Digital Image Quality

digital images have ___ spatial resolution and ____ contrast resolution

bad, good

what type of error occurs when the computer cannot detect the borders of the IR exposure

histogram error

small pixels result in ____ spatial resolution

better

a low exposure to the IR will result in what type of digital artifact

quantom mottle

this controls the number of shades of greay available to a digital imaging system

bit depth

a system that displays a greater number of shades of gray has been ___ resolution

contrast

window width control

contrast

window level controls

brightness

digital detectors are ___ sensitive to scatter

more

the adjusting of the image by the computer program to present an image with predetermined brightness is called

automatic rescaling

an expression of how well the signal of a digital system is preserved in an image compares to the amount of noise present

signal to noise ratio

how well subject contrast of a body part is represented in the image

MTF

how efficiently a system converts xray input into a useful output signal

DQE

what type of error most commonly reults in the need to repeat an image with digital

positioning errors

measure of luminance of a soft copt monitor expressed in candela per sq meter

brightness

the measurement from the center of one DEL to the center of the next determines

pixel pitch

this states, the scan frequency must be 2X the bandwidth for a quality image

nyquist theorem

picture element

pixel

how often data is acquired from the detector

sampling frequency

true or false: kVp is no longer important in determining beam quality with full field digital systems

false

cassette less digital systems use _____ as an indicator of exposure to meausre actual energy absorbed vs radiation exposure

DAP

how many shades of gray are available using a system with a bit depth of 14

16,384

an extremely overexposed IR will display poor

contrast

the higher the sampling frequency, the ____ the spatial resolution

better

what is the pixel size with a matrix of 1024 and a FOV of 24 cm

0.23 mm

with digital imaging, what has the greatest control over image contrast

computer algorithms

a digital systems response to xray exposure is

linear

what type of grid frequency is recommended for use with digital systems

high

true or false: mAs no longer controls beam quantity with digital imaging

false

this determines the exposure indicator value

histogram analysis

with CR, the plate is coated with _____ that as acts as an active substance

barium fluorohalide (europium)

in CR, where is the latent image held

in the europium

how is the latent image released with CR

as the laser beam scans the plate

what kind of energy is emitted as it is released from the plate

blue/violet light

how is resolution determined with CR

laser scanning frequency and size of the laser beam

with DR, the image receptor is made up of an array of

DELS

what are DELs measured in

microns

what two substances can a DEL be made out of

amorphous silicon or amorphous selenium

what captures x-ray signal and stores briefly in TFT read out

DEL

what does ADC stand for

analog to digital converter

electronic compontnets layered into glass substrate that includes the readout, charge collector, and light sensitive elements

TFT

wha

what does TFT stand for

thin film transistor

what is a determining factor for detail or spatial resolution

the size of the DEL

what is the term that describes the center of one pixel to the center of the next

pixel pitch

what type of pixel pitch results in improved detail

lower

how frequently the signal is sampled

sampling frequency

true or false: a higher sampling frequency yields improved detail

true

determinds number of shades of gray available to the system which helps determine the contrast resolution

bit depth

what is the formula to calculate the number shades of gray

2^n (n=bit depth)

digital systems offer superior ____ resolution

contrast

digital systems require a tissue difference of ___ in adjacent tissues to assign a different shade of gray to the image where film system requires a ___ difference

1%, 10%

what are two words for an array of hardward pixels

DEL and DEXEL

histogram must be able to detect a minimum of ____ image borders to build an accurate histogram

3

what are the requirements to avoid a histogram error

anatomy should be centered, borders equidistant, collimation must be symmetrical

must expose a minimum of _____ of the IR to avoid histogram error

20-30%

contains histograms for the average exam

look up table

what does a look up table determine

image brightness and contrast

what will happen in the image histogram doesn’t match the stored histogram in the look up table

computer will adjust pixel values to match the average histogram more closely

an underexposed image will appear

noisy

an overexposed image will exhibit

poor contrast

processing in spatial domains

breaking data into spatial components

processing in frequency domain

breaking data into intensity components

what is calculated and determines whether the exposure recieved by the IR is adequate

exposure index number

expressed the patient exposure, considering the size of the field of view in the calculation ( also used as an indication of the exposure to the IR )

DAP

what does DAP stand for

dose area product

no matter how great the quality of the “captured” information, if a poor-quality viewing monitor is used…

detials will not be visualized

what viewing monitor is 2K

primary

what viewing monitor is 1K

secondary

the monitor is made up of rows and columns of pixels also known as

matrix

pixel size

FOV in mm/matrix

what conversion should pixel size always be in

millimeters

the better the resolution, the bigger the file, the more storage required…

the longer it takes to transmit the data

common computer language that allows different systems to communicate

DICOM

Why must PACS systems have back up storage

to ensure imaged are not lost during an emergency or down time

what are the two greatest benefits of digital imaging systems

wide dynamic range and superior contrast resolution

if the image receptor is sensetive to subtle differences in signal (resulting in differences in attenuation) is has a what dynamic range

wide

the ability of an imaging system to demonstrate subtle differences in contrast of adjacent tissues

contrast resolution

digital systems require a tissue difference of ___% resulting in superior contrast resolution

1

what helps to determind contrast resolution

dynamic range and bit depth

what assigns contrast to specific histograms

image processing (Look up table)

what type of noise occurs when there is not enough exposure to the IR

mottle

what type of noise occurs from the electronic components of the system itself

snow

what type of noise occurs when the system is non-functioning

dead pixels

what type of noise occurs when there is a group of dead pixels

clumping

what type of noise occurs when the plate is exposed to heat

heat blur

what type of noise occurs when there is incomplete erasure of IR

ghosting

what type of noise occurs when the detector cannot get rid of the signal from the previous exposure

image lag

what is the most common cause of repeats with digital imaging

poor positioning

true of false: CR delivers less patient dose then DR

false

spatial resolution in order of worst to best

CR, indirect capture, direct capture, detailed film systems

expressed whether all the information from the anatomy is present in the image

modulation transfer function

meausurment of recorded detail, sharpness, resolution

modulation transfer function

the ability of a system to convert signals from the xray beam to pixel values

modulation transfer function

the ability of a system to record the available spatial frequencies

modulation transfer function

exposure to the IR is expressed in

mR

what type of relationship does FUJI have with exposure

indirect

what type of relationship does KODAK have to an exposure

direct

luminance should not vary more than ___%

10

criteria for digital image quality

brightness, contrast, SNR, spatial resolution, shape resolution, size distortion, artifacts

shades of gray present in LUT for that exam

optimal brightness