Exam 3 Flashcards
1
Q
binary # system
A
lang of 1’s & 0’s that comp’s use to process data
2
Q
bit
A
single unit of data (binary unit)
3
Q
byte
A
8 bits; amount of mem needed to store 1 alphanumeric character
4
Q
RAM
A
random access memory; short-term storage for open programs (MB, GB, TB) that can be stored/accessed at random from anywhere in about equal amounts of T
5
Q
ROM
A
read-only memory; data storage device that contain info supplied by manufacturer that cannot be written on or erased
6
Q
teleradiology
A
transfer of imgs & pt reports to remote sites
7
Q
LAN
A
local area network; sm area networked w a series of cables/wireless access points allowing comps to share info
8
Q
WAN
A
wide area network; spans lg areas; connected by telephone wires, satellites, other comm cables
9
Q
imaging plate. what does it replace? what occurs? what is it capable of doing?
A
replaces rad film; img’s formed by interaction of XRs w PSP; capable of storing latent img
10
Q
PSP
A
photostimulable phosphor, active layer of IP
11
Q
what chem is used as the PSP in an imaging plate?
A
Ba Fluoro Halide coated w Europium (and a dye that differentially absorbs the stimulating light)
12
Q
prompt emission
A
when XR exposes PSP, resultant energy transfer excites e-‘s into metastable state; 50% of these e-‘s immediately return to their ground state, resulting in a prompt emission of light
13
Q
metastable e-‘s?
A
e-‘s excited from the energy transfer when an XR exposes a PSP
14
Q
what percentage of e-‘s is converted into normal stage soon after exposure?
A
50%
15
Q
process of img production in CR? (4)
A
- expose (–> XR-induced img-forming signal)
- stimulate (laser interacts w PSP to stim latent img)
- read (light signal emitted after stimulation is detected/measured)
- erase (residual metastable e-‘s moved to ground state by intense light)
16
Q
color of laser commonly used in CR to scan imaging plate?
A
infrared
17
Q
factors affecting spatial resolution (amount of detail present in img) of CR img? (5)
A
- phosphor layer thickness (thinner better)
- pixel size (smaller better)
- matrix size (bigger better)
- # pixels (more better)
- diameter of laser (smaller better)
18
Q
primary erase?
A
erases latent img
19
Q
secondary erase?
A
erases scatter
20
Q
explain img fading in CR and what should be done to overcome problem?
A
remaining metastable e-‘s (from stimulated laser) return to their ground state over T causing latent img to fade; process img soon after exposure
21
Q
element used in gas laser?
A
He/Ne
22
Q
explain how wavelength of laser beam affects detail
A
stimulating laser light is monochromatic & resultant emitted light is polychromatic; the longer the laser wavelength, the greater difference btw it’s wavelength and that of the emitted light, causing less confusion/interference when img is read
23
Q
a ______ wavelength of laser gives better resolution
A
long
24
Q
a _____ diameter laser produces img’s w better spatial res
A
sm
25
ADC?
analog to digital conversion
26
DAC
digital to analog converter
27
______ and _______ are the processes of analog to digital conversion (ADC)
sampling & quantization
28
What does an IR response of a CR system look like on a graph and what is the x & y axis?
straight climbing line; Optical Density on y-axis and µGy(mR) on x-axis
29
a 12 bit CR img has ______ gray levels
4096
30
if the bit depth is 7 what is the dynamic range of the CR img?
128 shades of gray
31
CCD?
charged-coupled device (a silicon based semi-conductor); used in indirect conversion systems
32
____________ is the ability of the CCD to respond to a wide range of light intensity, from very dim to very bright
dynamic range
33
explain DR indirect system and the chems used
XR absorbed by thin layer of cesium iodide (changes XR to light), a scintillation phosphor, which then produces a flash of light which interacts w a layer of amorphous silicon photodiode to create electric charge (2 steps - XR to light, light to signal)
34
explain DR direct system and chems used
XR directly interacts w a layer of amorphous selenium, which produces the electric charge (1 step - XR to signal)
35
spatial res in DR is ______ limited
pixel limited (limited by pixel size)
36
TFT? f(x)?
