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Radiation Physics
final
| Question | Answer |
|---|---|
| 1901 | Roetgen wins the first nobel prize in physics |
| 1913 | Coolidge hot cathode xray tube is introduced |
| 1895 | Roetgen discovers xrays |
| 1907 | Snook transformer is developed |
| Energy | ability to do work |
| Ionizing radiation | Special type of radiation that includes xrays |
| Air kerma | effective dose |
| Acceleration | the rate of change of velocity |
| FLuro | real time imaging |
| Matter | anything that occupies space |
| Mass | Quantity of matter contained in any physical object |
| Collimation | Restricts the useful xray beam to the part of the body being imaged |
| Gonadal shielding | should be used on all persons within child bearing age |
| Velocity | measures how fast something is moving |
| Weight | force on a body caused by the pull of gravity on it |
| Momentum | Product of the mass of an object and its velocity |
| work | Product of force and distance |
| energy | ability to do work |
| heat | also known as air kerma |
| rem | unit of absorbed dose |
| Describe how weight is different then mass | weight is determined by the force of gravity. weight changes in value with position in a gravitational field such as the earth or the moon. Mass is constant and it is independent of position and is determined by the objects energy equivalance |
| Name four examples of electromagnetic radiation. | Xrays, radiowaves, viable light, and microwaves |
| How does x-ray interaction differ from that seen in other types of elecromagnetic radiation? | X-rays interact at the electron level or nuclear level, ionizing an atom or ejecting a nuclear particle, respectively. Lower-energy electromagnetic radiation interacts with molecules, cells, and larger objects in a way that will usually elevate the temper |
| What is the purpose of x-ray beam filtration | Absorb low-energy x-rays before they reach the patient. |
| What is the velocity of the mobile x-ray imaging system if the hospital elevaor travels 20m to the next floor in 30 s? | Velocity = Distance divided by time = 20 m/30 s = 0.67 m/s. |
| A radiographer has a mass of 58kg. What is her weight on the earth? On the moon? | Weight on Earth = 58 kg × 9.8 m/s2 = 568 N. Weight on the moon = 58 kg × 1.6 m/s2 = 93 N. |
| Name four devices designed to minimize radiation exposure to the patient and the operator? | X-ray beam filtration, x-ray beam collimation, protective apparel and barriers, fluoroscopic cumulative timer, and the protective tube housing. |
| Liquid hydrogen with a boiling temperature of 77 K is used to cool some superconducing magnets. What is this temperature in degrees Celsius? In degrees Fahrenheit? | Temperature in °C = 77K – 273 = –196 °C. Temperature in °F = [(–196) × 1.8] –32 = –385 °F. |
| What are the three natural sources of whole-body radiation exposure? | Cosmic rays, terrestrial radiation, and internally deposited radionuclides |
| What naturally occuring radiation source is responsible for radiation dose to lung tissue? | Radon |
| What are the four special quantities of radiation measurement? | Roentgen- radiation in air Rad- radiation dose absorbed Rem- occupational radiation exposure Curie- measures amount of radioactive material |
| How would you define radiation? | The transfer of energy from one area or medium to another. |
| If you started with 88mAs @ 90kVp, what would the new mAs be if you increased the kvp to 93? | increased kVp by8% so we would decrease mAs by 25% = 66mAs |
| If you started with 14mAs @ 55kVp, what would the new mAs be if you decreased kVp to 51? | 21 mAs |
| which of the following items is considered to be matter | wet snot |
| A radiographic exposure requires 400 ms. This is also: | 0.4 s |
| A radiation monitoring report would express a radiographer's dose equivalent in which of the following? | Sievert |
| Absorbed dose can be measured in: | Grays or rads |
| If atoms large enough to have electrons in the T shell existed, what would be the maximum number allowed in that shell? | 200 |
| What is Mendeleev remembered for? | Periodic table of the elements. |
| Who developed the concept of the atom as a miniature solar system? | Niels Bohrs 1913 |
| List the fundamental particles within an atom. | Electron, proton and neutron |
| What property of an atom does binding energy describe? (2 types of binding energy) | 1. The energy required to hold nucleons together as a nucleus (nuclear binding energy). 2. The energy required to maintain electrons in orbit about the nucleus (electron binding energy). |
