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Exposure Final - Worksheets > Final Study Guide > Flashcards

Final Study Guide Flashcards

1
Q

An increase of 15% in kVp is equal to how much of an increase in mAs?

A

double the mAs.
A decrease of 15% in kVp is equal to half the mAs.

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2
Q

Grid conversion factors

A

5:1 = 2
6:1 = 3
8:1 = 4
10:1 = 5
12:1 = 5
16:1 =6

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3
Q

(Original mAs)/(new mAs)= (Original grid conversion factor)/(New grid conversion factor)

A
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4
Q

FOV/(Matrix size)=pixel size

A
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5
Q

Coherent scatter

A

X-rays with energies below 10 keV, causes excitement but no ionization

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6
Q

Compton scatter

A

An incident x-ray photon interacts with an outer shell electron and causes ionization (removal of an electron), this results in a scattered photon. Responsible for occupational dose.

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7
Q

Describe factors that affect image resolution.

A

Spatial resolution is improved with: increased matrix size, decreased pixel size, increased SID, decreased OID, smaller focal spot size, decreased patient/part thickness, decreased CR angle, increased fill factor, smaller PSP phosphor size, smaller laser beam, decreased pixel pitch, increased sampling frequency

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8
Q

Pair Production

A

Occurs at energy levels of 1.02 MeV or greater, produces 2 electrons (1 + positron, 1 – negatron) that share the energy. Does not occur in diagnostic range. Found in PET imaging

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9
Q

Photodisentigration

A

Occurs at energy levels of 10 MeV or greater. Incident photon interacts with the nucleus and is completely absorbed, creates a nuclear fragment.

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10
Q

Photoelectric effect

A

An interaction with an inner shell electron, results in absorption and a photoelectron. Responsible for patient dose.

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11
Q

Determine scale of contrast given a set of exposure factors.

A

Increased kVp = decreased contrast, increased grid ratio = increased contrast, increased collimation = increased contrast, increased grid ratio = increased contrast

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12
Q

Determine which set of exposure factors will produce the most IR exposure.

A

Exposure is directly related to mAs, so increased mAs = increased exposure. As kVp increases, exposure increases; as distance decreases, exposure increases; as grid ratio decreases, exposure increases; as field size increases, exposure increases.

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13
Q

How are atomic #, photoelectric interactions & IR exposure related?

A

An increase in atomic number increases photoelectric absorption and decreases IR exposure.

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14
Q

How are kVp & quality related?

A

directly related.
An increase in kVp = an increase in quality

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15
Q

How are mAs and IR exposure related?

A

directly related.
An increase in mAs = an increase in IR exposure

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16
Q

How can you minimize distortion?

A

Distortion can be minimized by using the longest practical SID, the shortest OID, and no angulation of CR, IR, or part.

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17
Q

How can you reduce the amount of scatter reaching the IR?

A

Increasing collimation, decreasing kVp, increasing grid ratio, and increasing OID

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18
Q

How do Compton interactions affect IR exposure?

A

Compton interactions result in more scatter radiation reaching the IR, therefore IR exposure is increased with increasing Compton interactions.

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19
Q

How do you determine grid ratio?

A

Grid ration = height of the lead strips divided by width of interspace material R=H/D

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20
Q

How do you reduce magnification?

A

by using the longest practical SID & the shortest OID

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21
Q

How does added filtration affect pt dose?

A

Added filtration reduces patient dose by absorbing low energy photons, so the patient receives less entrance skin exposure.

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22
Q

How does an increase in kVp affect exposure latitude?

A

An increase in exposure latitude.

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23
Q

How does an increase in kVp affect scale of contrast?

A

results in a decrease in contrast. High kVp = low contrast, long scale, many shades of gray.

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24
Q

How does an increase in kVp affect scatter radiation?

A

an increase in scatter production.

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25
Q

How does atomic # affect Compton interactions?

A

Results in an increase in Compton interactions

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26
Q

How does filtration affect kVp?

