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MIDTERMS Flashcards

1
Q

tomography has as its root tomo, meaning to?

A

cut, section, or layer from the Greek tomos (a cutting).

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2
Q

It is a sophisticated computerized method is used to obtain data and transform them into “cuts,” or cross-sectional slices of the human body

A

Tmography

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3
Q

All early scanners produced what type of cuts?

A

axial

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4
Q

What do you call older scanning systems?

A

computerized axial tomography/CAT scan

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5
Q

The thickness of the cross-sectional slice is
referred to as ______

A

Z-axis

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6
Q

CT image quality is typically evaluated using a number of what criteria?

A

Spatial resolution
Low contrast resolution
Temporal resolution

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7
Q

It describes the ability of a system to define small objects distinctly

A

Spatial resolution

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8
Q

It refers to the ability of a system to differentiate, on the image, objects with similar densities.

A

Low contrast resolution

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9
Q

It refers to the speed at that the data can be acquired. This speed is particularly important to reduce or eliminate artifacts that result from
object motion, such as those commonly seen when imaging the heart

A

Temporal resolution

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10
Q

It uses a computer to process information collected from the passage of x-ray beams through an area of anatomy

A

Computed tomography

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11
Q

The Z axis determines what?

A

thickness of the slices

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12
Q

What does selecting a slice thickness do?

A

s limits the x-ray beam so that
it passes only through this volume

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13
Q

Width and height in CT is indicated by what?

A

Width - x, height -y

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14
Q

Most common matrix size in CT

A

512 pixels down and across

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15
Q

The structures in a CT image are represented by what?

A

varying shades of gray

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16
Q

An x-ray beam consists of bundles of energy known as

A

photons

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17
Q

The degree to which a beam is reduced is a phenomenon referred to as

A

attenuation

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18
Q

x-ray photons that pass through objects unimpeded are represented by a black area on the image. These areas on the image are commonly referred to as having __________

A

low attenuation

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19
Q

X-ray that is entirely absorbed by an object and cannot be detected; the place on the image is white. An object that has the ability to absorb much of the X-ray beam is often referred
to as having

A

High attenuation

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20
Q

It is defined as the mass of a substance
per unit volume

A

density

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21
Q

It is the degree to which matter is crowded together, or concentrated

A

Density

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22
Q

____________________ those with a high atomic number, have many circulating electrons and
heavy nuclei and, therefore, provide more opportunities for photon interaction than elements of less density

A

Dense elements

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23
Q

In general, the attenuation coefficient __________ with increasing photon energy and ______ with increasing atomic number and density

A

decreasing, increasing

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24
Q

Measurements are expressed in what units?

A

Hounsfield Units

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25
Q

Hounsfield units is named after?

A

Godfrey Hounsfield

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26
Q

It quantifies the degree that a structure attenuates an x-ray beam.

A

Hounsfield units

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27
Q

The Hounsfi eld unit value is directly
related to the linear attenuation coefficient:

A

1 HU equals a 0.1% difference between the linear attenuation coefficient of the tissue as compared with the linear attenuation coefficient of water

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28
Q

Beam-hardening artifacts appear as dark streaks or vague areas of decreased density, sometimes called

A

cupping artifacts

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29
Q

Artifacts that result from preferential absorption of the low-energy photons, which leaves higher-intensity photons to strike the detector array, are called

A

beam-hardening artifacts

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30
Q

The smaller the object being scanned, the
___________ the CT slice required

A

thinner

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31
Q

_______ CT slices increase the likelihood of missing very small objects

A

Thicker

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32
Q

The process in CT by which diff erent tissue attenuation values are averaged to produce one less accurate pixel reading is called

A

volume averaging

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33
Q

another term for volume averaging

A

partial volume effect

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34
Q

Thinner slices result in?

A

higher radiation dose to the
patient.

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35
Q

The larger the X and Y dimensions (i.e., the larger the pixel), the ______________

A

more chance that the pixel will contain tissues of different densities

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36
Q

All of the thousands of bits of data acquired by the system with each scan are called _______-

A

raw data

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37
Q

They have not yet been sectioned to create pixels; hence, Hounsfield unit values have not yet been assigned.

