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Physics 2 final

Radiology Physics

QuestionAnswer
State the maximum permissible tube leakage. Less than 100 mR/hr @ 1 meter at maximum when operating at capacity and at 2 meters should be less than 25 mR
Give the primary and secondary purpose of the oil that surrounds the tube Reduces electric shock, electrical insulation and heat dissipation
Explain what is meant by thermionic emissions When filament is heated enough, ion production begins the boiling off of electrons (the creation of ions through heat)
State the temperature required for thermionic emission with a tungsten filament 2200 degrees C
Recognize the melting point of tungsten 3410 degrees C
List the materials used in a tungsten filament Thoriated tungsten (tungsten with thorium)
Name the materials used in a focusing cup Nickel with rhenium
Compare the benefit of a smaller focal spot to the benefit of a larger focal spot Small has more detail (greater spatial resolution) from 0.1-1mm and large has greater heat capacity (mA) from 0.3-2mm
Compare the production of heat to the production of x-rays in the x-ray tube 99% heat and 1% x-ray
Compare the speeds of a normal rotating anode with a high speed anode Normal is 3400 rpm and high speed is 10,000 rpm
Name the device that is used to enable a rotating anode to rotate Induction motor
Explain what the stator is and where it is located Part of the induction motor series of fixed electromagnets in stationary coil windings located in the protective housing but outside the x-ray tube glass envelope at the anode end of tube
Explain what the rotor is and where it is located Rotating part of an electromagnetic induction motor located inside the glass envelope at the anode side of tube
Explain the line focus principle and how it is used in the design of an x-ray tube Design incorporated into x-ray tube targets allows a large area for heating while a small focal spot is maintained by angling the anode (EFS size much less than AFS)
Actual focal spot size area on the anode target that is exposed to electrons from the tube current
Effective focal spot size area projected onto the patient and the image receptor
Compare the actual focal spot size to the effective focal spot size AFS – area struck by electron beam. EFS – area from IR perspective by angling of the anode (AFS always larger than EFS)
Compare relationship between anode angle and effective focal spot size As anode angle increases the effective focal spot will increase (never angle more than 45 EFS would actually be greater than AFSNO BENEFIT) the greater the angle the greater the EFS
State what happens to anode heat capacity as anode angle increases As anode angle increases so does anode heat capacity
State what happens to field coverage as anode angle increases As anode angle increases field coverage increases
State what happens to resolution as anode angle increases Spatial resolution decreases as anode angle increases
Heel effect absorption of x-rays in the heel of the target resulting in reduced x-ray intensity to the anode side of the central axis. The smaller the anode angle the larger the heel effect
Explain how to use the anode heel effect to improve image quality Image quality improves with anode directed over smaller area cathode over thicker side FAT CAT
Compare resolution on the anode side of the tube to the cathode side of the tube Spatial resolution greater on anode side with more focal spot blur (less resolution) on cathode side
State the effect SID has upon the anode heel effect As SID increases anode heel effect decreases (divergence of beam?)
State the effect field size has upon anode heel effect Smaller field size decreases heel effect (from last test larger IR better than smaller IR- more scatter more density)
State the effect anode angle has upon the anode heel effect As anode angle increases anode heel effect decreases
Explain what is meant by extra focal or off-focus radiation X-rays produced at the anode but not at the focal spot. Electrons bounce off the focal spot and land on other areas of the target
List three ways in which heat is dissipated in an x-ray tube Radiation, conduction and convection
Read a tube rating chart and determine whether an exposure is safe Common sense- if mA + kVp + time is higher than the line it is an unsafe exposure under the line is safe
Calculate heat units produced in a single phase x-ray machine when given a technique HU = mA x time in seconds x kVp
Calculate the heat units produced in a three phase 12-pulse x-ray machine when given a technique HU = mA x time in seconds x kVp x 1.41 (for one exposure!) for multiple exposures you have to multiply by the number of exposures
Read an anode cooling chart or housing cooling chart to determine the exposure capacity of an x-ray tube Exposure capacity - divide capacity by total exposures made (total exposure capacity and divide by total exposures (HU) made) heat capacity divided by heat units per exposure
State two types of interactions that produce diagnostic x-rays Characteristic and Brems
State which of these two is an ionizing event Characteristic
Explain how a characteristic interaction produces x-radiation X-rays after ionization (projectile electron removes an inner shell electron) of a K-shell electron. When an outer-shell electron fills the vacancy in the K-shell results in an x-ray emitted.