A

An increase in filtration increases the average energy of the x-ray beam, but does not affect the maximum energy of the x-ray beam.

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27
Q

How does filtration affect x-ray energy?

A

Increases the average energy of the x-ray beam.

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28
Q

How does filtration affect x-ray quality?

A

increases beam quality

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29
Q

How does filtration affect x-ray quantity?

A

Results in a decrease in x-ray quantity since the lower energy x-ray photons are absorbed by the filtration.

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30
Q

How does tissue density affect Compton interactions?

A

Results in an increase in Compton interactions (more matter = more scatter)

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31
Q

How is kVp related to exit radiation?

A

Results in an increase in exit radiation since higher kVp allows more x-rays to penetrate the patient.

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32
Q

How is kVp related to IR exposure?

A

Results in an increase in IR exposure. They are directly related but not directly proportional. An increase of 15% in kVp results in double the exposure.

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33
Q

How is kVp related to patient dose?

A

Results in a decrease in patient dose because more radiation passes through the patient and is not absorbed.

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34
Q

How is kVp related to penetrating ability?

A

kVp and penetrating ability are directly related. An increase in kVp results in an increase in penetration.

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35
Q

How much should you increase mAs to see a noticeable difference in IR exposure?

A

To see a noticeable difference in IR exposure, you need to increase the mAs by 30%.

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36
Q

How will an image appear if the anatomy has low subject contrast?

A

Anatomy with low subject contrast results in an image with low contrast.

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37
Q

How would you adjust your technique if your image appears with insufficient contrast and too much exposure?

A

To increase contrast you should decrease kVp. To decrease exposure you should decrease mAs. However, a decrease in kVp will also result in a decrease in exposure.

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38
Q

How would you describe a radiograph with minimal differences in densities?

A

low contrast.

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39
Q

What affect does an increase in x-ray beam energy have on contrast?

A

An increase in x-ray beam energy (kVp) results in decreased contrast.

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40
Q

What affect does an increase in x-ray beam energy have on interactions with matter?

A

An increase in x-ray beam energy results in decreased interactions.

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41
Q

What affect does an increase in x-ray beam energy have on patient dose?

A

An increase in x-ray beam energy results in decreased patient dose.

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42
Q

What affect does an increase in x-ray beam energy have on the number of x-rays transmitted to the IR?

A

An increase in x-ray beam energy results in an increase in the number of x-rays transmitted to the IR.

43
Q

What are causes of insufficient IR exposure?

A

Causes include too little mAs, too little kVp, an increase in patient tissue density or atomic number, an increase in SID, and grid cutoff.

44
Q

What are the differences between CR and DR?

A

CR requires the use of a cassette with a photostimulable phosphor. The CR cassette must be processed in a digitizer or image reader.
DR does not require the use of a cassette. With DR, images are seen almost instantaneously. DR can be direct or indirect. DR has a higher DQE than CR.

45
Q

What can you use to provide a more uniform radiographic exposure when there is severe variation in patient anatomy or tissue density?

A

A compensating filter

46
Q

What causes foreshortening?

A

Foreshortening is a type of shape distortion that occurs when the body part is angled in relation to the CR and IR.

47
Q

What device is used to protect the x-ray tube and patient from overexposure if the AEC device does not shut off?

A

A back-up timer is used as a protective device to terminate the exposure in case of equipment malfunction.

48
Q

What device is used to restrict the primary x-ray beam?

A

A collimator is used to restrict the primary x-ray beam. Other beam restricting devices include an aperture diaphragm, cones, and cylinders.

49
Q

What do direct capture systems use to convert incoming x-ray photons to an electronic signal?

A

amorphous selenium

50
Q

What do sensitivity numbers measure?

A

or exposure index numbers measure the amount of exposure to the IR.

51
Q

What does a histogram represent?

A

a graphical representation of exposure values, pixel values, or grayscale values.

52
Q

What does elongation mean?

