203 pt 1

radiographic image quality

the exactness of representation of the patient’s

anatomy on the image.

FILM FACTORS

GEOMETRIC FACTORS

SUBJECT FACTORS

three major interrelated categories of radiographic quality:

radiographic quality

anatomic structure being examinged is imaged on the radiograph

resolution

ability to image two separate objects and visually distinguish one from the other.

spatial resolution

refers to the ability to image small object that have high subject contrast

cpnventional radiography

has excellent spatial resolution

contrast resolution

to distinguish anatomic structures of similar subject contrast

computed tomography

has excellent contrast resolution

detail or recorded detail

sometimes used instead of spatial and contrast resolution

refere to the degree of sharpness of structursl lines.

visibility of detail

The ability to clearly see and distinguish anatomical structures on a radiographic image.

noise

is the random fluctuation in the OD of the image.

film graininess

refers to the distribution in size and space of the silver halide grains in the emulsion.

inherent in the image receptor

structure mottle

refers to the phosphor of the radiographic intensifying screen

inherent in the image receptor

caused by physical structures or imperfections

quantum mottle

refers to the random in which x-rays interact with the image receptor

- is radiographic noise caused by too few X-ray

photons reaching the image receptor, resulting in a

grainy or mottled appearance.

film factors

are the factors that affect the quality

of a radiographic film image, particularly its density

(darkness) and contrast

sensitometry

the study of the relationship between the intensity of exposure of the film and the blackness after processing.

- the study of how film emulsion responds to

radiographic exposure.

characteristic curve

the primary use is to describe the contrast characteristics of the film throughout a wide exposure range

H&D curve hunter and driefield

sensitometric curve

D-log E curve

other names for characteristic curve

horizontal

log relative exposure

horizontal or vertical?

vertical

optical density

horizpntal or vertical?

toe, shoulder, straight line portion

three portions of the curve:

toe

The lower, gently rising portion. At low exposure, the

film produces only a small increase in density. Details

may be difficult to distinguish

straight line portion

The steep, nearly linear portion. A change in

exposure produces a relatively predictable change in

density. This is where film contrast is commonly

evaluated

shoulder

The upper portion where the curve flattens.

Increasing exposure produces progressively smaller

increases in density, approaching the film's

maximum useful density.

base plus fog

region to the left of toe

straight line portion

region between toe and shoulder

d max

ragion to right of shoulder

expose and process the film

measuring the densities produced

plotting a graph

how to obtain characteristic curve:

time scale sensitometry

kVp, mAs, focal spot

setting, ffd used are constant but exposure time will

vary

intensity scale sensitometry

using step wedge

densitometry

used to measure

the densities produced on each part of the film.

plotting a graph

a graph is plotted with recoded optical density

film speed / sensitivity

contrast

latitude

information provided by characteristic curve: (3)

below 0.2

optical densities of Refion left of toe (base plus fog)

base density and fog density

optical density on the film is due to inherent density its called ___ and ___.

base density

due to absorption of light transmitted through the film base

fog density

produced by the development of silver halide grain due to unintentional exposure.

storage fog

due to poor storage condition (high temp, high humidity fumes)

safe light fog

due to exposure to dark room

- safe light illumination

chemical fog

due to:

1. excessive development

2. high development temperature

3. chemical contamination

4. hyper active developer

0.2 and 2.5

optical densities of region between toe and shoulder:

subject contrast

It is the difference in x-ray intensities transmitted through different parts of patient.

it depends on:

patient thickness

tissue density

photon energy

effective atomic number

contrast media

scatter radiation

film contrast

Inherent in the film and influenced by processing

it depends on charqcteristic curve of film

film density

processing

film gamma

max slope of the characteristic curve

it tells us how much the film density changes when the film demsity changes when exposure changes

average gradient

is the average slope of the characteristic curve between two specified density

points, representing the overall contrast of the film.

film latitude

refers to the range of exposure that produces diagnostically useful densities on a radiographic film.

exposure error

is the difference between the exposure used and the exposure needed to produce

the desired radiographic image density.

over exposure and under exposure

two types of exposure: