In service XR Flashcards

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1
Q

Threshold dose for early transient erythema

A

2 Gy

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2
Q

When does a 180 degree backscattered photon occur?

A

When the incident photon transfers the max amount of energy to the emitted electron. (This is a Compton interaction)

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3
Q

all the incident photon energy is transferred to an electron, which is ejected from an atom

A

photoelectric effect

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4
Q
A

Photoelectric effect

The probability of this effect is maximum when:

  • the energy of the incident photon is equal to or just greater than the binding energy of the electron in its shell (absorption or k edge)
  • and the electron is tightly bound (as in K shell).

The electron that is removed is then called a photoelectron and the incident photon is completely absorbed in the process. Hence, the photoelectric effect contributes to the attenuation of the x-ray beam as it passes through matter.

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5
Q

What is the photoelectric effect?

A

all the incident photon energy is transferred to an electron, which is ejected from an atom

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6
Q

What is the maximum leakage radiation allowed at 1 meter from the xray tube source when the system is operated at the maximum continuous allowable tube current and kilovoltage?

A

100 mR/hr NCRP report no. 91, the allowable max limit for leakage radiation is 100 mR/hr at 1 meter when at max continuous kVP and mA

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7
Q
A

Rayleigh (Coherent) scattering

Coherent scattering (also known as unmodified, classical or elastic scattering) is one of three forms of photon interaction which occurs when the energy of the x-ray or gamma photon is small in relation to the ionization energy of the atom. It, therefore, occurs with low energy radiation.

Upon interacting with the attenuating medium, the photon does not have enough energy to liberate the electron from its bound state (i.e. the photon energy is well below the binding energy of the electron) so no energy transfer occurs. There is no energy deposition and thus no dose resulting from coherent scattering. The only change is a change of direction (scatter) of the photon, hence ‘unmodified’ scatter. Coherent scattering is not a major interaction process encountered in radiography at the energies normally used.

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8
Q

What is Rayleigh scattering?

A

“coherent scattering” an xray photon of the same energy and slightly different direction is emitted

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9
Q

Why do screen film detectors require a low kV?

A

a fixed film contrast and typically require low kV to ensure adequate subject contrast that is mapped to radiographic contrast by the film characteristic curve

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10
Q

What is Bremsstrahlung radiation?

A

Bremsstrahlung radiationis electromagnetic radiation emitted from the slowing down of electrons due to interactions between the negative charge of the electron and the positive charge of the nucleus.

The energy of the bremsstrahlung photon is equal to the energy lost by the electron after it slowed compared to its initial energy.

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11
Q

Threshold dose for skin necrosis

A

>16Gy

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12
Q

Digital detectors are often referred to as “_____ limited” while screen film detectors are often referred to as “_______ limited”

A

Digital detectors are often referred to as “ SNR limited” while screen film detectors are often referred to as “contrast limited”. Image contrast with a digital system is freely adjustable as long as there is sufficient signal to noise ratio of the statistical information in the image.

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13
Q

Permanent epilation occurs at what dose?

A

7-10 Gy

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14
Q

What is the maximum leakage radiation allowed outside the x-ray room from the xray tube source when the system is operated at the maximum continuous allowable tube current and kilovoltage?

A

2 mR/week

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15
Q

When do effects of early transient erythema begin?

A

at 2 Gy, within hours after irradiation and peak at about 24 hrs

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16
Q

an electron is emitted and the incident photon is scattered at some angle with reduced energy.

A

Compton interaction

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17
Q

In digital radiography, what determines spatial resolution?

A

detector element area and sampling pitch (distance between detector elements)

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18
Q

In which Xray interaction does back scattering occur?

A

Compton interaction. For a compton interaction, an electron is emitted and the incident photon is scattered at some angle with reduced energy.

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19
Q

an xray photon of the same energy and slightly different direction is emitted

A

Rayleigh scattering

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20
Q

Threshold dose for dry desquamation

A

14

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21
Q

>16 Gy skin entrance dose will result in what skin injury?

A

skin necrosis

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22
Q

6 Gy skin entrance dose will result in what skin injury?

A

Main erythema

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23
Q

14 Gy skin entrance dose will result in what skin injury?

A

dry desquamation

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24
Q

Increased dynamic range in digital mammography as compared to screen film mammography results in:

A

increased contrast resolution. different exposure levels mapping to a wider range allows for increased contrast in a digital image

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25
Q
A

Compton scatter

It is the main cause of scattered radiation in a material. It occurs due to the interaction of the photon (x-ray or gamma) with free electrons (unattached to atoms) or loosely bound valence shell (outer shell) electrons.

