Objective review principles of Radiology

List the 12 properties of x-rays.

1. Invisible and highly penetrating 2. Electrically and magnetically neutral: not affected/deflected by electric or magnetic fields 3. Form a polyenergetic or heterogeneous beam (wide variety of energies/wavelengths)4. Can liberate heat/release minute or small amounts of heat when interacting with matter 5. Travel in straight lines and diverge from the source 6. Travel at the speed of light in a vacuum 7. Can cause some substances to fluoresce 8. Cannot be focused by a lens (optics) 9. Affect photographic film: causes chemical changes to occur in radiographic and photographic film 10. Can ionize matter 11. Can cause chemical and biologic damage to living tissue by ionization and excitation 12. (By ionization) can produce secondary and scattered radiation when interacting with matter (tissue).

electromagnetic radiation

A form of radiation that is a result of electric and magnetic disturbance. EMR is a form of energy resulting from a change in velocity (speed/direction) of a moving charged particle. (Carlton P30)

Voltage,

A measure of electrical force or pressure.

Prep or rotor switch

A rotor switch supply's a current to the coil in the magnetic field an induction motor. Consists of bars of copper around an iron core.

9) Describe the composition and design of the anode. (Orth P100- P101)

Anode is made up of tungsten/rhenium as it undergoes many different properties. Tungsten and rhenium are materials that survive a high atomic number, which has a high conversion efficiency for electrons into x-rays. A high melting point so that the large amount of heat released during an exposure causes minimal damage to the anode. Lastly a high heat conduction ability to remove heat rapidly away from the anode. The anode is made up of this material to be able to function as it needs. The machine needs it to be a thermal conductor, electrical conductor, and target/focal track. The anode is made up of the anode, stator (motor) and rotor. With this design it allows for a higher heat loading capability and a higher x-ray intensity output. It spreads the heat over a larger area permitting exposures using much larger tube currents and extended exposure time.

Explain the process of heat production occurring at the target of the x-ray tube.

As the kinetic energy of the incident electrons increases so does the efficiency of photon production. By the time the therapeutic MeV range is reached, most of the energy is producing photons of heat. Due to the high kinetic energy incident electrons seldom transfer enough energy to the outer shells of target atoms to cause ionization. They transfer enough energy to excite the outer shell electrons to the point where they will emit infrared radiation as heat. These electrons then return to their normal state where they will be re-excited again and again, each time emitting infrared radiation as heat.

octet rule

Atoms that contain exactly eight electrons in their outermost shell are considered inert and chemically stable.

Explain the dual nature of x-ray energy (wave-particle duality).

Behave both like waves and particles. X-rays act like waves when traveling through space. X-rays act like particles when interacting with matter. Wave theory is when the x-rays behave like waves as it travels (has wavelength and frequency). Particle theory is when x-rays behave like particles when it interacts with matter. Sees x-rays as small, discrete packets of energy known as a photon which can result in damage to biological tissue.

Briefly Describe Bohr's theory of atomic structure.

Bohr's atom is likened to a miniature solar system where electrons orbit around a central nucleus just as the planets revolve around the sun. Most widely used in explaining the composition of matter. A distinction between Bohr's model and an actual atom is that electrons orbit the nucleus in many planes whereas the planets orbit the sun in essentially the same plane.

Explain the production of Bremsstrahlung radiation

Brems interactions may occur only when the incident electron interacts with the force field of the nucleus. The incident electron must have enough energy to pass through the orbital shells and approach the nucleus of the atom. The atomic nuclei have a positive charge, and the incident electron has a negative charge resulting in a mutual charge between the two. The amount of kinetic energy lost by the incident electron in a brems interaction is determined by the distance the electron is from the nucleus. At far distances very little kinetic energy is lost resulting in lower energy brems radiation while at closer distance more kinetic energy is lost resulting in higher energy brems radiation.

Discuss / explain the line focus principle.

