Digital Imaging Flashcards
system that uses a thin, active layer within a protective case to record and store x-ray energy as an unprocessed image
computed radiography (CR)
initial exposure of a CR plate results in what
latent image
5 layers of a CR cassette
protective layer, photostimulable phosphor, conductive layer, support layer (base), reflective layer (light shield)
active component of the CR plate
photostimulable phosphor
component that grounds the CR plate and reduces electrostatic charge
conductive or antistatic layer
component that directs emitted light in the imaging plate reader
reflective layer
where the latent image is produced in a CR plate
photostimulable phosphor
layer composed of extremely small particles which store and release energy in a CR plate
photostimulable phosphor
the photostimulable phosphor in a CR plate is commonly made of
barium fluorohalide bromides and iodides with europium activators
energy transfer process that takes place in photostimulable phosphor
photoelectric absorption
the number of electrons trapped during photoelectric absorption is proportional to
the number of x-ray photons that interact with the imaging plate
what is the conductor layer within the CR plate responsible for?
decreasing electrostatic charge
the term latent image in CR is used to describe the
stored energy within the fluorohalides
what is another name for the conductive layer of a CR plate?
antistatic layer
what type of laser is used in a CR imaging plate reader
helium neon laser
which component of a CR reader monitors and stabilizes the laser?
reference detector
what motion does the laser move in along the CR plate in a CR imaging reader?
Raster pattern (like we read text)
laser from CR plate reader interacts with the CR imaging plate, doing what?
causes each individual phosphor to glow in photostimulated luminescence, which is then directed to the photomultiplier tube
how are light photons from photomultiplier tube in CR image reader turned into an image?
analog to digital converter collects light and converts it to a string of numbers, creating a digital signal
how is a CR plate erased ?
entire plate is exposed to an intense white light
what takes the place of the photomultiplier tube in some CR imaging readers?
charge-coupled device
what is responsible for storing the latent image within the CR imaging plate?
photo-stimulable phosphor
what is the purpose of the laser within the CR digitizer?
release latent image from the photo-stimulable phosphor layer
what is the role of the photomultiplier tube within the CR system?
collect and multiply light photons and convert them to electrons
what is the primary function of the analog to digital converter within the CR plate digitizer?
convert electrical signals into a digital signal
what is the order of events after the imaging plate is inserted into the CR reader?
imaging plate is extracted by rollers, hit with a laser, laser moves in a raster pattern, and energy is released as light photons
For which reason is conventional film radiography advantageous over digital radiography?
spatial resolution
what happens after the computer reconstructs a digital image?
the image is re scaled according to the predetermined algorithm
digital images are further enhanced by the computer program through:
digital filtering
in order to increase contrast resolution to better visualize small fine detailed structures, the image can be manipulated by
decreasing window width
The fundamental component of a computer involved with feeding information into the CPU is termed a
input device
what does the dynamic range of digital imaging refer to?
the number of signal values an IR is capable of capturing
what does one pixel represent?
one value of brightness
what does spatial resolution of a digital image depend on?
matrix size
failure of the IR laser reader to find the collimation edges of an image during image processing will result in
the image being too bright or too dark
what is the end result of automatic rescaling of images?
uniform contrast and image brightness
what does the DQE or detective quantum efficiency refer to?
the ability of the image detector to create an output signal that accurately reflects the input signal
T / F: the higher the sampling frequency of the reader, the more information is extracted from the image receptor thus higher resolution
true
what is a histogram of pixel values used to do?
make adjustments in image brightness, determine the level of brightness of pixels in image, determine the level of the exposure
T / F: air kerma is the measurement of radiation energy absorbed in a unit of air
true
what is an advantage of direct capture digital radiography?
no loss of resolution from converting analog to digital data
a wider window width increases the range of densities and therefore:
lowers contrast
when an image reader is unable to detect image exposure borders as a result of misalignment, what occurs?
the reader reads all information outside the borders creating an unacceptable image
what is the active element in a CR imaging plate storage phosphor
barium fluorohalide
what is the standard that allows the CPU to communicate to OUTPUT devices?
DICOM
the term used in digital imaging to indicate the exposure latitude (range) is
dynamic range
the process of digital imaging programs automatically changing the appearance of an image based on predetermined image quality factors
rescaling
conversion of x-rays for direct conversion digital radiography
converts x-rays directly to electronic signals
conversion of x-rays for indirect conversion digital radiography
converts x-rays to visible light, then into electronic signals
what is the photoconductor in a direct conversion digital imaging system plate made of?
amorphous selenium
path of x-ray to digital signal in direct conversion digital radiography
electrical charge applied to photoconductor before exposure, charge is collected by DEL storage capacitors, charge converted to signal by ADC
two versions of indirect conversion DR systems
either scintillation layer connects to charged coupled device, or scintillation layer connects to photodiode which connects to a thin film transistor
what is the scintillation layer in indirect conversion DR made of?
cesium iodide or gadolinium
what does the scintillation layer in indirect DR systems convert?
x-ray photons into light photons
what does the charged coupled device convert in an indirect DR system?
light photons into an electrical signal, which passes to ADC
what is the photodiode layer in indirect DR plates made of ?
amorphous silicon
what does the photodiode layer convert in indirect DR plates?
light photons into an electrical signal, which is sent to the TFT, then to ADC
which indirect conversion system is generally used for angiography and fluoroscopy?
thin film transistor system
which imaging modality uses direct conversion DR systems?
mammography
which component of an indirect capture detector converts visible light into electrons?
photodiode
what does the thin film transistor layer of a flat panel detector system do?
collects electrical charge
which two flat-panel detector components can collect and convert light into an electrical signal?
