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Chapter 13 Flashcards

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1
Q

exposure factor

A

the factors that influence and determine the quantity and quality of x-radiation to which the patient is exposed

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2
Q

four prime exposure factors

A

kVP, mA, exposure time, SID

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3
Q

kVP and mAs

A

the most important factors principally responsible for x-ray quality and quantity. focal spot size, distance, and filtration are secondary factors that may require manipulation for particular examinations

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4
Q

kVP

A

affects quality and therefore, beam penetrability,with increasing kVP, more x-rays are emitted, and they have higher energy and greater penetrability. but because they have higher energy, they also interact more by Compton effect and produce more scatter radiation, which results in reduced image contrast.
the kVP selected helps to determines the number of x-rays in the image forming beam, and hence the resulting average optical density (OD).
finally, and most importantly, the kVP controls the scale of contrast on the finished radiograph because as kVp increases, less differential absorption occurs, therefore, high kVP results in reduced image contrast.

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5
Q

Milliamperes

A

the mA selected determines the number of x-rays produced and therefore the radiation quantity. the unit of electric current is the ampere (A) one ampere is equal to 1 coulomb (c) of electrostatic charge flowing each second in a conducter.

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6
Q

fallng load generator

A

on an x-ray imaging system in which only mAs can be selected, exposure factors are adjusted automatically to the highest mA at the shortest exposure time allowed by the high voltage generator

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7
Q

Distance

A

affects exposure of the image receptor according to the inverse square law, the SID largely determines the intensity of the x-ray beam at the image receptor.

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8
Q

direct square law

A

is derived from the inverse square law, it allows a radiologic technologists to calculate the required change in mAs after a change in SID to maintain constant OD.

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9
Q

focal spot size

A

for general imaging, the large focal spot is used. this ensures that sufficient mAs can be used to image thick or dense body parts. the large focal spot also provides for a shorter exposure time, which minimizes motion blur.
one difference between large and small focal spots is the capacity to produce x-rays. many more x-rays can be produced with the large focal spot because anode heat capacity is higher. with small focal spot, electron interaction occurs over a much smaller area of the anode, and the resulting heat limits the capacity of x-ray production.
a small focal spot is reserved for fine-detail radiography, in which the quantity of x-rays is relatively low. small focal spots are always used for magnification radiography. these are normally used during extremity radiography and in examination of other thin body parts in which higher x-ray quantity is not necessary.

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10
Q

filtration

A

three types of x-ray filtration are used: inherent, added, and compensating.

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11
Q

inherent filtration

A

all x-ray beams are affected by the inherent filtration properties of the glass or metal envelope of the x-ray tube. the value of the inherent filtration is approximately 0.5 mm the required total filtration of 2.5 mm is needed.

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12
Q

compensating filters

A

are shapes of aluminum mounted onto a transparent panel that slides in grooves beneath the collimator. these filters balance the intensity of the x-ray beam so as to deliver a more uniform exposure to the image receptor. they may be shaped like a wedge for examination of the spine or like a trough for chest examination.
as added filtration is increased, the result is increased x-ray beam quality and penetrability. the result on the image is the same as that for increased kVP, that is, more scatter radiation and reduced image contrast.

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13
Q

three basic types of high voltage generators are available

A

single phase, three phase, and high frequency

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14
Q

high wave rectified generator

A

has 100% voltage ripple. during exposure with a half wave rectified generator, x-rays are produced and emitted only half the time. during each negative half cycle, no x-rays are emitted.

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15
Q

full wave rectification

A

identical to half wave rectification except there is no dead time. during exposure, x-rays are emitted continually as pulses. consequently, the required exposure time for full wave rectification is only half that for half wave rectification.

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16
Q

three phase power

A

comes in two principal forms: 6 pulse or 12 pulse. the difference is determined by the manner in which the high voltage step up transformer is engineered.
the difference between the two forms is minor but does cause a detectable change in x-ray quantity and quality. three phase power is more efficient than single phase power. more x-rays are produced for a given mAs setting, and the average energy of those x-rays is higher. the x-radiation emitted is nearly constant rather than pulsed.

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17
Q

patient factors

A

such as anatomical thickness and body compositon

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18
Q

image quality factors

A

such as OD, contrast, detail, and distortion

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19
Q

exposure technique factors

A

such as kVP, milliamperage, exposure time, and SID, as well as grids, screens, focal spot size, and filtration.

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20
Q

body habitus

A

sthenic – meaning “strong, active” patients are average.
hyposthenic–are thin but healthy appearing; these patients require less radiographic technique.
hypersthenic—are big in frame, and usually overweight.
asthenic are small, frail, sometimes emaciated, and often elderly.

