Comprehensive Exam Flashcards
1
Q
What occurs if the number of pixels in a matrix increases and the field of view remains the same?
A
spatial resolution increases
2
Q
What occurs if the number of pixels in a matrix decreases and the field of view remains the same?
A
spatial resolution decreases
3
Q
What is the pixel size in millimeters of a 256 x 256 matrix with a 10-cm2 field of view?
A
0.39
4
Q
spatial resolution calculation
A
FOV (cm) / matrix (mm)
change FOV cm to mm
5
Q
To alter image brightness (density), the __________ is changed.
A
window level
6
Q
What adjusts the range of densities displayed on the monitor?
A
window width
7
Q
Making the digital image appear with low contrast, many shades of gray, is done by
A
increasing the window width (wide WW)
8
Q
Why can an acceptable image be produced with computed radiography (CR) or digital radiography (DR) equipment even when the input exposure was underexposed or overexposed?
A
wide dynamic range of the digital detector
9
Q
The range of exposures that produce acceptable information to be used in image formation is
A
exposure latitude
10
Q
The range of exposure intensities that an IR can respond to and acquire image data is
A
dynamic range
11
Q
The distance from the center of one pixel to the center of the one next to it is
A
pixel pitch
12
Q
Spatial resolution can be increased by:
- Increasing the pixel pitch
- Increasing the pixel density
- Decreasing the pixel pitch
A
Increasing the pixel density and decreasing the pixel pitch only
13
Q
What is pixel density?
A
Number of pixels in a given area
14
Q
The number of visible shades of gray available per pixel in a digital image is determined by _____.
A
bit depth
15
Q
If a pixel has a bit depth of 10, this means that:
A
It can produce 2^10 shades of gray
16
Q
Which of the following is a method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image?
A
signal-to-noise ratio
17
Q
Does increasing or decreasing SNR improves the quality of digital image?
A
increasing
this means that the strength of the signal is high in comparison with the amount of noise
18
Q
Does increasing or decreasing the SNR mean that there is increased noise compared with the strength of the signal, which decreases the quality of the image?
A
decreasing
19
Q
Which of the following is correct regarding spatial frequency?
- small objects have lower spatial frequency
- small objects have higher spatial frequency
- large objects have lower spatial frequency
A
small objects have higher spatial frequency and large objects have lower spatial frequency only.
20
Q
The number of lead lines per inch or centimeter is the grid
A
frequency
21
Q
Differential absorption occurs because different tissues have varying amounts of
A
photoelectric interactions
22
Q
Varying anatomic parts do not absorb the primary beam to the same degree. Anatomic parts composed of bone absorb more x-ray photons than parts filled with air
A
Differential absorption
23
Q
Increasing the thickness of the part being imaged results in
A
increased attenuation
24
Q
Decreased attenuation results in
A
more x-ray photons reaching the image receptor.
25
A high-energy beam results in
decreased attenuation
26
Total photon absorption depends on the energy of the incoming x-ray photon and the atomic number of anatomic tissue
Photoelectric absorption
27
do you increase or decrease kVp to have a greater chance of PE absorption?
decrease
28
What is bright on a radiograph? Why?
Bone, metal, or contrast are brighter on an x-ray because of their higher Z#
29
The thicker the part the more beam attenuation
X-rays are reduced by ___% for each _____cm of tissue thickness
50%, 4-5cm
30
the higher the Z# the ____ beam attenuation
more
31
How should mAs be adjusted for increased pt thickness?
Increase mAs by 2 for every 5cm of extra thickness
32
Need higher spatial frequency for _____ objects
small
33
Because it reduces spatial resolution, it is always best to minimize shape distortion in radiographic imaging. (Think about it before you answer the question)
false
34
Misalignment of the central ray among these three factors - tube, part, or image receptor - alters the shape of the part recorded
distortion
35
Scattering in the diagnostic range is due to
the Compton effect
36
What does scatter radiation do?
decreases the visibility of anatomic structures.