| Can atoms be ionized by changing the number of positive charges? | no |
| Describe how ion pairs are formed. | An ion pair is formed when an electron is removed from an atom by ionizing radiation. |
| What determines the chemical properties of an element? | The arrangements of electrons in the outermost shells. |
| Why doesn't an electron spontaneously fly away from the nucleus of an atom? | Electrostatic force of attraction or electron binding energy |
| Describe the difference between alpha and beta emission. | Mass and charge on the particle. An alpha particle has four units of mass and two units of positive charge. A beta particle has essentially no mass and one unit of negative charge. |
| Photon | it has no mass and no charge |
| The RUtherford atom | first description of an atom having a nucleus |
| Positron | Positively charged beta particle |
| Necleons | neutrons and protrons |
| Radioactice half-life | time required to reduce radioactivity to half its original value |
| k shell | innermost electron shell |
| radiolucency | characteristic of materials that allow xrays to penetrate with a minimumn of attenuation |
| inverse sqaure law | the intensity is inversley porportional to the square of the distance of the object to the source. |
| frequency | the number of wavelengths passing a point per second |
| the law of conservation of energy | energy that can be transformed into another form or into matter, but it cant be created or destroyed. |
| gamma rays | a form of inonizing electromagnetic radiation emitted from the nucleus of a radioactive atom |
| electromagnetic spectrum | the wide range of electromagnetic radiation described by its frequency, wavelength or energy |
| square law | a mathmatical formula for calculating the new mAs when changing the distance for a particular image. |
| attenuation | the reduction of xray beam intensity because of absorption and scatter |
| wavelength | distance from one crest to another |
| amplitude | on half the range from crest to valley over which sine waves travel |
| the law of conservation of matter | matter can be neither created or destroyed |
| The output intensity of a normal radiographic imaging system is 0.05 mGy/mAs at 100cm. What is the output intensity of such a system at 200cm? | 0.05/x = 200² / 100² 0.0125 mGya/mAs (1.25 mR/mAs). |
| A mobile x-ray imaging system has an output intensity of 0.04mGy at 100cm. Conditions require that a particular examination be conducted at 75 cm SID. What will be the output intensity at this distance? | 0.04/x = 75² / 100² 0.071 mGya/mAs (7.1 mR/mAs) |
| Write the wave equation | Velocity = frequency × wavelength |
| How are frequency and wavelength related? | Inversely. As frequency increases, wavelength decreases proportionately. |
| Write the inverse square law. | original intensity/ new intensity = new sid^2 / old sid^2 |
| The intensity of light from a reading lamp is 200mlm at a distance of 2m. What is the intensity of the light at 3m? | 200/x = 3² / 2² = 89 mlm |
| What are the three imaging windows of the electromagnetic spectrum, and what unit of measure is applied to each? | Radiofrequency by frequency (Hertz), visible light by wavelength (meters), and x-radiation by energy (electron volts). |
| What is the energy range of diagnostic x-rays? | Range of energies of diagnostic x-rays is: 20 – 150 keV. |
| What is the difference between x-rays and gamma rays? | X-rays are emitted from the electron cloud. Gamma rays are emitted from the nucleus. |
| Some regions of the electromagnetic spectrum behave like waves, and some regions behave like particles in their interaction with matter. What is this phenomenon called? | wave partical duality |
| The inverse square law is a result of: | divergence |
| An x-ray can also be correctly called a | photon |
| electrodynamics | electrical charges in motion |
| electric power | = electrical current x electrical potential |
| electrostatics | stationary elctric charges |
| dipole | object with two poles |
| induction | the ability to transfer energy from one object to another without touching |
| autotransformer | an iron core transformer with only one winding |
| electrical potential | the energy per unit charge that causes electrons to move in an electric conductor |
| transformer | changes the intensity of alternating voltage and current |
| solenoid | a coil of wire |