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21
Q

calipers

A

are used to measure the thickness of the anatomy that is being irradiated

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22
Q

composition

A

when only soft tissue is being imaged, low kVp and high mAs are used. with an extremity, which consists of soft tissue and bone, low kVp is used because the body part is thin.
when imaging the chest, the radiologic technologist takes advantage of the high subject contrast. lung tissue has very low mass density, bony structures have high mass density, andd the mediastinal structures have intermediate mass density. consequently, high kVp and low mAs can be used to good advantage. this results in an image with satisfactory contrast and low patient radiation dose.

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23
Q

radiolucent

A

attenuates few x-rays and appears black on the radiograph

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24
Q

radiopaque

A

tissue absorbs x-rays and appears white on the radiograph

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25
Q

pathology (destructive)

A

causing the tissue to be more radiolucent

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26
Q

pathology (constructively)

A

increase mass density or composition, causing the tissue to be more radiopaaque

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27
Q

image quality factor

A

refers to characteristics of the radiographic image; these include OD, contrast, image detail, and distortion. image quality factor are considered the “language” of radiography.

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28
Q

Optical density

A

is the degree of blackening of the finished radiography. OD has a numeric value and can be present in varying degrees, from completely black, in which no light is transmitted to almost clear. whereas black is numerically equivalent to an OD of 3 or greater, clear is less than 2 a radiograph that is too dark has a high OD caused by overexposure. this situation results when too much x-radiation reaches the image receptor. a radiiograph that is too light has been exposed to too little x-radiation, resulting in underexposure and low OD.

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29
Q

Optical density controller

A

two major factors mAs and SID
it can be affected by other factors, but the mAs becomes the factor of choice for its control. a change in mAs of approximately 30% is required to produce a visible change in OD. as a general rule, when only the mAs setting is changed, it should be halved or doubled. the simplest method used to increase or decrease OD is to increase or decrease the mAs.

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30
Q

contrast

A

the function of contrast in the image is to make anatomy more visible. contrast is the difference in OD between adjacent anatomical structures, or the variation in OD on a radiograph. Contrast is perhaps the most important factor in radiographic quality.

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31
Q

penetrability of the x-ray beam is controlled by

A

kVP

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32
Q

gray scale of contrast

A

refers to the range of ODs from the whitest to the blackest part of the radiograph

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33
Q

high contrast radiographs produce short gray scale.

A

they exhibit black to white in just a few apparent steps

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34
Q

low contrast radiographs produce long gray scale

A

appearance of many shades of gray.

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35
Q

high contrast

A

” a lot of contrast” or a “short scale of contrast” is obtained by using low kVp exposure techniques

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36
Q

low contrast

A

is the same as “long scale of contrast” and results from high kVp

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37
Q

detail

A

describes the sharpness of appearance of small structures on the radiograph. with adequate detail, even the smallest parts of the anatomy are visible.

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38
Q

image detail

A

evaluated by two means–recorded detail and visibility of image detail

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39
Q

sharpness of image detail

A

refers to the structural lines or borders of tissues in the image and the amount of blur of the image. factors that usually control the sharpness of image detail are the geometric factors —focal spot size, SID, and OID. To produce the sharpest image detail, one should use the smallest appropriate focal spot and the longest SID and place the anatomical part as close to the image receptor as possible.

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40
Q

visibility of image detail

A

describes the ability to see the detail on the radiograph and is best measured by contrast resolution.

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41
Q

distortion

A

the misrepresentation of object size and shape on the radiograph.

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42
Q

elongation

A

means that the anatomical part of interest appears bigger than normal

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43
Q

foreshortening

A

means that the anatomical part appears smaller than normal

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44
Q

4 image quality factors

A

Optical density
contrast
detail
distortion

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45
Q

Optical density

A

controlled by
mAs

influenced by

kVp
distance
thickness of part
mass density
development time or temperature
image receptor speed 
collimation
grid ratio
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46
Q

Contrast

A

controlled by
kVp

influenced by

mAs (toe, shoulder)
development time or temperature
image receptor used
collimation
grid ratio
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47
Q

Detail

A

controlled by

focal spot size

influenced by

SID
OID
Motion
All factors related to density and contrast

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48
Q

Distortion

A

controlled by

patient positioning

influenced by

Alignment of tube
anatomical part
image receptor

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49
Q

exposure technique charts

A

kVP
mA
exposure time
SID

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50
Q

types of grids

A

stationary

moving grid

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51
Q

parallel or non focused grid

A

lead lines run parallel to one another

used primarily in fluoroscopy and mobile imagine

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52
Q

focused grid

A

has lead lines that are angled to approximately match the angle of divergence of the primary beam

Advantage
allow more transmitted photon to reach the film than parallel grid

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53
Q

convergent point

A

if imaginary lines were drawn from each of the lead lines in a linear focused grid, these lines would meet to form an imaginary point.

