Image production and evaluation Flashcards
what factors provide a means for the radiographer to produce, review and evaluate radiographs
image quality factors
what are the 4 image quality factor
contrast
density
detail
distortion
this is the visible differences seen in adjacent anatomic structures on the radiograph
contrast
what results from the amount of penetration of the x-ray beam as it passes through different parts of the body
contrast
what have very few gray tones. They are mostly black and white
high contrast
High contrast is also known as
short scale contrast
images contain many shades of gray
low contrast
low contrast is also referred to as
long scale contrast
kV has an _ relationship to contrast
inverse
kV ^ contrast
goes down
what is the primary controlling factor for the penetrability of the x-ray beam and therefore directly controls contrast
kVp
as kV increases, x-ray penetrability of scatter radiation is _ causing more scatter to reach the image receptor
increase
high kV= _ contrast= _ scale contrast
low
long
low kV= _ contrast= _scale contrast
high
short
increase contrast by reducing the amount of scatter reaching the film
grids
limits the area being irradiated and thus reduces the amount of scatter being produced
beam restriction
less scatter= _ contrast
more
as OID increases, contrast _
increases
when OID increases contrast increases because a great deal of scatter radiation now misses the image receptor why
air gap technique
this is the amount of blackness on the radiograph
density
density is also known as
optical density
the amount of density on a film is controlled by
- the # of exit rays striking the film-screen striking the film-screen combination
- the speed of the film-screen combination
- processing
is the primary controlling factor for the quantity of x-rays being produced and therefore has a great deal of influence over the blackening of the image
mAs
is the primary controlling factor for the quality of x-rays being produced
kVp
more mAs= _ density
more
increasing kVp, _ photons frequency and _ photon wavelength, producing _ beam
increases
decreases
more powerful, penetrating
what is the secondary controlling factor of density
kVp
kVp is also known as
potential difference and electromotive force
increasing kVp, _ density and why
increases
because the more powerful beam doesn’t get attenuated in the body. more x-rays reach the image receptor
kVp affects density according to the
15% rule
if kVp increases by 15%, density is
doubled
if kVp decreases by 15%, density is
halved
A _% change in kVp will create a noticeable change in density on our image
4%
as film-screen speed increases, density
increases
as film-screen speed decreases, density
decreases
these decrease the amount of scatter reaching the film and thereby decrease density
grids
this decreases density by limiting the size of the x-ray beam and reducing the amount of scatter being produced
beam restriction
this affects density through its variation of atomic number and tissue thickness
anatomy
this affects density by altering tissue integrity and thickness
pathology
distance is affected by distance according to the
inverse square law
if distance (SID) is doubled, density
decreases 4 time
if distance (SID) is halved, density
increases 4 times
detail is also called
detail
sharpness
definition
image resolution
increasing OID= _ magnification= _ detail
increasing
decreasing
increasing SID= _ magnification= _ detail
decreasing
increasing
large focal spot size = _ in detail
decrease
small focal spot size = _ in detail
increase
large silver halide crystals in film = _ film speed = _ detail
fast
decreased
large phosphor crystals in intensifying screen = _ screen = _ detail
fast
decreased
any motion by the patient results in
image blur
loss of detail
this is the misrepresentation of an anatomic structure on an image receptor
distortion
there are 2 types of distortion
size
shape distortion
magnification makes anatomic structures appear larger on film than in reality
size distortion
Size distortion is caused by
excessive OID ( major factor) insufficient SID
shape distortion is divided into 2 categories
elongation
foreshortening
what makes structures to appear longer than they are in reality
elongation
elongation is is caused by
improper tube angulation
cassette alignment
what makes structures appear shorter than they are in reality
foreshortening
foreshortening is caused by
improper body part alignment with the cassette
there are 2 main types of technique charts
- fixd kVp charts
2. variable kvp charts
what are the most commonly used type of chart. For each anatomic part, an optimum kVp is selected. The mAs is then changed in order to accommodate changes in body part thickness
fixed kVp charts
have a set mAs value for each anatomic part and the kVp varies according to changes in body part thickness
variable kVp charts
is a device that measure the amount of radiation reaching the image receptor and then automatically terminates the exposure
AEC
There are 2 types of AEC devices
- Ionization chamber
2. photo timer
are the most commonly used AEC device. The gas filled chamber is located between the table top and the image receptor
Ionization chambers
utilize a fluorescent screen that is placed under the IR
phototimers
_ by the radiographer is of the utmost importance when using AEC
precise centering
_ have density control buttons that allow the radiographer to adjust the exposure to have more or less density
AEC devices
is a system in which the radiographer simply touches a picture or written description of the body part being imaged and the technique is set automatically
anatomically programmed radiography
_ is an important consideration when selecting film-screen combinations. The film and the intensifying screen must be sensitive to and emit the same color of light in order to work together efficiently
spectral matching
_ are sensitive to both blue and green light. These are used in radiography because we use rare earth intensifying screens which generally emit green light.
