Exam 2 -Qualities of digital and digital technique

the ideal brightness of an image is

optimum level in which all pixels within anatomy are displayed as level of gray

brightness in the displayed image is first set by

rescaling

after rescaling how can brightness be adjusted in the displayed image

window level

window level is the opposite of

brightness

increasing window level makes the radiograph

darker

holdover term from film days

density

density

darkness of any portion of the image

what is contrast

percentage/ratio between the brightness of two adjacent areas of the image

what is necessary for visibility

minimum contrast

what is gray scale

range of different brightness levels

the term "windowing" referes to

window width

too long of a gray scale can cause

too little difference between details

contrast in the displayed image is first set by

look-up table (LUT)

after LUT how is contrast changed in the displayed image

windowing

window width is the opposite of

contrast

image noise

any non-useful contribution to the image that interferes with the visibility of anatomy or pathology of interest

T/F: we ideally want no noise whatsoever

False

image mottle has far exceeded what in the digital age

fog from scatter

proportion of diagnostic information to obstructing disinformation

signal to noise ratio (SNR)

all forms of destructive, non-useful input

noise

how can SNR be improved

reduce noise or increase signal

sharpness of details

spatial resolution

abruptness of edges of an image

sharpness

spatial resolution affected by

focal spot size, beam geometry, motion

T/F: digital processing has no affect on shape distortion

True

shape distortion caused by

tube, part, or IR misaligned

difference between size of a real object and size of its projected image

geometric magnification

change in size created by applying zoom or magnify of display monitor

display zoom

geometric magnification can lead to

diagnostic misinformation

display magnification can lead to

pixelated image, aliasing (moire artifact)

resolution can by lost by either

blurred edges or poor contrast

measurement of an imaging system's capability to convert alternating signals in remnant beam into alternating pixel values/brightness levels in captured image

Modulation Transfer Function (MTF)

role for digital radiographic technique

provide adequate signal at the IR for computer to be able to manipulate the data

what is used to achieve the maximum signal/noise ratio

digital radiographic technique

T/F: mAs can compensate for inadequate kVp

False

percentage/ratio of x-rays that make it through the patient, tabletop, and grid to incident on IR

penetration

what does the IR care about

total exposure level from remnant beam

total exposure at the IR based on

combination of kVp and mAs

ratio between adjacent areas of the remnant beam representing different tissues within body

subject contrast

higher contrast resolution

digital

higher spatial resolution

film

digital has _____ the contrast resolution of film

10x

what allows for dose saving methods in digital radiography

extended exposure latitude of digital systems

conventional film required a minimum _____ subject contrast to distinguish between tissues

10%

digital radiography requires a minimum _____ subject contrast to distinguish between tissues

1%

margin of error when setting techniques

exposure latitude

exposure latitude aka

straight-line portion

exposure latitude

range of radiographic techniques that can produce an acceptable image

a high subject contrast allows what exposure latitude

narrower

a low subject contrast allows what exposure latitude

wide

all technical aspects of the original exposure become

less critical in digital

what does the wider exposure latitude mean for the technologist/patient

flexibility to use grids and filters less, lower grid ratios, higher kVps

increased exposure latitude of digital systems primarily in what direction

upward

for increase in technique the only restrictor factor is

effect on patient dose

how far over can you overexpose and still have a good displayed image

10x

increased latitude of digital systems allow flexibility to

use non-grid techniques and use lower grid ratios

both using non-grid techniques and lower grid ratios allow for what technical factors

less mAs reducing patient exposure

virtual grid is _____ as effective as conventional grid

85%

virtual grid causes the effect of scatter to be

increased slightly

virtual grid causes the likelihood of mottle to be

reduced

the risk of what is eliminated through use of a virtual grid

grid cut-off

how is patient exposure effected with the use of a virtual grid

reduced

what gray scale is preferred in the latent image

long gray scale

how is long gray scale achieved in the latent image

high kVp

if the gray scale is too short in the image what can this cause

the computer will lengthen the scale by interpolating artificial information

T/F: overexposure is not apparent in digital imaging

true

rescaling is so effective that mAs can be increased

>8x before any visible change occurs in the image

tendency to use too high mAs overexposing patient

dose creep

within normal ranges, mAs and kVp have what impact on displayed digital image

no substantial impact

what rule can be used to reduce patient dose

15% rule

for displayed image, brightness and contrast are controlled by

leveling and windowing

cutting the mAs in half results in what exposure to the IR and patient

half the exposure

15% increase in kVp restores exposure to the IR through

increased penetration and more brems x-rays being produced

increasing the penetration by 15% increase in kVp recovers how much of the exposure

recovers 2/3

increasing kVp by 15% results in how much of an increase in brems x-ray production

~35% increase

increasing brems x-ray production by increasing kVp by 15% recovers how much of the exposure

recovers 1/3

benefits of high kVp radiography

sufficient x-ray penetration, long gray scale input without interpolation, reduces exposure when combined with lower mAs values

digital software can identify and correct for

expected fog patterns