RI - 2.ppt

Duties of a Radiographic InterpreterDuties of a Radiographic Interpreter

Mask of any unwanted light from viewer

Ensure the background light is subdued

Check the radiograph for correct

identification

Assess the radiographs density

Calculate the radiographs sensitivity

Check the radiograph for any artifacts

Assess the radiograph for any defects

present

State the action to be taken, acceptable,

rejectable or repair

Radiographic FilmRadiographic Film

Base

Base must be :-

• Transparent - To allow white light to go through

• Chemically inert

• Must not be susceptible to expansion and contraction

• High tensile strength

• Flexibility

cellulose acetate / polyester

Base

Supercoat

Supercoat

Subbing

Subbing


What are the advantages of Double Coated Film?

• Improve contrast

• Reduce the exposure time


Image formationImage formation

When radiation passes through an object it is differentially absorbed depending upon the materials thickness and any differing densitiesThe portions of radiographic film that receive sufficient amounts of radiation undergo minute changes to produce the latent image (hidden image)

1. The silver halide crystals are partially converted into metallic silver to produce the latent image

2. The affected crystals are the amplified by the developer, the developer completely converts the affected crystals into black metallic silver

3. The radiograph attains its final appearance by fixation

Film Types

Grain SizeSpeed Quality Film factor Coarse Fast Poor 10Medium Medium Medium 35Fine Slow Good 90Ultra Fine V.Slow V.Good 200

Film emulsion produced by mixing solutions of nitrate and salt such as potassium bromide.

• The rate and temperature determine the grain structures

1. Rapid mixing at low temperature - Finest grain structure

2. Slow mixing at high temperature - Large grain structure

Dev

elop

er

Sto

p

bath

Fix

er Running water

Processing Systems

Manual System

DevelopmentDevelopment Metallic Silver converted into Black metallic silver

3-5 min at 20OC

Main ConstituentsMain ConstituentsDeveloping agent metol-hydroquinoneAccelerator keeps solution alkalineRestrainer ensures only exposed silver halides convertedPreservative prevents oxidation by air

Processing Systems

Replenishment Replenishment

Purpose – to ensure that the activity of the developer and the

developing time required remains constant

Guideline – 1. After 1m2 of film has been developed,

about 400 ml of replenisher needs to be added

FixerFixer

• Sodium thiosulphate or ammonium thiosulphate Functions:- 1. Removes all unexposed silver grains 2. Hardens the emulsion gelatin

• Clearing time - The time taken for the radiography to loose its milky appearance.

• Fixing time - Twice the clearing time

Processing Systems

Processing Systems

Running waterRunning water

• Films should be washed in a tank with constant running water for at least 20 minutes.

• Insufficient washing the film can caused the yellow fog appears.

Characteristic CurvesCharacteristic Curves

• Increasing exposures applied to successive areas of a film

• After development the densities are measured• The density is then plotted against the log of the

exposure

Characteristic curve

Sensitometric curve

Hunter & Driffield curve

Characteristic Curves

Information which can be obtained from a films characteristic curve

• The position of the curve on the exposure axis gives information about the films speed

• The gradient of the curve gives information on the films contrast

Characteristic CurvesCharacteristic Curves

Log Relative Exposure

Density (Log)

Density obtained in a photographic emulsion does not vary linearly with applied exposure

The steeper the slope the greater the contrast






Density

A B C D E

Film A is faster than Film B

Film B faster then C




• The gradient of the curve gives information on the films contrast

• The position of the straight line portion of the curve against the density axis will show the density range range within which the film is at its optimal

Changing DensityChanging Density


DensityDensity achieved 1.5

Density required 2.5

Determine interval between logs

1.8 - 1.3 = 0.5

2.5

1.5

1.3 1.8

Antilog of 0.5 = 3.18

Therefore multiply exposure by 3.18

(measured density is lower than the required density)(measured density is lower than the required density)

Original exposure 10 mA mins

New exposure 31.8mA mins

Changing FilmChanging Film


DensityObtain Logs for Films A and B at required density

Interval between logs = 0.15

1.7 1.85

Antilog of 0.15 = 1.42

Multiply exposure by 1.42

Original exposure 10 mA mins

New exposure 14.2 mA mins

2.5 A B

RADIOGRAPHIC DEFINITION

DEFINITION is the sharpness of the DEFINITION is the sharpness of the dividing line between areas of dividing line between areas of different densitydifferent density

Radiographic Definition

Geometric unsharpness Inherent unsharpness

• FFD/SFD too short

• OFD too large

• Source size too large

• Vibration/movement

• Poor screen contact

• Coarse grain film

• Salt screens

• Wavelength too short

DEFINITION

Geometry Unsharpness ( Ug)Geometry Unsharpness ( Ug)

• Controlled by focal spot, focal to film distance ( FFD), object to film distance (OFD)