Orthochromatic films
for Orthochromatic films, prior to 1970, calcium tungstate screens were used and they emitted a
blue/violet light
Radiographic film has 2 main parts
the base
the emulsion
most x-ray film has the emulsion on both sides of the base and is therefore called
double emulsion film
double emulsion filme is used to
increase film speed
The base of the film is made of _ and it is used to support the
polyester
emulsion
the base is _ and has a _ tint
lucent
blue tint
the emulsion consists of 2 main ingredients
- gelatin
2. silver halide crystals
The gelatin is a clear substance that is used to hold the layer of _ in place
silver halide crystals
the silver halide crystals are made of both
silver iodide and
silver bromide
The size and concentration of the silver halide crystals determines the
speed of the film
bigger crystals = _ film speed
faster
films can also be designed to display different levels of contrast. The lower the contrast of a film, the _ the exposure latitude
wider
this is the range of exposure techniques that can be used to produce an acceptable image
exposure latitude
sensitometric curves, characteristic curves, and D-log E curves
H and D Curves
Hurter and Driffield
H & D, this is a graphic representation of the relationship between
density and exposure
In radiography, the useful range of optical density is between
0.25 to 2.5
the closer the curve to the y axis, the faster the film
speed
the steeper the curve, the _ the contrast
the more shallow the curve, the _ the contrast
higher
lower
the steeper the curve, the _ the latitude.
the more shallow the curve, the _ the latitude
more narrow
the wider
Less than _% of the radiographic image is created by x-rays striking the film
1
Over _% of the image is made by light from the intensifying screens striking the film
99
The main purpose of intensifying screens is to reduce pt dose by converting
x-rays into a great deal of visible light
4 layers of film
- protective
- emulsion-silver halide, black metallic (active layer
- adhesive
- base
4 layers of screen
- protective
- phosphor
- reflective
- base
a screen that can produce a great deal of light is said to be a _ speed intensifying screen
high
screen speed is detrained by
phosphor crystal size
thickness of phosphor layer
bigger crystals= _ speed
faster
thicker phosphor layer= _ speed
faster
while bigger crystals and thicker phosphor layers _ patient dose, _ screen speed, _ image detail
reduce
increase
decreasing
a rating of 100 is considered a
par speed screen
anything rated below 100 is considered a
detail or extremity screen
anything above 100 is a
high speed screen
Before the invention of the automatic film processor, it took _ to completely develop a film
60 min
The standard time to develop a film with an automatic processor is
90 sec
the automatic processor has 3 separate tanks
- developer tank
- fixer tank
- wash tank
the job of the _ is to change the exposed silver halide crystals into metallic silver. This creates the black and gray areas of the film
developer
what stops the development process and makes sure that the image on the film doesn’t fade. It also clears all of the unexposed silver halide crystals from the film
fixer
developer and fixer temperature is set at
95 degrees F
what removes the chemicals that remain on the film
wash
wash temperature is set at
90 degrees
once the film has traveled through the 3 tanks, it is
blown dry in the dryer
Dryer temperature is
120 degrees
moves film through processor
transport
replaces chemicals after film travel
replenishment
regulates temperature
temperature regulation
keeps chemicals from settling at bottom of processor
recirculation
dries
dryer
6 steps for the start up procedure
- close wash tank valve
- turn on water
- turn on processor
- put lid in place
- run several old 14 x 17 films
- wait for proper chemical temperatures
4 steps for the shut down procedures
- turn off water
- turn off processor
- open wash tank valve
- leave lid open
what is the measurement of the responses of film to exposure and processing.
