Exam 3 Flashcards
binary # system
lang of 1’s & 0’s that comp’s use to process data
bit
single unit of data (binary unit)
byte
8 bits; amount of mem needed to store 1 alphanumeric character
RAM
random access memory; short-term storage for open programs (MB, GB, TB) that can be stored/accessed at random from anywhere in about equal amounts of T
ROM
read-only memory; data storage device that contain info supplied by manufacturer that cannot be written on or erased
teleradiology
transfer of imgs & pt reports to remote sites
LAN
local area network; sm area networked w a series of cables/wireless access points allowing comps to share info
WAN
wide area network; spans lg areas; connected by telephone wires, satellites, other comm cables
imaging plate. what does it replace? what occurs? what is it capable of doing?
replaces rad film; img’s formed by interaction of XRs w PSP; capable of storing latent img
PSP
photostimulable phosphor, active layer of IP
what chem is used as the PSP in an imaging plate?
Ba Fluoro Halide coated w Europium (and a dye that differentially absorbs the stimulating light)
prompt emission
when XR exposes PSP, resultant energy transfer excites e-‘s into metastable state; 50% of these e-‘s immediately return to their ground state, resulting in a prompt emission of light
metastable e-‘s?
e-‘s excited from the energy transfer when an XR exposes a PSP
what percentage of e-‘s is converted into normal stage soon after exposure?
50%
process of img production in CR? (4)
- expose (–> XR-induced img-forming signal)
- stimulate (laser interacts w PSP to stim latent img)
- read (light signal emitted after stimulation is detected/measured)
- erase (residual metastable e-‘s moved to ground state by intense light)
color of laser commonly used in CR to scan imaging plate?
infrared
factors affecting spatial resolution (amount of detail present in img) of CR img? (5)
- phosphor layer thickness (thinner better)
- pixel size (smaller better)
- matrix size (bigger better)
- # pixels (more better)
- diameter of laser (smaller better)
primary erase?
erases latent img
secondary erase?
erases scatter
explain img fading in CR and what should be done to overcome problem?
remaining metastable e-‘s (from stimulated laser) return to their ground state over T causing latent img to fade; process img soon after exposure
element used in gas laser?
He/Ne
explain how wavelength of laser beam affects detail
stimulating laser light is monochromatic & resultant emitted light is polychromatic; the longer the laser wavelength, the greater difference btw it’s wavelength and that of the emitted light, causing less confusion/interference when img is read
a ______ wavelength of laser gives better resolution
long
a _____ diameter laser produces img’s w better spatial res
sm
ADC?
analog to digital conversion
DAC
digital to analog converter
______ and _______ are the processes of analog to digital conversion (ADC)
sampling & quantization
What does an IR response of a CR system look like on a graph and what is the x & y axis?
straight climbing line; Optical Density on y-axis and µGy(mR) on x-axis
a 12 bit CR img has ______ gray levels
4096
if the bit depth is 7 what is the dynamic range of the CR img?
128 shades of gray
CCD?
charged-coupled device (a silicon based semi-conductor); used in indirect conversion systems
____________ is the ability of the CCD to respond to a wide range of light intensity, from very dim to very bright
dynamic range
explain DR indirect system and the chems used
XR absorbed by thin layer of cesium iodide (changes XR to light), a scintillation phosphor, which then produces a flash of light which interacts w a layer of amorphous silicon photodiode to create electric charge (2 steps - XR to light, light to signal)
explain DR direct system and chems used
XR directly interacts w a layer of amorphous selenium, which produces the electric charge (1 step - XR to signal)
spatial res in DR is ______ limited
pixel limited (limited by pixel size)
TFT? f(x)?
(thin film transistors) absorbed rad is converted into electric signals, and that electric charge is temporarily stored in TFT until readout (the pattern of electrical charges constitute the latent img)
spatial frequency? whats the unit?
of line pairs in a given length; line pairs per millimeter (lp/mm);
line pair?
a high contrast line separated by an interspace of equal width (so it’s ONE line & ONE space)
spatial resolution?
ability to img sm objects that have high subject contrast; ability of imaging system to resolve/render on the img a sm high-contrast object
contrast resolution?
ability to distinguish many shades of gray from black to white
pixel size is related to ______ resolution
spatial res
laser beam diameter relates to _____ resolution of CR imaging system
spatial res
dynamic range is related to _______ resolution
contrast res
bit depth is related to _____ resolution
contrast res
how is spatial frequency related to spatial resolution?
(direct) higher spatial frequency –> better spatial resolution
what is modulation transfer f(x)?
the ratio of img to object as a f(x) of spatial frequency; ideal img system has MTF of 1
what is indicated by a low MTF?
the img is a closer representation of the object, giving better resolution (best MTF is 1)
dynamic range?
of shades of gray that an image system can produce
window level?
controls brightness/density in post-processing
window width?
controls contrast in post-processing
a higher SNR indicates ____ resolution (more/less)
more
contrast resolution is limited by _______
noise/SNR
spatial resolution in screen film radiography is determined principally by _____________
geometric factors (primarily focal-spot size)
DQE?
