Test 4 Flashcards
(388 cards)
1
Q
What is a digital image
A
any imaging process that creates an electronic image that can be viewed and manipulated on a computer
2
Q
digital vs traditional
A
no more physical film just digital and can be manipulated after exposure
3
Q
when was the first digital manipulation of angiography
A
1977
4
Q
when did it become common to use digital manipulations
A
1980
5
Q
when was the first computerization of CT and ultrasound
A
1970-1990
6
Q
what helped change radiography to digital? what were the changes?
A
insurance requirements pushed
change: film to digital allowing film processing systems
7
Q
what is concerned as digital radiography
A
computer radiography and direct capture radiography
8
Q
what do cassette based systems use?
A
traditional type film
imaging plate stimulated by phosphors and storage
9
Q
what uses cassette based systems
A
computed radiography
10
Q
what is indirect digital
A
radiographers have to move imaging plate
11
Q
is cassette based systems indirect digital? cassette-less?
A
yes
no –> direct digital
12
Q
what is direct digital
A
detector and reader are permanent part of table or wall unit
13
Q
why are detectors important for direct digital
A
small detectors = active matrix array = enhanced contrast resolution
14
Q
where is the matrix visible in
A
IR and monitor
15
Q
what forms a matrix
A
digital image acquisition
numerical values stored in the computer’s memory
cells in each row and column
16
Q
what is a pixel
A
picture element –> each cell in the matrix
17
Q
how do we improve digital image quality
A
larger matrix size
18
Q
what does a large matrix size give better images
A
more smaller pixels within matrix = more contrast
19
Q
what is the smallest element in matrix
A
pixel
20
Q
how does a pixel work
A
each pixel assigned single number to represent brightness by location in matrix
21
Q
what does a pixel correspond to
A
area of patient’s tissue
22
Q
what is an analog image
A
captures or measures continuously changing signals
23
Q
what does analog signals control (3)
A
level of brightness
shapes
colors
24
Q
difference between analog and digital
A
analog:
- xray enters IR in analog form and converted into digital
- single sample exposure
digital:
- records as multiple numeric values and divides into several small elements to be process in many ways
- multiple sampling
25
how does an analog system convert to digital
xray energy --> light waves
26
how does a digital system produce an image
analog signals --> numbers
27
what controls digitizing data? how?
pixel values limits number values --> difference between white and black
28
why do we want a limited digitizing data set?
for pre-set pixel values --> contrast
29
what does a analog-to-digital converter (ADC) do
digitizes incoming analog data
30
Steps for digitizing an image
scanning
sampling
quantization
31
what is scanning
the field of the image divided into a matrix of small cells
32
how does scanning work
it detect activated cells (pixels) through detector to make up initial matrix
ex. collimator
33
what is sampling
detection and measurement of signal intensity coming into the system from each pixel location
34
what controls sampling? pro?
mAs controls each pixel = better contrast
35
what is quantization
leveling out brightness level for each pixel to nearest available gray level in preset dynamic level
36
why is quantization vital?
compares given data to move/fix to preset values
37
what is dynamic range
range of pixel values (shades of gray) available from computer system (hardware/software) to create final digitalized image
38
limitation of dynamic range? pro?
control: subset of bit depth of system
pro: allows image manipulation
39
what is a subset of dynamic range
grayscale (displayed image) --> contrast
40
what is pixel bit depth
- max range of pixel values that computer or hardware can store
- number of bits within a pixel
41
what is the number of gray tones within a pixel
2 to the power of bit depth
42
what does gray level determine
image contrast resolution
43
____ grayscale = ____ constrast = _____ pixelation
more
more
less
44
spatial resolution
distinguishes one dot between another dot
45
what determines the size of a pixel
size of matrix
46
____ pixel = ___ detail
smaller
greater
47
size of pixel is directly related _____
amount of spatial resolution or detail in image
48
which number of pixels in a matrix is better?
