Physics Test 1 Flashcards
(156 cards)
1
Q
Decreasing scatter radiation reaching the film, does what to pt. exposure and image resolution/detail/quality?
A
Decreases pt. exposure
increases image resolution/detail/quality
2
Q
what type of patient increases scatter
A
thicker
3
Q
before scatter reaches the patient, what factors reduce scatter reaching the image receptor?
A
collimation, cones & cylinders, grid, decrease kvp.
4
Q
as kvp increases, the likelihood of a photoelectric effect…
A
decreases
5
Q
what are some important components of film?
A
base
adhesive layer
emulsion
protective layer
6
Q
what is the purpose of the base layer in film?
A
-support
dimensional stability
lucent
often polyester
7
Q
emulsion is considered what type of layer?
A
active
8
Q
what are the different layers of alternative image receptors?
A
backing base reflective layer photostimulable phosphor protective layer
9
Q
what does the photostimulable phosphor consist of?
A
barium fluorohalide crystals coated with europium.
10
Q
gelatin and silver halides in film emulsion are made of what?
A
silver bromide and silver iodide.
11
Q
what formation are halides typically in today?
A
tabular grain
12
Q
what is the sensitivity speck?
A
(silver sulfide) introduced near surface of crystal structure. It attracts photoelectrons and silver ions during exposure.
13
Q
What is the reciprocity law?
A
Image density remains the same as long as you use the same mAs, regardless of combination of mA and time.
14
Q
what type of exposure does the reciprocity law ALWAYS hold true?
A
direct exposure
15
Q
when does the reciprocity law fail?
A
for exposure of film from screens at time extremes. Very long or very short exposures.
16
Q
What are some specialty films?
A
mammo
laser
duplicating film
cine film
17
Q
mammo
A
single emulsion, designed for use with single screen (load cassette with emulsion in contact with screen)
18
Q
laser
A
use in laser printers, now with many modalities
19
Q
duplicating film
A
designed for exposure by white light, for copying traditional images- single emulsion
20
Q
cine film
A
like movie camera film
21
Q
Direct or screen exposure, which is the slowest system?
A
Direct exposure.
22
Q
Direct exposure results in:
A
best image quality (recorded detail) at highest patient dose.
23
Q
Screen exposure does what to patient dose, recorded detail and scale of contrast?
A
less patient dose with less recorded detail and shorter scale of contrast.
24
Q
as screen systems get faster, what happens to patient dose and image quality?
A
pt. dose continues to decline along with image quality
25
Within inherent speed, Large grain emulsion is:
typically "faster" thus thicker emulsion
26
Within inherent speed, small grain emulsion is:
typically "slower" thus thinner emulsion
27
For inherent contrast, how is film designed to produce shorter scale contrast?
Smaller halide grains of more uniform size
28
For inherent contrast, how is film designed to produce longer scale contrast?
larger halide grains of more variation.
29
What are some potential problems with film contrast and speed?
Crossover
30
what is crossover?
undesirable image blur caused when light from the screen on one side goes through the emulsion and base to expose the emulsion on the other side.
31
how is crossover reduced?
with tabular grain emulsion since you have a larger surface area, intercepting more of the light photons on the same side as they are produced.
32
for spectral matching, how does the film emulsion need to be designed?
to be sensitive to the light wavelengths produced by the intensifying screen in use.
33
how do tungsten screens produce light?
blue/violet region-use blue sensitive film
34
how do the rare earth screens produce light?
green region- use a film sensitive to these wavelengths- orthochromatic
35
what does improperly matched screen/film result in?
reduced image density
36
the darkroom safe light needs what color filter?
red to be safe with green or blue sensitive film
37
how do you test a safe light of a dark room?
putting film out on darkroom cabinet for periods and then processing
38
exposed or unexposed film is more sensitive to subsequent fog?
exposed
39
what type of device is used to test film resolution?
lp/mm test device (most can record more then the human eye can detect unaided)
40
what are the layers of the intensifying screen?
base
reflective layer
phosphor layer
protective coating
41
what does the base do in an intensifying screen?
support-rugged yet flexible
42
what does the reflective layer do in an intensifying screen?
bounce light back toward film
43
what are some phosphor characteristics?
high atomic number
high conversion efficiency
proper spectral match
minimal afterglow
44
high atomic number (phosphor characteristic)
absorbs more x-rays- creating environment for max PE
45
high conversion efficiency (phosphor characteristic)
lots of light emitted per x-ray absorbed
46
proper spectral match (phosphor characteristic)
emits light in a wavelength range that matches the emulsion sensitivity
47
minimal afterglow (phosphor characteristic)
light emission stops promptly when exposure is terminated.
