Test 1 Flashcards
Patient thickness affects image quality by affecting
magnification, radiographic contrast, focal spot blue
The best way to minimize magnification is to use a
long SID
small OID
The most commonly used beam restricting device is the
variable collimator
The purpose of a grid is to achieve
improved image contrast
Which is the linear grid with the widest latitude for catering and focus?
6:1
If 10% of the viewbox light is transmitted though an area of film, what is the optical density in that area?
1
The three primary geometric factors affecting image quality are
magnification, distortion, and focal spot blur
Focal spot blue can be reduced by using a
small focal spot
? is defined as the ability to image two separate objects and visually detect one from the other
resolution
What is the formula for optical density?
OD=log10 (I0/It)
Which kVP selection would result in the most scattered x-rays in the image forming beam?
90 kVP
Decreasing the kVP will increae
patient dose
Contrast resolution is improved by
tight collimation, lower kVP, patient compression
The use of a compression device will increaee
Contrast
The use of ? improves contrast and reduces patient dose.
collimation
How can you improve image contrast with a heavy patient without increasing patient dose?
use tight collimation
Image contrast improves when more of ? radiation is removed.
scattered
Foreshortening is caused by
a(n) angled body part when the beam is perpendicular to the image receptor
A grid is constructed with ? strips and ? interspace material.
radiopaque
radiolucent
A radiograph with a long scale of contrast will also have ? latitude and ? contrast.
wide, low
Grids are designed to remove scattered x-rays before they reach
the image receptor
What is the grid ratio of a grid with 3mm height, 0.025mm thick lead grid strips, and 0.3 mm thick interspace material?
10:1
Optical density is directly controlled by changing the
mAs
Subject contrast is affected by
patient thickness
The three primary factors influencing the intensity of scatter in the image forming beam
kVP, fieldd size, and patient thickness
The positive beam limiting device (PBL) ensures that the x-ray beam is collimated to
the image receptor size
? is the degree of difference in optical density (OD) between areas of an image.
contrast
The amount of scatter absorption in a grid depend on
The angle of the scattered photon
The height of the grid strips
The width of the interspace material
The purpose of a grid is to achieve
improved image contrast
The interspace material in grids is made of
aluminum, plastic
Grids generally have a frequency of
60-110
The most critical consideration when uing a crossed grid is
alignment (positioning latitude)
How could contrast be improved on a bedside radiograph of a very large
use a grid
lower the kVp
use tight collimation
Spatial resolution improves with decreased
screen blur, motion blue, geometric blur
Radiographic ? is random fluctuation in the optical density of a radiograph
noise
The slope of the ? portion of the characteristic curve shows the film contrast.
straight line
A film with a characteristic curve showing a high slope would be useful when ? is needed
high contrast
The three primary geometric factors affecting image quality are
magnification
distortion
focal spot blur
Distortion can be reduced by
placing the object plane parallel to the image plane
How could contrast be improved on a bedside radiograph of a very large patient?
use a grid
lower the kVp
use tight collimation
Radiographic image quality is improved when the ? is increased
Source image distance
Higher speed image receptors generally produce images with
increased noise
An image receptor with ? can be use over a greater range of exposures
wide latitude
The densities above 2.5 on a film are represented in the ? portion of the characteristic curve.
base and fog
sharpness of detail can be improved by increasing
SID
Lowering kVp ? patient dose and ? image contrast.
Increases, increases