By angling the anode target, a large actual focal spot can be maintained while a smaller effective focal spot is created. If the target were angled to 45 degrees, the size of the actual and effective focal spot would be identical; this would do nothing to improve the sharpness of the resultant image.

) Explain the process of thermionic emission. (Orth p98)

Causes a change in the number of projectile electrons boiled off the filament. Thermionic emission causes electrons to boil off the filament wire and to form a thermionic cloud.

Explain the production of Characteristic radiation and what the minimum kVp will be needed in order to produce this.

Characteristic radiation is produced from the electronic transition in an excited atom. Excitation consists in removal of an electron from an inner shell. This happens from fast electrons providing energy to form excitation. The minimum kVp that will be needed to produce this is 75 kVP.

Discuss off-focus radiation and explain how it appears in the image.

Consists of x-rays produced at locations outside of the focal spot. It occurs when projectile electrons strike other parts of the anode away from the focal spot. These electrons cause low-intensity x-ray photons over the entire anode causing issues with the radiographic images. For instance, the radiographic images will appear to have geometric blurring, reduce image contrast, and expose the patient's tissue outside the intended imaging area.

Actual focal spot

Describes the actual area on the focal track that is impacted. The actual focal spot is determined by the length of the filament and the width of the focusing cup depression.

milliampere,

Directly proportional to tube current. The number of electrons reaching the target is also controlled by the length of time the tube is energized. mA is the number of electrons per second.

Describe how the electrons are accelerated to the "high speed" necessary for x-ray production.

Electrons are accelerated by a high voltage towards the metal target, x-rays are produced when the electrons collide with the nuclei of the metal target. The envelope also provides some insulation from electrical shock which may occur because of the high voltage within the tube, and it dissipates the heat that builds up in the tube during an exposure.

kVp

Increasing the kilovoltage on an x-ray control panel will cause an increase in the speed and energy of the electrons applied across the x-ray tube.

fluorescence

Instantaneous production of light resulting from the interaction of some type of energy (X-ray) and element or compound. (ex. Barium)

atom

Is the smallest particle of an element that still possesses the chemical properties of that element.

11) Explain the functions of the x-ray tube protective housing. (Orth P97)

It is the outer portion of the tube that you see when you look at the x-ray tube. It is mainly made from steel to protect the x-ray tube and be the "protective housing." It prevents excessive radiation from exiting the tube or off-focus radiation, isolates high voltages, and provides means to cool the tube.

electron

Negatively charged subatomic particle of an atom.

proton

Positively charged subatomic particle of an atom.

Explain the difference between QUALITY versus QUANTITY of radiation.

Quantity is a measure of the number of x-ray photons in the useful beam. Also known as x-ray output, intensity, or exposure. Factors that directly affect the x-ray quantity are milliamperage-second, kilovoltage, distance, and filtration. X-ray quality is a measurement of the penetrating ability of the x-ray beam. This describes the distance an x-ray beam travels in matter. High-energy x-ray photons travel farther in matter than low-energy photons and are, therefore, more penetrating.

exposure (mR and R):

Roentgen represents a unity of exposure in air and was defined as the quantity of x-rays or gamma rays required to produce a given amount of ionization (charge) in a unit mass of air. The roentgen is limited to the measurement of exposure in air only and is not applicable to photons of energy above 3 Mev or to particulate radiations.

exposure switch

Simply a connection that permits current to flow through the circuit. Activates the rotating anode of the x-ray tube. The exposure switch must be attached to the control console in such a manner that it is impossible for the operator to be exposed.

photon, (quantum)

Small discrete bundle of energy. The energy of an individual photon is measured in units of electron volts (Ev) Photon energy and frequency are directly proportional. Quantum: is the singular form of photon.

neutron

Subatomic particle of an atom containing no charge.

binding energy

The amount of energy needed to remove the electron from the atom.

Describe the anode heel effect and its importance to the clinical setting.

