FSIAPIA 2.1 to 2.3 (Imaging Accessories)

1. Direct exposure / Non-Screen

2. Indirect exposure / Screen Film

General types of film

Direct exposure/Non-Screen

Film that uses thicker emulsion, and is outdated

• Decreased parallax effect or crossover

• Decreased quantum mottle

• Increases image quality

Advantage of direct exposure film

Increased px dose

Increased development time (because of thick emulsion)

Disadvantage of direct exposure film

Intraoral dental radiography

Application of direct exposure

Indirect exposure / screen film

Uses thinner emulsion, and uses indirect exposure. It is more sensitive to light.

Light: 90-99%

X-ray: 1-10%

Conversion percentage of x-ray and light when using indirect exposure

1. Duplitized / Double Emulsion Film

2. Single Coat

Basic Film Types According to Construction

Duplitized / Double Emulsion Film

Films that have emulsion layer coated on both sides of the film base. Can be screen or non-screen

Single Coated Film

Films that have emulsion layer on one side only

Base and emulsion

Structure of the Film

What are the basic parts of the film?

Adhesive layer and overcoat

Other parts of the film

150-300 um

Thickness of film

Biggest: 35×43 cm or 14×17 in

Smallest: 20×25 cm or 8×10 in

Film

Biggest size:

Smallest size:

Topcoat, super coat, overcoat

A protective covering of gelatin that encloses the emulsion, made up of gelatin

Prevent damage to sensitive emulsion layer

Protects emulsion from scratches, pressure, and contamination

Allows rough manipulation of film

Purpose of topcoat

Emulsion

Heart of the radiographic film, the active layer and contains the SHC, therefore is radiosensitive

3-5 or 10-20 micrometer

Thickness of emulsion

SHC and gelatin

Composition of emulsion

Silver bromide (98-99%) and silver iodide (2% or 1-10%) held together by the gelatin

Composition of SHC

SHC

Recording medium of the emulsion

SHC

Active layer of the emulsion, has high Z

Tabular, cubic, octahedral, polyhedral, and irregular

Shapes of the SHC

Tabular

Mostly used shape of SHC

Mechanical binder of SHC, holds the SHC uniformly dispersed in place

What is the purpose of gelatin in the emulsion?

Clear and sufficiently porous

Characteristic of gelatin

To provide mechanical support for SHC

Principal function of gelatin

Adhesive layer

Substratum

Adhesive/ Substratum layer

A thin coating located between the emulsion and base, adheres one layer of the film

Allow emulsion and base to maintain proper contact and integrity

What is the purpose of the adhesive or substratum layer?

Base

Foundation or framework of the film

Provide rigid structure onto which the emulsion can be coated

Purpose of base

Polyester/plastic

Composition of base

175 or 200 or 150-300 micrometer

Size of base

1. Superior physical / dimensional stability

2. Tinted with blue dye (reduces eye strain, reduces crossover for monochromatic films, increases contrast)

3. Flexible and fracture resistant

4. Semirigid

5. Inert to processing chemicals

6. Chemical memory

7. Non-flammable

8. Waterproof

Characteristics of a good film base

Glass plate

Original film based on, fragile (1900s)

Cellulose Nitrate

Standard base, flammable (1910)

Cellulose Triacetate

Safety base, not flammable but easily torn (mid-1920s)

Polyester (1960s)

Film base of choice, composed of ethylene glycol and dimethyl terapthalate. More resistant, superior stability

1. Speed

2. Contrast

3. Exposure latitude

Film characteristics

Film Speed

⬆ speed ⬆ sensitivity ⬆ density

Degree to which the emulsion is sensitive to x-rays and light

High speed film

RT can reduce technical mAs factor and lower px dose, but there will be higher quantum mottle

Film contrast

The ability of the radiographic film to provide a certain level of image contrast

High contrast = exhibit ⬇ shades of gray

High contrast = exhibit ___ shades of gray

Low contrast = exhibit ⬆ shades of gray

Low contrast = exhibit ___ shades of gray

Exposure latitude (margin of error)

Range of exposures that produce OD within the straight line region of a sensitometric curve

Exposure latitude

Number of shades of gray displayed in a radiograph

Wide latitude = ⬆ shades of gray = low contrast

Narrow latitude = ⬇ shades of gray = high contrast

Wide latitude = ___ shades of gray = _____ contrast

Narrow latitude = ___ shades of gray = _____ contrast

extremities

High contrast films or narrow latitude, for imaging of _____.

abdomen

Low contrast films or wide latitude, for imaging of _____.