1024 x 1024 or 16 x 16
1024 x 1024
49
what is attenuation coefficient
% or ratio of original xray beam intensity absorbed by each different type of tissue area within body
50
what does attenuation coefficient create
3D projection onto 2D IR
51
voxel
volume of tissue to pixel
averaged by dexel
52
dexel function
rounds average attenuation coefficient to nearest preset value in dynamic range
53
imaging chain of events
1. patient placed between Xray source and IR
2. technique and geometric factors selected
3. capture image and latent image is formed
54
how is a latent image formed?
an invisible image is created from the remnant beam altering the atomic structure of photostimulable phosphors
55
what are the types of digital radiography
digital radiography (DR)
computed radiography (CR)
56
types of DR conversions
direct
indirect
57
difference between DR and CR
DR: IR directly connected to digital processor electromagnetically
uses TFT
CR: uses PSP
58
what is a AMA? what does it contain?
active matrix array
flat panel with thousands of individual dexels
59
what is the main component of all DR detectors
AMA
60
what is the size of one dexel
100 microns square or 1/10th of a pinhead
61
what material is the detection surface of a dexel made of in Direct DR
amorphous selenium
62
why is amorphous selenium good
high absorption efficiency for xrays
63
how does a AMA work in direct DR
converts remnant beam directly into electrical charges for computer to read
64
3 components of dexel
radiation-sensitive detector surface (a-Se)
thin-film transistor (TFT)
small capacitor
65
function of radiation-sensitive detector surface (a-Se)
semiconductor sensitive to xrays (direct) or light (indirect)
66
function of TFT
individual switch for each pixel to change states on/off quickly
67
function of capacitor
stores electrical charge
68
function of amorphous selenium
converts xray energy to electrical charge
69
what does ionization of selenium produce? what ionizes selenium?
electron hole pair (+)
dexel electrode (-)
xray ionizes
70
direction of electrical charge movement in direct DR
+ moves down toward dexel electrode and stored in capacitor
- moves up to be collected and drained off
71
types of wires in AMA in direct DR
gate lines
data lines
72
gate line function
reads out information on exposed DR detector by changing bias voltage from -5 to +10 volts
73
data line function
sudden change in gate line = electricity flow and charge stored up in capacitor flows to data line
74
what material is indirect detector dexel made of?
amorphous silicon
75
indirect vs direct AMA
indirect: has phosphorescent screen (aka scintillator) laid over AMA
photodiode (a-Si)
direct: photoconductor (a-Se)
76
function of phosphorescent screen
phosphor converts xray into light --> light goes to hit AMA
77
how does AMA work in indirect DR
remnant beam hits phosphor screen to fluoresce (visible light) when exposed
then same process as direct DR occurs
78
difference between DR and CR
DR uses TFT
CR uses PSP plate
79
function of amorphous silicon
high absorption efficiency of visible light
80
components of CR
cassette
processor (CR reader)
IR --> PSP plate
81
construction of cassette
material: plastic
memory chip in corner for patient/procedure information
82
components of PSP plate (7)
front protective layer
phosphor layer
reflective layer
electroconductive layer
polyester base layer
light-shielding layer
back protective layer
83
function of protective layer and material
function: protects PSP from mechanical damage
material: low absorbing carbon fiber
84
function of phosphor layer
active layer containing europium activated barium fluorohalide (phosphor)
85
function of reflective layer
reflects emitted light photons towards photomultiplier tube during scanning (NO INTERACTIONS OCCUR)
86
function of electroconductive layer
prevents static build up --> no artifacts on image
87
light shielding layer
prevents extra light from erasing later before its scanned
88
what material would stimulated phosphorescence occur
barium fluorochloride and barium fluorobromide
89
why use barium fluorochloride and barium fluorobromide
contains defects (metastable sites) in crystals to trap free electrons in, when ionized
90
ability of metastable sites
traps free electrons and store them until excitation occurs to release electrons
91
steps for CR processing
PSP removed from cassette by processor --> scanned by helium-neon red laser beam moving across plate to index down one row at a time
92
what occurs during scanning with red laser beam
metastable sites activated by electromagnetic energy to emit dim light --> image electronically amplified to be displayed
93
what is fluorescence and example
immediate emission of light by substance under some type of stimulation
ex. xray exposure of phosphor plate
94
what is phosphorescence and example
delated emission of stored energy in the form of light
ex. laser beam
95
what occurs in CR reader (processor)
PSP plate pulled by suction cups and rollers --> fast scan and slow scan
96
what occurs in fast scan
laser beam is deflected off rotating mirror to scan across PSP plate
97
what occurs in slow scan
rollers are used to direct/move PSP plate
98
what determines pixel size in DR and CR
DR --> IR size
CR --> defined during processing
99
fast scan controls?