48
what are two screen phosphors?
```
calcium tungstate
rare earths (gadolinium, lanthanum, yttrium)
```
49
What does the lower atomic number of the elements gadolinium, lanthanum, and yttrium provide?
light absorption advantage for rare earth screens in the energy range between the k-shell binding energies.
50
You get the k-edge jump in the frequency of PE interactions at a what type of energy?
lower- which encompasses lots of dx range- since e' binding energy is lower.
51
which screen phosphor absorbs 5x's more photons and emits more light per photon than the other?
rare earth over calcium tungstate.
52
what two types are luminescence?
fluorescence
| phosphorescence
53
fluorescence
light emitted only during stimulation by x-rays
54
phosphorescence
light continues to be emitted when stimulus has quit
55
how is screen speed expressed?
numerically. higher number, faster screen
56
as screens get faster, do they get thicker or thinner?
thicker
57
with a thick screen some interactions occur farther from the film emulsion, there fore there is more...
blur.
58
image resolution (recorded detail) declines with what type of screen speed?
increasing screen speed.
59
what is a screen intensification factor?
lets you know how patient dose is impacted by that particular screen
60
A screen IF "without" screen
is ALWAYS going to be greater than with screen. So resulting comparison is >1 (greater than 1)
61
the higher the IF, what happens to patient dose?
greater patient dose reduction
62
screens have a higher atomic number than film emulsion so absorption is..
.
63
where are screens mounted on the cassette?
both sides
64
screens must provide good contact and be
light tight
65
quality control for screens
wire mesh test instrument
66
latent image
invisible
67
manifest image
visible
68
where does the latent image convert to manifest in image processing?
chemistry in the processor
69
how does latent become manifest?
electrons released during Compton and photoelectric interactions in the emulsion congregate at the sensitivity speck- causing a region of "negativity"- which then attracts positive silver ions, combining to form metallic silver.
70
what are the screen/film processing steps?
develop
fix
dry
71
develop
convert latent image to manifest (change silver ions to metallic silver)
72
fix
remove unexposed silver halide and harden gelatin (establish archival quality
73
what are the steps in automatic processing?
```
transport
temperature control
circulation
replenishment
dryer
```
74
what is the transport phase in automatic processing?
rollers (controls time and agitates solutions) & microswitch (controls replenishment)
75
for screen/film technique, is it better to use the shortest or longest time possible?
shortest
76
for screen/film technique, use kvp for desired...
contrast level
77
for film/screen technique, use mAs that gives..
desired quantity of photons
78
for film/screen, what interaction dominates at high kvp?
Compton, there is less absorption/reduced subject contrast- resulting longer scales!
79
for film/screen, mAs chosen should result in densities:
in useful range
80
for film/screen, you should use the longest or shortest SID possible?
longest acceptable.
81
kvp controls what?
quality (penatribility)
| influences quantity
82
Increasing kvp does what?
increases scatter production and forward direction. more likely to strike image receptor. (longer scale of contrast)
83
mA is directly proportional to what?
quantity of x-rays produced. (number of electrons available at cathode)
84
what is the major controlling factor of the number of electrons that flow cathode to anode?
mA
85
time should be short to minimize
motion
86
time combined with mA impacts:
quantity
87
mAs
quantity, can use time & mA to compensate for one another
88
Falling Load Generator
tech sets mAs
| Machine automatically picks high mA & short time
89
what potential problems exist with a falling load generator
when mA and focal spot size are automatically linked
90
SID affects what about an image?
density
91
density maintenance
allows you to determine new mAs necessary to produce same density at new distance.
92
for equal image density, higher mAs is needed at ? distance
higher distance
93
on an imaging system- Focal spot size
special microfocus tubes image very small objects at short SIDs (mammo)
94
to stay within the heat loading capacity, what size focal spot would you use?
large focal spot to allow desired mAs with short time.
95
high mA uses what size focal spot
large unless detail is primary concern.
96
what are three patient factors?
part thickness
| body composition
97
part thickness
measure, takes more photons to get through a thick abdomen than a thin one
98
body composition
consider range of anatomic mass densities involved
99
select kvp depending on
subject contrast and part thickness
100
which pathologies require an increase in technique?
additive
101
which pathologies require a reduction in technique?
destructive
102
high kv technique chart does what to patient dose?
reduces patient dose even more
103
wide latitude has what scale of contrast?
long scale
104
what is most important when dealing with AEC
positioning in front of aec
105
what are some options for AEC
phototimers or ionization chambers
106
what do phototimers or ionization chambers do?
detect radiation exiting the patient and reaching image receptor, between patient and IR or behind IR
107
there are often 3 cells, exposure time safety limit. how long is the back up timer?
typically 2 sec. or maybe 600 mAs.