The resultant incident photon is scattered (changes direction) and imparts energy to the electron (recoil electron). The scattered photon will have a different wavelength (observed phenomenon) and thus a different energy (E=hc/λ). Energy and momentum are conserved in this process.

The Compton effect is a partial absorption process and as the original photon has lost energy, known as Compton shift (i.e. a shift of wavelength/frequency).

The wavelength change of the scattered photon can be determined by 0.024 (1- cos θ), where θ is scattered photon angle. Thus, the energy of the scattered photon decreases with increasing scattered photon angle.

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26
Q

Threshold dose for main erythema

A

6

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27
Q

2 Gy skin entrance dose will result in what skin injury?

A

early transient erythema

28
Q

The graph shows an estimated x-ray spectrum for a molybdenum anode x-ray tube. The “spikes” at 17.6 keV and 19.7 keV are characteristic x-rays associated with molybdenum. The source of these spikes is due to:

A

The energy emitted by a outer shell electron that has filled a K-shell vacancy

29
Q

In DIGITAL radiography, the kV and mAs are selected to provide optimal ____________ at the lowest possible dose the the patient

A

Signal to noise ratio. Unlike screen film detectors that have a fixed film contrast and typically require low kV to ensure adequate subject contrast that is mapped to radiographic contrast by the film characteristic curve, digital detectors have extremely wide exposure latitude (also known as dynamic range). This permits flexibility in determining the best combination of kV and mAs to achieve proper signal to noise ratio that subsequently can be adjusted (contrast and spatial resolution enhancement) with image processing algorithms.

30
Q

How does an indirect conversion digital detector work?

A

Indirect conversion digital flat panel detectors(Flat panel dectector) first convert incident x-rays to light via a scintillator (phosphor screen (cesium iodide or gadolinium oxysulfide)). The visible light is then converted into electrons in a charge-coupled device (CCD) or a photodiode.

Indirect flat panel = XRAY –> light –> charge

Direct flat panel = XRAY –> charge

Unlike film-screen systems, digital detectors have a linear response to the log of the input exposure, and also a larger dynamic range than film-screen systems.

Digital detectors, but also computed radiography systems, can have a Moiré pattern type artifact when mismatched or misaligned grids are used.

31
Q

Image taken on a digit detector

A

Reason for loss of soft tissue visibility = overexposure (saturated regions are black or dark gray)

CR and DR have extened dynamic rane (latitude) compared with analog screen film photographic technology, but it is still possible to exceed the latitude of the detector and cause saturation.

When oversaturated, window/level adjustments can do nothing to recover the lost information.

32
Q

relationship of air kerma to mAs

A

Directly proportional.

Air kerma is directly proportional to mAs.

33
Q

Equation for magnification:

A

M = SID/SOD

SID : Source to image distance

SOD: Source to object distance

Ex) A SID is 65 cm, placing the object 36cm (SOD) from the source will result in magnification of:

M= 65/36

= 1.8

34
Q

A SID is 65 cm, placing the object 36cm (SOD) from the source will result in magnification of:

A

1.8

M= SID/SOD

= 65/36

= 1.8

http://xrayphysics.com/radio.html

35
Q

Why does iodine contrast media cause an increase in the blood’s ability to attenuate xrays?

A

Higher atomic number of iodine increases photoelectric effect

The photoelectric effect is highly accentuated at the k-edge of a material; materials with k-edges in the relevant range include iodine and barium. The k-edges are typically low energies, and the closer your x-ray energy is to the k-edge (as long as it is above it), the more likely a photoelectric event is to occur.

http://xrayphysics.com/attenuation.html#:~:text=The%20photoelectric%20effect%20is%20highly,photoelectric%20event%20is%20to%20occur.

36
Q

What is the primary source of scatter radiation in diagnostic radiography?

A

Most scatter is due to Compton interactions in the diagnostic energy range. It is the dominant interactino in soft tissue above 26 keV

37
Q

What effect will increasing the skin to image receptor distance have on entrance skin dose?

A

Increase dose. Increasing the distance from the skin to the image receptor will require the automatic exposure rate control (AERC) to increase the radiation output of the x ray tube to maintain a constant exposure to the image receptor in order to maintain image quality. This will increase the patient’s entrance skin exposure

38
Q

What physical property allows contrast media to provide enhanced contrast at certain xray energies?

A

K-absoprtion edge

K-absorption edge (K-edge) refers to the abrupt increase in the photoelectric absorption of x-ray photons observed at an energy level just beyond the binding energy of the k-shell electrons of the absorbing atom.

K-shell binding energies are specific to each element. As the atomic number (Z) of an element increases, so does its corresponding k-shell binding energy, and therefore the greater the photon energy at which the K-edge occurs.

39
Q

What is the MOST LIKELY consequence of a conceptus radiation dose of 10 mSv during the major
organogenesis period of gestation (2 to 8 weeks)?

