Digital chapters 7-8 Flashcards
what are the prime factors for radiographic exposure?
- mA
- exposure time (sec.)
- kVp
- SID
what factors does mA control?
- radiographic density
- quantity of x-rays produced
- controlled by adjusting the mA
what is the relationship between quantity of exposure and mA?
direct
what factors does exposure time control?
- radiographic density
- quantity of x-rays produced
- controlled by adjusting the timer in an x-ray circuit
- duration of exposure
what is the relationship between quantity of exposure and exposure time?
direct
what factors does kVp control?
- radiographic density
- x-ray penetration
- quantity and quality of the x-ray beam
increased kVp results in _____ quantity of photons
increased
increased kVp results in ______ penetration of the body part
increased
SID affects the-
density and intensity of the x-ray beam
what is the relationship between quantity of exposure and the square of the distance (SID)?
inversely proportional
which factors affect x-ray quantity?
- mA
- exposure time
- mAs
- kVp
- SID
- Filtration
what factors affect x-ray quality?
- kVp
- filtration
what factors affect both x-ray quantity and quality?
- kVp
- filtration
if mA is doubled, quantity exposure-
doubles
if mA is reduced by 50%, quantity exposure is-
halved
what is the relationship between mA and patient exposure?
direct
- if mA doubles, patient exposure doubles
define mAs
the total quantity of x-rays in an exposure
what is the formula to find mAs?
mA x time = mAs
the unit mA is the _____ controller of radiographic density
primary
kVp is the ____ controller of the penetration of x-rays
primary
kVp is the _____ controller of radiographic contrast
primary
high kVp produces ____ contrast
low
low kVp produces ____ contrast
high
what’s low contrast
- densities are harder to distinguish between tissues
- more shades of gray (long-scale)
what’s high contrast
- densities are more noticeable
- less shades of gray (short-scale)
define SID
- source to image distance
- distance between the tube target and the IR
SID affects the _____ of the x-ray beam and the quantity of x-rays
intensity
define the inverse square law
the intensity is inversely proportional to the square of the distance
what is the formula of the inverse square law?
I2/I2 = D2^2/D1^2
what are the four primary factors that directly affect how an image looks?
- density
- contrast
- distortion
- spatial resolution
which two factors are considered photographic properties?
density and contrast
what two factors are considered geometric properties?
distortion and recorded detail
define density
the overall blackness or darkness of the radiographic image.
when an image is too dark, it is said to be-
over-exposed
- too much black
when an image is too light, it is said to be-
underexposed
- very light, more whites
define tissue density
the mass density of the body part
why is bone seen white on an image?
it has an increased tissue density, absorbing more of the primary beam
increased radiographic density means that the image is -
darker
decreased radiographic density means that the image is-
lighter
what is the relationship between radiographic density and tissue density?
inverse
brightness is also known as ____. Though brightness is used in digital imaging
density
define contrast
difference in radiographic density between adjacent portions of the image
- makes the anatomy more visible
when an image has low contrast, they appear
- a flat, gray appearance
- cannot tell the difference between adjacent tissues
when an image has high contrast, they appear-
- more black and gray
- contain some areas that are very dark and others that are very light
define optimum contrast
sufficient differences in density to easily make out details in all portions of the image
what contrast is needed for a hand x-ray?
high contrast
- short scale
what contrast is needed for a chest x-ray?
low contrast
- long scale
a decrease in kVp causes _____ contrast
high
- short scale
an increase in kVp causes ____ contrast
low
- long scale
define subject contrast
the range of differences in the intensity of the x-ray beam after it has been attenuated by the patient
define fog
- unwanted exposure to the radiographic image
- overall increase in density that causes all parts of the image to appear as though seen through a gray veil.
- causes areas that would otherwise be bright or white to appear gray.
what causes fog?
scatter radiation
define distortion
geometric property and refers to differences between the actual subject and its radiographic image
- unequal magnification of different portions of the same object.
define digital imaging
is the process of acquiring images of the body using x-rays, displaying them digitally, and viewing and storing them on a computer and in computer files
define Computed radiography
- cassette based
- the image of the body part is obtained using a cassette that contains a storage phosphor plate
the CR cassettes are often referred to as
imaging plates (IP)
the imaging plate in CR contains what type of phosphor?
photostimulable phosphor (PSP)
the PSP is made out of-
barium fluorohalide with europium
what are the 2 types of distortion?