37
the loss of some energy of the incoming photon occurs when it ejects an outer-shell electron from a tissue atom. The ejected electron is called the Compton electron and it changes direction and may leave the anatomic part to interact with the image receptor
Compton scatter
38
an interaction that occurs with low-energy x-rays, typically below the diagnostic range. The x-ray does not lose energy but changes direction. Doesn't ionize atom
Coherent scatter
39
What is the result of under-penetration?
quantum noise
40
Quantum noise is a result of
too few x-ray photons reaching the image receptor.
41
With digital imaging using AEC, what factor is increased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)
quantum noise
42
When the image is distorted, spatial resolution is also decreased
true
43
A measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
The higher this is, the lower the radiation exposure to produce a quality image, thereby decreasing patient exposure
Detective Quantum Efficiency (DQE)
44
The resolution of the monitor used to display the digital image has an enormous effect on spatial resolution
true
45
Increased matrix of detector = _________ sharpness/spatial resolution
increased
46
The ideal expression of digital detector image resolution is the
modulation transfer function (MTF)
values range between 0-1.0
47
modulation transfer function (MTF) calculation
MTF = (maximum intensity - minimum intensity) / (maximum intensity + minimum intensity)
48
Which of the following imaging systems uses a cassette, a photostimulable phosphor plate, a plate reader, and a computer workstation?
Computed Radiography
49
The histogram is
a graphic representation of a data set
50
The values of interest (VOI)
determine what section of the histogram data set should be included in the displayed image
51
Digital imaging preprocessing includes
rescaling and histogram analysis
52
The value that indicates exposure to the IR with a DR imaging system is the
dose-area product (DAP)
53
Depends on the exposure factors and field size and is expressed in centigray-meter squared (cGY-m2)
Dose Area Product (DAP)
54
The primary factor influencing contrast with digital imaging is the
lookup table (LUT)
55
Digital imaging quality control focuses on
the display monitors and the viewing environment
56
__________ allows for the acquisition, display, and storage of digital images
PACS
57
__________ is the standard format for digital medical images
DICOM
58
Whenever magnification is increased
spatial resolution is decreased
59
Grids are typically used when:
1. Part measures more than 10 cm
2. At least 60 kVp needed for the exam
3. Part transmits little scatter radiation
part measures more than 10 cm and at least 60 kVp needed for the exam only
60
Increasing tube filtration
increases the beam energy
61
mAs is directly proportional to ______ ______ reaching the patient and the amount of ________ radiation reaching the IR
radiation quantity, remnant
62
mAs calculation
mA x seconds = mAs
63
Increasing the kVp
increases the quantity of x-ray photons
increases the penetrating power of x-ray photons.
increases the energy of the x-ray photons
(all of these)
64
Decreasing kVp results in
better contrast
65
The relationship between kVp and the quantity of remnant radiation is known as the
15% rule
66
Increasing the kVp by 15% has the same effect as
doubling the mAs
67
When the intensities of radiation exiting the patient are very similar, the resulting radiographic image has
low contrast, long-scale contrast
68
a radiograph with few densities but great differences among them is said to have high contrast
Short-scale contrast
69
a radiograph with a large number of densities but little differences among them is said to have low contrast
Long-scale contrast
70
Increasing the kVp has what affect on wavelength and frequency?
decreases wavelength and increases frequency
71
As photon energy increases wavelength _______ and frequency _______
decreases, increases
72
Standard radiographic x-ray tubes have small focal spots that measure approximately
0.5–0.6 mm
73
Focal spot size is determined by and what does it effect?
cathode filament size
sharpness
74
Which of the following is the correct formula for the inverse square law?
I1/I2 = (D2)^2/(D1)^2
75
Using a longer SID
decreases magnification
76
Which of the following is the formula to determine magnification factor?