A

Childhood cancer

Childhood cancer risk is thought to have no lower threshold, though the risk is low – 6 in 10,000 for a
10 mSv exposure.

40
Q

What is the annual permissible effective dose equivalent for a radiation worker in the United States?

A

50 mSv

41
Q

In a patient with acute chest pain and suspected pulmonary embolism, the MOST appropriate initial
imaging test is a:

A

CXR

The chest radiograph is to exclude other causes of acute chest pain. It is also the cheapest study with a minimal relative radiation level.

42
Q

In a patient with clinically suspected avascular necrosis of the hip, the initial imaging study should be:

A

an anteroposterior (AP) radiograph of the pelvis.

radiographs. AP radiograph of the
pelvis (answer D) is essential for initial evaluation in patients at risk for AVN who present with hip
pain. It also has a low relative radiation level.

43
Q

What is the average energy of a 100 kVp xray beam?

A

40 keV

The average energy of the filtered spectrum is typically 1/3 to1/2 the maximum energy, which is 100 keV for a 100 kVp x-ray
beam.

44
Q

For an abdominal radiograph of a very large patient, which method is MOST likely to improve x-
ray transmission?

A

Increasing the kVp

Increasing the kVp increases the average beam energy, making the beam more penetrating. A greater percentage of the beam is transmitted through the
patient.

45
Q

Compared to standard contact imaging, what commonly compromises image quality
of magnification views in mammography? Why?

A

motion –> motion blur

Correct. The small focal spot limits the tube current, so that exposure times are longer. Motion during the long exposure time can cause
blurring.

46
Q

What type of TFT flat panel array is direct?

A

Amorphous selenium – TFT flat panel array

Amorphous selenium is a semiconductor. When x rays are absorbed the energy is converted directly into charge, producing electron hole pairs in proportion to incident x ray energy.

47
Q

To keep patient dose as low as reasonably achievable for digital radiography examinations using
a CR or DR detector, the mAs is selected to provide acceptable:

A

signal to noise ratio.

48
Q

Amorphous selenium (aSe) semiconductor is what type of digital detector?

A

direct flat panel

Amorphous selenium is a semiconductor. When x rays are absorbed the energy is converted directly into charge, producing electron hole pairs in proportion to incident x ray energy.

49
Q

Collimation to a smaller field of view reduces ______, which improves _____________.

A

Collimation to a smaller field of view reduces scatter, which improves image contrast.

50
Q

Will increasing the focal spot, increase or decrease motion blur?

A

decrease

focal spot increased –> power incident on the target can be increased –> increased power –> decreased exposure time – > decreased motion

51
Q

increasing focal spot size will do what to geometric unsharpness?

A

increase geometric unsharpness

52
Q

xray beam quality is independent of what factor?

A

Tube output (mAs)

53
Q

What ist he purpose of a 0.1mm Cu filter?

A

eliminate low energy photons, resulting in a more penetrating beam

54
Q

Does contrast go up or down if a 0.1mm Cu filter is used (in general radiography)?

A

Down

55
Q

What happens when mA decreases with automatic exposure control (AEC)?

A

Increased exposure time –> image sharpness decreases

56
Q

Do portable xray machines have AEC?

A

No

AEC:

Automatic exposure control is a device incorporated into radiographic and mammographic imaging systems. Its function is to automatically terminate exposure when a preset amount of radiation has been detected.

Automatic exposure control systems help to provide a consistent optical density/signal-to-noise ratio, regardless of patient-centric factors such as size and density.

Automatic exposure control systems also help to reduce ‘dose creep’ that can occur with inadvertent radiation overexposure by the technologist.

The first generation of automatic exposure control systems are phototimers, which have now largely been superseded by ionization chambers.

In radiography, the automatic exposure control device is placed in front of the image receptor. In mammography, the automatic exposure control device is placed underneath the image receptor.

57
Q

What part of an xray tube is resposible for heel effect

A

Target.

Differential attenuation in the tungsten target

58
Q

What grid ratio is typically used to perform a cxr on a dedicated departmental imging system?

A

10:1

59
Q

What grid ratio is typically used to perform a cxr on mammo?

A

5:1

60
Q

What percentage of primary xray photons is typically lost in grids used when performing adult abdominal radiography?

A

30%

70% will pass through the grid

61
Q

factors that affect xray quality

A

Anode material (Z)

Tube potential (kVp)

62
Q
A
63
Q
A

Detector drop

Wireless flat-panel detectors get dropped. Drops can damage the detector system in several ways through fracturing of the flatpanel detector, through disruption of readout electronics, or through shifting gain and offsets.

64
Q
A
65
Q
A
66
Q
A