- shape distortion
- size distortion
define size distortion
- always in the form of magnification enlargement
- dealing with SID and OID
define magnification
It is a function of the relationship between the SID and the distance between the subject and the IR (OID)
how do we reduce magnification?
keeping OID to a minimum, and increasing SID
what happens when we increase OID?
magnification will occur
- the body part will be bigger (than what it actually is)
define shape distortion
- result of unequal magnification of the actual shape of the structure
- can occur with angulation, poor positioning, incorrect CR angle, and IR angulation
how do we reduce shape disortion?
keeping the IR and body part parallel, and keeping the CR perpendicular to both
What are 2 types of shape distortion?
- foreshortening
- elongation
define foreshortening
projects the part so it appears shorter than it really is
define elongation
projects the object so it appears longer than it really is.
what factors affect size distortion?
SID and OID
what factors affect shape distortion?
- alignment
- CR
- part
- IR
- CR angulation
- direction
- degree
define spatial resolution
the sharpness of the image, and is more casually referred to as resolution, sharpness, definition, or simply detail
- determines whether the image appears sharp or blurred.
what factors affect spatial resolution?
- patient motion
- OID
- SID
- focal spot
poor resolution can make the image appear-
blurry or fuzzy
what factors control the formation of an image?
- SID
- OID
- focal spot size
define umbra
anatomic area/body part/structure shown in the radiographic image
define penumbra
the “unsharp edges” of the umbra, or body part
- blur or geometric unsharpness
- shadow on the edges of the image
how do we reduce blurriness in an image
reduce penumbra as much as possible
define focal spot
- The rectangular area of the target where the electrons strike
- where x-ray photons are emitted
what are the two types of focal spot?
- large focal spot
- small focal spot
what is the size of the large focal spot?
1.2 mm
what is the size of the small focal spot?
0.6 mm
the smaller the focal spot, the-
the less penumbra and greater spatial resolution
the larger the focal spot, the-
the more penumbra and less spatial resolution
how does OID affect penumbra and spatial resolution?
- when OID decreases, penumbra decrease, and spatial resolution increases
- when OID increases, penumbra increases, and spatial resolution decreases
how does SID affect penumbra and spatial resolution?
- when SID increases, magnification and penumbra decreases, and spatial resolution increases
- when SID decreases, magnification and penumbra increases, and spatial resolution decreases
which focal spot is desirable?
small focal spot
define motion
any movement during radiography will cause blurring of the image, reducing spatial resolution
what are factors that causes motion?
- patient movement
- IR movement
- x-ray tube movement
what are 2 different types of patient movement?
- voluntary
- involuntary
define involuntary motion
movements over which the patient has no control
what are some examples of involuntary motion?
- tremors
- peristalsis
- heartbeats
define voluntary motion
normally controllable, although certain patients may be unable to control themselves
how can one avoid motion?
Effective communications with both adults and children are key in avoiding motion
- Immobilization devices
how do we control incoluntary motion?
use a short exposure time (high mA)
define quantum mottle
a grainy or mottled (spotty) image is created.
why does quantum mottle happen?
usually due to a low mAs = lack of photons
- will occur when either the mAs or the kVp is set too low. (mainly mAs)
how does quantum mottle affect an image?
- reduces spatial resolution due to its grainy/noisy image
what factors control spatial resolution?
- OID
- SID
- focal spot
- motion
- quantum mottle
what components are needed to process and view an image in CR?
- CR reader unit
- a limited operator computer workstation
- computer system with monitors for the radiologist to view the images
- printer if images need to be printed on film
- a computer server to store the images
what are the most common CR plate sizes?
- 8 x 10” / 18 x 24cm
- 10 x 12” / 24 x 30cm
- 14 x 14” / 35 x 35cm
- 14 x 17” / 35 x 43cm
- 14 x 36” / 35 x 91cm
define sampling frequency
as the more signal is sampled, more information is obtained and spatial resolution is improved
how is an image erased in CR?
using a very intense white light
how many times can a PSP be used until it needs to be replaced?
10,000 times
collimation and kVp accuracy are very important because the IP’s in CR-
absorb more low-energy scatter compared to flim/screen
- IP is more sensitive to scatter radiation both before and after exposure to the x-ray beam
- also sensitive to background radiation
what happens if the IP in CR is not erased within 48 hours?
fog will appear in the image
define digital radiography
- digital imaging system that does not use a cassette
define flat panel detectors (FPD)
- converts the x-ray photons directly tino electrical energy
- can use a scintillation or photoconductor
- it is hard wired in the x-ray table and upright unit
what is the dimension of an FPD?
43 x 43 cm
what are the two types of DR?
- indirect
- direct
define indirect conversion DR
- two-step process
- x-ray energy is first converted to light, then converted to an electrical signal
what device is used in Indirect DR to convert the x-ray photons into light?
scintillator
define scintillator
a device that glows when hit by the high-energy x-ray photons
what is the scintillator made out of?
cesium iodide
define photodiode
converts light into electrical signal
what is the photodiode made out of?
amorphous silicon
define photoconductor
- used in direct conversion
- converts the x-ray photons into electrical signals
what is the photoconductor made out of?
amorphous selenium
define thin film translator (TFT)
- used to convert X-rays into electrical signals that are then used to create images.
