MIDTERMS Flashcards
1
Q
tomography has as its root tomo, meaning to?
A
cut, section, or layer from the Greek tomos (a cutting).
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
3
Q
All early scanners produced what type of cuts?
A
axial
4
Q
What do you call older scanning systems?
A
computerized axial tomography/CAT scan
5
Q
The thickness of the cross-sectional slice is
referred to as ______
A
Z-axis
6
Q
CT image quality is typically evaluated using a number of what criteria?
A
Spatial resolution
Low contrast resolution
Temporal resolution
7
Q
It describes the ability of a system to define small objects distinctly
A
Spatial resolution
8
Q
It refers to the ability of a system to differentiate, on the image, objects with similar densities.
A
Low contrast resolution
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
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
11
Q
The Z axis determines what?
A
thickness of the slices
12
Q
What does selecting a slice thickness do?
A
s limits the x-ray beam so that
it passes only through this volume
13
Q
Width and height in CT is indicated by what?
A
Width - x, height -y
14
Q
Most common matrix size in CT
A
512 pixels down and across
15
Q
The structures in a CT image are represented by what?
A
varying shades of gray
16
Q
An x-ray beam consists of bundles of energy known as
A
photons
17
Q
The degree to which a beam is reduced is a phenomenon referred to as
A
attenuation
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
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
20
Q
It is defined as the mass of a substance
per unit volume
A
density
21
Q
It is the degree to which matter is crowded together, or concentrated
A
Density
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
23
Q
In general, the attenuation coefficient __________ with increasing photon energy and ______ with increasing atomic number and density
A
decreasing, increasing
24
Q
Measurements are expressed in what units?
A
Hounsfield Units
25
Hounsfield units is named after?
Godfrey Hounsfield
26
It quantifies the degree that a structure attenuates an x-ray beam.
Hounsfield units
27
The Hounsfi eld unit value is directly
related to the linear attenuation coefficient:
1 HU equals a 0.1% difference between the linear attenuation coefficient of the tissue as compared with the linear attenuation coefficient of water
28
Beam-hardening artifacts appear as dark streaks or vague areas of decreased density, sometimes called
cupping artifacts
29
Artifacts that result from preferential absorption of the low-energy photons, which leaves higher-intensity photons to strike the detector array, are called
beam-hardening artifacts
30
The smaller the object being scanned, the
___________ the CT slice required
thinner
31
_______ CT slices increase the likelihood of missing very small objects
Thicker
32
The process in CT by which diff erent tissue attenuation values are averaged to produce one less accurate pixel reading is called
volume averaging
33
another term for volume averaging
partial volume effect
34
Thinner slices result in?
higher radiation dose to the
patient.
35
The larger the X and Y dimensions (i.e., the larger the pixel), the ______________
more chance that the pixel will contain tissues of different densities
36
All of the thousands of bits of data acquired by the system with each scan are called _______-
raw data
37
They have not yet been sectioned to create pixels; hence, Hounsfield unit values have not yet been assigned.
Raw data
38
The process of using the raw data to create an image is called
Image reconstruction
39
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 ______
Image data
40
The reconstruction that is automatically produced during scanning is often called
prospective reconstruction
41
The same raw data may be used later to generate new images. This process is referred to as
retrospective reconstruction
42
The scanning systems of the 1980s operated exclusively in a ____________ mode
step & shoot
43
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
Step and shoot scanning
44
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
step & shoot scanning
45
Another term for step & shoot scanning
axial scanning, conventional scanning, or serial scanning.
46
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.
Helical (Spiral) Scanning
47
This technology was expanded in 1992
when scanners were introduced that contained two rows of detectors, capturing data for two slices per gantry rotation.
Multidetector Row CT Scanning
48
In CT, All directional terms are based on the body being viewed in the
anatomic position
49
The ability of the tube to withstand the resultant heat is called its
heat capacity
50
ability of the tube to rid itself of the heat is its
heat dissipation
51
each detector cell is sampled and converted to a digital format by the
Data Acquisition System
52
often referred to as the brain of the CT scanner.
CPU
53
The CT process can be broken down into three general segments:
data acquisition, image reconstruction, and image display
54
It is the ring-shaped part of the CT scanner. It
houses many of the components necessary to produce and detect x-rays
gantry
55
The range of aperture size of the gantry is typically
70-90 cm
56
The degree of tilt in the gantry varies among systems, but __________ is usual
±15° to ±30°
57
This are located on either side of the gantry opening allows the technologist to control
the alignment lights, gantry tilt, and table movement
control panels
58
It is embedded in the gantry to allow communication between the patient and the technologist throughout the scan procedure
microphone
59
It y houses many of the components necessary to produce and detect x-rays. Components are mounted on a rotating scan frame
gantry
60
It permits the gantry frame to rotate continuously, making helical scan modes possible
slip rings
61
They are small enough so that they can be located within the gantry
high frequency generators
62
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
high kV (generally 120–140 kV)
63
What is high kv used for in CT scan?
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
They can take different forms, such as blowers, fi lters, or devices that perform oil-to-air heat exchange
cooling systems
65
They are important because many imaging components can be affected by temperature fluctuation.
Cooling systems
66
They produce the x-ray photons that create the
CT image.