(detective quantum efficiency) measure of XR absorption efficiency; measurement of % of absorbed XRs when they hit the detector
Which has the highest DQE? (film, CR, DR)
DR
if a system has a dynamic range of 512, what is the bit depth?
9 bit
teleradiology
transfer of imgs & pt reports to remote sites
factors affecting spatial resolution (amount of detail present in img) of CR img? (5)
- phosphor layer thickness (thinner better)
- pixel size (smaller better)
- matrix size (bigger better)
- # pixels (more better)
- diameter of laser (smaller better)
in CR, which IP layer stores the latent img?
PSP (active layer)
Hounsfield scale?
math calculation used to assign numerical value to gray
which laser wavelength is better and why?
longer wavelength bc easier to differentiate from emitted pt info light, causing less noise
which laser is better? why? solid state or gas?
solid state bc has higher/longer wavelength
photomultiplier?
amplifies light (increases intensity –> increase signal) and sends to digitizer (which assigns values to pixels)
In order from best to least spatial resolution, list the systems and their spatial frequency
- mammo (15 lp/mm)
- film (10 lp/mm)
- DR (5 lp/mm)
- CR (3 lp/mm)
optical filter?
helps differentiate laser from pt info (to reduce noise)
2 causes for moiré artifact
laser lines II to grid lines, frequency harmonics (scanning frequency matches grid frequency)
cones v rods
cones for bright/photopic vision, and rods for dim/scotopic vision
Exposure Indicator for Fuji systems?
S# = 200-400, (indirect relation to exposure)
exposure indicator for Kodak/Carestream systems?
Ei = 2000, (direct relation to exposure)
exposure indicator for Agfa?
log mean = 2.2, (direct relation to exposure)
4 IP artifacts, and how they appear (white/black)?
- cracks (w, - density)
- adhesive tape (w, - density)
- hair (w, - density)
- back scatter (b, + density)
how do you reduce the IP artifact of backscatter?
collimate
Indirect conversion system?
XR + CsI (Cesium Iodide) –> light;
light + a-Si (amorphous silicon) –> electric signal
Direct conversion system?
XR + a-Se (amorphous selenium) –> electric charge/signal
typical grid frequency in digi?
150+ lines/in
underexposure in digi causes what?
quantum mottle (grainy)
overexposure in digi causes what?
an affect on contrast
all DR systems use what to temporarily store the latent img?
TFT
Which network is faster?
LAN (PACs rooms)
dynamic range is IDed by?
bit capacity of ea pixel
principle descriptor of contrast res?
dynamic range
the greater area of TFT, the greater the _____, which means ____ rad required to make img
DQE; less
A bigger Hounsfield scale means what?
better contrast res
what is found in the reader that helps to improve the SNR, which increases spatial resolution?
optical filter
pixel pitch?
space btw pixels
how do you determine pixel size?
FOV/matrix size (make sure they are in the same units)
how many bytes usually constitute a word?
2 bytes
+ pixel pitch –> ?
- spatial res
what do you increase to increase SNR?
+ mAs
what makes up dynamic range?
Hounsfield scale
shuttering?
(post-processing) black bg is added to original coll. edges
dynamic range is IDed by?
bit capacity of ea pixel
principle descriptor of contrast res?
dynamic range
what do you increase to increase SNR?
+ mAs
the greater area of TFT, the greater the _____, which means ____ rad required to make img
DQE; less
A bigger Hounsfield scale means what?
better contrast res
what is found in the reader that helps to improve the SNR, which increases spatial resolution?
optical filter
histogram?
data w/in coll. area produce a graphic representation of the optimal densities (can be changed using window level/width or LUT - lookup table)
reflective layer of IP sends light in a ______ direction and is ______ to reduce light spread
forward; black
phosphor center?
stimulated e-‘s (from XR interaction w BFH crystals in PSP) enters conductive layer where they get trapped in a “phosphor center”
Raster pattern
laser scanning beam sweeps horizontally from L to R
photomultiplier?
detects (blue) light emitted from IP –> amplifies light –> sends to digitizer
digitizer?
(ADC) divides analog img into matrix & assigns ea pixel a value based on brightness
which system has the most exposure latitude?
digital
how do you reduce quantum mottle?
+ mAs
Europium is the _______ of PSP
activator
PSP screen is handled in ________?
reader
With CR, contrast is ______ regardless of exposure
constant
principle source of noise in CR is?
scatter rad
output signal from PSP is converted (ADC) by ________
photodetector
ghosting is prevented by?
erasing w white light
CR produces __________ gray levels
10,000
In DR, the latent img is formed on the ____________
rad detector
brightness of region is determined by what 2 things?