The anode heel effect produces an intensity variation in the x-ray beam between the cathode and anode sides of the x-ray field. This causes a variation in image density or image receptor exposure from the anode side to cathode side, where the radiation intensity is greater on the cathode side. In the clinical setting you can notice this when you use different fields sizes, and image receptor distances. Smaller field sizes and a larger SID reduce the anode heel effect. The anode heel effect is applied in clinical situations to achieve a more uniform density when there is a large variation of body thickness across the x-ray field.

Effective focal spot

The area of the focal spot that is projected out of the tube in a downward path and toward the object being imaged in other words primary radiation. Because of the angle of the anode, the effective focal spot is always smaller than the actual focal spot.

tube current

The current flowing from the cathode to the anode in the X-ray tube. The tube current is adjusted according to the contaminant to be detected.

wavelength:

The distance between any two successive points on a wave.

Electron shells

The distance from the nucleus determines the energy level or shell the electron occupies.

Explain the terms dual focus x-ray tube and focal track. (Orth P102)

The dual focus x-ray tube contains two filaments and two anodes. This tube is functioned by an alternating electric current which accelerates electrons toward the aluminum plate. The dual focus x-ray tube was able to produce x-rays at both ends of the tube. The focal track is the circular path that will be bombarded with the electron beam. The stationary anode has the one area of impact while the rotating anode has the focal track. In the stationary anode tubes, it is a small area with dimensions of a few millimeters. In the rotating anode tube, the focal spot tack is much larger because of the movement of the anode in relationship to the electron beam.

Describe the space charge effect.

The electrons reach a point where their negative charges begin to oppose the emission of additional electrons. The space charge effect limits x-ray tubes to maximum mA ranges of 1,000 to 1,200. When the filament current is high enough for thermionic emission a small increase in filament current result in a large increase in tube current.

Explain what happens to the conversion of energy of the high-speed electrons when they are suddenly stopped at the anode.

The energy then converts into another form. The energy that is emitted from the anode in the form of electromagnetic radiation waves, including infrared, visible light, ultraviolet waves, and x-rays. As the electron slows down it will lose kinetic energy that is emitted as an x-ray photon. The x-ray photon will have the same energy as the lost kinetic energy.

Explain how electrons are focused from the cathode to anode. (Orth p97)

The focusing cup has a very large negative charge and it repels the electrons into a group overcoming their own smaller negative charge and tendency to repel each other. The tube current is applied across the x-ray tube from cathode to anode then affecting the energy and number of electrons released. The anode end is a positively charged electrode that acts as a target for electrons while the cathode end is the negatively charged end. The vacuum permits electrons to flow from cathode to anode without encountering the gas atoms of air.

Describe the construction of the x-ray tube. (Orth P97)

The major components of the x-ray tube include the cathode, anode, rotor/stator, glass or metal envelope, tube port, and tube housing. The tube components are sealed inside an evacuated (vacuum) glass or metal envelope. The vacuum allows the electrons to travel freely from the negative cathode to the positive anode. Electrical current will flow through negative to positive. The x-ray tube must supply moving charged particle (e- at the cathode) and stop the particle (at the anode).

atomic number

The number of nuclear protons in an atom. Each element has its ownspecific number of nuclear protons which is a key characteristic that distinguishes one element from another.

kilovoltage,

The peak potential applied to the x-ray tube, which accelerates the electrons from the cathode to the anode in radiograph.

ionization

The process of adding or removing an electron from an atom.

absorbed dose, and:

The rad was developed as a unit of absorbed energy or dose and is applicable to any material. The rad is defined as 100 ergs of energy absorbed in 1gram of absorbing material.

nucleus

The small dense center which is surrounded by electrons that orbit it at various levels. The nucleus contains two of the three basic particles of the atom, protons, and neutrons, which are responsible for almost all the mass of an atom.