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54
Q

convergent line

A

if convergent points were connected along the length of the grid they would form an imaginary li

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55
Q

focal distance

A

distance between the grid and the convergent line or point

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56
Q

focal range

A

focal range is the recommended range of SIDs that can be used with focused grid.

the convergent line or point always falls within the focal range.

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57
Q

grid cassette

A

an image receptor that has a grid permanently mounted to its front surface.

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58
Q

grid cap

A

a grid cap contains a permanently mounted grid and allows the image receptor to slide in behind it.

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59
Q

disadvantage of stationary grid

A

causes shadows of the grid lines on the image

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60
Q

moving or reciprocating grid

A

they are part of the bucky (potter bucky diaphragem)

located directly below the radiograhic table top just above the tray that hold the film

grid motion is controlled electrically by the exposure switch

grid moves back and forth in a lateral direction over the image receptor during the entire exposure.

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61
Q

contrast improvement factor

A

principal function of a grid is to improve contrast

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62
Q

grid conversion factor (bucky factor)

A

grid also absorb some of the primary radiation

to compensate for this you need to increase the mAs

GCF = mAs with grid/mAs without grid

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63
Q

bucky factor/grid conversion factor

A

grid ratio bucky factor/GCF

non grid 1

5: 1 2
6: 1 3
8: 1 4
12: 1 5
16: 1 6

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64
Q

grid cutoff

A

grid cutoff is defined as a decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid.

higher grid ratio results in more grid cutoff.
high ratio grid has less positioning latitude

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65
Q

upside down focused grid

A

appears radiographically as significant loss of density along the edges of the image.

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66
Q

off level grid cutoff

A

caused from angling the x-ray tube across the grid lines or angling the grid itself during exposure

appears as an overall decrease in density

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67
Q

off center grid cutoff

A

also called lateral decentering.

occurs when the central ray of the x-ray beam is not aligned with the center of a focused grid (side to side misalignment)

appears as an overall loss of density

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68
Q

off focused grid cutoff

A

occurs when using an SID outside of the recommended focal range.

occurs if the SID is less than or greater than the focal range.

appears as a loss of density at the periphery of the film.

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69
Q

grid selection

A

below 90 kVp 8:1 grid is used

above 90 kVp grid ratio above 8:1 is used

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70
Q

grid selection factors

A

patient dose increase with increasing grid ratio

high ratio grids are used for high kVp examinations

patient dose at high kVp is less than that of low kVp

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71
Q

air gap technique

A

image receptor is 10 to 15 cm from the patient

alternate to grid

improve image contrast

10% increase in maS for every cm of gap.

image magnification with associated focal spot blur

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72
Q

film construction

A

radiographic film has many layers

  1. supercoat
  2. emulsion
  3. adhesive layer
  4. film base
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73
Q

supercoat (overcoat)

A

supercoat is a durable protective layer that is intended to prevent damage to the sensitive emulsion layer underneath it.

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74
Q

emulsion layer

A

emulsion layer is the radiation and light sensitive layer of the film.

the emulsion of the film consists of silver halide crystals suspended in gelatin

silver halide contains 90 to 99% of silver bromide acid 1% to 10% of silver iodide.

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75
Q

adhesive layer

A

adhesive layer keep the emulsion sticking to the film base.

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76
Q

film base

A

the final layer of the film is base

base is made of polyester (plastic) which gives the film physical stability

most film base has a blue tint.

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77
Q

historic development of film base

A

glass: break easily, difficult to store

cellulose nitrate: highly flammable

cellulose acetate: could damage when it is wet

polyester base: most modern. dimensional stability

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78
Q

characteristics to be considered when selecting radiographic film

A 
contrast 
speed
spectral matching 
anti-crossover layer
requirement for safelight
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79
Q

contrast

A

contrast of an IR is inversely propertional to its exposure latitude

exposure latitude = range of exposure techniques that will produce an acceptable radiograph.

depends on size and distribution of the silver halide crystals.

low, medium, or high

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80
Q

screen film

A

screen films are available with many contrast levels.

high contrast emulsion: smaller silver halide grains with uniform grain size.

low contrast emulsion: larger grains having wide range of sizes.

