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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
How does atomic # affect Compton interactions?
Results in an increase in Compton interactions
26
How does filtration affect kVp?
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.
27
How does filtration affect x-ray energy?
Increases the average energy of the x-ray beam.
28
How does filtration affect x-ray quality?
increases beam quality
29
How does filtration affect x-ray quantity?
Results in a decrease in x-ray quantity since the lower energy x-ray photons are absorbed by the filtration.
30
How does tissue density affect Compton interactions?
Results in an increase in Compton interactions (more matter = more scatter)
31
How is kVp related to exit radiation?
Results in an increase in exit radiation since higher kVp allows more x-rays to penetrate the patient.
32
How is kVp related to IR exposure?
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.
33
How is kVp related to patient dose?
Results in a decrease in patient dose because more radiation passes through the patient and is not absorbed.
34
How is kVp related to penetrating ability?
kVp and penetrating ability are directly related. An increase in kVp results in an increase in penetration.
35
How much should you increase mAs to see a noticeable difference in IR exposure?
To see a noticeable difference in IR exposure, you need to increase the mAs by 30%.
36
How will an image appear if the anatomy has low subject contrast?
Anatomy with low subject contrast results in an image with low contrast.
37
How would you adjust your technique if your image appears with insufficient contrast and too much exposure?
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.
38
How would you describe a radiograph with minimal differences in densities?
low contrast.
39
What affect does an increase in x-ray beam energy have on contrast?
An increase in x-ray beam energy (kVp) results in decreased contrast.
40
What affect does an increase in x-ray beam energy have on interactions with matter?
An increase in x-ray beam energy results in decreased interactions.
41
What affect does an increase in x-ray beam energy have on patient dose?
An increase in x-ray beam energy results in decreased patient dose.
42
What affect does an increase in x-ray beam energy have on the number of x-rays transmitted to the IR?
An increase in x-ray beam energy results in an increase in the number of x-rays transmitted to the IR.
43
What are causes of insufficient IR exposure?
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
What are the differences between CR and DR?
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
What can you use to provide a more uniform radiographic exposure when there is severe variation in patient anatomy or tissue density?
A compensating filter
46
What causes foreshortening?
Foreshortening is a type of shape distortion that occurs when the body part is angled in relation to the CR and IR.
47
What device is used to protect the x-ray tube and patient from overexposure if the AEC device does not shut off?
A back-up timer is used as a protective device to terminate the exposure in case of equipment malfunction.
48
What device is used to restrict the primary x-ray beam?
A collimator is used to restrict the primary x-ray beam. Other beam restricting devices include an aperture diaphragm, cones, and cylinders.
49
What do direct capture systems use to convert incoming x-ray photons to an electronic signal?
amorphous selenium
50
What do sensitivity numbers measure?
or exposure index numbers measure the amount of exposure to the IR.
51
What does a histogram represent?
a graphical representation of exposure values, pixel values, or grayscale values.
52
What does elongation mean?
Elongation occurs when the CR or IR are angled and results in the object appearing longer than it actually is.
53
What does the term latitude mean?
Latitude describes the range of acceptable exposures. An increase in kVp results in an increase in latitude.
54
What effect does grid use have on contrast?
an increase in contrast. The higher the grid ratio the higher the image contrast.
55
What effect does mAs have on digital imaging?
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
What grid errors result in grid cutoff on the outer edges of the image?
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
What happens to pixel size as matrix size increases?
pixel size decreases.
58
What happens to resolution as matrix size increases?
As matrix size increases, resolution increases.
59
What happens to the amount of scatter when the volume of tissue increases?
As the volume of tissue increases, the amount of scatter produced increases (more matter = more scatter)
60
What is an algorithm?
a series of instructions.
61
What is differential absorption?
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
What is pixel pitch?
the distance from the center of 1 pixel to the center of an adjacent pixel.
63
What is the activator used with barium fluorohalide?
Barium fluorohalide is doped with europium. Europium is the activator that makes the barium fluorohalide luminesce in response to x-rays.