pixel width
100
slow scan controls?
pixel length
101
what prevents distortion in CR
equal frequency in fast/slow scan
102
what occurs during erasing process
after scanning --> PSP plate moved by rollers into eraser section
PSP plate exposed to intense white light --> removes remaining information
plate reloaded and ejected from machine
103
cons to PSP plate
very sensitive to background radiation --> prefogging
1mGy = noticeable fog
FIX: always erase before use
104
difference between scatter and background radiation
background: can change how image is processed
scatter: can be corrected during processing
105
what are characteristics for image quality? (5)
brightness
grayscale (contrast resolution)
noise
spatial resolution (sharpness)
distortion
106
what characteristics is classified as visibility
brightness
grayscale
107
what characteristics is classified as sharpness
resolution
distortion
108
what determines the overall quality of a radiographic image
visibility
sharpness
109
what is a photographic property? Geometric property?
P: visibility
G: sharpness and distortion
110
what is brightness
luminous intensity of the display monitor's light emission
111
what does brightness measure
amount of light emission of a display monitor
112
if an image is too light....
excessive brightness to allow visualization of anatomic structures
113
if an image is too dark...
insufficient brightness and anatomic part cannot be seen well
114
is brightness and IR exposure related? why?
no brightness is a monitor control that can change lightness and darkness of an image on a display monitor
115
what controls brightness
window leveling and technique
116
what is brightness measured in? (unit)
candela
117
how does adjusting window level affect brightness
changes average gray level --> center gray shade on dynamic range
118
what occurs if window leveling is unchanged
average brightness level is uncahnged
119
how can we change brightness without changing window leveling
minimum change of mAs by 30%
120
which post processing method is preferred and why?
window leveling because window width has a narrower dynamic range which can cause misdiagnosis and potential legal issues
121
what does window level correspond to?
pixel value
122
increasing level = _______ image
decreasing level = ______ image
darker
brighter
123
what occurs during underexposure
exposure to IR is too low for anatomic area
124
what effect would underexposure cause
excessive quantum noise
125
what effect would overexposure cause
saturation --> super black and white
126
what does an exposure indicator provide
numeric value indicating level of radiation exposure to digital IR
127
when does dose creep occur? issue?
lack of attention to wide dynamic range
issue: overdosing patient
128
why is digital IR bad?
allows exposure errors to occur --> wide range of IR exposures = dose creep
129
what is contrast resolution
ability of digital system to display subtle changes in shades of gray
130
contrast resolution is directly related to what?
bit depth of pixels
131
high contrast resolution = ?
enhanced densities
132
what is grayscale also known as?
image contrast
133
how is grayscale represented?
percentage or ratio of differences between IR exposures
134
what does grayscale measure
differences of clear white through varying shades of gray to black
135
what does grayscale affect
visibility of detail on displayed digital image and differences between IR exposures
136
what does dynamic range describe
describes contrast concept displayed and is a characteristic of overall image system
137
what is dynamic range
the range of brightness of display monitor light emission
138
what does dynamic range represent? limited by?
number of shades of gray
Limited by computer system
139
what is actual dynamic range
max number of shades of gray represented by numeric range of each pixel or bit depth
140
what does actual dynamic range represent
capabilities of the overall system
141
can the actual dynamic range be less than bit depth
yes
142
what does bit depth represent?
hardware components
143
what is high contrast
difference between adjacent IR exposures that greatly affect contrast
144
how does high contrast affect images
less varying grays
145
high contrast is also known as?
short scale
146
what is low contrast?
differences between adjacent IR exposures are minimal
147
how does high contrast affect images
more various shades of gray
148
low contrast is also known as?
long scale
149
what is the primary method to adjust display contrast?
window width
150
does kVp and mAs affect grayscale?
no because image processing will correct
151
how does the system adjust the grayscale
Histogram (linear range algorithm) and look up table (LUT)
152
what does the look up table do? affect on image?
provides proper grayscale
consistent image
153
what is on the look up table
stored data to sub new values for each pixel during processing
154
look up table limitations?