Z & mass density
increasing FOV does what?
reduces spatial res (makes pixel size bigger)
dynamic range determines contrast res and _________
motion blur
what has the best spatial resolution? why?
mammography; highest spatial frequency (most lp/mm)
speed determined by?
PSL (photostimulable luminescence); more PSL –> more speed (and less dose)
extremities and mammo IR’s have…?
highest resolution
salt and pepper effect?
grainy quantum mottle; salt/white - XR doesn’t reach IR; pepper/black - XR reaches IR
what is the typical grid frequency in digi?
150+ lines/in
4 IP artifacts and whether they represent pos/neg densities?
- cracks - neg (white)
- adhesive tape - neg
- hair - neg
- backscatter - pos (black)
plate reader artifacts?
intermittent appearance of extraneous line patterns
horizontal white lines may be caused by _____ on ____________ in plate reader
dirt; light guide
loading multiple IP’s in 1 cassette can cause what?
ghosting
what specific problem can cause a moire pattern plate reader artifact?
grid orientation (if grid lines II to plate reader’s scan lines –> grid lines SHOULD be perpendicular to plate reader’s scan lines)
electric charge is briefly stored in ______ until readout (in both systems)
TFT
DR systems use ____________________ to absorb rad & converts the energy into electrical signals which are temp. stored in TFT (constituting the latent img)
flat panel direct capture detector
line spread f(x) is largest for ___________ and least for __________
screen-film mammo; a-Se digi mammo
what eliminates distracting white/clear areas?
shuttering
what is the data recognition program?
searches for the anatomy on the IR by finding the collimated edges and eliminates the scatter outside the coll.
what happens if the data recognition program fails to find the coll. edges?
incorrect data collection –> img will be too bright/dark
what is generated from the img data collected from CR sampling?
histogram
what ID’s all densities on an IP in form of a graph?
histogram?
what is on the x- and y-axis of a histogram?
x: amount of exposure read
y: # of pixels for ea. exposure
the shape of a histogram is _________? and ______________ per part exposed
anatomy specific; stays fairly constant
Nyquist theorem?
when sampling a signal (ADC), sampling frequency must be greater than twice the bandwidth of the input signal (so img reconstruction nearly perfect)
3 conversions that cause loss of detail (or - res) in CR
- e- –> light
- light –> digi info
- DAC
when _________ is greater than Nyquist frequency and ______ occurs less than 2x’s/cycle –> info is lost and a fluctuating signal is produced (called?)
spatial frequency; sampling
wrap around image
wrap around img is? causing what kind of artifact?
2 superimposed img’s slightly out of alignment (from spatial freq.>Nyquist freq.; samplings/cycle); causes moire artifact
what states that at least 2x’s the # of pixels needed to form the img must be sampled to combat the loss of resolution?
Nyquist theorem
CT/MRI have a dynamic range of what?
12 bit dynamic range
Digi Mammo has what dynamic range?
16 bit
img noise limits ______ resolution
contrast
spatial res. (img detail) is determined by?
MTF (sm better)
contrast res. is determined by?
noise and SNR (bigger SNR better)
Dose creep?
digi is capable of - pt dose by 20-50% but bc tech’s tend not to use optimal exposures, pt’s dose actually + w digi
higher DQE means what?
less rad required to make img
Out of DR, CR and film, which has highest and lowest DQE?
highest DQE - DR
lowest DQE - film
the _____ has higher sensitivity for rad & much wider dynamic range than screen-film IRs
CCD
2 types of indirect conversion systems?
CsI/CCD and CsI/a-Si
_______(contrast/spatial) resolution is more important for soft tissue radiography
contrast
imaging system spatial resolution is spatial frequency at ________
10% MTF
with increasing spatial frequency, img ____ worsens in radiography
blur
output hardware?
devices that translate comp info into a form ppl understand (i.e. display screens, printers)
input hardware?
devices that convert data into a form comps can use (i.e. keyboards, mice, fax, scanners, etc)
_______ allows visualization of all shades of gray
postprocessing
spatial res. in screen-film radiography is determined principally by?
focal-spot size
_________ is preserved in digital imaging, regardless of dose
contrast res.
___________ should replace dose creep.
technique creep
pt dose in DR should be _____ bc of high _____
low; DQE
the ____ XR beam has lower energy than the _______ XR beam
scatter; primary
7 factors that affect contrast resolution?
- IR size (sm better)
- coll. (+ better)
- overexposure ( - contrast)
- dynamic range/Hounsfield units (+ better)
- bit depth (+ better)
- SNR (+ better)
- Acquisition Error - incomplete charge transfer (electronic noise/memory artifact)