sensitometry
some of the tools used for sensitometry are
penetrometer
sensitometer
densitometer
this may also be called a step wedge. Its used to produce a series of densities on a film by exposing it to x-rays. This is a method for monitoring both x-ray equipment and film-screen combinations
penetrometer
this is designed to expose a reproducible, uniform, optical step wedge onto a film. It contains its own light source and is used for processor quality control
sensitometer
this device provides a readout of the amount of blackening (density) on a film
densitometer
each image is created in a square frame called a
matrix
THe matrix is made up of small boxes that contain a numeric value. These boxes are called
pixels
the numeric value of each pixel is converted into a certain amount of density that is then displayed on the monitor. The higher the numeric value of the pixel, the appears on the
screen
the number of shades of gray that a digital system can display is called is
dynamic range
the smaller the size of the pixels, the more of them that can be placed in the
matrix
as more pixels are placed in the matrix,
image resolution increases
the minimum acceptable resolution in digital imaging is a matrix size of
2048 x 2048
each pixel represents a 3 dimensional volume of tissue that is called a
voxel
the # of photons striking the detector
signal
background information which is placed in the image but does not contribute to image quality
noise
noise has the same appearance on the image as
quantum mottle
is the comparison of these 2 characteristics on the image.
signal to noise ratio
a signal to noise ratio is what and why
desirable
indicates little noise in the image
what allows both the technologist and the radiologist to alter the image that has been produced in many different ways
post processing
digital imaging has what vs conventional film
wider exposure latitude
this adjusts both the contrast and the brightness of the image
windowing
controls the contrast
window width
when window level is increased, density
increased
parts of the image can be magnified
magnification
brightness can be increased along edges of structures
edge enhancement
the removal of background anatomy to visualize contrast filled vessels
subtraction
dark and light pixels are reversed
image reversal
adding text to an image
annotation
the numeric value that is representative of the amount of exposure the image receptor received. The number must be within a specific range in order for the image to be acceptable
exposure index
the 2 types of digital imaging are
Computed radiography (CR) digital radiography
uses a photostimulable storage phosphor imaging plate (PSP or IP) inside a cassette. This captures the latent image. The IP is then placed in an Image reader device (IRD)
computed radiography
uses a laser beam to convert the image into an electronic signal that is then sent to the television monitor
image reader device (IRD)
Layers of an imaging plate
protective layer phosphor layer conductor layer support layer light shield layer
insulates IP from trauma
protective layer
active component of IP/ made of barium flourohalide bromides with europium activators
phosphor layer
grounds the plate
conductor layer
support base
support layer
prevents light from erasing data
light shield layer
what is much more sensitive to scatter than conventional film, so correct kVp and grid use is important
IP
the latent image will lose _% of its energy in 8 hrs, so the image must be processed shortly after exposure
25%
Does not use a cassette
directly converts the x-ray photons into an electrical signal.
the photons strike a flat panel detector that creates the conversion
digital radiography
There are 2 types of digital radiography. They are separated by the type of flat panel detector they use
direct digital radiography
indirect digital radiography
has an amorphous selenium flat panel detector. This releases electrons when struck by the x-ray photons
direct digital radiography
has amorphous silicon flat panel detector. this detector requires a phosphor to create light when struck by x-ray photons. The light then causes the silicon to release electrons
indirect digital radiography
Direct digital radiography advantage over indirect digital radiography ; direct digital radiography has the advantage of
creating a more accurate image because no divergent light beam (phosphor screen) is being used
Indirect digital radiography has the advantage over direct digital radiography by
reducing patient dose because its phosphors work in the same way an intensifying screen
both systems contain _ which collect the electrical charges and send the signal to the television monitor
Thin Film Transistors
a disadvantage of both CR and DR when compared to conventional film
is a loss of resolution
PACS stand for
picture archiving and communication systems
incorporate the acquisition, storage, transmission and display of digital images into one computer network
PACS
if an imaging center does not have digital imaging, actual films can be sent to a _ by using a film digitizer
PACS system
the 2 types of film digitizers are
laser digitizers
charged coupled devices
which is the least expensive and therefore the most commonly used film digitizer
CCD
What does DICOM stand for
Digital Imaging and Communications in medicine
what is a universal standard for the storage of medical images. This allows images to be passed back and forth on a PACS system, no matter who manufactures the imaging equipment
DICOM