needs correct histogram selection
cannot compensate exposure values outside normal range
155
what is window width
range of pixel values thats incorporated into display width
156
increasing window width = _______ contrast
lower
157
decreasing window width = _______ brightness
increase
158
what is subject contrast
range of difference in intensity of xray beam after being attenuated by subject
159
how does subject contrast occur
differential absorption
160
what is subject contrast dependent on
kVp
amount and type of irradiated material
161
what is the primary controller of subject contrast
kVp
162
if kVp adequate
low kvp = _____ subject contrast
high
163
what is the easiest way to improve contrast
use collimator
164
is contrast same throughout the whole body?
no because of difference densities
165
what do radiologist want on images
uniform contrast
166
can mAs compensate for inadequate kVp
no use 15% rule
167
factors that affect final displayed image contrast/grayscale
look up table
kVp
mAs
168
how can final displayed image contrast/grayscale be altered
window width
169
what is the final displayed image contrast/grayscale mainly affected by
look up table
170
collimation affects?
contrast
patient dose
171
negatives of noise
interferes with formation of image
no useful diagnostic information
172
what type of noise is there? (4)
anatomic
radiographic
equipment
quantum (mottle)
173
what is signal to noise ratio
the strength of radiation exposure compared with amount of noise apparent in digital image
174
why is SNR important
it shows how much noise can be tolerated in an image
175
how to improve image quality with SNR? con?
increase SNR (higher signal) --> less noise
CON: increases patient dose
176
how do we get quantum noise?
little xray photons reaching IR to reach latent image
177
what other factors can cause mottle? (3)
materials such as:
IR
electrical current
computer algorithms
178
ways to lower noise to best capabilities
why do we do this?
set appropriate target exposure value (IE#)
routine monitoring
avoid exposure creep
179
what is considered appropriate exposure value
image production with acceptable noise level without excessive or unnecessary exposure to the patient
180
optimal image = ______
may not be the best image
181
spatial resolution is also known as?
definition
sharpness
recorded detail
182
spatial resolution in relation to a system
ability for system to show small details of an object
183
how do we know that we have good spatial resolution
dots are very distinguishable between each other
184
what does spatial resolution control
detail or sharpness of structural lines
185
what is considered as a geometric property
spatial resolution
distortion
186
what is spatial resolution
the degree of geometric sharpness or accuracy of structural lines actually recorded in a image
187
what is spatial frequency
digital imaging recorded detail based on frequency of wavelength
188
what is high spatial frequency?
Pros?
high frequency with shorter wavelength
signal pair of lines are closer together
high resolution
better for smaller objects
189
what is low spatial frequency?
Pros?
low frequency long wavelength
signal pair of lines are further apart
low resolution
better for larger objects
190
what determines sharpness?
matrix size
pixel size
grayscale bit depth
191
how is sharpness measured? (4)
point spread function (PSF)
line spread function (LSF)
modulation transfer function (MTF)
system noise
192
what is sharpness
characteristic of final displayed digital image
193
what is MTF
modulation transfer function
trueness or fidelity of an image
194
what does MFT measure
accuracy of image compared to original object (scale 0-1)
percentage of object contrast that is recorded
195
if MFT is 0 ....
no image --> no signal
196
if MFT is 1....
perfect exactness
197
if spatial frequency increases = MFT _____
decreases
198
what does detective quantum efficiency (DQE) measure?
efficiency of IR in converting xray exposure it receives to quality radiographic image
199
if we have 1.0 DQE what does that mean?
no information lost during conversion --> 100% DQE
200
higher DQE = _____
decrease radiation exposure/patient dose
201
factors affecting spatial resolution in order
eliminate motion
reduce OID --> affected side close to IR
reduce focal spot size --> penumbra
increase SID --> use 46" instead of 40"
202
what is distortion? types?
misrepresentation of size or shape of the structures examined
TYPES: size and shape
203
how can we tell if something is distorted?
by understanding normal radiographic anatomy
204
what property is distortion? what does it affect?
geometric
affects image quality
205
what are factors that affect size distortion
magnification --> SID and OID
post processing --> resizing images
206
to control magnification we want.... SID/OID
maximize SID
minimize OID --> further away = increase mag
207
_____ magnification = _____ spatial resolution
decrease
increase
208
what is the main effector of magnification
SID --> source-IR
209
longer SID = ____ magnification
shorter SID = ____ magnification
decreases
increases
210
given spine or chest exam what would we use for SID
large SID whenever possible
211
objects _____ to IR = _____ magnification
closer
decreases
212
magnification factor?
