Radiology Physics
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| 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
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| Give the primary and secondary purpose of the oil that surrounds the tube | Reduces electric shock, electrical insulation and heat dissipation
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| 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)
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| State the temperature required for thermionic emission with a tungsten filament | 2200 degrees C
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| Recognize the melting point of tungsten | 3410 degrees C
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| List the materials used in a tungsten filament | Thoriated tungsten (tungsten with thorium)
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| Name the materials used in a focusing cup | Nickel with rhenium
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| 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
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| Compare the production of heat to the production of x-rays in the x-ray tube | 99% heat and 1% x-ray
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| Compare the speeds of a normal rotating anode with a high speed anode | Normal is 3400 rpm and high speed is 10,000 rpm
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| Name the device that is used to enable a rotating anode to rotate | Induction motor
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| 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
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| 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
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| 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)
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| Actual focal spot size | area on the anode target that is exposed to electrons from the tube current
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| Effective focal spot size | area projected onto the patient and the image receptor
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| 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)
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| 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 AFSNO BENEFIT) the greater the angle the greater the EFS
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| State what happens to anode heat capacity as anode angle increases | As anode angle increases so does anode heat capacity
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| State what happens to field coverage as anode angle increases | As anode angle increases field coverage increases
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| State what happens to resolution as anode angle increases | Spatial resolution decreases as anode angle increases
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| 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
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| 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
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| 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
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| State the effect SID has upon the anode heel effect | As SID increases anode heel effect decreases (divergence of beam?)
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| 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)
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| State the effect anode angle has upon the anode heel effect | As anode angle increases anode heel effect decreases
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| 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
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| List three ways in which heat is dissipated in an x-ray tube | Radiation, conduction and convection
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| 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
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| Calculate heat units produced in a single phase x-ray machine when given a technique | HU = mA x time in seconds x kVp
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| 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
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| 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
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| State two types of interactions that produce diagnostic x-rays | Characteristic and Brems
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| State which of these two is an ionizing event | Characteristic
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| 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.
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| 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
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| State the relationship between x-ray energy and wavelength | Inversely proportional- as x-ray energy increases wavelength decreases (gets smaller)
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| Explain how changes in mAs affect x-ray beam quantity and quality | mAs changes beam quantity does NOT change quality
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| Explain how changes in kVp affect x-ray beam quantity and quality | Increasing kVp increases quantity and quality (and vice versa)
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| Explain how changes in filtration affect x-ray beam quantity and quality | As filtration increases quantity decreases and quality increases
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| Explain how changes in target Z number affect x-ray beam quantity and quality | Target Z number increases beam quantity and quality increases
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| 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
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| List three terms that can be used to refer to the number of photons in the x-ray beam | Quantity, exposure and intensity
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| List two major units used to measure radiation exposure (measure of beam) | mR and Graya (milliroentgens or gray in air
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| Explain relationship between x-ray quantity and radiographic density | X-ray quantity and radiographic density are directly proportional
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| Explain relationship between x-ray quantity and patient dose | X-ray quantity increases patient dose increases
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| List four major factors affecting x-ray quantity | mAs, kVp, distance and filtration
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| 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)
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| 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
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| State the relationship between kVp and x-ray intensity | kVp increases intensity increases (double the kVp and 4x the intensity)
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| 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
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| Use the inverse square law to calculate the change in radiation exposure as distance from the source changes (apply) | I1÷I2 = (D2÷D1)2
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| 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]
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| Explain the relationship between filtration and patient dose | As filtration increases patient dose decreases
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| Explain the relationship between x-ray beam energy and penetrability | As energy increases penetrability increases
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| Explain what is meant by quality of the beam | Quality is the penetrability of the beam. (increase quality = increased penetrability)
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| State how the quality of an x-ray beam is measured | HVL
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| Explain the relationship between HVL and beam penetrability | HVL is a measurement of beam quality. As HVL increases beam penetrability increases.