(thin film transistors) absorbed rad is converted into electric signals, and that electric charge is temporarily stored in TFT until readout (the pattern of electrical charges constitute the latent img)
37
spatial frequency? whats the unit?
of line pairs in a given length; line pairs per millimeter (lp/mm);
38
line pair?
a high contrast line separated by an interspace of equal width (so it's ONE line & ONE space)
39
spatial resolution?
ability to img sm objects that have high subject contrast; ability of imaging system to resolve/render on the img a sm high-contrast object
40
contrast resolution?
ability to distinguish many shades of gray from black to white
41
pixel size is related to ______ resolution
spatial res
42
laser beam diameter relates to _____ resolution of CR imaging system
spatial res
43
dynamic range is related to _______ resolution
contrast res
44
bit depth is related to _____ resolution
contrast res
45
how is spatial frequency related to spatial resolution?
(direct) higher spatial frequency --> better spatial resolution
46
what is modulation transfer f(x)?
the ratio of img to object as a f(x) of spatial frequency; ideal img system has MTF of 1
47
what is indicated by a low MTF?
the img is a closer representation of the object, giving better resolution (best MTF is 1)
48
dynamic range?
of shades of gray that an image system can produce
49
window level?
controls brightness/density in post-processing
50
window width?
controls contrast in post-processing
51
a higher SNR indicates ____ resolution (more/less)
more
52
contrast resolution is limited by _______
noise/SNR
53
spatial resolution in screen film radiography is determined principally by _____________
geometric factors (primarily focal-spot size)
54
DQE?
(detective quantum efficiency) measure of XR absorption efficiency; measurement of % of absorbed XRs when they hit the detector
55
Which has the highest DQE? (film, CR, DR)
DR
56
if a system has a dynamic range of 512, what is the bit depth?
9 bit
57
teleradiology
transfer of imgs & pt reports to remote sites
57
factors affecting spatial resolution (amount of detail present in img) of CR img? (5)
1. phosphor layer thickness (thinner better)
2. pixel size (smaller better)
3. matrix size (bigger better)
4. # pixels (more better)
5. diameter of laser (smaller better)
58
in CR, which IP layer stores the latent img?
PSP (active layer)
59
Hounsfield scale?
math calculation used to assign numerical value to gray
60
which laser wavelength is better and why?
longer wavelength bc easier to differentiate from emitted pt info light, causing less noise
60
which laser is better? why? solid state or gas?
solid state bc has higher/longer wavelength
61
photomultiplier?
amplifies light (increases intensity --> increase signal) and sends to digitizer (which assigns values to pixels)
62
In order from best to least spatial resolution, list the systems and their spatial frequency
1. mammo (15 lp/mm)
2. film (10 lp/mm)
3. DR (5 lp/mm)
4. CR (3 lp/mm)
63
optical filter?
helps differentiate laser from pt info (to reduce noise)
64
2 causes for moiré artifact
laser lines II to grid lines, frequency harmonics (scanning frequency matches grid frequency)
64
cones v rods
cones for bright/photopic vision, and rods for dim/scotopic vision
65
Exposure Indicator for Fuji systems?
S# = 200-400, (indirect relation to exposure)
65
exposure indicator for Kodak/Carestream systems?
Ei = 2000, (direct relation to exposure)
66
exposure indicator for Agfa?
log mean = 2.2, (direct relation to exposure)
66
4 IP artifacts, and how they appear (white/black)?
1. cracks (w, - density)
2. adhesive tape (w, - density)
3. hair (w, - density)
4. back scatter (b, + density)
67
how do you reduce the IP artifact of backscatter?
collimate
67
Indirect conversion system?
