Contrast

Question 1

Image contrast

Answer 1

Differences between adjacent optical densities/gray shades, or range of shades available in image
Functions to make details visible

Question 2

Dynamic range

Answer 2

Describes the concept of contrast as it is displayed on soft copy monitor for DR
Proper term for range of brightness

Question 3

3 types of contrast to consider

Answer 3

Radiographic, image, or displayed
Subject contrast
Image receptor, inherent, or detector

Question 4

Radiographic contrast

Answer 4

The contrast on finished image, contrast that we see in the final image

Question 5

Subject contrast

Answer 5

Range of differences in the quantity of radiation transmitted by a particular part as a result of the different
absorption characteristics of the tissues and structures of that part
Helps determine radiographic contrast

Question 6

Low contrast, long scale

Answer 6

High range of grays, mostly appear gray, also known as decreased contrast

Question 7

High contrast, short scale

Answer 7

Low range of grays, appears mostly black and white, also known as increased contrast

Question 8

Image receptor contrast

Answer 8

the contrast that is
built into the image receptor system by the manufacturer

Question 9

Major control of image contrast in film screen

Answer 9

kVp

Question 10

Lower kVp

Answer 10

Lower energy=cant penetrate through the body, less shades of gray
Long wavelength

Question 11

High kVp

Answer 11

More energy=can penetrate through body, more shades of gray
short wavelength

Question 12

Optimum kVp values

Answer 12

Extremities - 60-80
Chest- 110-125
Ribs & cervical - 60-75
Thoracic spine - 75 for AP, 90 for lateral
Lumbar Spine – 80 for AP and 90
to 115 for lateral
Skull - 85

Question 13

Digital imaging

Answer 13

kVp will influence, but not control displayed contrast
Computer processing will correct shade values

Question 14

Factors affecting subject contrast

Answer 14

Internal:
anatomic part - homogenous vs heterogenous
Pathology - changes tissue density
External:
Radiation quality
Contrast Media
Scatter Radiation
Fogging

Question 15

Chest vs abdomen

Answer 15

Chest has high subject contrast because there’s only bone and air. Abdomen has low subject contrast because there are lots of tissue, and fluids

Question 16

Tissue densities

Answer 16

Tooth enamel - most dense tissue
bone
solid organs
hollow organs (full)
muscle
hollow organs (empty)
cartilage
fat
gas

Question 17

Pathology

Answer 17

Changes subject contrast because it can change normal tissue density
Edemas and hemorrhaging tend to decrease subject contrast

Question 18

Radiation quality

Answer 18

As quality of radiation increases, subject contrast decreases
causes radiographic contrast to decrease

Question 19

Radiation quality is affected by:

Answer 19

kVp - affects maximum energy of beam
beam filtration - affects average energy of beam
type of xray generator - affects average energy of beam

Question 20

Beam filtration

Answer 20

Removing low energy xrays, reduce patient dose, increase energy of beam to pass through patient

Question 21

Contrast media

Answer 21

Often used in areas where tissue densities are more homogenous to increase subject contrast

Question 22

2 basic types of contrast media

Answer 22

Positive - absorbs xrays, causing decrease in optical density
Negative - allows xrays to pass through with minimal absorption increasing optical density

Question 23

Scatter radiation

Answer 23

Causes fogging or noise
decreases subject contrast = decrease in radiographic contrast
The more scatter removed, the higher the contrast

Question 24

Fogging

Answer 24

will decrease contrast by adding extra shades of gray

Question 25

IR contrast factors in film/screen

Answer 25

Film emulsion(speed) - faster speed emulsions yield higher inherent contrast
Film development - Proper time, temp, concentration, pH are essential to contrast. Any change will decrease inherent contrast
Intensifying Screen/Scintillator Speed - the faster the speed of the
screen, the higher the inherent contrast

Question 26

Sensitometry

Answer 26

Study of relationship between the intensity y of radiation exposure (light or
x-rays) and the optical density that is
produced
Developed by Hurter & Driffield

Question 27

Sensitometric curve

Answer 27

Optical density readings are plotted on y-axis and the log exposure on the x-axis

Question 28

3 main parts of the sensitometric curve

Answer 28

toe - indicates base + fog
Straight line portion - contains useful optical densities
Shoulder - indicates saturation point or maximum optical density
Slope - used to indicate the inherent contrast

Question 29

Calculation of film gamma

Answer 29

2 slope values that can be utilized to measure inherent contrasts are:
1. Film gamma - maximum slope measured at the steepest point
Normal ranges are 2.0 to 3.5
Subjective and not as accurate
2. Film average gradient - mean slope between the optical densities of 0.25-2.0 above base + fog
Better indicator
Average gradient range - 2.5-3.5

Question 30

Film speed or sensitivity

Answer 30

relative exposure necessary to produce an optical density of
1.0

Question 31

Exposure latitude

Answer 31

Range of exposures over which xray film respond with optical densities between 0.25 and 2.0 above the base + fog
High contrast film has narrow latitude

Question 32

Solarization or image reversal

Answer 32

A decrease in optical density as exposure increases
Caused by rebromination
Used in duplicating film, pre exposed to solarization point