cr dr test1

analog images are for ___________ viewing as digital images are for ______________ systems

human viewing
computer systems

4 bits can have ____ different values 16

16

8 bits can have ___ different values

256

8 bits = how many bytes? how many gray levels?

1
256 gray levels

number of gray shades available for display

bits

controls the number of possible gray levels in the image

bit depth

will small pixels or large pixels give a crisper photo?

small pixels

determines the number of shades of gray the digital system is capable of displaying

number of bits

increasing pixel bit depth with improve/worsen image quality?

improve

which combo of matrix and pixel size will create greater spatial resolution size

larger the matrix and smaller the pixel

digital image is recorded as a combo of rows and columns known as

matrix

smallest component of the matrix

a pixel is measured in ______

microns

The location of the pixel within the image matrix corresponds to an area within the patient or to a 3D volume of tissue called a _____

voxel

is a higher or lower kVp needed to stimulate electron traps?

higher

CR/DR are kVp or mAs dependent?

kVp

what controls contrast?

computer

pt position accounts for __% of repeats

85%

3 stages of CR latent image digitization:

-scanning
-sampling
-quantization

______ enegery (kVp) gives a wider histogram

low

______ enegery (kVp) gives a narrow histogram

high

shows the distribution of pixel values for any given exposure

histogram

Nyquist Theorem

sampling twice

doing this will increase spatial resolution and image quality

decreasing the pixel size or sampling pitch

distance between the midpoint of adjacent pixels

pixel pitch

born as a result of our long experience in the field of CR; digital imaging technology

exposure data recognizer

phosphors emit light according to the width and intensity of the laser beam as it scans the plate, resulting in a relative speed that is roughly equivalent to a 200 speed film screen system

speed

T/F: rubbing alcohol is recommended for cleaning storage screens false

f

how often should storage phosphor screens be cleaned?

every 200 exposures, every 30 days

portrait = length or crosswise?

lengthwise

landscape = length or crosswise?

crosswise

unlike film screen, where acquisition, processing and display are all in one (film), digital imaging seperates these three processes:

image processing
image display
image acquisition

one of the fundamental physical variable related to image quality in radiography and refers to the efficiency of a detector in converting incident xray energy into an image signal.

DQE: detective quantum efficiency

cesium iodide is to _________ as amorphous selenium is to ____

CR & DR

flat panel detector system: indirect conversion (5 steps)

- radiation
- scintillator
- visible light
- electronic charge
- digital image

flat panel detector system: indirect conversion (3 steps)

- radiation
- electronic charge
- digital image

big difference between CR and DR is the step between plate and digital data, which is?

reader (laser) in CR

control brightness

windowing

reduces noise

smoothing

edges appear more prominent

edge enhacement

more uniform image appearance

equalization

removal of background anatomy

subtraction

makes anatomic structures more visible

contrast enhancement

results in smoothing of the structures contrast reduction

contrast enhancement

provides sharper delineation of the fine structures

edge enhancement

each pixel is assigned a numeric value that represents a shade of gray or brightness level based on the attenuation characteristics of the volume fo tissue imaged

quantization

amount of error that still results in a quality image

latitude

if exposure is more than 50% below ideal exposure, what will happen?

quantum mottle

if exposure is more than 200% above ideal exposure, what will we loose?

contrast

biggest difference between digital and film/screen radiography lies in the ability ..........

to manipulate the digital pixal values, resulting in greater exposure latitude

why do digital systems have significantly greater latitude (3)

- linear responses give the imaging plates
- area recieiving little radiation can be enhanced by the computer
- higher densities can be separated and brought down to the visible density ranges

where does sampling and quantilization happen?

_analog digital converter

PMT

Photo multiplier tube. For every 5 photons hitting the photocathode, 1 electron is produced in the is accelerated to multiple dynodes which produce more e

collects, amplifies, and converts happens where?

PMT

caused by incorrect grid alignment with the laser scan

aliasing or moire effect

refers to the minimum resolvable separation between contrast objects high

spatial resolution

T/F: increasing the radiation applied to the detector will improve the maximum spatial resolution

false, it will not

intrinsic spatial resolution for selenium based direct conversion detectors is higher or lower than that for indirect conversion detectors

higher

distance between the midpoint of adjacent pixels

pixel pitch

pixel pitch can affect?

spatial resolution

decreasing the pixel or sampling pitch will increase/decrease spatial resolution and image quality

increase

in CR, increasing the IP for a fixed matrix will increase/decrease the pixel size and increase/decrease spatial resolution

increase pixel size
decrease spatial resolution

each pixel is assigned a number that reflects the precision with which each sampled point is recorded. in which category dose this happen?

quantization

determines the systems ability to display a range of shades of gray to represent anatomic tissues

bit depth

two types of DR:

direct and indirect

what happens in indirect capture (4)

- machine absorbs x-rays and converts them to light
- CCD or thin-film transistor (TFT) converts light to electric signals
- computer processes electric signal
- images are viewed on computer monitor

what happens in direct capture (4)

- photoconductor absorbs x-rays
- TFT collects signal
- electrical signal is sent to computer for processing
- image is viewed on computer screen

main difference between indirect and direct conversion

direct = scintillator
indirect = selenium

with DR, the size and pitch of the pixel is determined by?

DEL (detector element size)

will smaller or larger DEl size have better spatial resolution

smaller

ability of a system to record available spatial frequencies

MTF (Modulation transfer function)

a perfect system would have an MTF of?

1 or 100%

capacity of the detector to transfer the modulation of the input signal at a given spatial frequency to its output

modulation transfer function

this is responsible for converting contrast values of different sized objects into contrast intensity levels in the image

MTF

measure of the signal response of a detector that is exposed to xrays

dynamic range

in conventional screen

S shaped

for ________ detectors, dynamic range is the range of xray exposure over which a meaningful image can be obtained

digital detectors

digital detectors have a ________ and ________ dynamic range, which, in clinical practice, virtually eliminates the risk of a failed exposure

wider and linear

efficiency of a detector in converting incident xray energy into an image signal

detective quantum efficiency (DGE)

high DQE values indicates that less/more radiation is needed to achieve identical image quality

less

increasing the DQE and leaving radiation exposure constant will do what to image quality

improve it

the most obvious way to minimize patient exposure is to greatly reduce....

number of failed exposures

post processing is done by?

tech

graphic representation of a data set or all pixel values within the exposed image

histogram

histogram analysis is also employed to maintain consistent image brightness despite overexposure or underexposure of the IR, known as:

automatic rescaling

how does the system produce an image when significant exposure errors occur?

automatic rescaling

what is a reference histogram?

look up table

this is used by radiologists for diagnostic interpretation must be of higher quality than those used for routine image review (secondary)

primary display monitors

display monitors used for diagnostic interpretation are typically......

monochrome high resolution monitors

once the image is processed, regions viewed on the image can be altered, also known as shuttering or electronic collimation: it removes increased brightness and removes info that is not useful

electronic masking

low density = high/low brightness

high

high density = high/low brightness

low

the range of image densities is created by the variation in xray absorption and transmission as the xray beam passes through anatomic tissues

density/brightnesss

intensity of light representing individual pixels in image

brightness

differences in brightness between light and dark areas of image

contrast resolution

recorded sharpness structures on image

spatial resolution

controlling factors of spatial resolution (2)

- acquisition pixel size
- display matrix

misrepresentation of object size or shape

distortion

controlling factors of distortion

- SID
- OID
- CR alignment

T/F: CR exposure indicators are vendor specific and not currently standardized

true