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81
Q

speed

A

sensitivity of the screen film combination to x-rays and light

different film emulsion and different intensifying screen phosphors contribute to different speed.

for direct exposure film, speed is affected by the concentration and total number of silver halide crystals.

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82
Q

factors affecting screen film speed

A

silver halide grain size

shape of the grains

concentration of the grains

double emulsion films are twice as fast as single emulsion films

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83
Q

covering power of the emulsion

A

current emulsions contain less silver, yet produce the same density per unit exposure because of its increased covering power.

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84
Q

cross over effect

A

crossover refers to a phenomena in which light from one intensifying screen cross over the film base and expose the emulsion on the opposite side of the base.

it causes increased blur on the image

crossover is a problem that is unique to double emulsion film used with intensifying screen.

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85
Q

crossover can be reduced by

A

tabular grain emulsion

anti crossover layer

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86
Q

tabular grain or T grain technology

A

this technology increases the recorded detail

T-grain film uses flat silver halide crystals that can be dispersed more evenly in the emulsion

87
Q

Crystal types

A

irregular grain
tabular grain
cubic grain

88
Q

spectral matching

A

matching the spectral sensitivity of the film with the spectral emission of the intensifying screen increases the speed of the image receptor

a film that is sensitive to blue color must be placed with an intensifying screen that produce blue light.

89
Q

spectral emission

A

calcium tungstate screens emit blue and blue violet light.

rare earth phosphor emits ultraviolet, blue, green, and red.

ortho-chromatic films are sensitive to blue and green lights (two colors)

pan chromatic films are sensitive to the entire visible light spectrum.

90
Q

safelights

A

most safelights are incandescent lamps with color filter

provide enough light to illuminate the darkroom without exposing the film.

a 15 watt bulb should not be closer than 1.5 meter (5 ft) from the work surface.

91
Q

safelights

A

blue sensitive film–amber color filter.

transmit wavelengths longer than 550 nanometer (above blue region)

green sensitive film–red color filter. transmit wavelengths longer than 600 nm

red filter is suitable for both blue and green lights.

92
Q

types of film

A

direct exposure film

screen film
double emulsion
single emulsion

93
Q

direct exposure film

A 
film is enclosed in an envelope that will not transmit light
no intensifying screen
thicker emulsion
higher concentration of silver halide
exposed by direct x-ray interaction
increased patient dose
used to image thin body parts
94
Q

mammography film

A

originally used direct exposure film with double emulsion.

currently uses single emulsion film with single intensifying screen

green sensitive film

terbium doped gadolinium oxysulfide screens

has antihalation coating

95
Q

antihalation coating

A

the surface of the base opposite to the screen is coated with special light absorbing dye to reduce the reflection of screen light, which is transmitted through the emulsion and base.

antihalation layer is present in all single emulsion films.

96
Q

handling and storage of films

A

improper handling cause artifiacts on the image

should not bend, crease, or handle roughly

clean hand with no lotions

store in a cool dry places

68 and 40 degrees–60% humidity

97
Q

effect of temperature and humidity

A

increased heat causes fog

increased humidity also causes fog and loss of contrast

humidity below 40% causes static artifact.

tree, crown or smudge

98
Q

handling and storage of films

A

film must be stored and handled in the dark

well sealed darkroom (light and radiation proof)

proper safelights

light proof storage bin

99
Q

handling and storage of films

A

the thickness of the lead barrier is designed to keep the total exposure of unprocessed film below 2 micro Gy (0.2 mR).

radioactive materials used in nuclear medicine can fog the film

100
Q

formation of latent image

A

the latent image is the invisible change that is induced in the silver halide crystal.

with proper chemical processing the latent image becomes visible image (manifest image)

101
Q

latent image formation

A

the term latent image refers to the image that exists on film after the film has been exposed but before it has been processed.

the term manifest image refers to the image that exists on film after exposure and processing.

102
Q

sensitivity specks

A

physical imperfections in the crystal lattice of the emulsion layers occur during the film manufacturing process.

these imperfections are called sensitivity specks.

each sensitivity specks serves as electron trap, trapping electrons lost by the bromide when x-ray or light exposure occurs.

therefore, sensitivity speaks are negatively charged.

103
Q

sensitivity specks

A

since sensitivity specks are negatively charged, the positive silver ions that are liberated from bromide are attracted to them.

every silver ion that are attracted to an electron becomes neutralized to metallic silver

the more x-ray or light exposure, the more electrons and silver ions available

104
Q

latent image centers

A

several sensitivity specks with many silver ions attracted to them become latent image centers.

these latent image centers appear as radiographic density on the manifest image after processing.

for a latent image center to appear it must contain at least three sensitivity specks that have at least three silver atoms each.

the more exposure to the film, the more metallic silver that is present on the radiograph as radiographic density.