A

Elongation occurs when the CR or IR are angled and results in the object appearing longer than it actually is.

53
Q

What does the term latitude mean?

A

Latitude describes the range of acceptable exposures. An increase in kVp results in an increase in latitude.

54
Q

What effect does grid use have on contrast?

A

an increase in contrast. The higher the grid ratio the higher the image contrast.

55
Q

What effect does mAs have on digital imaging?

A

In digital imaging, mAs effects IR exposure directly. Too little mAs can result in quantum mottle (grainy image) mAs also affects patient exposure directly.

56
Q

What grid errors result in grid cutoff on the outer edges of the image?

A

Grid cutoff that results from an off-focus grid or an upside down grid results in an image that is brighter on the edges (less exposure on the outer edges)

57
Q

What happens to pixel size as matrix size increases?

A

pixel size decreases.

58
Q

What happens to resolution as matrix size increases?

A

As matrix size increases, resolution increases.

59
Q

What happens to the amount of scatter when the volume of tissue increases?

A

As the volume of tissue increases, the amount of scatter produced increases (more matter = more scatter)

60
Q

What is an algorithm?

A

a series of instructions.

61
Q

What is differential absorption?

A

The difference between x-rays that are scattered, absorbed, and transmitted. Differential absorption is the result of attenuating characteristics of tissue. It is responsible for contrast present on the image.

62
Q

What is pixel pitch?

A

the distance from the center of 1 pixel to the center of an adjacent pixel.

63
Q

What is the activator used with barium fluorohalide?

A

Barium fluorohalide is doped with europium. Europium is the activator that makes the barium fluorohalide luminesce in response to x-rays.

64
Q

What is the best method to control voluntary motion?

A

good communication. To reduce the effects of involuntary motion, the technologist should use the shortest possible exposure time.

65
Q

What is the contrast improvement factor?

A

the contrast with a grid compared to contrast without a grid.

66
Q

What is the formula for calculating the magnification factor?

A

SID/SOD or (image size)/(object size)

67
Q

What is the function of shuttering or masking used for?

A

Shuttering or masking is a post-processing function used to eliminate the bright, unexposed areas of an image outside the collimated field. It should NEVER be used as a replacement for collimation.

68
Q

What is the main difference between direct and indirect capture digital imaging?

A

Direct capture is a two step process – x-ray photons are converted directly into an electronic signal. Indirect capture is a three step process – x-ray photons are converted to light photons and then converted to an electronic signal.

69
Q

What is the most common material used for added filtration?

A

aluminum.

70
Q

What is the primary advantage of a variable kVp technique chart compared to a fixed kVp chart?

A

A variable kVp technique chart results in an increase in image contrast over a fixed kVp chart.

71
Q

What is the primary purpose of positive beam limitation?

A

PBL restricts the primary beam to no larger than the IR.

72
Q

What is the primary source of scatter radiation?

A

The patient

73
Q

What is the purpose of a back up time in AEC?

A

A back-up timer is used as a protective device to terminate the exposure in case of equipment malfunction. This prevents over-exposure of the patient.

74
Q

What is the relationship between matrix size and spatial resolution?

A

Matrix size is directly proportional to spatial resolution. As matrix size increases, spatial resolution increases.

75
Q

What is the relationship between pixel pitch and resolution?

A

Pixel pitch and resolution are inversely proportional. As pixel pitch increases, resolution decreases.

76
Q

What is the relationship between SID and receptor exposure?

A

Receptor exposure is inversely proportional to the square of the distance. As SID increases, receptor exposure decreases. (Inverse square law)

77
Q

What is the relationship between SID and x-ray beam intensity? (intensity refers to quantity)

A

SID and x-ray beam intensity are inversely proportional. As SID increases, x-ray beam intensity decreases.

78
Q

What is the term used to describe a graphical representation of pixel values?

A

histogram.

79
Q

What is the term used to describe a structure in which x-rays do not easily pass through?

A

radiopaque.