photodiode and charge-coupled device
what element used in the construction of a flat-panel detector is able to convert x-ray photons directly into an electrical signal?
amorphous selenium
which device acts as a switch within a flat-panel detector to release the electric charge collected by the detector element?
thin film transistor
cesium iodide is the perferred material for the scintillation layer because it can be formed into
columns which focus light photons
in a CCD system, what two ways do the scintillation layer connect to the CCD sensor chips ?
lenses or fiber optics
the digital image receptor is comprised of small elements called:
Detector elements (DELs)
what are the components of a single DEL?
capture area, storage capacitor, TFT gate
what are the components of the capture area of a DEL?
top electrode, detection layer, bottom electrode
what part of the DEL detects radiation
capture area
the storage capacitor of the detector element (DEL) stores what?
a positive charge
what is the percentage of the DEL devoted to the detection layer called?
fill factor
what is the relationship between the fill factor and spatial resolution?
directly proportional
if the fill factor is decreased, what happens to patient dose and beam intensity?
beam intensity is increased, patient dose increased
what is the term for the distance between the DELs?
pitch
most common digital imaging pixel matrix size
1024 x 1024
definition of spatial frequency and how it is measured
number of line pairs in a given length, measured in line pairs per millimeter
smallest element in a digital image
pixel
what is the spatial frequency if the pixel size is 0.07mm?
7.14 lp/mm
total number of possible brightness levels that can be assigned to any given pixel in the digital image
bit depth
formula for calculating bit depth or amounts of shades of gray per pixel
2^x (whatever the bit used is, 2-bit, 8-bit, etc)
process of assigning brightness levels to a given pixel
quantization
during digital image formation and processing, where does quantization take place?
analog to digital converter
what is the smallest exposure difference that can be detected and displayed by the imaging system?
contrast resolution
approximate representation of the distribution of numerical data
histogram
process of assigning a number to identify a set of discrete values within a continuous process
quantization
range of exposures that produces quality images at an appropriate patient dose
exposure latitude
what step in digital image processing identifies the useful exposure values in raw image data?
histogram analysis
what is the process that corrects slight under or over exposure erros made by the technologist
rescaling
what process is used to display the digital image with ideal brightness and contrast
look up table LUT adjustments
in a radiographic histogram, what does the Y axis represent
frequency of specific signal intensity values
In a radiographic histogram, what does the X axis represent
specific signal intensity values from low to high
T / F: In a digital imaging system, brightness reflects the amount of radiation the image receptor received
false, brightness is determined through histogram processing
compares the amount of signal in an image to the amount of noise in an image
signal to noise ratio
mottled appearance caused by an insufficient number of photons striking the image receptor
quantum noise, quantum mottle, photon starvation
random information created by the electronic components within the imaging system
system noise
random information created by the background radiation striking the image receptor
ambient noise
photons that are no longer aligned with the anatomy
scatter radiation
which type of noise cannot be reduced?
ambient noise, caused by presence of background radiation which always exists
photons that add information but do not represent the anatomic structures are considered:
scatter radiation
a score that describes the ability of the imaging system to convert the remnant x-ray beam into a high quality image
detective quantum efficiency (DQE)
a system with high DQE posesses what?
high efficiency in converting the x-ray signal into an image
amorphous selenium is a material used in which imaging system?
direct digital radiography
score that measures accuracy of the image compared to the actual object
modulation transfer function (MTF)
another name for modulation transfer function (MTF)
image fidelity
as spatial frequency (lp/mm) increases, modulation transfer function
decreases
what is the relationship between MTF and spatial frequency?
indirect relationship
range of exposure values that can be captured by an image receptor
dynamic range
range of exposures that can produce quality images at an appropriate patient dose
exposure latitude
formula for calculating pixel size based on spatial resolution
1 / (spatial frequency in lp/mm x 2)
In adjusting the appearance of a digital image, window levels can be adjusted from
-1000 (air) to +1000 (bone)
Digital image data is acquired through
Direct capture digital sensors
Digital filtering enhances the contrast resolution of a digital image by
reassigning an average gray scale value to each pixel according to its neighbor’s value
Computers store and display visible images in columns and rows possessing depth, each of these cells is called a
Voxel
in digital imaging, the x-ray beam intensity that interacts with the image receptor is reffered to as
signal
the range of exposure values the image detector is able to produce is
latitude
a lead apron could cause an exposure indicator miscalculation because the image data would be misrecognized as
gross underexposure
how dark or light a digital image appears on a display monitor is known as
brightness
the ability of a digital system to display subtle changes in shades of gray is called
contrast resolution
the primary causes of quantum noise/mottle are
excessive fog, insufficient signal strength, excessive scatter
the x-ray energy is absorbed and the phosphors of the IR emit light, and the latent image is formed by
some of the light energy being retained by the plate
what determines the density/brightness value of each image pixel?
pixel depth
when a CR plate is not erased sufficiently, energy will be retained and if used for another exposure, what will occur?
a higher signal strength
what component of a laser reader is responsible for extracting the light image from the PSP?
light collecting guide assembly
electrons are released during image conversion and are released from the
F traps
DELS stands for
detector element size
once the signal is detected, the algorithm used by KODAK is called
tonescaling
quantization of collected exposure data occurs by
histogram analysis
the process of returning pixel values to their original levels by a reverse process is called
deconvolution
systems using the S number exposure index like Fuji systems are typically
200-400 and inverse to the beam intensity
LME or Log Mean Exposure Index usually range from
1.9 - 2.1
what sampling control reduces image blur with PSPs?
high frequency sampling
The S Number exposure indicator used by Fugi, Konica and Philips maintains what type of relationship with the actual radiation exposure received by the image receptor/ detector?
Inverse