105
Q

intensifying screen

A

located inside the cassette
contains phosphors
phosphors convert the x-ray energy to light.
the light exposes the radiographic film

the phosphor is a chemical compound that emits light when struck by radiation.

106
Q

purpose of intensifying screen

A

decrease the patient’s radiation exposure
in direct exposure radiography, the film is exposed only by the exit radiation
with screens the total amount of energy to which the film is exposed is divided between x-rays and light.
use of intensifying screen reduces patient dose but also reduces recorded detail.

107
Q

luminescence

A

luminescence if the essence of light from the screen when stimulated by radiation.

there are two types of luminescence

1) fluorescence
2) phosphorescence.

108
Q

fluorescence

A

refers to the ability of phosphors to emit visible light only while exposed to x-rays.

109
Q

phosphorescence

A

occurs when phosphors continue to emit light after the x-ray exposure has stopped.

phosphorescence is also known as screen lag or after glow..

cause fog on the film

110
Q

screen construction

A

an intensifying screen has four different layers

protective layer
phosphor layer
reflecting layer or absorbing layer
base

111
Q

protective layer

A

the outermost layer
10 to 20 micro meter
resistant to abrasions and damage
protect the fragile phosphor material beneath it.
eliminate the build up of static
provides surface for routine cleaning without damaging the phosphor layer.

112
Q

phosphor layer

A

also known as active layer
contains the chemical (phophor) that converts x-ray photon in to visible light.
50 to 300 micro meter

calcium tungstate
zinc sulfide
barium lead sulfate
oxysulfide of rare earth elements

113
Q

rare earth elements

A

gadolinium
lanthanum
yttrium

114
Q

discovery of x-rays

A

accidental discovery by Roentgen
observed luminescence on barium platinocyanide.
thomas edison developed calcium tungstate

115
Q

favorable properties of phosphors

A 
high atomic number
high x-ray absorption (DQE)
emit large amount of light (CE)
spectral matching
minimum after glow
should not be affected by heat and humidity
116
Q

detective quantum efficiency (DQE)

A

phosphors with high atomic numbers absorb more x-rays. this is called detective quantum efficiency.
rare earth phosphors have higher DQE

117
Q

conversion efficiency (CE)

A

the phosphor should emit large amount of light per x-ray absorption. this is called x-ray conversion efficiency.
higher conversion efficiency results in increased noise.
rare earth phosphors have higher CE

118
Q

the reflecting layer

A

25 micrometer
consists of either magnesium oxide or titanium dioxide.
light is emitted isotropically with x-ray interaction of the phosphor
reflective layer intercepts with light headed in other direction and redirects it to the film

119
Q

the absorbing layer

A

consists of a light absorbing dye
absorb the light directed towards the base
reflecting and absorbing layers are not present at the same time

120
Q

base

A

the bottom layer of the intensifying screen
made of polyester or cardboard
provide support and stability for the phosphor layer.

121
Q

luminescence

A

occurs when an outer shell electron is raised to an excited state and returns to its ground state with the emission of a light photon

122
Q

image noise

A

increases with higher CE but not with higher DQE

123
Q

spatial resolution

A

reduction in spatial resolution is greater when phosphor layers are thick
reduction is also greater when crystal size is large
these same conditions increase screen speed by producing more light photons per incident x-ray.

124
Q

front screen and back screen

A

back screen is more faster than the front screen

125
Q

rare earth elements

A

most commonly used phosphors
absorb more x-rays
convert x-rays to visible light more efficiently
improved recorded detail
very rare and hard to extract from the earth

126
Q

spectral matching

A

spectral sensitivity of the film should match with the spectral emission of the intensifying screen.

blue sensitive film should be used with blue light emitting intensifying screen
failure to match the screen and film results in inappropriate radiographic density. (less density)

127
Q

screen speed

A

the capability of a screen to produce visible light is called screen speed

faster screen produce more light

faster screen require less exposure and therefore less patient dose

screen speed and density are directly proportional

disadvantage: reduction in detail

128
Q

intensification factor

A

intensification factor is the ratio of the exposure without screen to the exposure with screen

IF=exposure without screen/exposure with screen

129
Q

relative speed

A

relative speed results from comparing screen film systems, based on the amount of light produced for a given exposure

the amount of light produced with a par speed (medium) calcium tungstate screen system is used as the standard for comparison and is assigned a relative value of 100.