80
Q

What is the term used to describe absorption of the useful beam by the grid?

A

Grid cut-off refers to absorption of the useful beam by the grid.

81
Q

What is the term used to describe an image with few shades of gray between black and white?

A

An image with few shades of gray is said to have high contrast or short scale of contrast.

82
Q

What is the term used to describe the reduction in intensity or energy of the x-ray beam as it passes through matter?

A

Attenuation

83
Q

What is the term used to describe when pixel brightness is measured?

A

sampling.

84
Q

What occurs to an image if the body part is angled?

A

If the body part is angled, the image may appear distorted. The part will be foreshortened.

85
Q

What occurs when the x-ray beam is restricted?

A

With increased collimation (smaller x-ray field) you have reduced scatter production, reduced IR exposure, reduced patient dose and increased spatial resolution.

86
Q

What occurs when there is a misalignment of the tube-part-IR?

A

When there is misalignment the image will demonstrate distortion. If the CR and/ or IR are misaligned the image will appear with elongation. If the part is misaligned, the image will appear with foreshortening.

87
Q

What part of a CR system receives the electric signal from the photomultiplier and creates the digital signal?

A

The analog to digital converter (ADC) is responsible for receiving the electronic signal from the photomultiplier tube to create the digital signal

88
Q

What part of the CR cassette records the radiographic image?

A

The photostimulable phosphor plate (PSP)

89
Q

What term is used to describe the number of bits per pixel?

A

bit depth.

90
Q

What term is used to describe the percentage of incoming x-ray photons that are detected and absorbed by the image receptor?

A

Detective quantum efficiency (DQE)

91
Q

What things can impact receptor exposure?

A

Receptor exposure is impacted by: mAs, kVp, SID, OID, patient factors, and grid use

92
Q

What type of contrast will be displayed when a body part is composed of many different atomic numbers?

A

Body parts composed of many different atomic numbers result in images with high contrast.

93
Q

What type of pathologies require an increase in exposure factors?

A

Additive pathologies require an increase in exposure factors. When a pathology increases tissue density, increases the atomic number, increases tissue thickness or increases.
Additive pathologies include: Atelectasis, bronchiectasis, cardiomegaly, CHF, Empyema, pleural effusion, pneumoconiosis, pneumonectomy, pneumonia, pulmonary edema, TB, ascites, cirrhosis, acromegaly, hydrocephalus, metastases, Paget’s disease, sclerosis, osteopetrosis. Destructive or subtractive pathologies include: COPD, emphysema, pneumothorax, bowel obstruction, arthritis, multiple myeloma, osteomalacia, and osteoporosis.

94
Q

What type of technical factors will result in the lowest patient dose?

A

Using techniques with high kVp and low mAs will provide the lowest patient dose. In addition, using a low ratio grid or no grid reduces patient dose.

95
Q

When should a grid be used?

A

part measures 10 cm or more or the kVp is at 70 or more.

96
Q

Where are grids placed?

A

between the pt and the IR

97
Q

Where does a photoelectric interaction occur?

A

with an inner shell electron within the patient

98
Q

Which interaction is responsible for most occupational dose?

A

from Compton scatter from the patient.

99
Q

Which technical factors are directly related to patient radiation dose?

A

mAs is directly related to patient dose. Double the mAs = double the radiation dose.

100
Q

Identify the types of positive contrast agents.

A

barium compounds and iodinated compounds.

101
Q

Describe what factor affects the wavelength of an x-ray.

A

Wavelength is affected by energy or kVp. Wavelength and frequency are inversely proportional. The longer the wave length = lower frequency = lower energy. Shorter wavelength = higher frequency = higher energy.

102
Q

Describe an incident photon.

A

a photon that has not interacted with anything yet.

103
Q

When using AEC, what effect does increasing kVp have?

A

When using AEC, an increase in kVp will require less mAs to produce the expected exposure. Therefore, higher kVp will result in a shorter exposure time.

Exposure Final - Worksheets (6 decks)

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