Film & Intensifying Screens

List 4 layers of radiographic film

• base

• adhesive layer

• emulsion

• protective layer (supercoat)

What silver halide crystals does the emulsion layer contain?

• silver bromide

• silver iodide

• silver chloride

What determines the film’s characteristics (emulsion layer)?

the size of the crystals and the thickness of the emulsion layer

(define) speed

the relationship between exposure and density on the film

(define) resolution

the ability to accurately image an object

(define) contrast

the film’s ability to produce many or few shades of gray

(define) latitude

The amount of change in technical factors that will produce a diagnostic radiograph (the radiographer’s margin for error)

Double emulsion film

____ the speed as single emulsion film

____ the patient dose

_____ resolution

twice

½

less

The characteristics of a film can be graphically demonstrated on a _________.

D log E curve

other names:

• characteristic curve

• sensotemetric curve

• H & D curve (Hurter and Driffield)

Identify

A

B

C

D

E

A= base + fog

B= toe

C= straight line portion

D= shoulder

E= Dmax

Which film has a faster speed?

film A

The further to the left the straight line portion of the graph is, the ____ the speed.

The faster the speed, the ____ the patient dose, but the ___ the resolution.

• faster

• less, less

The contrast of the film is measured by the ….

average gradient (slope) of the line

What is the average gradient (slope) of the line also called?

the film’s Gamma

The steeper the slope (more vertical) the _____ the contrast.

The greater the contrast, the _____ the latitude.

• greater

• narrower

Which film gives the radiographer more margin of error? Why?

film b, because the more horizontal = less contrast = more latitude (wider) = more margin of error

What do intensifying screens convert the energy of x-rays into?

large amounts of light

What is the purpose of intensifying screens?

reduce patient dose

___ ___% of the latent image is formed by the light from the intensifying screens.

___ ____% of the image is produced by x-ray photons

over 99%

less than 1%

What are the 4 layers of an intensifying screen?

1. base

2. reflective layer

3. phosphor

4. protective coating

What is the phosphor of a intensifying screen?

a material that is capable of absorbing x-ray energy and converting it to light

Modern phosphors are either _______ ______ or one of the _____ ______.

calcium tungstate, rare earths

List 3 rare earths used in intensifying screens:

• gadolinium

• lanthanum

• yttrium

Define Spectral Matching

the be the most effective, the intensifying screens should emit the same color of light to which the film is sensitive

List the 3 systems of classifying screen speed

1. intensification factor

2. descriptive rating

3. relative speed

Formula for Intensification Factor

IF = exposure without screens/exposure with screens

When using an intensifying screen, it takes 200 mR to produce a certain density. It takes 450 mR to produce the same density without using screens. What is the intensification factor of these screens?

2.25

The 4 different descriptive rating

• ultra high speed

• high speed

• par speed

• slow speed (detail or extremity screens)

List the different relative speeds (IRS)

• par speed = 100 RS

• ultra high = 400 to 1200 RS

• high = 200 RS

• slow = 20 to 80 RS

What is the relationship between Relative Speed and radiographic density?

directly proportional

What is the equation used to determine the change in mAs necessary to compensate for a change in Relative Speed?

mAs1/mAs2 = RS2/RS1

What is the proper mAs to use with a 400 RS system when 80 kVp and 50 mAs produce an acceptable image with a 200 RS system?

25 mAs

A radiograph is produced using 500 mA, .04 second, 62 kVp, 40'“ SID, and a 200 RS image receptor. What new mAs should be used to keep the density the same if an 800 RS system is employed?

5 mAs