XR + CsI (Cesium Iodide) --> light;
| light + a-Si (amorphous silicon) --> electric signal
68
Direct conversion system?
XR + a-Se (amorphous selenium) --> electric charge/signal
68
typical grid frequency in digi?
150+ lines/in
69
underexposure in digi causes what?
quantum mottle (grainy)
69
overexposure in digi causes what?
an affect on contrast
70
all DR systems use what to temporarily store the latent img?
TFT
71
Which network is faster?
LAN (PACs rooms)
72
dynamic range is IDed by?
bit capacity of ea pixel
73
principle descriptor of contrast res?
dynamic range
74
the greater area of TFT, the greater the _____, which means ____ rad required to make img
DQE; less
75
A bigger Hounsfield scale means what?
better contrast res
76
what is found in the reader that helps to improve the SNR, which increases spatial resolution?
optical filter
77
pixel pitch?
space btw pixels
77
how do you determine pixel size?
FOV/matrix size (make sure they are in the same units)
77
how many bytes usually constitute a word?
2 bytes
77
+ pixel pitch --> ?
- spatial res
77
what do you increase to increase SNR?
+ mAs
77
what makes up dynamic range?
Hounsfield scale
118
shuttering?
(post-processing) black bg is added to original coll. edges
120
dynamic range is IDed by?
bit capacity of ea pixel
121
principle descriptor of contrast res?
dynamic range
122
what do you increase to increase SNR?
+ mAs
123
the greater area of TFT, the greater the _____, which means ____ rad required to make img
DQE; less
125
A bigger Hounsfield scale means what?
better contrast res
126
what is found in the reader that helps to improve the SNR, which increases spatial resolution?
optical filter
127
histogram?
data w/in coll. area produce a graphic representation of the optimal densities (can be changed using window level/width or LUT - lookup table)
132
reflective layer of IP sends light in a ______ direction and is ______ to reduce light spread
forward; black
133
phosphor center?
stimulated e-'s (from XR interaction w BFH crystals in PSP) enters conductive layer where they get trapped in a "phosphor center"
134
Raster pattern
laser scanning beam sweeps horizontally from L to R
135
photomultiplier?
detects (blue) light emitted from IP --> amplifies light --> sends to digitizer
136
digitizer?
(ADC) divides analog img into matrix & assigns ea pixel a value based on brightness
137
which system has the most exposure latitude?
digital
138
how do you reduce quantum mottle?
+ mAs
139
Europium is the _______ of PSP
activator
140
PSP screen is handled in ________?
reader
141
With CR, contrast is ______ regardless of exposure
constant
142
principle source of noise in CR is?
scatter rad
143
output signal from PSP is converted (ADC) by ________
photodetector
144
ghosting is prevented by?
erasing w white light
145
CR produces __________ gray levels
10,000
146
In DR, the latent img is formed on the ____________
rad detector
147
brightness of region is determined by what 2 things?
Z & mass density
148
increasing FOV does what?
reduces spatial res (makes pixel size bigger)
149
dynamic range determines contrast res and _________
motion blur
150
what has the best spatial resolution? why?
mammography; highest spatial frequency (most lp/mm)
151
speed determined by?
PSL (photostimulable luminescence); more PSL --> more speed (and less dose)
152
extremities and mammo IR's have...?
highest resolution
153
salt and pepper effect?
grainy quantum mottle; salt/white - XR doesn't reach IR; pepper/black - XR reaches IR
154
what is the typical grid frequency in digi?