M = SID/SOD
213
what does magnification radiography do? how?
enhances visualization of small structures by purposely increasing OID while keeping SID constant
HOW: use magnification factor
214
when would magnification radiography be uses
interventional radiography
mammography
215
Pros and cons of magnification radiography? Fix for con?
PRO: no grid necessary
CON: increased patient dose and decrease in image detail/spatial resolution
FIX: use small focal spot to reduce loss of image detail
216
what is shape distortion
misrepresentation by unequal magnification of actual shape of structure examined
217
how does shape distortion occur? how is the degree of distortion determined?
object plane and image plane are not parallel
Determined: object's angle of incline and lateral position from central axis
218
how to reduce shape distortion?
making body part and IR parallel with CR perpendicular
219
factors that affect shape distortion
object thickness
object position
object shape
220
types of shape distortion and affect
elongation --> longer than it really is
foreshortening --> shorter than it really is
221
thick object = ____ OID = ______
increased
increased distortion
222
how do we get elongation effect
tube angle or IR is improperly aligned
223
how do we get foreshortening effect
body part is improperly aligned
224
what is spatial distortion
misrepresentation in image of the actual spatial relationships among objects
225
how do we get spatial distortion
when object positioned shifted laterally from CR
226
how do we fix spatial distortion
by getting 2 or more projections to get more 3D examination
227
do we ever want distortion?
Yes --> controlled distortion
removes superimposition by tube angulation
228
what does conventional film measure
how much chemical changes occurred within exposure through ionization
229
conventional vs digital processing
conventional: development, fixing, washing and drying
digital: pre/post processing
230
what does digital film measure
how much electrical charge is built up within exposure
231
digital imaging is recorded as what?
pixel values
232
preprocessing steps (4)
Field uniformity corrections
Noise and del drop-out corrections
Image and histogram analysis
Rescaling (processing)
233
what is preprocessing
all computer operations that compensate for flaws in image acquisition
234
what is preprocessing also known as
basic image acquisition
235
postprocessing steps (3)
gradation processing (LUTs)
detail processing
preparation for display
236
what is postprocessing
customized refinements specific to radiographic procedure
237
what is postprocessing also known as
specific anatomical procedure
238
displayed image steps (2)
operator adjustments
application of special features
239
what is segmentation? pre or post processing?
when 2 or more images are taken on the same PSP plate and the computer but segment/separate the images out
PREprocessing
240
what is segmentation failure
computer's inability to segment or separate individual exposure areas
241
does segmentation failure occur on all systems?
No --> DR systems sent directly to computer after each exposure
242
what is correcting for dexel dropout? pre or post processing?
computer scans for dead pixels through noise reduction software (kernel)
PREprocessing
243
what are dead pixels
dexel areas that did not receive enough data due to electronic failure
244
what is interpolation
noise reduction software (kernel) reads and averages pixel values surrounding dead pixel and inserts the relative number into dead spot
245
correcting for mottle types? pre or post processing?
quantum mottle (random)
electronic mottle (periodic)
PREprocessing
246
what is quantum mottle? How is it fixed?
occurs from xray beam being randomly distributed (Poisson distribution)
FIXED: kernel
247
what is electronic mottle? How is it fixed?
occurs in consistent size and intervals (forms pattern)
FIX: filtering algorithms (frequency processing)
248
can we avoid noise? which type of mottle is the worst?
no it is unavoidable
electronic mottle --> severe mottle is impossible to distinguish
249
what is field uniformity? pre or post processing?
electronic amplification (computer software) used to compensate for areas that are outside the range of uniformity
PRE processing
250
why do we need field uniformity?
all digital system have flaws in receptor system --> uneven distribution of background density of image
251
what helps field uniformity
anode heel effect partially compensates
252
what does histogram display? pre or post processing?
bar graph representing brightness value of each pixel
PREprocessing
253
how do you read a histogram?
left to right --> light to dark
histogram shape displays each body part
254
how to make a histogram
count is made up of all pixels sharing the same pixel value (density/brightness) in dynamic range
255
what is histogram analysis? pre or post processing?
elimination of extreme data that skews the rescaling of image so that it is not too light or too dark --> identifies useful pixels
PREprocessing
256
how does histogram analysis occur?