- acts as a holder
- helps move the process from sending the electrical signals to the ADC
- are used in both direct and indirect
define matrix
- a series of thousands of very small boxes or squares.
- made up of rows and columns
define pixels
- The individual matrix squares
- smallest element in a matrix
- represents a brightness level in a digital image
define dead pixels
a single pixel on a digital X-ray detector that is malfunctioning and fails to register any signal, appearing as a blank spot (usually white) on the image
- may cause a loss of patient information
define fill in
when surrounding pixels “fill in” the surrounding dead pixel with their information
the larger the matrix-
the smaller the pixel, and the higher the spatial resolution
the smaller the matrix-
the bigger the pixel, and the lower the spatial resolution
define contrast resolution
the ability to distinguish anatomical structures of similar subject contrast, such as liver–spleen and gray matter–white matter.
define dynamic range
range of values that can be displayed by an imaging system
- range of intensities
what is another name for pixel?
picture element
define signal to noise ration (SNR)
the ability of the digital system to convert the x-ray input electric signal into a useful radiographic image.
- if there is an increase in signal, noise is reduced, and image quality is higher
- if there is a decrease in signal, noise is increased, and image quality is reduced
define quantum mottle
- occurs when there are not enough photons in the detectors to provide a high-quality image,
- mainly a result from low mAs, but can also be caused by kVp
define module transfer function (MTF)
- measure the capacity or accuracy of the digital detector to pass its spatial resolution characteristics to the final image.
- how well an X-ray imaging system transmits contrast from an object to an image
define histogram
a graph of the minimum and maximum signals in the image
define look up table (LUT)
- a file of stored images for each projection.
- LUT is used as a base image reference when adjustments are made on an image.
define window level
controls density
define window width
controls contrast
define electronic cropping
- also known as masking or shuttering
- used to blacken out the white collimation borders
- eliminates the glare to the eyes
masking should never be used when-
never be used to mask poor collimation
define image stitching
- When anatomy or the area of interest is too large to fit on one IR, multiple images can be “stitched” together
- commonly used for a full PA spine scoliosis series
define image annotation
add text that is useful to have on the image.
what are some examples of image annotation?
- time
- technique
- patient position
annotation should never be used-
to place R or L markers on the image
define edge enhancement
images can be made sharper and have greatly increased contrast; however, it does introduce some noise.
- image processing filter that enhances the edge of the image
define smoothing
- low pass filtering
- used to remove noise
what does ALARA stand for?
as low as reasonably achievable
define automatic rescaling
that images are produced with uniform density and contrast, regardless of the amount of exposure
define exposure indicator number
indicates how much radiation was absorbed in the phosphors, which gives only an idea of what the patient received
- the amount of the exposure reaching the plate.
define postprocessing
any image of a body part can be further adjusted with the computer software to visualize areas of interest better
what are 2 types of processing?
subtraction and contrast enhancement
define subtraction
computer can remove anatomy such as the bones or organs.
define contrast enhancement
contrast can be changed from very high to very low
what is a disadvantage of postprocessing
too much can reduce the information that is transferred to the physician
- manipulation of the image should be kept to a minimum.
define DICOM
- Digital imaging and communications in medicine
- exchanging medical radiographic images within the institution and in the many areas where the images are viewed
- MUST be in DICOM format to get all details for diagnosis, analyzation
define DICOM gray scale function
provides methods for calibrating a particular viewing monitor display system for the purpose of presenting images consistently on different display monitors and printers.
define artifacts
an error in the image
list the different types of artifacts
- quantum mottle
- moire effect
- light spots
- white line
- histogram analysis error
- phantom/ghost image
- scratches/tears
- extraneous line patters
- fogging
define moire pattern
when the grid lines are not aligned with the laser scanning frequency of the CR reader
define light spots
usually caused by dust or other foreign material on the IP
define white line
appear along the length of travel on the image due to dust on the light guide.
define histogram analysis error
improper collimation, improper technique, beam alignment error, scatter, and extreme subject density differences.
define phantom/ghost image
a result of incomplete IP erasure
define scratches/tears
permanent artifacts caused by damage to CR plates
define extraneous line patterns
linear lines caused by noise in the image reader electronics
define fogging
background or scatter radiation is caused by the CR plates being much more sensitive than the former film.
define PACS
- contain all the digital images that are produced in the department, including CT, MRI, ultrasound, and nuclear medicine images.
- picture archival and communication system.
- allows multiple users inside and outside the department to view images