given the same exposure a 200 system will produce twice as much as light (and density)
a 400 system will produce four times more light and density

130
Q

mAs conversion formula

A

the mAs conversion formula is a formula for the radiographers to use in determining how to compensate or adjust mAs when changing intensifying screen system speeds

131
Q

factors affecting screen speed

A

1) type of phosphor material
2) absorption efficiency
3) conversion efficiency
4) thickness of the phosphor layer
5) size of the phosphor crytal
6) concentration of the phosphor crystal
7) the presence or absence of a reflecting layer

rare earth screen produce 3-4 times faster than calcium tungstate screen

132
Q

screen speed and recorded detail

A

when a phosphor material is energized by a photon light it is emitted from the crystal and spreads out towards the film emulsion

therefore the actual physical area of the film exposed to light is greater than the area of the film that would be exposed by an x-ray photon

this spreading of radiographic information decreases the recorded detail, creating more image un-sharpness.

133
Q

quantum mottle

A

commonly called as image noise

quantum mottle is the statistical fluctuation in the quantity of x-ray photon that contribute to image formations per square millimeter.

when a very low number of photons are available the image appears mottled or splotchy.

this appearance can be described as a “salt and pepper” look.

quantum mottle decreases the recorded detail

134
Q

spatial and contrast resolution

A

spatial resolution refers to how small an object can be imaged

contrast resolution refers to the ability to image similar tissues such as liver and pancreas or gray matter and white matter

conditions that increase intensification factor by reduces spatial resolution

135
Q

spatial resolution

A

expressed by number of line pairs per millimeter

higher the number of line pairs, smaller is the object that can be imaged and better is the spatial resolution

fast screens = 7 lp/mm

fine detail screens = 15 lp/mm

direct exposure film = 50 lp/mm

136
Q

screen maintenance

A

two important maintenance procedures

1) regular cleaning
2) Maintaining good screen film contact.

cleaning is accomplished by a commercially available antistatic intensifying screen cleaner fluid and gauze pads.

137
Q

Screen film contact

A

poor screen film contact greatly reduces recorded detail

it appears as a localized area of unsharpness on the radiograph

first step in testing for poor screen-film contact is identifying the problem cassettes.

perform a wire mesh test to test the screen film contact

138
Q

wire mesh test

A

place a wire mesh tool on the cassette in question and radiograph it using an appropriate technique

the resultant radiograph is viewed from a distance of approximately 6 feet to determine any areas of unsharpness.

areas of poor contact will appear darker than areas of good contact

the screen film contact test should be done every 6 to 12 months.

139
Q

cassettes

A

cassette serves as a container for both the film and the intensifying screen
cassette must be light proof
must be of little weight
must be rigid enough so that it will not bend under a patient’s weight
should allow maximum amount of radiation to pass through and reach the screen
must provide a good screen-film contact

140
Q

cassette continuation

A

low x-ray absorbing material such as bakelite, magnesium or graphite carbon is used to construct the front of the cassette
the inside back of the cassette may be a thin sheet of lead foil, designed to absorb backscatter.

141
Q

processing sequence

A 
wetting
developing
rinsing in stop bath
fixing 
washing
drying
142
Q

processing sequence

A

wetting:
swells the emulsion to permit subsequent chemical penetration

developing:
the latent image is converted to visible image..

rinsing
terminates development and remove excess chemical from the emulsion

143
Q

processing sequence

A

fixing
removes remaining silver halide from emulsion and hardens gelatin

washing
removes excess chemicals

drying
removes water and prepares radiograph for viewing

144
Q

developiing

A

developing change the silver ions in the exposed silver halide crystals to metallic silver

silver ion is reduced to metallic silver

the chemical responsible for this is called reducing agent

principal component of developer is hydroquinon

the secondary components are phenidone and metol

145
Q

synergism

A

the action of two agents working together is greater than the sum of the action of each agent working independently.

usually hydroquinone and phenidone are combined for rapid processing.

hydroquinone: responsible for the black shades of gray, acts slowly
phenidone: responsible for the lighter shades of gray, acts rapidly

146
Q

fixing

A

when developing is complete, the film must be treated so that the image will not fade. this stage of processing is called fixing.

the image is fixed on the film

improves archival quality

archival quality refers to the permanence of the radiograph. the image does not deteriorate with age but remains the original stage.

147
Q

automatic processing

A 
transport system
temperature control
circulation system
replenishment system
dryer system
148
Q

transport system

A

begins at the feed tray
the entrance rollers grip the film
a micro switch is activated to control replenishment
the shorter dimension of the film should always be against the side rail, so that proper replenishment rate is maintained.

