Contrast Flashcards

1
Q

Image contrast

A

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

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2
Q

Dynamic range

A

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

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3
Q

3 types of contrast to consider

A

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

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4
Q

Radiographic contrast

A

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

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5
Q

Subject contrast

A

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

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6
Q

Low contrast, long scale

A

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

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7
Q

High contrast, short scale

A

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

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8
Q

Image receptor contrast

A

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

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9
Q

Major control of image contrast in film screen

A

kVp

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10
Q

Lower kVp

A

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

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11
Q

High kVp

A

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

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12
Q

Optimum kVp values

A

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

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13
Q

Digital imaging

A

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

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14
Q

Factors affecting subject contrast

A

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

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15
Q

Chest vs abdomen

A

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

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16
Q

Tissue densities

A

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

17
Q

Pathology

A

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

18
Q

Radiation quality

A

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

19
Q

Radiation quality is affected by:

A

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

20
Q

Beam filtration

A

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

21
Q

Contrast media

A

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

22
Q

2 basic types of contrast media

A

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

23
Q

Scatter radiation

A

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

24
Q

Fogging

A

will decrease contrast by adding extra shades of gray

25
IR contrast factors in film/screen
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
26
Sensitometry
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
27
Sensitometric curve
Optical density readings are plotted on y-axis and the log exposure on the x-axis
28
3 main parts of the sensitometric curve
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
29
Calculation of film gamma
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
30
Film speed or sensitivity
relative exposure necessary to produce an optical density of 1.0
31
Exposure latitude
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
32
Solarization or image reversal
A decrease in optical density as exposure increases Caused by rebromination Used in duplicating film, pre exposed to solarization point