DR p1 Flashcards
define elongation
type of distortion where anatomical parts appear bigger than norma
define foreshortening
type of distortion where anatomical parts appear smaller than normal
what aspect of RT does distortion impact
treatment planning
aren’t able to plan accurately
image produced is dependent on 3 main things
pt factors - thickess, composition, pathology
exposure factors - kVp, mAs, distance
imagine system characteristics - high voltage gen, filtration, focal spot size
digital vs analog
digital - 0s and 1s
analog - stream of info
in the initial stages of digital detectors are signals analog or digital? what happens to them?
analog -packets of electronic current
they are converted by a ADC (analog to digital converter) during image readout
the digital image is composed of tiny cells of numerical data in a _____ of ____ and ____
matrix
columns
rows
each cell in a matrix is called a ____. they are the smallest elements of a digital image
pixel/picture element
greater the number of pixels, the higher the _____
spatial resolution
an image is described by how many ______ it contains
pixels
what limits the spatial resolution?
pixel size
can pixels represent multiple shades of grey?
no only one
What is spatial resolution best at measuring
recorded detail
what is each pixel assigned
a numerical value that corresponds to a shade of grey somewhere between white and black
what is a voxel?
volume element (of the pixel)
define dynamic range
range of grey scale values that can be assigned to each pixel
does digital imagine have more or less spatial resolution than screen film
less spatial resolution
what is special about the monitors displaying digital radiographic images
they have liquid crystal displays
when an electric current passes through the liquid crystal display what happens
causes the molecules to change shape/direction
either letting light pass through or not (if necessary)
what type of light do passive screens use
fluorescent light
what type of light do active screens use
LED - light emitting diode
fyi - these are brighter, have superior contrast resolution, and better viewing angles then fluorescent
define photometry
science of response of the human eye to visible light
what are the 2 laws of photometry
define each
ISL - luminous intensity decreases in proportion to the inverse square of the distance from the source
Cosine law - maximum luminous intensity occurs when a monitor is viewed straight, luminous intensity and contrast decrease when viewing from an angle
define DICOM
digital imaging and communication in medicine
protocol/standard to produce, manipulate, exchange, and store imaging data
used so that no data is lost through its transfer
data is viewed consistently
what is GSDF
grey scale display function
allows for display of DICOM compatible device with consistent gray scale and appearance
what are the 5 objectives of DICOM
RT images RT plan RTSS - pt anatomy RT dose RT treatment record
define PACS
picture archiving and communication systems
universal system for DR images to be stored and transffered
what are the 4 components of PACS
image acquisition
display system
network
storage
what does PACS improve
image interpretation, processing, viewing, storage and recall
what are the 4 stages of digital radiography
image acquisition
image processing
image display
image storage
what are the 2 main classes of imaging systems
indirect and direct radiography
define indirect radiography (CR)
phosphors react with xrays and store energy for a vrief time until processed
define direct radiography
sensors detect radiation leaving the pt and send data to a computer in digital format
what does PSP stand for
what are other names it goes by
what does it do
photostimulable phosphor detector systems
aka storage phosphors or imaging plates
PSP screen traps energy from xrays that can be read out later
PSP + Cassette =
imaging plate
CR cassettes and imaging plates also have integrated _____
grids
in CR what happens to electrons
electrons are trapped in a higher energy metastable state inside the slate
they then become stable in the reader
what happens when the electron becomes stable in the reader
light is given off
this light is the signal that creates the images
which is able to produce more shades of grey screen film or CR
CR (16000 while SF is only 32)
computed radiography
a) CONVERTS AN ANALOG SIGNAL TO DIGITAL
b) CONVERTS A DIGITAL SIGNAL TO ANALOG
c) HAS A PURE DIGITAL SIGNAL
d) HAS A PURE ANALOG SIGNAL
a
The image receptor used in CR is:
a) Flat panel receptor
b) Film
c) Digital
d) PSP screen
d
Spatial resolution (in CR) is determined by:
a. Distance
b. kVp
c. Number of pixels
d. High voltage generator
c
spatial resolution
a. Is higher in screen-film radiography than digital
b. Is limited by digital file size
c. Allows us to see fine details
d. All of the above
d
Which of the following is not a part of PACS:
a. A computer for image display
b. An mRI computer
c. A PET scan
d. Hospitals mainframe
c
