancies
- as the shell transitions occur, x-radiation is produced
- When an outer shell electron fills the vacancy in the K shell, a K x-ray is produced.
- only the K x-rays, having an effective energy of 69 keV are useful for creating
- Bremsstrahlung Radiation Production
- As a projectile electron nears the positively charged nucleus an electrostatic force is encountered.
This force causes the electron to slow down, or brake, and change direction. The loss of kinetic
energy, due to the braking process, is in the form of an x-ray photon.
- Bremsstrahlung x-rays can be produced at any energy from 0 to the peak kilovoltage used.
- In the diagnostic range , most of the x-rays are of bremsstrahlung origin.
X-Ray Emission Spectrum
The combination of bremsstrahlung and characteristic x-rays together forms what is know as the
x-ray emission spectrum.
A spectrum is a representation of the range of numerical values that can be observed.
If an individual could count every x-ray photon in a given exposure, determine its energy and then plot/graph the results, an x-ray emission spectrum could be created.
Brems = The Continuous Spectrum
Characteristic = The Discrete Specrtrum
Quality - the overall energy of the beam.
Quantity - the number of x-ray photons in the beam
Various factors influence the quantity and quality of the beam. These changes can be graphically demonstrated as a change in the height (amplitude) and the position (shifts of the curve to the right or left) for each component of the spectrum.
- A change in the height or amplitude of either component indicates a change in the number of
x-rays having a specific energy.
- A change in the position of the peaks of either component along the horizontal axis represents a
change in the energy of the x-ray photons within the beam.
At the completion of this unit, the student will be able to:
- Differentiate between inherent and added filtration.
- List various types of added and inherent filtration
- List the amount of minimum total filtration necessary in the beam at the following kVp levels:
- below 50
- 50 – 70
- above 70
- List the standard filter material used in diagnostic radiography.
- Define half-value layer.
- Understand what is meant by compensation filtration.
- List examples of compensation filters used in radiography.
- Understand how filtration affects patient dose and beam intensity.
- Understand how filtration affects radiographic contrast and density.
- List the main advantage to using filtration.
Filtration is used in radiography to eliminate the undesireable low-energy (longer wavelength) photons from the heterogeneous/polyenergetic beam.
The process of filtration is often referred to as "hardening the beam" - the "soft" energy (low energy) photons are removed.
The material used in radiography for filtering purposes is aluminum (Z# = 13).
Filtration of the beam occurs between the x-ray tube and the patient.
Filtration serves as a mean of patient protection by absorbing the low energy photons that would otherwise be absorbed by the patient (especially at the skin level).
Filtration is specifically expressed in terms of half-value layer.
Half Value Layer = the amount of absorbing material necessary to decrease the intensity of the beam to 1/2 of its original value.
The federal government specifies minimum half value layers (HVLs) for all diagnostic x-ray tubes operating at specific kilovoltage peaks.
Aluminum equivalency = all filtering material in the path of the x-ray beam (i.e. collimator mirror, oil, etc.)
inherent filtration = result of tube and its housing
- examples include: glass envelope, oil surrounding tube, vaporized tungsten on glass envelope
added filtration = filtration occurring outside of the tube and housing
- examples include: additional aluminum filtration, collimator mirror (which is in the path of the primary beam)
Compound filters - use two or more materials which complement each other's absorbing abilities
- example: Thoreaus filter used in radiation therapy (tin, copper and aluminum)
Compensating Filters: filters which solve a problem involving unequal subject densities
- examples: wedge (used in chest radiography - evens out densities between mediastinum and lungs) and trough (used primarily with radiography of the foot (AP) - evens out density between the tarsals and metatarsals
Total FIltration = Inherent filtration + Added filtration
Recommended Minimum Total Filtration Levels for tubes having the potential to operate at various kVp ranges
below 50 kVp = .5 mm aluminum
50 - 70 kVp = 1.5 mm aluminum
greater than 70 kVp = 2.5 mm aluminum
Filtration eliminates low energy photons (a portion of the beam) and therefore, as filtration is increased the radiographic technical factors must also be increased to maintain the same image receptor exposure.