computer compares actual histogram from exposed image to expected histogram for that specific procedure
257
what is exposure field recognition? what type of preprocessing is it apart of?
identifies field as "false" densities to not overcompensate --> keeps collimation tight
histogram analysis
258
what types of histogram analysis is there? how do we choose which type to use?
type 1, type 2, type 3
select procedure from computer menu that auto assigns which type to be used
259
what does type 1 analyze? ex?
analyzes two lobe histograms with tail spike in background densities
ex. chest
260
what does type 2 analyze? ex?
analyzes single lobe histograms
ex. AB or extremities
261
what does type 3 analyze? ex?
analyzes three lobes with some metallic metal present
ex. contrast exam
262
cons in histogram analysis (5)
segmentation errors
fail to match histogram to actual image taken
patient with prosthetic or lead appears in collimated area
pre-fogging of IR from background radiation
LARGE amount of scatter radiation
263
what is normalizing an image
overall brightness of image and degree of grayscale/contrast are manipulated mathematically until it has a normal appearance to a conventional radiograph
264
what is a rescaled image that has undergone post processing
normalized image
265
why do we want to have a normalized image
rescaling gives ideal level of brightness and balanced grayscale regardless of technique
266
what is the primary goal of RAD technique
give enough signal to reach IR so computer can successfully process
267
will digital processing always produce a diagnostic image?
almost always --> fails only under extreme/unusual circumstances
268
what are Q-values
standardized labels assigned with preset pixel values that represent certain brightness levels for pixels
processed data
269
how can rescaling be done?
electronically or with software (most common)
270
what are S-values
data that has not been rescaled
271
how does the computer rescale images
computer program gets S-values and reassigns them as Q-values --> places into permanent LUT
272
is there anything that can affect the rescaling process? why?
no --> regardless of incoming pixel values --> output pixel values are always adjusted to same output Q values set by permanent LUT
273
why is rescaling important? limitations?
align image brightness levels perfecting
Limitations: can only align overall image grayscale partially because of min/max Q values
274
how is an anatomical LUT set?
when tech selects radiographic procedure from menu on xray console
275
what are the 3 adjustments made to a histogram before displaying image?
histogram analysis --> selects useful pixel values of interest
rescaling to fit average histogram for body part and fixes small exposure errors
LUT --> gives image correct amount of brightness and contrast
276
types of digital processing domains (3)
spatial location
shade (intensity)
size (frequency)
277
where does an image begin and end in?
spatial location domain
278
what are the subdivisions of spatial domain (3)
point processing operations
area processing operations
global operations
279
what does spatial domain deal with
pixels acted upon depending on their location in the matrix
280
what operations does spatial domain include? (5)
magnification
translation (flipping)
inversion (flopping)
image subtraction
all kernel operations
281
what does point processing do? ex?
performs a specific algorithm on each individual pixel in sequence ---> pixel by pixel
ex. image subtraction
282
what is image subtraction? ex?
values in each specific pixel is subtracted from the value in the corresponding pixel from another image by comparing non-contrast and contrasted images
ex. angiography --> mask image subtracted from contrast image
283
what does area processing do? ex?
area/local processing operations use mathematical function on subsection of image
ex. magnification
284
how do you magnify an image? what occurs?
select portion of image and zoom
value of each single pixel spreads out across 4 hardware pixels
285
what does global operations do?
all image reorientations across matrix --> inversion, flipping, or translating
286
what is translation?
switches corresponding columns' pixel values except for the middle column
287
what is shade/intensity domain deal with
operates on pixel values --> brightness or darkness
288
what does size/frequency domain deal with?
the number of pixels per row in matrix
289
what operations are in shade/intensity domain? (3)
windowing
construction of original histogram
histogram analysis
290
low frequency are for...? wave?
large objects/details
long waves
291
high frequency are for...? wave?
small details
short waves
292
does size/frequency domain alter?
structures or objects within images
293
how does size/frequency domain occur
identify object --> sort and group by size into binds
294
detail processing operations (4)
smoothing
edge-enhancement
background suppression
local contrast of only fine details
295
purpose of gradation processing? pre or post processing?
edit final image brightness and contrast based on anatomy and predominant pathologies displayed
post-processing
296
what does a gradient curve describe
brightness and grayscale relating to IR
curves superimpose over the histogram
297
high gradient = ____ contrast = _____ curve
high
steep
298
low gradient = ____ contrast = _____ curve
low
steadier incline
299
body of each curve represents?