Name and describe the parts of the cathode. (Orth P98-P99)

The three parts of the cathode are the filament, focusing cup, and connecting wires. The purpose of the filament is to provide projectile electrons for acceleration to the positively charged anode. It is made of tungsten materialbecause of the high atomic number and high melting point. The filament is connected to the filament current, termed milliamperes which produces change in the filament temperature. The focusing cup is made of nickel and molybdenum with two depressions that contain the filaments. The connecting wires are used to establish electrical conductivity between two devices of an electrical circuit. These connecting wires is responsible for heating the filament up to the temperature that corresponds to the mA station selected for the exposure. These wires create a filament current that flows into and through the filament before flowing out of the filament the current flows through one wire. The second wire entering the filament carries the tube current form the high-voltage main circuit. This wire supplies enough charge to force the electrons boiled off the filament to go across the tube to bombard the anode.

2n²

This equation determines the maximum number of electrons that can occupy a given shell. N equals the shell or principal quantum number with K being the first shell.

excitation

Transferring energy to an atom through electromagnetic radiation. In this excitation process, electrons in an atom are moved to a higher energy state without being removed from the atom.

atomic number

When an atomic number of increases or decreases it will become a different element that will have a different number of atoms. For example, Radium with an atomic number of 88, decays over a very long period to form the element radon, which has atomic number 86. Radon is a naturally occurring gas that is also radioactive.

List the conditions required for the production of x-ray photons.

X-ray photons are produced when the high-speed electrons from the cathode strike an anode target. The greater the mass or speed of the incident electrons, the greater the quality (energy) and quantity (number) of photons produced.

Describe the events surrounding the discovery of x-rays.

X-rays were discovered on November 8th, 1895, by Dr. Wilhelm Conrad Roentgen with his experiment using cathode rays. He developed equipment noticing the effects of electricity on vacuum glass tubes. After many times continuing the experiment he noticed the effects of the electrical glow (cathode rays) coming exiting from the tube. This glow caused a fluorescent effect on a small cardboard screen painted with barium while it was being placed over the aluminum window. Further in his experiment he discovered by placing his hand in between the energized tube and the barium platinocyanide coated paper, he would be able to see his bones from his hand glow on the paper. As he continued to move his hand the fluoroscopic image moved.Rontgen became the first radiographer as he produced four photographs to put next to his first draft. The hand of his wife, a set of weights, a compass, and a piece of metal.

X-ray

classified as a specific type of energy termed electromagnetic radiation (EMR). X-ray is a form of energy which has the power to penetrate many forms of matter and can record an image of that matter on a photographic emulsion or image receptor. (Orth p46)

State the characteristics of electromagnetic radiation.

electromagnetic radiation references are the radiation that has both electrical and magnetic properties. Travels through space as a combination of electrical and magnetic fields. Spans across a continuous spectrum of wide ranges of energy. For instance, radio waves, visible light, x-ray, cosmic rays, microwaves, and infrared light.

mA.

mA is the number of electrons per second. This means that changes in the length of time of exposure will affect the total number of electrons flowing from cathode to anode. As mA increases, so does the number of electrons that are able to cross the tube to reach the x-ray target. mA is proportional to tube current. As mA doubles so does the number of electrons able to cross the tube.

frequency

number of waves that pass a particular point in each time frame, or the number of cycles per second.

10) Discuss the purpose of the vacuum in the glass envelope. (Orth P97-P98)

the purpose of the vacuum in the glass envelope is because it permits the electrons to flow from the cathode to the anode without using the gas adams of air. It can withstand the tremendous heat produced during an exposure. The x-ray tube is a vacuum tube with two electrodes the cathode and the anode. These components are evacuated in the envelope where all the air is removed from the envelope creating a vacuum.

effective dose:

the sum of the weighted equivalent doses for all irradiated tissues and organs. It considers the fact that not all tissues are equally sensitive to the effects of ionizing radiation.