MF = SID/SOD
77
Restriction of the primary beam to the anatomy of interest does what?
reduces patient exposure and reduces the amount of scatter produced
78
The unrestricted primary x-ray beam is
round
79
The most effective and often used radiographic beam-restriction device is the
collimator
80
The device used to absorb scatter radiation in the radiation leaving the patient before it reaches the image receptor is the
grid
81
Which of the following is the correct formula to determine how mAs should be adjusted when different ratio grids are used?
mAs1/mAs2 = grid conversion factor1/grid conversion factor2
82
Grids absorb scatter radiation because the scattered photons
travel at an angle to the transmitted photons
83
The material between the lead strips of a grid must be
radiolucent
84
The relationship between the height of the lead strips and the distance between them is the grid
ratio
85
Which of the following is the formula used to determine grid ratio?
Grid ratio = height of the lead strips/distance between the lead strips
86
Using a higher the grid ratio will
1. increase spatial resolution
2. increase scatter clean up
3. increase radiographic contrast
increase scatter clean up and increase radiographic contrast only.
87
To determine the amount of mAs to be increased when making grid changes, it is necessary to use the GCF (calculation)
GCF = mAs with grid/mAs without grid
88
The formula to use when changing from one grid to another is
mAs1/mAs2 = GCF1/GCF2
89
The air gap technique is based on creating a gap by increasing the ______
OID
90
With digital imaging using AEC, what factor is increased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)
quantum noise
91
With digital imaging using AEC, what factor is decreased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)
exposure time
92
The primary purpose of AEC is to
control the amount of radiation reaching the IR
93
The predetermined level of radiation exposure needed to terminate the exposure when using AEC is set by
the equipment service personnel
94
The two types of detectors used in AEC are
phototimers and ionization chambers
95
Ionization chamber AEC detectors are entrance-type devices because the x-rays must
enter the detector before getting to the IR
96
When the x-rays enter the ionization chamber
atoms give up electrons
atoms become ions
electrons become electricity
(all of the above)
97
These can be adjusted to increase or decrease the amount of radiation needed to terminate the exposure using AEC
exposure adjustment
98
With digital imaging using AEC, if an AP thoracic spine is imaged with the exposure adjustment changed from 0 to +2, the exposure time is _______________________. (Assume all other factors are appropriate.)
longer
99
Anatomically programmed technique is a system in which the radiographer selects
preset settings based on the part being imaged
100
Pre-established guidelines used by the radiographer to select standardized manual or AEC exposure factors for each type of radiographic examination are called
exposure technique charts
101
What information during fluoroscopy should be documented in the patient’s record?
1. Total amount of fluoroscopy time
2. Cumulative air kerma
3. Dose-area product
total amount of fluoroscopy time, cumulative air kerma, and dose-area product
102
______________ refers to how long each exposure lasts
Pulse width
103
Which of the following is an advantage of flat panel detectors used in fluoroscopy?
60 times larger operational dynamic range because they do not exhibit veiling glare.
Less electronic noise.
Much lighter and more compact.
Produce a digital signal directly
(all of the above)
104
The fiber optic bundle or optical lens system is used to
link the output phosphor and camera or CCD
105
On fluoroscopic units that have an image intensifier, magnification of the fluoroscopic image results in improved
spatial resolution
106
Each capacitor in a CCD represents a(n)
pixel
107
A light-sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor is the
charge coupled device (CCD)
108
The Charge Coupled Device (CCD) is light-sensitive device that generates an electrical signal when stimulated by visible light
true
109
When a CCD is exposed to light, it generates and briefly stores light energy
true
110
Increasing the mA is the way to correct a fluoroscopic image that has
noise
111
When operated in magnification mode, the electrostatic lenses have ________ of a negative charge
more
112
The ________________ is (are) found along the entire length of the image intensifier
electrostatic focusing lenses
113
The electrostatic focusing lenses have a ___________ charge
negative
114
The term that means an expression of the degree to which the image is made smaller from input phosphor to output phosphor is the
minification gain
115
This part of the image intensifier absorbs light and produces electrons
photocathode
116
What is the relationship between kVp and subject contrast?
high kVp creates low subject contrast
117
Which of the following contribute to subject contrast?
Effective atomic number
Differences in tissue density
Differences in tissue thickness
(all of the above)