Xray tubes
67
It is often used for the anode target material because it produces a higher-intensity x-ray beam
Tungsten
68
what is the atomic number of tungsten
74
69
They reduce the radiation dose to the patient and help to minimize image artifact
Compensating filters
70
What kind of radiation is emitted by the CT x-ray tubes?
polychromatic
71
They restrict the x-ray beam to a specific area,
thereby reducing scatter radiation.
collimators
72
They control the slice thickness by narrowing or widening the x-ray beam
Collimators
73
Scanners vary in the choices of slice thickness available. Choices range from
0.5-10mm
74
It refers to a single element or a single type of detector used in a CT system.
detector
75
It is used to describe the entire collection of detectors
detector array
76
The optimal characteristics of a detector are as follows:
1) high detector efficiency
2) low, or no afterglow
3) high scatter suppression;
4) high stability
77
Overall detector efficiency is the product of a number of factors. These are:
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
refers to the ability with which the detector obtains photons that have passed through the patient.
Capture efficiency
79
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)
Absorption efficiency
80
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
Response time
81
It is the ratio of the maximum signal measured to the minimum signal the detectors can measure.
Dynamic range
82
It fills hollow chambers to produce detectors that absorb approximately 60% to 87% of the
photons that reach them.
pressurized xenon gas
83
It is used because of its ability to remain stable under pressure.
xenon gas
84
A xenon detector channel consists of _____ tungsten plates
3
85
A disadvantage of xenon gas is that it
must be kept under pressure in an aluminum casing
86
Another term for the solid state detectors
scintillation detectors
87
This generation of scanners is produced by
the now-defunct EMI medical division had a design that is referred to as the first generation
first generation
88
The scan times for this generation were very long
first generation
89
what is the angle of the arc in the first generation
180
90
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
2nd generation
91
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
3rd generation
92
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
3rd generation
93
What is the 3rd generation's disadvantage?
more frequent occurrence of ring artifacts
94
Another term for the 3rd generation scanners
rotate-rotate scanners
95
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
4th generation scanners
96
What is an overscan
tube arc greater than 360
97
This measures the number of photons that strike the detector, convert the information to a digital signal, and send the signal to the computer
data acquisition system (DAS)
98
It is a finite set of unambiguous steps performed in a prescribed sequence to solve a problem.
algorithm
99
They are the basis for most computer programming
algorithms
100
Who developed the fourier transform?
Baron Jean-Baptiste-Joseph Fourier
101
It is a method to study waves of many different sorts and also to solve several kinds of linear differential equations.
Fourier transform
102
Computers generally rely on a version
known as
discrete Fourier transform (DFT)
103
An efficient algorithm to compute DFT and its inverse is called
fast Fourier transform (FFT)
104
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
fast Fourier Transform
105
It is a mathematical method of estimating the
value of an unknown function using the known value on either side of the function
interpolation
106
It is the simplest type and is frequently used in mathematics and science
linear interpolation
107
It assumes that an unknown point falls
along a straight line between two known points
Linear interpolation
108
It is the portion of the computer that can be physically touched
hardware
109
It is instructions that tell the computer what to do and when to do it.
software
110
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
Hard disk/ hard drive
111
These are ancillary pieces of computer hardware designed to feed data into the computer or accept processed data from the computer
Input & output devices
112
Give examples of input devices
keyboard, mouse, touch-sensitive
plasma screen, and CT detector mechanisms
113
Give examples of output devices
monitor, laser camera, printer, and archiving
equipment such as optical disks or magnetic tape
114
It is the component that interprets computer
program instructions and sequences tasks. It contains the microprocessor, the control unit, and the primary memory
CPU
115
Another term for CPU
vector processor
116
What does ROM, RAM, WORM mean?
read-only memory (ROM),
random access memory (RAM),
write-once read-many times (WORM) memory
117
This memory is imprinted at the factory and is used to store frequently used instructions such as those required for starting the system
ROM
118
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
RAM
119
What is the opposite of RAM
serial access memory (SAM)
120
This memory refers to computer storage
devices that can be written to once, but read from many times.
WORM
121
2 types of WORM
CD-R (compact disk-recordable)
DVD-R (digital video disk-recordable)
122
All of the thousands of bits of data acquired by the system with each scan are called
raw data
123
process of using raw data to create an image is called
image reconstruction
124
These are those which result once the computer has processed the raw data. One Hounsfield unit value is assigned to each pixel
image data
125
This compiles the information from all of the
attenuation profiles to create an image
back projection
126
This determines the area, within the gantry, from which the raw data are acquired
Scan field of view
127
another term for scan field of view?
calibration field of view
128
Another method of image reconstruction has been recently introduced for use in CT image reconstruction known as
iterative reconstruction
129
It determines how much of the collected raw data is used to create an image
display field of view
130
ANother term of DFOV
zoom/target
131
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
Output device
132
It is an output device that transfers the image from the monitor to the film
camera
133
It transfers the image displayed on the monitor to fi lm
multiformat cameras
134
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.
laser cameras
135
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
Display processor
136
It is used to display CT images. This system
assigns a certain number of Hounsfi eld units to each shade of gray.
Gray scale
137
This determines the quantity of Hounsfield units represented as shades of gray on a specific image
Window width
138
This selects which Hounsfield values are displayed as shades of gray.
window level
139
The window level should be set at a point that is roughly the _____________
the same value as the average attenuation number of the tissue of interest
140
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
white, black
141
It is an area on the image defined by the operator.
Region of interest
142
The amount of CT number variance within the region of interest is indicated by the
standard deviation
143
Image magnification is __________ decreasing the display field of view.
not the same as
144
It allows more than one image to be displayed in a single frame.
Multiple image display function
145
It is a graphical display showing how frequently
a range of CT numbers occurs within an ROI
histogram