150+ lines/in
156
4 IP artifacts and whether they represent pos/neg densities?
1. cracks - neg (white)
2. adhesive tape - neg
3. hair - neg
4. backscatter - pos (black)
157
plate reader artifacts?
intermittent appearance of extraneous line patterns
158
horizontal white lines may be caused by _____ on ____________ in plate reader
dirt; light guide
159
loading multiple IP's in 1 cassette can cause what?
ghosting
160
what specific problem can cause a moire pattern plate reader artifact?
grid orientation (if grid lines II to plate reader's scan lines --> grid lines SHOULD be perpendicular to plate reader's scan lines)
161
electric charge is briefly stored in ______ until readout (in both systems)
TFT
162
DR systems use ____________________ to absorb rad & converts the energy into electrical signals which are temp. stored in TFT (constituting the latent img)
flat panel direct capture detector
163
line spread f(x) is largest for ___________ and least for __________
screen-film mammo; a-Se digi mammo
164
what eliminates distracting white/clear areas?
shuttering
165
what is the data recognition program?
searches for the anatomy on the IR by finding the collimated edges and eliminates the scatter outside the coll.
166
what happens if the data recognition program fails to find the coll. edges?
incorrect data collection --> img will be too bright/dark
167
what is generated from the img data collected from CR sampling?
histogram
168
what ID's all densities on an IP in form of a graph?
histogram?
169
what is on the x- and y-axis of a histogram?
x: amount of exposure read
y: # of pixels for ea. exposure
170
the shape of a histogram is _________? and ______________ per part exposed
anatomy specific; stays fairly constant
171
Nyquist theorem?
when sampling a signal (ADC), sampling frequency must be greater than twice the bandwidth of the input signal (so img reconstruction nearly perfect)
172
3 conversions that cause loss of detail (or - res) in CR
1. e- --> light
2. light --> digi info
3. DAC
173
when _________ is greater than Nyquist frequency and ______ occurs less than 2x's/cycle --> info is lost and a fluctuating signal is produced (called?)
spatial frequency; sampling
| wrap around image
174
wrap around img is? causing what kind of artifact?
2 superimposed img's slightly out of alignment (from spatial freq.>Nyquist freq.; samplings/cycle); causes moire artifact
175
what states that at least 2x's the # of pixels needed to form the img must be sampled to combat the loss of resolution?
Nyquist theorem
176
CT/MRI have a dynamic range of what?
12 bit dynamic range
177
Digi Mammo has what dynamic range?
16 bit
178
img noise limits ______ resolution
contrast
179
spatial res. (img detail) is determined by?
MTF (sm better)
180
contrast res. is determined by?
noise and SNR (bigger SNR better)
181
Dose creep?
digi is capable of - pt dose by 20-50% but bc tech's tend not to use optimal exposures, pt's dose actually + w digi
182
higher DQE means what?
less rad required to make img
183
Out of DR, CR and film, which has highest and lowest DQE?
highest DQE - DR
| lowest DQE - film
184
the _____ has higher sensitivity for rad & much wider dynamic range than screen-film IRs
CCD
185
2 types of indirect conversion systems?
CsI/CCD and CsI/a-Si
186
_______(contrast/spatial) resolution is more important for soft tissue radiography
contrast
187
imaging system spatial resolution is spatial frequency at ________
10% MTF
188
with increasing spatial frequency, img ____ worsens in radiography
blur
189
output hardware?
devices that translate comp info into a form ppl understand (i.e. display screens, printers)
190
input hardware?
devices that convert data into a form comps can use (i.e. keyboards, mice, fax, scanners, etc)
191
_______ allows visualization of all shades of gray
postprocessing
192
spatial res. in screen-film radiography is determined principally by?
focal-spot size
193
_________ is preserved in digital imaging, regardless of dose
contrast res.
194
___________ should replace dose creep.
technique creep
195
pt dose in DR should be _____ bc of high _____
low; DQE
196
the ____ XR beam has lower energy than the _______ XR beam
scatter; primary
197
7 factors that affect contrast resolution?
1. IR size (sm better)
2. coll. (+ better)
3. overexposure ( - contrast)
4. dynamic range/Hounsfield units (+ better)
5. bit depth (+ better)
6. SNR (+ better)
7. Acquisition Error - incomplete charge transfer (electronic noise/memory artifact)