range of exposures
300
how to read gradient curve graph
average brightness level --> left to right
contrast level --> curve slope
301
windowing controls?
brightness and contrast (grayscale)
302
when is gradation processing used? using?
on every image before displayed
uses LUT --> look up table
303
window width controls?
window level controls?
grayscale
brightness
304
when does data clipping occur
when either bit depth of hardware/dynamic range of the system are too limited to allow for windowing adjustments
305
why is data clipping bad? fix?
limits radiologist's ability to window the image = misdiagnosis
FIX: do not save before sending to PACS
306
why does data clipping occur?
pixel values too large for dynamic range or computer system --> pixel values/data lost because values too dark for system to handle
307
what is dynamic range compression (DRC)
removal of darkest and lightest extremes of pixel values from grayscale
308
why is DRC better than data clipping?
allows windowing
saves computer space by eliminating unneeded data that human eye cannot identify
adjusts grayscale to be within dynamic range without removing data
309
what soft tissue adjustment to technique is used? why?
film screen --> 20% kVp and no mAs change
lightens image
less penetration to tissue --> increased differential absorption
lightens bones
310
how does the computer adjust to soft tissue techniques? (digital imaging)
rescales and adjust images based on LUT
uses dynamic range compression to equalize tissue/contrast and control dynamic range
311
what does detail processing do
selects structures in images based on size and singled out for contrast enhancement or suppression
312
how does detail processing affect very small details?
contrast increased so it can stand out more
313
how does detail processing affect mid-size structures
image suppressed = contrast decreased
moves structure into background
314
how does detail processing work? (4 steps)
digital algorithms fix fine details of image separately
image sorted by size of object and into own file/bin
alters contrast/brightness of each individual object
separates local contrast from global contrast so fine details are more visible but whole image has about the same amount of contrast
315
pixel waveform represents?
alternating densities
316
pixel waveform
peaks =
dips =
black (darkest) pixels
white (brightest) pixels
317
zero point of each individual wave corresponds to?
transition border between each pair of pixels
318
wavelength of each pulse represents?
pixel size
319
smaller pixels = ____ frequency
higher
320
how to read frequency on display monitor
left to right
number of up/down cycles = distance
321
each cycle = _____
each pulse = _____
2 pulses
1 pixel
322
given 300 cycles
how many pixels are there?
600 pixels
323
frequency of objects correlate to?
number of pixels that occupy in each row
324
large objects = ______ wavelengths = ____ frequency
large
low
325
why do large objects have low frequency
fewer photons to fit across the screen
326
small objects = ____ wavelengths = _____ frequency
short
high
327
waveform interpretation
amplitude =
wavelength =
tall waves =
wide waves =
gray level/pixel value
number of pixels in object across the row (laterally)
darker object
larger object with more pixels occupying row
328
tall skinny spike in wave =
dark and small object
329
what is fourier transformer
mathematical process that allows frequency processing to separate structures according to size
330
how does fourier transformer work?
it breaks up complex waveforms into component waves (long, medium and short) based on pulses with different wavelengths
331
what does wavelengths represent in fourier transformation
different sizes of objects or structures in one row in image
332
what is multiscale processing?
Decomposition of original image into 8+ frequency layers to perform various operations on selected individual layers and recomposing the image
333
how does multiscale processing determine splitting the layers
repeatedly splits into high frequency component and low frequency components and so on until there are 8+ levels
334
how does multiscale processing end?
completed image laters are put back together using inverse fourier transformation = final image
335
what is filtering in multiscale processing
selected layer is left out when reconstructing final image
336
when is band-pass filtering used
noise reduction --> electronic mottle
337
what does low pass filtering do
an algorithm passes through low frequency layers
338
most common filter? what does it do? con?
smoothing function
removes noise from image
losses some fine detail
339
what does high pass filtering do? aka?
passes through highest frequency layers
edge enhancement
340
what does background suppression do
eliminates very lowest frequencies
341
how does image domains transition?
spatial --> intensity --> spatial --> frequency --> spatial = final image
or
spatial to frequency or intensity then spatial whatever is needed
342
why is the intensity domain important for image transition
histogram analysis and gradation processing
343
why does it go back to spatial domain to go to frequency domain?