| magnetic field | any charged particle in motion creates this |
| conductor | any substance in which electrons flow easily |
| semi-conductor | behaves like a conductor or insulator depending on the situation |
| insulator | any substance that doesnt allow electrons to flow |
| Describe the three types of transformers. | Closed Core- Has a magnetic core changes the voltage or current of AC to another Autotransformers- Primary or secondary coils share windows there is a step up which increases voltage and a step down which decreases voltage Shell- transmission of high an |
| What are the three ways to electrify an object? | Contract, friction and induction |
| List the four laws of electrostatics. | 1. Un like charges attract and like charges repel 2. Coulombs law 3. electric charge distribution is uniform throughout or on the surface 4. Electric charge or a conductor is concentrated along the sharpest curve of the surface. |
| What is the role of magnetism in the study of x-ray imaging? | The high-voltage generators in x-ray imaging systems are magnetic devices. Magnetic resonance imaging deals with static and varying magnetic fields. |
| List the three principal types of magnets. | Natural, permanent, electromagnents |
| Describe an electromagnet | A current carrying device coil of wire wrapped around an iron core that intensifies the induced magnetic field. |
| What happens when a bar magnet is heated to a very high temperature? | It loses its magnetic properties. |
| What is the formula for voltage? | Voltage= electric current X electric resistance |
| List the three diamagnetic materials? | Wood, water and plastics. |
| The magnitude of the induced current depends on four factors, what are they? | 1.) The strength of the magnetic field 2.) The velocity of the magnetic field as it moves past the conductor 3.) The angle of the conductor to the magnetic field. 4.) The number of turns in the conductor |
| Electric power is measured in | watts |
| Describe AC & DC currents. | AC- alternating current goes in either directions DC- direct current we use in xray only flows one way |
| The term electromagetic induction refers to the production of | An electric current |
| The radiographic table must be radiolucent. Define radiolucent. | Allow relatively undiminished intensity of x-rays through the tabletop. |
| Describe movements of a patient couch. | 90 degrees to vertical so that the patient is standing; 20 degrees head-down. |
| List the five major controls on the operator's console. | On/off control, kVp selection, mA selection, time selection, and automatic-exposure controls. |
| What is the purpose of the autotransformer? | To vary and control the amplitude of the voltage supplied to the high-voltage step-up transformer and the filament transformer. |
| What does the pre-reading kVp meter allow? | The precise adjustment of the supply voltage and monitoring the kVp before the x-ray exposure. |
| The operating console controls are set at 200mA with an exposure time of .067 seconds. What is the mAs? | 13.4 mAs |
| In an examination of a pediatric patient, the operating console controls are set at 600 mA and 30ms. What is the mAs? | 18 mAs |
| What is the difference between a high-voltage generator and a high-voltage transformer? | A high voltage transformer is in a high voltage generator. High voltage generators increase the output voltage from autotransformer to kVp. |
| Why does the x-ray circuit require rectification? | In order that a reverse voltage is not applied across the x-ray tube. And x-ray tubes operate most efficiently on DC current. |
| smeiconductor | a material that can sometimes conduct an electrical current and sometimes not |
| AEC | An electronic device designed to terminate x-ray exposure after properly exposing an image receptor |
| line compensation | a method of adjusting the voltage to the xray imaging system to a constant value, to compenstate for fluctuations in voltage supplied by the power company |
| capacitor | an electrical circut device that stores electrical charge. |
| mA meter location | placed in the tube circut, connected at the center of the secondary winding of the high voltage step up transformer in the series of an xray tube |
| Diode | an electrical device that contains two electrodes |
| voltage ripple | the fluctuation in the voltage applied to the xray tube expressed as a percentage of kilovoltage peak |
| rectification | the process of changing alternating current and voltage into direct current and voltage |