Explain how a Bremsstrahlung radiation is produced Result from interaction between a projectile electron and a target nucleus. The electron is slowed, its direction is changed and leaves with reduced kinetic energy. This loss of kinetic energy reappears as an x-ray. Can have energy up to 70 kVp
State the relationship between x-ray energy and wavelength Inversely proportional- as x-ray energy increases wavelength decreases (gets smaller)
Explain how changes in mAs affect x-ray beam quantity and quality mAs changes beam quantity does NOT change quality
Explain how changes in kVp affect x-ray beam quantity and quality Increasing kVp increases quantity and quality (and vice versa)
Explain how changes in filtration affect x-ray beam quantity and quality As filtration increases quantity decreases and quality increases
Explain how changes in target Z number affect x-ray beam quantity and quality Target Z number increases beam quantity and quality increases
Explain how changes in generator power (voltage waveform/ripple) affect x-ray beam quantity and quality As generator power increases (voltage waveform/ripple decreases), beam quality increases and quantity increases
List three terms that can be used to refer to the number of photons in the x-ray beam Quantity, exposure and intensity
List two major units used to measure radiation exposure (measure of beam) mR and Graya (milliroentgens or gray in air
Explain relationship between x-ray quantity and radiographic density X-ray quantity and radiographic density are directly proportional
Explain relationship between x-ray quantity and patient dose X-ray quantity increases patient dose increases
List four major factors affecting x-ray quantity mAs, kVp, distance and filtration
State the relationship between mAs and x-ray intensity Directly proportional (mA is a measure of tube current-what is traveling across the tube not x-rays)
Calculate the changes in x-ray intensity when a specific numeric change is made to the mAs of the beam Double the mAs double the x-ray intensity
State the relationship between kVp and x-ray intensity kVp increases intensity increases (double the kVp and 4x the intensity)
State the inverse square law The intensity of the radiation at a location is inversely proportional to the square of its distance from the source of radiation
Use the inverse square law to calculate the change in radiation exposure as distance from the source changes (apply) I1÷I2 = (D2÷D1)2
Calculate what change is needed in radiation exposure as distance from the source changes Density maintenance law or Square law: compensate for a change in SID by changing mAs by the factor SID2 [mAs1÷ mAs2 = (SID1÷SID2)2]
Explain the relationship between filtration and patient dose As filtration increases patient dose decreases
Explain the relationship between x-ray beam energy and penetrability As energy increases penetrability increases
Explain what is meant by quality of the beam Quality is the penetrability of the beam. (increase quality = increased penetrability)
State how the quality of an x-ray beam is measured HVL
Explain the relationship between HVL and beam penetrability HVL is a measurement of beam quality. As HVL increases beam penetrability increases.
State the effect increasing SID will have upon beam quantity (intensity) Increase in SID will decrease beam intensity (quantity)
State the effect increasing SID will have on beam quality SID has no effect on beam quality
State what happens to the HVL of a beam as the energy of a beam increases HVL increases as beam energy increases
State why we wish to reduce the number of low energy photons in the x-ray beam To decrease patient dose (skin dose)
Define a compensating filter Used to give a better image for part thickness (more uniform) EX: trough-chest, “bow-tie”-Computed Tomography, wedge-foot Used to give a better image for part thickness (more uniform) EX: trough-chest, “bow-tie”-Computed Tomography, wedge-foot
State what three factors determine the probability of an x-ray interaction with matter Energy of the beam, mass density, subject atomic number (Z number)
Name two interactions that are significant in the production of diagnostic radiographs Photoelectric and Compton
Recognize the three other names for coherent scatter Classical, Rayleigh, Thompson
Describe what happens during a coherent scattering event Incident x-ray interacts with a target atom, disappears, causing atom to become excited. The target atom immediately releases this excess energy as a scattered x-ray with a wavelength equal to that of the incident x-ray (almost instantaneously)
Compare the energy and direction of the incident photon and the scattered photon of a coherent scattering interaction Incident photon and scattered photon have same amount of energy. Direction of the scattered x-ray is different from that of the incident x-ray
Describe what happens during a Compton scattering event The incident photon interacts with an outer-shell electron and ejects it from the atom, thereby ionizing the atom. The x-ray continues in a different direction with less energy
Compare the energy and direction of the incident photon to the energy and direction of a Compton scattered x-ray Photon has a change of direction and a loss of energy
State what happens to a Compton electron Compton electron comes out of its shell and goes on its own way (usually somewhere in the body)
Explain what happens to the probability of a Compton interaction occurring as the energy of the incident photon increases As incident photon energy increases a decrease in Compton interactions
Explain what happens to the probability of a Compton interaction occurring as the atomic number of the subject atom increases As atomic number of subject atoms increases NO CHANGE in probability of Compton
Explain what happens to the probability of a Compton interaction occurring as the mass density of subject atom increases Increases proportionately – DOUBLE the MATTER = DOUBLE the SCATTER!!!!