frequency detail processing needs spatial domain in order to put reconstructed pixels back into the spatial matrix
344
example of submatrix?
kernel
345
what is a submatrix
a small matrix passed over a larger matrix of the whole image --> changes all of the pixel values mathematically
346
how does kernel move?
left to right along row and moves down to repeat
347
what is equivalent to frequency detail processing?
spatial detail processing
348
what does spatial detail processing affect? (4)
smoothing
noise reduction
edge enhancement
background suppression
349
what is a pro about spatial detail processing?
uses kernels to affect image --> no need to transition between domains
350
What is the imaging cycle in order?
exposure --> histogram --> permanent LUT (rescaling) --> anatomical LUT (gradation) --> default detail processing --> displayed image
351
can you alter a procedure algorithm? How?
yes by selecting an alternate histogram or altering window settings (brightness and contrast)
352
why would we select an alternate histogram? Con?
gives wider grayscale
CON: histogram errors, image storage issues, record-keeping and legal liability
353
when should we select an alternate histogram?
when approved by radiologist
354
window leveling corresponds with .....?
brightness
355
window level is also known as?
brightness
center
density
S number
356
increase brightness = _____ window level
decrease
357
window width corresponds with ....?
grayscale
358
does window width alter brightness or density?
no
359
wider window = _____ grayscale
longer
360
increase contrast = ______ window width
decrease
361
what does smoothing remove? con? overall effect?
removes highest frequency layers
CON: removes some shades of grey/fine details
Effect: edges are softened
362
how does smoothing occur?
noise reduced by mathematical interpolation --> averages pixel values of white/black specks (corrects for dead dexels)
363
what type of postprocessing feature do you use to correct for moderate amounts of mottle? Can it be used for severe mottle?
smoothing
no --> extreme underexposure cannot be corrected
364
what is the best method to alternate procedure algorithms?
alter windowing settings
365
what type of postprocessing feature do you use to better visualize small details? How?
edge enhancement --> increases contrast
366
con of edge enhancement
increases noise and possible loss in detail
367
what type of postprocessing feature do you use to better visualize specific tissues (ex. fat pads)?
background suppression
368
how does background suppression occur?
Algorithms reduce contrast of larger mid-frequency and low-frequency structures
369
targeted area brightness correction effect? how?
percentage of tissue equalization by correcting brightness of specific portions of the image
370
what type of postprocessing feature do you use to allow more diagnostic area in an image
targeted area brightness correction
371
what type of postprocessing feature do you use to visualize bones as black?
image reversal
372
how does image reversal occur?
all pixel values are swapped --> high = low and low = high
373
does image reversal create new information?
no improvement --> negative image turns to positive image
374
color of bone in negative image and positive image
neg: white
positive: black
375
what type of postprocessing feature do you use to fix vale glare?
dark masking
376
what does dark masking do? when to use?
image is cropped so that the white border (from suppression error) turns into black border
WHEN: before sending image to PACS
377
what type of postprocessing feature do you use to correct an upside down image? how?
image orientation
HOW: rotating or flipping image
378
method types of magnification
zoom technique: magnifies entire image
Magnifying glass: magnifying box placed over anatomy
379
con of magnification
creates pixelation
380
what type of postprocessing feature do you use for elongated anatomy (ex. long bone or spinal imaging)
image stitching
381
how does image stitching occur?
computer software uses grid to superimpose, crop, and combine multiple images to one image
382
what type of postprocessing feature do you use to identify lesion or fracture locations
dual-energy subtraction
383
how does dual-energy subtraction affect image
separates image to tissue or bone only image
384
how does the dual-energy subtraction occur?
high energy (kVp) and low energy (kVp) obtained and computer compares images to identify xray absorption drop = soft tissue areas --> allows image reconstruction
385
what type of postprocessing feature do you use to remove grid lines? when does this occur?
grid line suppression
WHEN: using stationary grids --> portables
386
how does the computer remove grid lines
frequency processing identifies lines as large structures with low frequency
387
collimating pros for computer system?
reduces failure of system to find collimation edges
reduces incorrect data collection
reduces extremes in image brightness/darkness
388
pros of proper anatomy centering
ensure appropriate densities can be located
reduces extremes in image brightness/darkness
