Optical Density

Question 1

Radiographic quality

Answer 1

fidelity with which an anatomic
structure is represented in a
radiograph.

Question 2

Radiographic imaging

Answer 2

multistep process in which the
measured parameter is transferred to
different types of information
carriers along the imaging chain.

Question 3

The pathway for imaging processing consist of:

Answer 3

Image Acquisition
* Image Processing
* Image Display
* Image Analysis
* Image Archiving

Question 4

Image acquisition

Answer 4

consists of all of
the steps leading up to and
including x-ray exposure to an
image receptor

Question 5

Image processing

Answer 5

converts the
latent image into a manifest
image, accomplished by chemical processing or digital processing

Question 6

Image display

Answer 6

allows the final
image to be seen using either a
viewbox illuminator (film-based)
or computer monitor

Question 7

Image analysis

Answer 7

analyzing
the image to determine if proper
image quality is present

Question 8

Major controller factor for optical density

Answer 8

mAs is the major controller of optical density, kVp influences optical density

Question 9

Image archiving

Answer 9

storing image for future reference

Question 10

Photographic properties

Answer 10

in film/screen imaging, optial density y and contrast are
considered photographic
properties, determine visibilty of detail

Question 11

Geometric properties

Answer 11

recorded detail and distortion are considered geometric properties, dependent on geometry of xray beam and IR

Question 12

Function of optical density

Answer 12

provide information in the radiographic image
3 possible definitions
Optical density is directly proportional to the amount of radiation absorbed by film emulsion

Question 13

Optical density

Answer 13

Amount of blackening on a finished image

Question 14

Densitometer

Answer 14

Measures optical density
Low optical density = more light transmitted through area
High optical density = less light transmitted through area

Question 15

Photometer

Answer 15

Measures pixel brightness by measuring luminance
Higher the number, greater the amount of luminance

Question 16

Diagnostically useful range of optical densities

Answer 16

0.5-2.5

Question 17

Major factors of optical density

Answer 17

mAs
kVp
SID
Part thickness/tissue density

Question 18

mAs

Answer 18

Has direct linear relationship to optical density/IR exposure
25-30% change in mAs is required to cause visible change in optical density (only in film)
Reciprocity failure can occur using extremely short or long exposure times, typically due to intensifying screen phosphors to produce the appropriate amount of light
Reciprocity failure results in underexposure of IR
Reciprocity failure is not seen in DR

Question 19

kVp

Answer 19

Increase in kVp causes OD/IR exposure to increase because beam is more penetrating and more scatter is produced
kVp and OD have an exponential or logarithmic mathematical relationship
15% rule: increase of 15% in kVp will double OD

Question 20

SID

Answer 20

SID and OD have an inverse square relationship. Density gets cut by 4 times if SID doubled
If SID cut in half, cut OD by 1/4

Question 21

mAs and part thickness

Answer 21

For every 5 cm change in thickness, mAs should change by a factor of 2

Question 22

Secondary factors affecting optical density

Answer 22

Development/processing
Field size
grid type/ratio
image receptor system speed
OID
Fogging/noise
Pathology
xray generator type
filtrtion
anode heel effect

Question 23

Field size

Answer 23

Larger field size means increase in OD compared to smaller field size taken with same part nd same technical factors
More scatter created with larger field size
scatter adds to overall OD
IF field size reduced significantly, mAs should be increased by 30-50%

Question 24

Developer processing

Answer 24

An increase in developer time,
temperature, pH,
concentration, or
replenishment rate will
increase optical density and
vice versa

Question 25

Grid ratio

Answer 25

Higher grid ratio will decrease OD unless a compensation is made, using the bucky factors of the grid

Question 26

IR system speed

Answer 26

Faster speed, greater OD and vice versa

Question 27

OID

Answer 27

Increase OID, a decrease of OD occurs due to reducion of scatter hitting IR like air gap technique

Question 28

Fogging

Answer 28

Fog is non-informational optical density
any fog resent increases overall OD
Caused by age, light exposure, processing parameters higher than specified

Question 29

Pathology

Answer 29

Different diseases and conditions affect OD because they can change the normal tissue density present in region

Question 30

2 basic categories of pathologies

Answer 30

Atropjic or destructive pathologies - decrease normal tissue density and require decrease in mAs by 30%
Additive diseases – these increase normal tissue density and require a
compensation of increasing mAs by 30%

Question 31

Type of xray generator

Answer 31

Constant potential
equipment (3-phase & high
frequency) generators will
emit more radiation/mAs
than single phase
generators, thereby
increasing IR exposure.
* The difference is
approximately 40%

Question 32

Filtration

Answer 32

Adding filtration decreases OD since radiation is absorbed from the beam
Relationship depends on type of filtering material

Question 33

Anode heel effect

Answer 33

Increase of radiation on cathode side, affects OD on cathode side
More OD on cathode side vs anode side

Question 34

Inherent optical densities

Answer 34

Optical densities in film based imaging
Found in film without any exposure taking place and come in 2 types
Base density- optical density caused by blue tint added to film base, value of 0.05
Fog density- development of silver grains that contain no useful information