A

Raw data

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38
Q

The process of using the raw data to create an image is called

A

Image reconstruction

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39
Q

Once raw data have been processed so that each pixel is assigned a Hounsfi eld unit value, an image can be created; the data included in the image is now referred to as ______

A

Image data

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40
Q

The reconstruction that is automatically produced during scanning is often called

A

prospective reconstruction

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41
Q

The same raw data may be used later to generate new images. This process is referred to as

A

retrospective reconstruction

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42
Q

The scanning systems of the 1980s operated exclusively in a ____________ mode

A

step & shoot

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43
Q

In this type of scanning, the x-ray tube rotated 360° around the patient to acquire data for a single slice, 2) the motion of the x-ray tube was halted while the patient was advanced on the CT table to the location appropriate to collect data for the next slice

A

Step and shoot scanning

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44
Q

This type of scanning was necessary because
the rotation of the x-ray tube entwined the system cables, limiting rotation to 360°. Consequently, gantry motion had to be stopped before the next slice could be taken

A

step & shoot scanning

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45
Q

Another term for step & shoot scanning

A

axial scanning, conventional scanning, or serial scanning.

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46
Q

In this type of scanning, the key among the advances was the development of a system that eliminated the cables and thereby enabled continuous rotation of the gantry. This, in combination with other improvements, allows for uninterrupted data acquisition that traces a helical path around the patient.

A

Helical (Spiral) Scanning

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47
Q

This technology was expanded in 1992
when scanners were introduced that contained two rows of detectors, capturing data for two slices per gantry rotation.

A

Multidetector Row CT Scanning

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48
Q

In CT, All directional terms are based on the body being viewed in the

A

anatomic position

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49
Q

The ability of the tube to withstand the resultant heat is called its

A

heat capacity

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50
Q

ability of the tube to rid itself of the heat is its

A

heat dissipation

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51
Q

each detector cell is sampled and converted to a digital format by the

A

Data Acquisition System

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52
Q

often referred to as the brain of the CT scanner.

A

CPU

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53
Q

The CT process can be broken down into three general segments:

A

data acquisition, image reconstruction, and image display

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54
Q

It is the ring-shaped part of the CT scanner. It
houses many of the components necessary to produce and detect x-rays

A

gantry

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55
Q

The range of aperture size of the gantry is typically

A

70-90 cm

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56
Q

The degree of tilt in the gantry varies among systems, but __________ is usual

A

±15° to ±30°

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57
Q

This are located on either side of the gantry opening allows the technologist to control
the alignment lights, gantry tilt, and table movement

A

control panels

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58
Q

It is embedded in the gantry to allow communication between the patient and the technologist throughout the scan procedure

A

microphone

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59
Q

It y houses many of the components necessary to produce and detect x-rays. Components are mounted on a rotating scan frame

A

gantry

60
Q

It permits the gantry frame to rotate continuously, making helical scan modes possible

A

slip rings

61
Q

They are small enough so that they can be located within the gantry

A

high frequency generators

62
Q

CT generators produce ________________ to increase the intensity of the beam, which will increase the penetrating ability of the x-ray beam and thereby reduce patient dose

A

high kV (generally 120–140 kV)

63
Q

What is high kv used for in CT scan?

A

increase the intensity of the beam,
increasing its penetrating ability and thereby reducing
patient dose. High kV settings also help to reduce the heat
load on the x-ray tube by allowing a lower mA setting.

64
Q

They can take different forms, such as blowers, fi lters, or devices that perform oil-to-air heat exchange

A

cooling systems

65
Q

They are important because many imaging components can be affected by temperature fluctuation.

A

Cooling systems

66
Q

They produce the x-ray photons that create the
CT image.

A

Xray tubes

67
Q

It is often used for the anode target material because it produces a higher-intensity x-ray beam

A

Tungsten

68
Q

what is the atomic number of tungsten

A

74

69
Q

They reduce the radiation dose to the patient and help to minimize image artifact

A

Compensating filters

70
Q

What kind of radiation is emitted by the CT x-ray tubes?

