Chapter 11

Question 1

Contrast

Answer 1

Arises from the areas of light, dark, and shades of gray on the x-ray image.

Question 2

Contrast Resolution

Answer 2

is the ability to image adjacent similar tissue

Question 3

X-Radiation Produced by Compton Scatter

Answer 3

produces noise, reducing image contrast, and contrast resolution, it makes the image less visible.

Question 4

Three factors contribute to increased scatter radiation:

Answer 4

increased kVP, increased x-ray field, and increased patient thickness

Question 5

Beam restricting devices

Answer 5

are designed to control and minimize scatter radiation by limiting the x-ray field size to only the anatomy of interest.

Question 6

The three principle types of beam restricting devices are-

Answer 6

aperture diaphragm, cones or cylinders, and collimators

Question 7

Scattered x-rays from remnant beam

Answer 7

the grid removes a major source of noise, thus improving radiographic image contrast

Question 8

Two principal characteristics of any image

Answer 8

spatial resolution and contrast resolution

Question 9

Spatial resolution and contrast resolution

together are referred to as:

Answer 9

image detail or visibility of detail

Question 10

Spatial resolution

Answer 10

is determined by focal spot size and other factors that contribute to blue.

Question 11

Contrast resolution

Answer 11

is determined by scatter radiation and other sources of image noise

Question 12

Two principal tools are used to control scatter radiation:

Answer 12

beam restricting devices and grids

Question 13

Two types of x-rays are responsible for the optical density and contrast on a radiographic image:

Answer 13

that that pass through the patient without interacting and those that are Comptom scattered within the patient

Question 14

x-rays that exit from the patient are

Answer 14

remnant x-rays

Question 15

x-rays that exit and interact with the image receptor are called

Answer 15

image-forming x-rays

Question 16

penguin

Answer 16

Collimation reduces patient radiation dose and improves contrast resolution

Question 17

Increase of scatter radiation

Answer 17

radiographic image loses contrast and appears gray and dull.

Question 18

three primary factors influence the relative intensity of scatter radiation that reaches the image receptor

Answer 18

kVp, field size, and patient thickness

Question 19

X-ray energy is increased

Answer 19

the absolute number of Compton interactions decreases, but the number of photoelectric interactions decreases much more rapidly. Therefore, the relative number of x-rays that undergo Compton scattering increases.

Question 20

low kVP

Answer 20

fewer x-rays reach the image receptor at low kVP, this is usually compensated for by increasing the mas. This result is higher patient dose.

Question 21

penguin

Answer 21

approximately 1% of x-rays incident on the patient reach the image receptor

Question 22

large patients

Answer 22

kVp must be high to penetrate the appropriate body type
increasing mAs usually generates enough x-rays to provide a satisfactory image but may result in high radiation dose.
on the other hand, a much smaller increase in kVP is usually sufficient to provide enough x-rays, and this can be done at a much lower patient radiation dose but when kVP is increased, the level of scatter radiation also increases, leading to reduced image contrast.

Question 23

penguin

Answer 23

scatter radiation increases as the x-ray beam field size increases

Question 24

patient thickness

Answer 24

imaging thick parts of the body results in more scatter radiation than imaging thin parts

Question 25

penguin

Answer 25

compression of anatomy improves spatial resolution and contrast resolution and lowers the patient radiation dose.

Question 26

Control of scatter radiation

Effect of Scatter Radiation on Image Contrast

Answer 26

One of the most important characteristics of image quality is contrast, the visible difference between the light and dark areas of an image.

Question 27

Optical density

Answer 27

contrast is the degree of difference in OD between areas of a radiographic image.

Question 28

Contrast resolution

Answer 28

is the ability to image and distinguish soft tissues

Question 29

remnant x-rays

Answer 29

are scattered even after the most favorable conditions

Question 30

penguin

Answer 30

reduced image contrast results from scattered x-rays

Question 31

two types of devices reduce the amount of scatter radiation the reaches the image receptor

Answer 31

beam restrictors and grids

Question 32

Beam restrictors

Answer 32

aperture diaphragm, cones or cylinders, and the variable aperture collimator

Question 33

Aperture diaphragm

Answer 33

simplest of all beam restricting devices, it is basically lead or lead lined metal diaphragm that is attached to the x-ray tube head.

Question 34

cones and cylinders

Answer 34

considered modifications of the aperture diaphragm.

in both, an extended metal structure restricts the useful beam to the required size.

Question 35

Variable aperture collimator

Answer 35

The light localizing variable aperture collimator is the most commonly used beam restricting device.