64
What is the best method to control voluntary motion?
good communication. To reduce the effects of involuntary motion, the technologist should use the shortest possible exposure time.
65
What is the contrast improvement factor?
the contrast with a grid compared to contrast without a grid.
66
What is the formula for calculating the magnification factor?
SID/SOD or (image size)/(object size)
67
What is the function of shuttering or masking used for?
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
What is the main difference between direct and indirect capture digital imaging?
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
What is the most common material used for added filtration?
aluminum.
70
What is the primary advantage of a variable kVp technique chart compared to a fixed kVp chart?
A variable kVp technique chart results in an increase in image contrast over a fixed kVp chart.
71
What is the primary purpose of positive beam limitation?
PBL restricts the primary beam to no larger than the IR.
72
What is the primary source of scatter radiation?
The patient
73
What is the purpose of a back up time in AEC?
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
What is the relationship between matrix size and spatial resolution?
Matrix size is directly proportional to spatial resolution. As matrix size increases, spatial resolution increases.
75
What is the relationship between pixel pitch and resolution?
Pixel pitch and resolution are inversely proportional. As pixel pitch increases, resolution decreases.
76
What is the relationship between SID and receptor exposure?
Receptor exposure is inversely proportional to the square of the distance. As SID increases, receptor exposure decreases. (Inverse square law)
77
What is the relationship between SID and x-ray beam intensity? (intensity refers to quantity)
SID and x-ray beam intensity are inversely proportional. As SID increases, x-ray beam intensity decreases.
78
What is the term used to describe a graphical representation of pixel values?
histogram.
79
What is the term used to describe a structure in which x-rays do not easily pass through?
radiopaque.
80
What is the term used to describe absorption of the useful beam by the grid?
Grid cut-off refers to absorption of the useful beam by the grid.
81
What is the term used to describe an image with few shades of gray between black and white?
An image with few shades of gray is said to have high contrast or short scale of contrast.
82
What is the term used to describe the reduction in intensity or energy of the x-ray beam as it passes through matter?
Attenuation
83
What is the term used to describe when pixel brightness is measured?
sampling.
84
What occurs to an image if the body part is angled?
If the body part is angled, the image may appear distorted. The part will be foreshortened.
85
What occurs when the x-ray beam is restricted?
With increased collimation (smaller x-ray field) you have reduced scatter production, reduced IR exposure, reduced patient dose and increased spatial resolution.
86
What occurs when there is a misalignment of the tube-part-IR?
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
What part of a CR system receives the electric signal from the photomultiplier and creates the digital signal?
The analog to digital converter (ADC) is responsible for receiving the electronic signal from the photomultiplier tube to create the digital signal
88
What part of the CR cassette records the radiographic image?
The photostimulable phosphor plate (PSP)
89
What term is used to describe the number of bits per pixel?
bit depth.
90
What term is used to describe the percentage of incoming x-ray photons that are detected and absorbed by the image receptor?
Detective quantum efficiency (DQE)
91
What things can impact receptor exposure?
Receptor exposure is impacted by: mAs, kVp, SID, OID, patient factors, and grid use
92
What type of contrast will be displayed when a body part is composed of many different atomic numbers?
Body parts composed of many different atomic numbers result in images with high contrast.
93
What type of pathologies require an increase in exposure factors?
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
What type of technical factors will result in the lowest patient dose?
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
When should a grid be used?
part measures 10 cm or more or the kVp is at 70 or more.
96
Where are grids placed?
between the pt and the IR
97
Where does a photoelectric interaction occur?
with an inner shell electron within the patient
98
Which interaction is responsible for most occupational dose?
from Compton scatter from the patient.
99
Which technical factors are directly related to patient radiation dose?
mAs is directly related to patient dose. Double the mAs = double the radiation dose.
100
Identify the types of positive contrast agents.
barium compounds and iodinated compounds.
101
Describe what factor affects the wavelength of an x-ray.
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
Describe an incident photon.
a photon that has not interacted with anything yet.
103
When using AEC, what effect does increasing kVp have?
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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