A

polychromatic

71
Q

They restrict the x-ray beam to a specific area,
thereby reducing scatter radiation.

A

collimators

72
Q

They control the slice thickness by narrowing or widening the x-ray beam

A

Collimators

73
Q

Scanners vary in the choices of slice thickness available. Choices range from

A

0.5-10mm

74
Q

It refers to a single element or a single type of detector used in a CT system.

A

detector

75
Q

It is used to describe the entire collection of detectors

A

detector array

76
Q

The optimal characteristics of a detector are as follows:

A

1) high detector efficiency
2) low, or no afterglow
3) high scatter suppression;
4) high stability

77
Q

Overall detector efficiency is the product of a number of factors. These are:

A

1) stopping power of the detector material;
2) scintillator efficiency (in solid-state types);
3) charge collection efficiency (in xenon types);
4) geometric efficiency,
5) scatter rejection

78
Q

refers to the ability with which the detector obtains photons that have passed through the patient.

A

Capture efficiency

79
Q

refers to the number of photons absorbed by the detector and is dependent on the physical properties of the detector face (e.g., thickness, material)

A

Absorption efficiency

80
Q

It is the time required for the signal from the detector to return to zero after stimulation of the detector by x-ray radiation so that it is ready to detect another x-ray event

A

Response time

81
Q

It is the ratio of the maximum signal measured to the minimum signal the detectors can measure.

A

Dynamic range

82
Q

It fills hollow chambers to produce detectors that absorb approximately 60% to 87% of the
photons that reach them.

A

pressurized xenon gas

83
Q

It is used because of its ability to remain stable under pressure.

A

xenon gas

84
Q

A xenon detector channel consists of _____ tungsten plates

A

3

85
Q

A disadvantage of xenon gas is that it

A

must be kept under pressure in an aluminum casing

86
Q

Another term for the solid state detectors

A

scintillation detectors

87
Q

This generation of scanners is produced by
the now-defunct EMI medical division had a design that is referred to as the first generation

A

first generation

88
Q

The scan times for this generation were very long

A

first generation

89
Q

what is the angle of the arc in the first generation

A

180

90
Q

This generation’s design is one in which the x-ray beam passes linearly across the patient before rotating. However, a fan-shaped x-ray beam was used, rather than the thin beam used with first-generation designs

A

2nd generation

91
Q

This generation’s scanner design is one in
which the x-ray tube is placed opposite the detector array. Both the tube and the detector move in a circle within the gantry

A

3rd generation

92
Q

This generation’s design made it no longer necessary to translate the beam and detector as both could move in a circle within the gantry

A

3rd generation

93
Q

What is the 3rd generation’s disadvantage?

A

more frequent occurrence of ring artifacts

94
Q

Another term for the 3rd generation scanners

A

rotate-rotate scanners

95
Q

This generation uses a detector array that
is fixed in a 360° circle within the gantry. The tube rotates within the fixed detector array and produces a fan-shaped beam

A

4th generation scanners

96
Q

What is an overscan

A

tube arc greater than 360

97
Q

This measures the number of photons that strike the detector, convert the information to a digital signal, and send the signal to the computer

A

data acquisition system (DAS)

98
Q

It is a finite set of unambiguous steps performed in a prescribed sequence to solve a problem.

A

algorithm

99
Q

They are the basis for most computer programming

A

algorithms

100
Q

Who developed the fourier transform?

A

Baron Jean-Baptiste-Joseph Fourier

101
Q

It is a method to study waves of many different sorts and also to solve several kinds of linear differential equations.

A

Fourier transform

102
Q

Computers generally rely on a version
known as

A

discrete Fourier transform (DFT)

103
Q

An efficient algorithm to compute DFT and its inverse is called

A

fast Fourier transform (FFT)

104
Q

These are of great importance to a wide variety of applications including acoustical and image analysis and have been used in fields as varied as geologic surveying to actuarial analysis for the insurance industry

A

fast Fourier Transform

105
Q

It is a mathematical method of estimating the
value of an unknown function using the known value on either side of the function

A

interpolation

106
Q

It is the simplest type and is frequently used in mathematics and science

A

linear interpolation

107
Q

It assumes that an unknown point falls
along a straight line between two known points

A

Linear interpolation

108
Q

It is the portion of the computer that can be physically touched

A

hardware

109
Q

It is instructions that tell the computer what to do and when to do it.