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| State the effect increasing SID will have upon beam quantity (intensity) | Increase in SID will decrease beam intensity (quantity)
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| State the effect increasing SID will have on beam quality | SID has no effect on beam quality
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| State what happens to the HVL of a beam as the energy of a beam increases | HVL increases as beam energy increases
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| State why we wish to reduce the number of low energy photons in the x-ray beam | To decrease patient dose (skin dose)
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| 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
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| 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)
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| Name two interactions that are significant in the production of diagnostic radiographs | Photoelectric and Compton
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| Recognize the three other names for coherent scatter | Classical, Rayleigh, Thompson
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| 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)
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| 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
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| 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
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| 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
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| 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)
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| 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
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| 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
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| 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!!!!
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| State the effect Compton scatter has upon radiographic contrast | Radiographic contrast decreases as Compton scatter increases
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| State the effect Compton scatter has upon radiographic density | Radiographic density increases as Compton scatter increases
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| 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
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| Describe what happens to the incident photon | Incident photon disappears - is absorbed
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| Compare photoelectric interaction with a characteristic interaction | Characteristic is because of an electron and a photoelectron is because of a photon
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| 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
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| 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)
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| 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
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| 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)
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| State how much energy is required for a pair production event to occur | 1.02MeV (0.51 MeV is mass equivalence of an electron)
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| 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
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| State how much energy is required for a photodisintegration event to occur | 10 MeV
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| Define radiopaque | Substance that absorbs x-rays (appears white on an x-ray)
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| Define radiolucent | Substance that easily transmits x-rays (black/dark on an x-ray)
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| 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
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| 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
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| 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
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| Give an example of a negative contrast material | Air (increases transmission of x-rays)
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| List which of the five interactions are ionizing events | Compton & photoelectric
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| Give the reaction that contributes greatest to technologist radiation dose | Compton
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| Give the interaction that contributes greatest to patient dose | Photoelectric
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| State the interaction that is the major cause of film fog | Compton
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| Differentiate between spatial resolution and contrast resolution | Spatial – differentiate by sizeContrast – differentiate between tissue (shades)
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| Define quantum mottle | Result of random nature of interaction with IR – not enough signal – photon starved
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| 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)
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| 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
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| 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)
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| Tell what the law of reciprocity states | Optical density is proportional to how much energy reaches the film (mAs=mAs)
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| Define radiographic contrast | Differences in optical density
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| Compare terms: High contrast & Low contrast | black and white (big differences) & many shades of gray (small differences)
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| Compare terms:Long scale & Short scale | low-contrast radiograph that has many shades of gray & high contrast radiograph that has few shades of gray
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| Compare terms:High kVp & Low kVp | low contrast & high contrast
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| 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
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| 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)
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| Define radiographic latitude | Range of exposure that will produce a diagnostically acceptable radiograph
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| State the effect developer time has on contrast, speed and fog | Increase developer time – contrast decreases and speed and fog increases
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| State the effect developer temperature has on contrast, speed and fog | As temperature increases – contrast decreases and speed and fog increases
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| List the three geometric factors of radiographic quality | Distortion, magnification and blur
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| 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
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| Explain how to minimize magnification | Large SID and small OID
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| Give the situation which will cause elongation | Tube or IR angulation
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| Give the situation which will cause foreshortening | Part misalignment
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| 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)
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| Calculate focal spot blur when given focal spot size, SID and OID | Focal spot blur = effective focal spot x (OID ÷ SOD)
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| focal spot size and magnification? | Focal spot size has no effect on magnification
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| Large focal spot will have more or less focal spot blur? | Large focal will have less softening (focal spot blur)
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| Explain the relationship between kilovoltage, contrast and latitude | Kilovoltage increases contrast decreases and latitude increases (wide) and vice versa
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| State the best way to reduce voluntary motion | Good patient instruction
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| Explain the best way to reduce involuntary motion | Short exposure time
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| State the relationship between image receptor speed and patient dose | As image receptor speed increases patient dose decreases
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| Explain the relationship between kilovoltage, contrast and latitude | Kilovoltage increases contrast decreases and latitude increases (wide) and vice versa
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| State the best way to reduce voluntary motion | Good patient instruction
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| Explain the best way to reduce involuntary motion | Short exposure time
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| State the relationship between image receptor speed and patient dose | As image receptor speed increases patient dose decreases
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