149
Q

transport system

A

rollers
transport racks
drive motor

guide shoes are used to turn the film 180 degrees

cross over rack is used to move film from one rack to the other

150
Q

temperature control system

A

developer temperature = 95 f

wash water temperature 5 f

151
Q

circulation system

A

continually mix the processing solution (agitation)
maintain constant temperature
aid exposure of the emulsion to chemicals
a filter is used to traps particles dislodged from thee emulsion
flow rate of 12L/min (3 gallons/min)

152
Q

replenishment system

A

replenishment system add proper quantity of chemicals into each tank to maintain volume and chemical activity.
60 to 70 ml of developer and 100 to 110 ml of fixer for ever 35 cm(inch) of film.

153
Q

dryer system

A

wet or damp radiograph picks up dust particles and cause artifacts
wet films are difficult to handle on view box
when stored it can become sticky and may be destroyed

154
Q

prime exposure factors

A

the factors that influence and determine the quanity and quality of x-radiation to which the patient is exposed are called exposure factors.

kVp
mA
exposure time
Distance

155
Q

kVp

A

primary control of beam quality
controls penetration
controls radiographic contrast
influence beam quanity

increase in kVp reduces differential absorption and reduce the image contrast.

156
Q

mA

A

controls radiation quanity
control the number of x-rays produced
with constant exposure time mA controls x-ray quantity and therefore patient dose.

157
Q

mA

A

does not change the kE of ellectrons.

does not increase penetration

x-ray quality remains fixed with a change in mA

158
Q

exposure time

A

kept as short as possible

short exposure time reduces motion blur

mAs controls optical density

doubling the mAs doubles the density

159
Q

mAs

A

mAs=mA times exposure time

time and mA can be used to compensate for each other in an indirect fashion.

mA1/mA2 =time2/time1

new mA = original mAs/new time

160
Q

exposure time and imagining system characteristics

A

single phase imaging system can not produce an exposure time less than 1/2 cycle = 1/120 second =8ms

three phase and high frequency generator can provide an exposure a short as 1 ms.

161
Q

falling load generator

A

on an x-ray imaging system in which only mAs can be selected, exposure factors adjusted automatically to the highest mA at the shortage exposure time allowed by the high voltage generator. such a design is called a falling load generator.

162
Q

distance

A

distance affects exposure of the image receptor according to the inverse square law.

determines the intensity of the x-ray beam at the image receptor

no effect on radiation quality

163
Q

inverse square law

A

i1/i2=d2 square /d1 square

164
Q

effect on longer SID on radiographs

A

less magnification
less focal spot
improved spatial resolution
requires more mAs

165
Q

focal spot size

A

most x-ray tube has two focal spot sizes

large focus

small focus

166
Q

focal spot size

A

changing the focal spot size for a given kVp/mAs setting does not change x-ray quanity or quality.

small focal spot size provide better detail

167
Q

FSS in conventional x-ray tubes

A
  1. 5mm/1.0mm
  2. 6mm/1.2mm
  3. 0mm/2.0mm
  4. 3mm/1.0mm for angio-interventional and magnification radiography
  5. 1mm/0.3mm for mammography (miro focus tube)
168
Q

filtration

A

inherent =0.5mm
added
compensating

169
Q

compensating filters

A

provide uniform density on the image when radiographing non-uniform objects

wedge filter for thoracic spine
trough filter for chest radiography

170
Q

high voltage generator

A

the quality and quantity of radiation is influenced by the type of generator

171
Q

half wave VS full wave

A

same radiation quality

double the quantity on full wave rectified generators

172
Q

power

A

three phase power results in higher x-ray quantity and quality
high frequency generator results in even greater x-ray quantity and quality

173
Q

body habitus

A

the general size and shape of a patient is called the body habitus

hypersthenic 5%
sthenic 50%
hyposthenic 35%
asthenic 10%

radiographic technique charts are based on the sthenic patient

174
Q

patient factors

A

thickness]
composition
pathology

175
Q

thickness

A

patient thickness should not be guess

always use a caliper to measure the patient

176
Q

fixed kVp technique

A

kVp remains fixed

mAs is changed based on patient thickness

177
Q

Variable kVp technique

A

mAs remains the same

kVp is changed based on patient thickness

178
Q

composition

A

high kVp for chest
low kVp for abdomen
low kVp for soft tissue

179
Q

pathology

A 
destructive pathology (radiolucent)
constructive pathology (radiopaque)
180
Q

half wave VS full wave

A

same radiation quality

double the quantity on full wave rectified generators

181
Q

power

A

three phase power results in higher x-ray quantity and quality
high frequency generator results in even greater x-ray quantity and quality