State the effect Compton scatter has upon radiographic contrast Radiographic contrast decreases as Compton scatter increases
State the effect Compton scatter has upon radiographic density Radiographic density increases as Compton scatter increases
Describe what happens during a photoelectric interaction Ionizing interaction with inner-shell electrons. Incident x-ray is totally absorbed during ionization of an inner-shell electron. The incident photon disappears, and the K-shell electron (now a photoelectron) is ejected from the atom
Describe what happens to the incident photon Incident photon disappears - is absorbed
Compare photoelectric interaction with a characteristic interaction Characteristic is because of an electron and a photoelectron is because of a photon
Explain what happens to the probability of a photoelectric interaction occurring as the energy of the incident photon increases As the energy of the incident photon increases less chance of a photoelectric interaction
Explain what happens to the probability of a photoelectric interaction occurring as the subject atomic number of the subject atom increases As subject atomic number increases photoelectric interaction increases dramatically (X3)
Explain what happens to the probability of a photoelectric interaction occurring as the mass density of the subject atom increases As mass density increases the probability of photoelectric interaction increases
Explain what happens during a pair production event High energy x-ray photon (greater than 1.02MeV) interacts with nuclear force field and its energy is converted into two particles that have opposite electrostatic charges are created. (positron and electron)
State how much energy is required for a pair production event to occur 1.02MeV (0.51 MeV is mass equivalence of an electron)
Explain what happens during a photodisintegration event to occur Photon absorbed directly by nucleus, nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment
State how much energy is required for a photodisintegration event to occur 10 MeV
Define radiopaque Substance that absorbs x-rays (appears white on an x-ray)
Define radiolucent Substance that easily transmits x-rays (black/dark on an x-ray)
Compare the changes in probability of a photoelectric interaction occurring to the probability of a Compton interaction occurring as x-ray energy increases Both decrease as energy increases but a HUGE decrease in photoelectric (X3) compared to decrease in Compton
Compare changes in probability of a photoelectric interaction occurring to the probability of a Compton interaction occurring as subject matter atomic number increases Compton there is no effect and photoelectric increases greatly
Compare changes in probability of a photoelectric interaction occurring to the probability of a Compton interaction occurring as subject mass density increases Both will increase proportionately
Give an example of a negative contrast material Air (increases transmission of x-rays)
List which of the five interactions are ionizing events Compton & photoelectric
Give the reaction that contributes greatest to technologist radiation dose Compton
Give the interaction that contributes greatest to patient dose Photoelectric
State the interaction that is the major cause of film fog Compton
Differentiate between spatial resolution and contrast resolution Spatial – differentiate by sizeContrast – differentiate between tissue (shades)
Define quantum mottle Result of random nature of interaction with IR – not enough signal – photon starved
Tell how quantum mottle can be reduced Increase number of x-rays High mAs, low kVp and slower image receptors will reduce quantum mottle (decrease in mA increases quantum mottle)
Distinguish between a densitometer and a sensitometer Densitometer measures the optical density of exposed filmSensitometer creates an optical step wedge electronically which is used to construct characteristic curve
State the change doubling exposure to a film will have upon optical density Optical density will increase by 0.3 (LOG of 2 = 0.3)
Tell what the law of reciprocity states Optical density is proportional to how much energy reaches the film (mAs=mAs)
Define radiographic contrast Differences in optical density
Compare terms: High contrast & Low contrast black and white (big differences) & many shades of gray (small differences)
Compare terms:Long scale & Short scale low-contrast radiograph that has many shades of gray & high contrast radiograph that has few shades of gray
Compare terms:High kVp & Low kVp low contrast & high contrast
Compare several characteristic cures and state which curve demonstrates the greatest or least contrast More vertical – more contrast, more speed – closest to y-axis, less latitudeMore horizontal – less contrast, less speed – farther from y-axis, more latitude
Calculate the new mAs required when a change in IR speed is made New IR speed ÷ old IR speed = old mAs ÷ new mAs (inversely proportional)
Define radiographic latitude Range of exposure that will produce a diagnostically acceptable radiograph
State the effect developer time has on contrast, speed and fog Increase developer time – contrast decreases and speed and fog increases
State the effect developer temperature has on contrast, speed and fog As temperature increases – contrast decreases and speed and fog increases
List the three geometric factors of radiographic quality Distortion, magnification and blur
Calculate on object size when given an image size, SID and OID Object size = image size (SOD ÷ SID) or image size ÷ object size = SID ÷ SOD
Explain how to minimize magnification Large SID and small OID
Give the situation which will cause elongation Tube or IR angulation
Give the situation which will cause foreshortening Part misalignment
Define focal spot blur Softening of the edges of structure on an image caused by the size of the focal spot (blurred region of radiograph)
Calculate focal spot blur when given focal spot size, SID and OID Focal spot blur = effective focal spot x (OID ÷ SOD)
focal spot size and magnification? Focal spot size has no effect on magnification
Large focal spot will have more or less focal spot blur? Large focal will have less softening (focal spot blur)
Explain the relationship between kilovoltage, contrast and latitude Kilovoltage increases contrast decreases and latitude increases (wide) and vice versa
State the best way to reduce voluntary motion Good patient instruction
Explain the best way to reduce involuntary motion Short exposure time
State the relationship between image receptor speed and patient dose As image receptor speed increases patient dose decreases
Explain the relationship between kilovoltage, contrast and latitude Kilovoltage increases contrast decreases and latitude increases (wide) and vice versa
State the best way to reduce voluntary motion Good patient instruction
Explain the best way to reduce involuntary motion Short exposure time
State the relationship between image receptor speed and patient dose As image receptor speed increases patient dose decreases
Created by: hapyday37 on 2010-05-03



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