Lec 4 Image Characteristics

Question 1

Degree of darkening or opacity of an exposed film.

Answer 1

Optical density

Question 2

Plot of relationship between film optical density and exposure.

Answer 2

Characteristic curve / Hurter-Driffield curve

Question 3

Overall film density depends on the number of photons absorbed by film emulsion.

Answer 3

Exposure

Question 4

The thicker the subject, the more the beam is attenuated, the larger the resultant image.

Answer 4

Subject thickness

Question 5

The greater the density of a structure within the subject, the greater the attenuation of the x-ray beam directed through that subject or area.

Answer 5

Subject density

Question 6

Dense objects cause radiographic image to be light and are said to be ______?

Answer 6

Radiopaque

Question 7

Objects with low densities are weak absorbers. They allow most photons to pass through, and they cast a dark area on the film that corresponds to the _______ object.

Answer 7

Radiolucent

Question 8

Defined as the difference in densities between light and dark regions on a radiograph.

Answer 8

Radiographic contrast

Question 9

An image that shows both light areas and dark areas has ___________.

Answer 9

high contrast

Question 10

An image that shows only light gray and dark gray areas has __________.

Answer 10

low contrast

Question 11

High contrast = ______ grayscale of contrast

Low contrast = ________ grayscale of contrast

Answer 11

• High = short
• Low = long

Question 12

The range of characteristics of the subject that influences radiographic contrast.

Answer 12

Subject contrast

Question 13

Describes the inherent capacity of radiographic films to display differences in subject contrast.

Answer 13

Film contrast

Question 14

Causes fogging of a radiograph — an overall darkening if the image — results in loss of radiographic contrast.

Answer 14

Scattered radiation

Question 15

The amount of radiation required to produce an image of a standard density.

Answer 15

Radiographic speed

Question 16

A measure of the range of exposures that can be recorded as distinguishable densities on a film.

Answer 16

Film latitude

Question 17

The appearance of uneven density of a uniformly exposed radiographic film.

Answer 17

Radiographic noise

Question 18

The ability of a radiograph to precisely define an edge.

Answer 18

Sharpness

Question 19

The ability of a radiograph to record separate structures that are close together.

Answer 19

Resolution / resolving power

Question 20

Image sharpness lost through movement of the film or subject during exposure.

Answer 20

Motion blurring

Question 21

Loss of image sharpness results in part because photons are not emitted from a point source (focal spot) on the target in the xray tube.

Answer 21

Geometric blurring

Question 22

Describes the subjective judgement by the clinician of the overall appearance of a radiograph.

Answer 22

Image quality

Question 23

Combines the features of:
- density
- contrast
- latitude
- sharpness
- resolution
- other parameters

Answer 23

Image quality

Question 24

The characteristic curve just shows that if you increase the _________, you increase the film’s _____________.

Answer 24

• exposure
• optical density

Question 25

One can increase the exposure by increasing? (3)

Answer 25

Increasing the milliamperage (mA), peak kilovoltage (kVp), or exposure time

Question 26

Subject contrast in influenced largely by? (3)

Answer 26

subject’s thickness, density, and atomic number

Question 27

___ influences radiographic contrast.

Answer 27

kVp

Question 28

kVp range of ___ to ___ is optimal for dental imaging.

Answer 28

60 to 80

Question 29

As the kVp of the x-ray beam increases, subject contrast ________ (increases / decreases?).

Answer 29

decreases

Question 30

Increasing the kVp _________ (increases / decreases?) the overall density of the image.

Answer 30

increases

Question 31

Measured by the average slope of the diagnostically useful portion of the characteristic curve.

Answer 31

Film contrast

Question 32

Low ___ and use of ____ will help prevent scatter radiation.

Answer 32

• Low kVp
• collimation

Question 33

TRUE OR FALSE

A film optimized to display wide latitude records a short range of subject contrasts

Answer 33

FALSE

A film optimized to display wide latitude records a WIDE range of subject contrasts

Question 34

TRUE OR FALSE

E/F-speed film is preferred because it requires approximately half the exposure time and thus half the radiation dose of D-speed film.

Answer 34

TRUE

Question 35

Shows as radiographic mottle which can be seen as film graininess, caused by the visibility of silver grains in the film emulsion

Answer 35

Radiographic noise

Question 36

TRUE OR FALSE

The finer the grain size, the finer the sharpness.

Answer 36

TRUE

Question 37

______-speed films have finer grains, and _____ films have larger grains

Answer 37

• slow
• faster

Question 38

TRUE OR FALSE

The larger the focal spot, the greater the loss of image sharpness.

Answer 38

TRUE

Question 39

A basic measure of the efficiency of an imaging system. It encompasses image contrast, blur, speed, and noise.

Answer 39

Detective quantum efficiency (DQE)