| power | the product of voltage and current. watt |
| housing cooling chart | graph showing the cooling rate of xray tube housing |
| leakage radiation | radiation emmited through the xray tube housing and not the primary beam |
| heat unit HU | thermal energy unit to express heat capacity |
| focusing cup | shroud inside the xray tube surrounding the cathode to concentrate the electrons on the target focal spot. |
| xray tube current | cathode to anode electron flow |
| space charge | electron cloud in the vicinity of the filament |
| convection | method of heat transfer by a moving fluid medium |
| projectile electrons | Electrons emitted by the filament and directed to the target |
| binding energy | The strength of attachment of electrons to the nucleus. |
| characteristic xrays | xrays produced by transitions of orbital electrons from outter to inner shells |
| bremsstrahulung xrays | xrays produced by interaction of a projectile electron with the nuclear force field of a target nucleus |
| xray quantity | mAs or xray intensity, measured in air kerma or millirogens |
| xray quality | kVp of effective energy of the xray beam penetrating ablity |
| effective energy | the monoenergetic equivalent of an xray beam |
| addedd filteration | section of metal added to the x ray tube housing which results in reduction of patient dose |
| emmision spectrum | the measure of xray energy of all xrays, a graphical repersentation of the relative quantities of photons of each type of energy beam |
| molybdenum | xray tube target material principally used in mamms |
| List three methods used to support x-ray tubes and briefly describe each. | Ceiling support- two sets of perpendicular rails that allow for movement. Floor to ceiling support- column with rollers at the end C-arm support- mounted to ceiling receptor attached. |
| Where in an x-ray imaging system is thoriated tungsten used? | Filament in cathode |
| What is saturation current? | When all available electrons are projected from the cathode to the anode. |
| Why are arcing and tube failure no longer major problems in modern x-ray tube design? | Heavy filaments and high-capacity anodes. |
| Why are x-ray tubes manufactured with two focal spots? | Small for better spatial resolution, large for higher radiation intensity. |
| Is the anode or the cathode the negative side of the x-ray tube? | cathode |
| List and describe the two types of anodes. | Stationary for things like dental xrays and Rotating used in radiology |
| What are the four functions the anode serves in an x-ray tube? | X-ray tube target, electrical conductor, mechanical support, and thermal radiator. |
| Describe the difference between actual and effective focal spot. | Actual is the physical area of the focal tract thats impacted. Effective is controlled by the size of the actual focal spot and the anode target angle smaller then the actual spot being projected out of the tube. |
| Define the heel effect and describe how it can effectively used. | Radiation intensity on cathode side is greater than anode side xrays towards the anode side travel greater thickness to cathode end intensities of rays emitted through the heel end. longer path through the target and increased absorption smaller anode equ |
| Give three causes of x-ray tube failure. | Too hot, max exposures with a cold tube, electron arcing when the tungsten disturbs the electron balance |
| What is a detent position? | X-ray tube locking-in at center and at a given SID. |
| Discuss the effect on the x-ray emission spectrum if a single-phase x-ray imaging system is changed to a three-phase system. | X-ray intensity and effective energy are increased. |
| Why is the x-ray tube considered an inefficient device? | only 1 percent of interactions is photons being released of that 1 percent only 80 percent gets absorbed in the patient thats why its inefficient. |
| List three factors that affect the shape of the x-ray beam emission spectrum and briefly describe each. | Effect of kVp affects amplitude and position Effect of added filtration increases energy of beam and reduces quantity Effect of target material increases efficiency and energy |
| Define and explain the 15% rule. | A 15% increase in kVp is equivalent to doubling the mAs. |
| What is the diagnostic range of x-rays? | 20–150 kVp. |
| What type of radiation is useful for general diagnostic exposures? | Bremsstrahlung |
| The principal purpose of the autotransformer is to do which of the following: | adjust voltage |