Spectral sensitivity

Refers to the color of light to which a particular film is most sensitive

Monochromatic

Orthochromatic

Blue sensitive:

Green sensitive:

Spectral emission

Specific color of light emitted by a phosphor

Spectral matching

Correctly matching the sensitivity of the film to the color of the emission of the intensifying screen

⬆

Spectral matching = ___ speed

Crossover (only for Duplitized films)

Parallax effect

Blue dye of film, absorbs parallax effect (only for monochromatic films)

Anti-crossover layer

Reciprocity Law

OD on a radiograph is proportional only to the total energy imparted on the radiographic film

Any combination of mA and time in the same total mAs exposure will produce the same optical density, because exposure=density

Another definition of reciprocity law

1. Base

2. Toe

3. Shoulder

4. Straight line Portion

Parts of the characteristic curve

Characteristic curve, H&D curve, Sensitometric curve

Graph representing the inherent sensitivity of the film to exposure and processing

Straight line portion

Determines the image contrast on the radiograph

Base Plus Fog: 0.18 OD

Lowest portion of the sensitometric curve

Toe: Dmin, Phenidone, lightest area of radiograph

Shoulder: Dmax, Hydroquinone, darkest area of radiograph

Sensitometric curve

Toe:

Shoulder:

Straight line portion: film gamma (steeper = good contrast)

Average gradient

Base density

Density from the manufacturer of the film, inherent to the film base

0.14 OD

Average of base density

Base plus fog, 0.18 OD

Inherent fog caused by processing conditions

Base: 0.14 OD

Fog: 0.04 OD

Base plus fog: 0.18 OD

Base:

Fog:

Base plus fog:

Minimum density /Dmin

Low density and midpoint density. The toe of the characteristic curve, slightly higher than B+F density

Maximum density / Dmax

Higher density and darkroom density, the shoulder of the characteristic curve

Reflects the film contrast which is measured at 0.25 density units above B+F and 2.0 density units above B+F

The more vertical this line, the greater the film contrast

What is average gradient?

Vertical, edge, straight, or upright

To prevent film from sticking to each other, and prevent pressure artifacts

Proper Film Storage

10-21 degrees C or 50-70 degrees F

40-60% humidity

Storage temperature for film

21 degrees C ➡ 30-45 days

10 degrees C ➡ greater than 1 year

0 degrees C ➡ stops film aging process but must be warmed up to room temperature before use, at 35 degrees C or 85 degrees F

Maximum storage in relationship to temperature

21 degrees C ➡

10 degrees C ➡

0 degrees C ➡

Temperature too high: increased fog level (heat fog)

Temperature too low: increased static discharges (due to high humidity)

Humidity too high: increased fog level (random fogging due to movement of crystals)

Humidity too low: increased static discharge (due to increased friction

Possible consequences of storing unexposed film

Temperature too high:

Temperature too low:

Humidity too high:

Humidity too low:

inversely

Temperature and humidity are _____ related.

⬆ temperature = ⬆ heat fog = ⬆ possibility of static artifact

⬆ temperature = ___ heat fog = ___ possibility of static artifact

Photo-inert polyethylene bag or metal foil, to protect film from moisture and light

What is the packaging of the film made of, and for what purpose?

First In First Out, to beat expiration date

FIFO

Hand cream (lead to fingerprint marks - negative/white density marks)

Rubber gloves (static artifacts - positive/black density marks)

What should be avoided when handling of films?

Cotton gloves

What can be used when the hands are too wet, during film handling?

1. Age fog

2. Chemical/Development fog

3. Safelight fog

4. Heat fog

5. Secondary Radiation fog

What are the kinds of fog that may affect film?

Age fog

Caused by expired film

Chemical or development fog

Caused by fumes

Safelight fog

Most common cause of fog

Heat fog

Caused by increased temperature

Secondary radiation fog

Caused by increased kVp that causes ⬆ in scatter radiation, which causes ⬆ fog