Excellent website for decription/mechanisms of H & D curves:
Final Examination Review
Units covered: Radiation Concepts
The X-Ray Tube
The Prime Factors
- Primary controlling factor for density = mAs
- Primary controlling factor for contrast = kVp
- A radiograph with excessive density appears dark
- Density = overall blackness/darkening on the radiographic image
- Increase anatomic part thickness = increase in scatter and a decrease in contrast
- To maintain radiographic density – increase kVp by 15% and decrease mAs by ½
- A step wedge may be radiographed to determine the scale of contrast
- Increase photon wavelengths – decrease the penetrating ability of the beam
- An image appears very gray and has excessive density – to remedy the problem the radiographer should decrease the kVp (produces a shorter scale/more contrasting image) and decrease the mAs (decreases the density)
- Decrease kVp, decrease scatter
- Contrast – the difference in optical densities on the image
- Use the reciprocity law in determining mAs values
- Increase kVp – increase density and decrease contrast (more scatter on image)
- Increase mAs, increase the quantity of photons
- Low kVp = short scale of contrast (more black/white)
- The least amount of motion = shortest time factor
- Increase kVp – increase density, decrease contrast (image more gray)
- Beam with low penetrating abilities = low quality beam
- Lead = high degree of radiopacity
- To demonstrate a noticeable change in density = mAs must be minimally increased by 30%
- The optical density = the amount of light from the view box that is transmitted through the film
- Principle means of controlling voluntary motion = proper patient instructions
- Principle means of controlling involuntary motion = short exposure times
- Increase the kVp – increase the speed of the electrons travelling between anode and cathode, speed of x-ray photons will not change
- Be able to identify all parts to the x-ray tube on a diagram: anode, cathode, focusing cup, focal spot, glass envelope, window, rotor, stator
- Be familiar with the diagram which describes the line focus principle
- Anode heel effect – intensity of the beam is greater beneath the cathode
- The number of photons in the beam (mAs) does not effect the penetrating ability of the beam
- A radiograph of a patient with an abdominal obstruction will appear dark because of the excessive penetration of the intestinal gas
- Remember when calculating mAs values, ms must be divided by 1000 to obtain seconds
- A high density tissue structure such as bone will appear light on a radiograph
- Increase tissue thickness, increase scatter production, decrease radiographic contrast
- The percentage of scatter produced is dependent on: kVp used, physical density/thickness of the anatomical part
- Gas as a contrast agent is radiolucent
- Barium, iodine as contrast agents are radiopaque
- Be able to use the mAs / distance formula
- Be able to use the inverse square law
- D log E curve – useful densities in the straight line portion of the curve (.25 to 2.5 OD)
- D log E curve – x axis = log relative exposure (increments of .3)
- D log E curve – y axis = optical density (0 – 4.0 OD)
- The slope/steepness of the curve is used to identify the radiographic contrast –steep curve = high contrast
- High contrast images have a narrow exposure latitude
- Processor developer temperature low and under-replenished developer chemical in a processor produce an image that lacks density
- Bone absorbs the most radiation – least optical density on the image
- Gas absorbs the least radiation – most optical density on the image
- Anode = positive
- Cathode = negative
- Space charge occurs during the prep/boost phase
- Induction motor spins the anode
- Increase the mA – increase the space charge
- Steepness of the anode effects the amount of anode heel effect and the field coverage
- Know how to calculate heat units for single phase, 3 phase/6 pulse and 3 phase/12 pulse units
- When a larger focal spot is chosen, the larger filament in the cathode is heated
- Roentgen discovered x-rays using a Crooke’s tube
- Space charge effect = collective repulsion of the electron cloud around the cathode that creates an eventual equilibrium
- Filament = thoriated tungsten
- Target angle of modern tubes is 7 – 17 degrees
- X-rays travel through glass, oil and aluminum as they leave the tube housing
- The steeper the anode angle – the smaller the effect focal spot
- Rotating anodes allow for increased heat dissipation
- Hot filament x-ray tube invented by Coolidge
- Majority of kinetic energy of the electrons in an x-ray tube is converted into heat
- Thermionic emission = liberation of electrons from the filament
- X-ray tube envelope = pyrex glass
- Window = thinned flattened area of glass allowing for minimal x-ray absorption
- Increase temperature of the filament = increase the number of electrons/quantity of photons produced
- Focusing cup confines electron cloud to desired part of target
- Image unsharpness occurs if the anode wobbles
- Oil in tube housing dissipates heat and acts as an electrical insulator
- Tube housing – absorbs leakage radiation, supports x-ray tube and contains the insulating oil
- X-ray beam is heterogeneous
- Increase mAs – increase density
- Increase SID – decrease density
- Increase filtration amount – decrease density
- Increase the anatomical part thickness – decrease density
- Faster film/screen systems used – increased density
Review Chapter 11 – X-Ray Tube (DeAngelis), Chapter 21 – Radiographic Quality (DeAngelis) and Chapter 22 - Radiographic Quality Advanced (DeAngelis)
*Review only those questions in the above chapters which pertain to material covered in class.