| An autotransformer has only one: | coil |
| The exposure timer on a three-phase radiographic imaging system will: | be electronic |
| Small (steep) target angles result in which of the following: | small focal spot size |
| Generally, a small focal sot allows longer exposure times than a large focal spot. | false |
| What is the formula for HU for a three-phase high-frequency generator? | 1.4 x kVp x mA x s |
| inherent filteration | filteration provided by the window and oil bath of the xray tube |
| the unit of xray quantity | milliroentgen or milligray |
| a kvp change equal to twice the mAs | a kVp increase of 15% is equal to doubling the mAs |
| three filter materials used with diagnostic xray beams | aluminum, molybdenum and rhodium |
| half value layer | the thickness of filer or other absorbing material that will reduce intensity to half its original |
| wedge filter | compensating filter desinged to shape the useful xray beam to the anatomic structure |
| the unit of xray quality | Identified numerically by half-value layer; also influenced by kVp and the added filtration in the useful beam. |
| xray intensity | intensity is another term for xray quantity |
| diffrential absorption | The relationship among transmitted x-rays, photoelectrically absorbed x-rays, and. Compton scattered x-rays resulting in the x-ray image. |
| classical scattering | scattering of very low energy xrays with no loss of energy |
| compton scattering | xray ionization resulting in xray scattering |
| attenuation | the reduction in xray beam intensity as a result of photoelectric absorption and compton scattering |
| photoelectric effect | An x-ray absorption interaction in which the x-ray is not scattered but totally absorbed. A photoelectron is then released from the atom. |
| An abdominal radiograph is taken at 84kVp, 150mAs resulting in patient radiation exposure of 6.5mGy. The image is too light and is repeated at 84kVp, 250mAs. What is the new radiation exposure? | 250/150 x (6.5) = 10.83 mGya (1083) mR |
| What is the square law & what is it used for? | mAs₁ / mAs₂ = old SID² / new SID² It is used to determine the new mAs when the SID is changed. |
| What is the primary purpose of x-ray beam filtration (inherent & added)? | Inherent filteration is the glass or metal enclosure of the xray tube filters the emitted xray, it is 0.5mm Al equivalent. It helps reduce scatter radiatin. Added filteration is a thin sheet of aluminum between the protective xray tibe housing and the xr |
| The kVp is reduced from 78 to 68 kVp. What, if anything, should be done with mAs to maintain radiographic density? | Double mAs (15% rule) |
| Define half-value layer. | The thickness of absorber necessary to reduce the x-ray beam intensity to half. |
| What is the relationship between mAs and x-ray quantity? | Directly proportional. Double mAs; double x-ray quantity. |
| Why is aluminum used in x-ray beam filtration? | Because it is efficient at removing low-energy x-rays, and because it is readily available, inexpensive, and easily shaped into filters. |
| Describe back scatter. | Compton-scattered x-rays leave the scattering object in the approximate direction of the incident x-ray beam. Backscatter from the back of the imaging cassette and the Bucky can cause an artifact. |
| Of the five basic mechanisms of x-ray interaction with matter, three are not important to diagnostic radiology. What are they and why are they not important. | Pair production and photodisintegration because they occur at MeV which is only reached in Nuculear medicane and Radiation therapy. Also the photoelectric effect it interacts with inner shell and excites it the excess energy is then kicked out. |
| When kVp is increased, what happens to the absolute probability of photoelectric effect versus Compton scattering? | The relative frequency of photoelectric interaction compared with Compton interaction decreases with increasing x-ray energy. |
| The HVL is affected principally by a change in which of the following | kVp |
| An x-ray beam can be made "harder" by increasing which of the following: | filteration |
| After Comptom scattering, the scattered x-ray has: | longer wavelengths |
| Briefly describe photoelectric effect. | Removal of an electron by the total absorption of an x-ray. |
| List two ways an x-ray beam can be shifted to a higher average energy on the beam spectrum. | Increase the kVp or add filtration. |
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