108
there are a variety of densities to choose from on the aec....T or F?
true
109
For the AEC what are four things to make sure you do?
set kvp
select density preset
set back up time
position precisely
110
what is a programmed automated system?
lets you choose some factors while automatically combining with short time
111
what is anatomically programmed?
pick body part, may need to put in measurement. (bone and joint)
112
tomography
- intentional/controlled motion unsharpness of objects anterior and posterior to the plane of interest.
- contrast enhancement by adjacent blurring
- the more the tube head moves and the more irregular the pattern of motion, increased image enhancement
113
as the tomo angle increases, what happens to the object plane?
it gets thinner
114
what is a fulcrum?
focal point/plain in tomo
115
SID is _____ throughout
constant
116
tomographic angle
angle of movement determines thickness of cut/object plane (larger angle, thinner cut) (larger angle, objects outside plane more blurred)
117
what does tomography do to patient dose?
increase it
118
simultaneous multi-image tomography
book cassette (image receptor speed must be varied to stabilize density while obtaining several cut levels with one exposure)
119
Magnification
SID
| SOD
120
Magnification Factor
Image
| Object
121
Intentional Magnification
requires small focal spot
| may not need grid if large OID creates air gap
122
with magnification, what happens to patient dose
it increases (the patient is closer to the source, inverse square law)
123
what is a triode on a grid controlled x-ray tube
has a third electrode (in additional to cathode and anode)
124
how does a grid controlled x-ray tube work
several crisscrossed wires bridging the cathode's focusing cup. when small negative potential is placed on the grid, it prevents capacitors from discharging through the x-ray tube. allowing the precision exposure switch.
125
what is a grid bias
when small (-2 kV) negative potential is placed on a grid
126
Why is grid bias reduced to near zero
to allow electrons to flow cathode to anode
127
when does exposure stop on a grid controlled x-ray tube?
when the preselected mAs or density is reached, grid bias is automatically reapplied and exposure is stopped.
128
what is a grid controlled x-ray tube mainly used for.
to stop discharge of capacitor discharge units (mobile units which store mAs when charged)
129
what are screen/film artifacts
irregular/undesireable densities that do not represent accurate exit radiation shadowing
130
exposure artifacts
grid/screen film/cassette errors. (interferes with collection of info)
131
processor artifacts
in processing, guide-shoe marks, pi lines, emulsion pickoff/gelatin buildup, chemical fog, wet pressure sensitization (in developer tank)
132
handling and storage artifacts
kinks/scratches, white light fog, static, safe light fog
133
guide-shoe marks
improper position of springing of guide shoes in turnaround assembly
134
pi lines
dirt or chemical stains on rollers
135
sharp increase or decrease in OD
dirty or warped rollers, which can leave sludge deposits on film
136
uniform dull, gray fog
improper or inadequate processing chemistry
137
dichroic stain or "curtain effect"
improper squeezing of processing chemicals from film
138
small circular patterns of increased OD
pressure caused by irregular or dirty rollers
139
yellow-brown drops on film
oxidized developer
140
milky appearance
underreplenished fixer
141
greasy appearance
inadequate washing
142
brittle appearance
improper dryer temperature or hardening in the fixer
143
moire effect/pattern
a wavy artifact pattern which occurs when the grid lines and the scanning laser are parallel
144
digital radiographic artifacts
on image receptor, software, object
145
image receptor artifacts
dust, dirt, scratches, pixel malfunction, ghost images
146
ssoftware artifacts
histograms, range/scaling, image compression
147
object artifacts
patient positioning, collimator/partition, backscatter.
148
histogram
graphic representation of frequency of digital value
149
what does histogram selection determine
the reconstruction algorithm applied to the final image
150
how does collimation influence histogram analysis
areas of max or absence of radiation detection
151
histogram partitioning
must have clear margins between multiple fields on same IP to avoid histogram errors
152
alignment of part and IP ALSO INFLUENCES HISTOGRAM ALALYSIS
.
153
window width
adjust contrast
154
window level
adjust brightness
155
narrow (decreased) window width displays what type of contrast?
shorter scale
156
wider (increased) window width displays what type of contrast?
longer scale