A

software

110
Q

It is an essential component of all CT systems. The number of images that the ________
can store varies according to the make and model of the scanner. It is important to remember than an enormous amount of information is collected for each image

A

Hard disk/ hard drive

111
Q

These are ancillary pieces of computer hardware designed to feed data into the computer or accept processed data from the computer

A

Input & output devices

112
Q

Give examples of input devices

A

keyboard, mouse, touch-sensitive
plasma screen, and CT detector mechanisms

113
Q

Give examples of output devices

A

monitor, laser camera, printer, and archiving
equipment such as optical disks or magnetic tape

114
Q

It is the component that interprets computer
program instructions and sequences tasks. It contains the microprocessor, the control unit, and the primary memory

A

CPU

115
Q

Another term for CPU

A

vector processor

116
Q

What does ROM, RAM, WORM mean?

A

read-only memory (ROM),
random access memory (RAM),
write-once read-many times (WORM) memory

117
Q

This memory is imprinted at the factory and is used to store frequently used instructions such as those required for starting the system

A

ROM

118
Q

This memory includes instructions that are
frequently changed, such as the data used to reconstruct images. It named so because all parts of it can be reached easily at random

A

RAM

119
Q

What is the opposite of RAM

A

serial access memory (SAM)

120
Q

This memory refers to computer storage
devices that can be written to once, but read from many times.

A

WORM

121
Q

2 types of WORM

A

CD-R (compact disk-recordable)
DVD-R (digital video disk-recordable)

122
Q

All of the thousands of bits of data acquired by the system with each scan are called

A

raw data

123
Q

process of using raw data to create an image is called

A

image reconstruction

124
Q

These are those which result once the computer has processed the raw data. One Hounsfield unit value is assigned to each pixel

A

image data

125
Q

This compiles the information from all of the
attenuation profiles to create an image

A

back projection

126
Q

This determines the area, within the gantry, from which the raw data are acquired

A

Scan field of view

127
Q

another term for scan field of view?

A

calibration field of view

128
Q

Another method of image reconstruction has been recently introduced for use in CT image reconstruction known as

A

iterative reconstruction

129
Q

It determines how much of the collected raw data is used to create an image

A

display field of view

130
Q

ANother term of DFOV

A

zoom/target

131
Q

It allows the information stored in computer memory to be displayed. The device used to display CT images are generally a black-and-white or color monitor

A

Output device

132
Q

It is an output device that transfers the image from the monitor to the film

A

camera

133
Q

It transfers the image displayed on the monitor to fi lm

A

multiformat cameras

134
Q

It bypasses the image on the display monitor and transfers data directly from the computer, bypassing the video system entirely, thereby significantly improving image quality.

A

laser cameras

135
Q

It assigns a group of Hounsfield units to each shade of gray. In this simplified illustration, 10 different shades are available to display the 300 HU in the window width

A

Display processor

136
Q

It is used to display CT images. This system
assigns a certain number of Hounsfi eld units to each shade of gray.

A

Gray scale

137
Q

This determines the quantity of Hounsfield units represented as shades of gray on a specific image

A

Window width

138
Q

This selects which Hounsfield values are displayed as shades of gray.

A

window level

139
Q

The window level should be set at a point that is roughly the _____________

A

the same value as the average attenuation number of the tissue of interest

140
Q

All values higher than those in the selected range will appear __________ on an image. All values lower than those in the selected range will appear ______ on the image

A

white, black

141
Q

It is an area on the image defined by the operator.

A

Region of interest

142
Q

The amount of CT number variance within the region of interest is indicated by the

A

standard deviation

143
Q

Image magnification is __________ decreasing the display field of view.

A

not the same as

144
Q

It allows more than one image to be displayed in a single frame.

A

Multiple image display function

145
Q

It is a graphical display showing how frequently
a range of CT numbers occurs within an ROI

A

histogram

CT (1 decks)

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