182
Q

body habitus

A

the general size and shape of a patient is called the body habitus

hypersthenic 5%
sthenic 50%
hyposthenic 35%
asthenic 10%

radiographic technique charts are based on the sthenic patient

183
Q

patient factors

A

thickness]
composition
pathology

184
Q

thickness

A

patient thickness should not be guess

always use a caliper to measure the patient

185
Q

fixed kVp technique

A

kVp remains fixed

mAs is changed based on patient thickness

186
Q

Variable kVp technique

A

mAs remains the same

kVp is changed based on patient thickness

187
Q

composition

A

high kVp for chest
low kVp for abdomen
low kVp for soft tissue

188
Q

pathology

A

destructive pathology (r

189
Q

image quality factors

A

optical density
contrast
detail
distortion

190
Q

optical density

A

degree of blackening of the finished radiograph
OD of 3 or greater is considered black
OD of 0.2 or less is considered as clear
At OD 2, only 1% of view box light passes through the film

191
Q

visibility of the image detail

A

ability to see the detail on the radiograph

best measured by contrast resolution

192
Q

optical density

A

30% change in mAs is required for a perceptible change in OD

4% change in kVp is required for a perceptible change in OD

15% increase in kVp will double the OD (15% rule)

193
Q

contrast

A

contrast is the difference in OD between adjacent anatomical structures.
kVp is the major factor used in controlling radiographic contrast

194
Q

high contrast radiographs

A

also known as short scale contrast

result from low kVp

radiograph of the ribs

195
Q

low contrast radiograph

A

long scale contrast

result from high kVp

radiographs of the chest

196
Q

factors influencing radiographic contrast

A

mAs
intensifying screen
collimation
grids

197
Q

5% rule

A

an increase of 5% in kVp may be accompanied by a 30% reduction in mAs to produce the same OD at a slightly reduce contrast scale.

198
Q

detail

A

detail describes the sharpness of appearance of small structures on radiograph

recorded detail
visibility of image detail

sharpness of image detail is best measured by spatial resolution

199
Q

factors affecting detail

A 
focal spot size
SID
OID
film speed
grain size
200
Q

visibility of the image detail

A

abi

201
Q

factors affecting visibility of detail

A

any factor that affects OD and contrast affects the visibility of image detail

key factors that provide the best visibility of image detail are collimation, use of grids, and other methods that prevent scatter radiation from reaching the image receptor.

fog reduces visibility of detail

202
Q

distortion

A

a misrepresentation of object size and shape on the radiograph

position of the x-ray tube, anatomical part and the image receptor could misrepresent the object

203
Q

distortion

A

poor alignment of the image receptor or the x-ray tube can result in elongation of the image.
elongation means that the anatomical part of interest appears bigger/longer than normal

204
Q

distortion

A

poor alignment of the anatomical part may result in foreshortening means that the anatomical part appears smaller than normal

205
Q

distortion

A

distortion is reduced by positioning the anatomical part of interest in a plane parallel to that of the image receptor.

206
Q

radiographic technique chart

A

tables that provide a means for determining the specific technical factors to be used in a given radiographic examination

variable kilovoltage
fixed kilovoltage
high kilovoltage
automatic exposure

207
Q

variable kVp technique chart

A 
fixed mAs
kVp varies according to thickness
provide shorter contrast scale (use low kVP)
higher patient dose
less exposure latitude
208
Q

variable kVp technique chart

A

kVp varies with the thickness of the anatomical part by 2kVp/cm

beginning kVp =2 times thickness + 23

209
Q

fixed kVp radiographic technique

A 
used most often 
developed by Arthur Fuchs
longer scale of contrast
select the optimum kVp for penetration
mAs is changed according to thickness
lower patient dose
greater latitude
210
Q

fixed kVp radiographic technique

A

establish a base technique
for small anatomical part reduce the mAs by 30%
for large anatomical parts increase the mAs by 30%
for part that is swollen as a result of trauma a 50% increase may be required

211
Q

high kVp technique chart

A

greater than 100 kVp
reduced patient dose

barium studies
chest

212
Q

Automatic expsoure techniques

A 
select an optimum kVp for penetration
select the desired mA station
select the appropriate sensors
position the patient accurately
collimate accurately
exposure time will be adjusted automatically
213
Q

anatomically programmed radiography (APR)

A

select the body habitus

select the anatomy

Physics (7 decks)

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