chapters 17 and 18 radio physics Flashcards
is it ever appropriate to repeat overexposed digital images?
no, unless there is analog-to-digital converter saturation
what does saturation cause in an image
causes the image to be clipped or burned out
what is data clipping
data is removed from the diagnostic range that can’t be recognized b/c it is above or below the diagnostic range
(OCCURS WHEN ADC REACHES SATURATION)
Philips DR uses __________ numbers
sensitivity (S)
Agfa CR uses_____________ numbers
log median exposure (LgM)
GE DR uses____________ numbers
detector exposure index (DEI)
Siemens uses_________ numbers
Exposure index (EXI)
what is the relation between S number and the amount of radiation striking the IP
the relationship is Inversely proportional
(EDR) exposure data recognizer is what?
optimal reading conditions are determined once the auto mode processing processes the image data in the IP
what allows more than one view be exposed on a single IP?
(EDR) Exposure data recognizer
what are the VOI (values of interest) for a Fuji
full anatomic area
what are the VOI (values of interest) for a Konica
recognition of relevant anatomy
how can you balance AEC
there are lots of ways b/c every manufacture comes up with different ways
does the EI number or the DI number have a direct relation to patient exposure
no there is no relation between EI/DI numbers and patient exposure
deviation index gives what to the technologist?
gives feedback to the technologist regarding technique and image quality based on signal-to-nosie ratio
what does a DI (deviation index) of 0 indicate
indicates that their is no diff. between the desired EI and the actual EI
diffrent IRs have________ detective quantum efficiency (DQE)
diffrent
A high DQE results in ______ noise level
lower
what is a usual EI number derived from
the mean detector entrance exposure which is derived from the MEAN PIXEL VALUE of the image
what is the dynamic range
the number of shades of gray an imaging system can produce
how do you calculate the amount of shades of gray
2^# of bit
what kind of function do Digital receptors have in a graph
linear receptor response function
CR and DR receptors____________ and does not________
can receive any radiation exposure; experience the toe and shoulder limitation of film/screen exposures
areas that receive very little radiation can be enhanced by the _____ instead of being______
computer; clumped at the toe
areas that receive greater exposure can be _____ into _____ instead of being _________
separated; visible densities; clumped around the shoulder
what = bite depth
2^n
how many bits make up a byte
8 bits make up 1 byte
spatial resolution
the ability to see small objects or fine recorded detail
spatial frequency
unit of line pairs per millimeter (ip/mm or in digital # of cycles/mm or micrometer
what happens to the image when we have a very high spatial resolution
this will increase blur even though the resolution will be better
which imaging system has the best spatial resolution
mammography 12 IP/mm
Modulation transfer function (MTF)
responsible for converting contrast values of diff. sized objects into contrast intensity levels in the image
what does high spatial frequency create
blur; results in reduced modulation- reduced amplitude of the signal
as spatial frequency increases what happens to MTF (transfer of object contrast to image contrast)
MTF (modulation transfer function) will go decrease
I.S spatial resolution is spatial frequency at ___ MTF
10%
spatial frequency and MTF make up what
Spatial resolution
in film screen radiography, what is the spatial resolution
8 Ip/mm
what spatial resolution does mammography have
15 Ip/mm (minimal blur)
what tool is used to measure spatial resolution in digital
lead bar pattern test tool
what tool is used to measure spatial resolution in conventional units
resolution test tool
the___ the # of line pairs the_____ the spatial resolution
greater, higher (remember we need a balance of line pairs and MFT)
what are the primary factors of spatial resolution
matrix size, pixel size and pixel pitch
pixel size in relation to spatial resolution
the smaller the pixel size the better spatial resolution
pixel pitch is what
the space from the center of a pixel to the center of the adjacent pixel
what does a narrow pixel pitch do to spatial resolution
increases spatial resolution
what is the spatial resolution for conventional radiography and CR
10 Ip/mm, 5Ip/mm (dynamic range makes up for it because it allows more contrast resolution due to its ability to give more detail
PSF
point spread function function unit (vert. line creates a point when it intersects with the horizontal imaging plane)
LSP
line spread function unit (vert. line creates a point when it intersects with the horizontal imaging plane)
ESF
Edge spread function unit (vert. line creates a point when it intersects with the horizontal imaging plane)
noise
degeneration of image begins with increased image noise (low mAs and kVp create this)
a 10x12 IP with 2k pixels will have a ______ spatial resolution than a 7x7 IP with 2k pixels b/c of the pixel size
worse
Pixel Size (formula)
FOV/ Matrix Size
DQE (detective quantum Efficiency)
is the measurement of x-ray absorption efficiency
what does high DQE do to patient dose
it should decrease patient dose
what is the speed class (DQE)
reflection of the amount of light (PSP); the level of exposure received by the IP (THE MEASURE OF X-RAY ABSORPTION EFFICIENCY)
a luminescent level of 200= how much speed class
200 speed class
what happens when speed class increases in relation to noise
noise will increase (b/c kVp is increased and mAs Isi decreased causing desist fluctuations as speed class increases
the exposure index is ______ proportional to the speed class of operation
indirectly proportional
E.I increased from 1400 to 1700 the speed class is ______ from 400 to ______
reduced, 200
image noise is what
a fluctuation is density/ overall brightness
if the signal is higher than the noise this will = ?
better spatial resolution
S/N; 10/1= 10
good spatial resolution
S/N; 1/10= .1
bad spatial resolution
what specific part of the dynamic range controls contrast resolution in DR?
the ADC via the bite depth (2^n)
does mAs affect contrast resolution?
yes mAs does have an effect on contrast resolution
what process ensures that unnecessary info., such as scatter, outside the collimated edges become eliminated from the histogram analysis
(PRIEF) pattern recognizer for irradiated exposure field
Auto mode processing?
allows IP image data to be sampled and used by the EDR
what determines the range of the histogram data that should be included in the displayed image
VOIs
a value that reflects the diff. between the desired or target exposure to the IR and the actual exposure to the IR is the
deviation index
DI (deviation index) above 0=
increased exposure
DI (deviation index) below 0=
decreased exposure