Inherent unsharpness (Ui) Inherent unsharpness (Ui)

• Controlled by the type of films being used (slow or fast), type of screens and amount of backscatter

Radiographic DefinitionRadiographic Definition

Penumbra Ug)

Ug= F x ofd fod

(Ug = 0.25mm)

ofd

Focal spot

size, F

fodffd

Source size as small as possible

Source to object distance as large as

possible

Object to film distance as small as

possible

Penumbra (Ug)

Penumbra = S x OFD FFD - OFD

S = 4mmOFD = 25mmFFD = 275

= 4 x 25 275 - 25

Penumbra = 0.4mm

Penumbra CalculationsPenumbra Calculations

Penumbra CalculationsPenumbra Calculations

= 4 x 25 0.25

+ 25

Min FFD = S x OFD Penumbra (0.25)

S = 4mmOFD = 25mmFFD = 275

+ OFD

Min FFD = 425mm

Inherent Unsharpness

Exposed radiographwith crack like indication

Stray electrons fromexposed crystals

Adjacent crystalsaffected by stray electrons

- -

-

--

-

-

- -

-

Inherent Unsharpness

Large film grain size increased inherent Unsharpness

Short wavelength increased inherent Unsharpness

Loose film crystal distribution increased inherent Unsharpness

Intensifying ScreensIntensifying Screens

Radiographic film is usually sandwiched between two intensifying screens

There are three main there are three main types of intensifying screens

•Lead screens

•Fluorescent screens

•Fluorometallic screens

Film placed between 2 intensifying screens

Intensification action achieved by emitting particulate radiation (electrons)

Generally lead of 0.02mm to 0.15mm

Front screen shortens exposure time and improves quality by filtering out scatter

Back screen acts as a filter only

Lead Intensifying ScreensLead Intensifying Screens


Intensification action achieved by emitting

Light radiation (Visible or UV-A)

Intensification action twice that of lead screens

No filtration action achieved

Salt used calcium tungstate

Salt Intensifying ScreensSalt Intensifying Screens


Intensification action achieved by emitting light

radiation (Visible or UV-A) and particulate radiation

electrons)

High cost

Front screen acts as a filter and intensifier

Salt used calcium tungstate

Fluorometallic Intensifying ScreensFluorometallic Intensifying Screens

ScatterScatter

• Radiation emitted from any other source than that giving the primary desired rectilinear propagation

• Scatter will lead to poorer contrast and definition and create spurious indications

• It may also cause radiological protection problems

ScatterScatter

• Internal scatter originating within the specimen

• Side scatter walls and nearby objects in the path of

the primary beam• Back scatter materials located

behind the film

Control of ScatterControl of Scatter

• Collimation

• Protection from back scatter

• Beam filtration

• Blocking

• Grids

• Increased beam energy

Sensitivity

IQI sensitivity Defect sensitivity

IQI sensitivityIQI sensitivity

The image on a radiograph which is used to determine the quality level

Defect sensitivity Defect sensitivity

Ability to assist the sensitivity and locate a defect on a radiograph

(Depend on the defect orientation)(Depend on the defect orientation)

Image Quality Indicators

IQI’s / Penetrameters are used to measure radiographic sensitivity and the quality of the radiographic technique used. They are not used to measure the size of defects detected

Standards for IQI’s include:

BS 3971

BS EN 462

DIN 62

Placement of IQIPlacement of IQI

• IQI must be placed on the maximum thickness of weld

• Thinnest required step or wire must be placed at the extreme edge of section under test

• IQI must be placed at the source side

• In case of access problem , IQI has to placed on the film side of the object, letter ‘FS’ should be placed beside the IQI.

• IQI material chosen should have similar radiation absorption/transmission properties to the test specimen

Ideally IQI should be placed on the source side IQI sensitivity is calculated from the following formula

Sensitivity % = Thickness of thinnest step/wire visible x 100

Object Thickness

IQI Sensitivity

Image Quality IndicatorsThickness BS 3971 DIN 54 109 BS EN 462-2 BS EN 462-1

(mm) STEP WIRE WIRE (DIN 62) STEP/HOLE WIRE1-6 7-12 13-18 4-10 9-15 15-21 1-7 6-12 10-16 H 1 H 5 H 9 H 13 W 1 W 6 W 10 W 13

0.050 70.063 7 60.08 6 50.10 5 7 7 40.125 6 4 6 6 6 30.150.16 5 3 5 5 5 20.20 4 2 7 4 4 4 10.25 3 1 6 7 3 3 7 30.300.32 2 5 6 2 2 6 6 20.350.40 1 4 5 1 1 5 5 10.50 6 3 4 4 40.600.63 5 2 3 3 30.750.80 4 1 7 7 2 2 6 7 20.901.00 3 6 6 1 1 5 6 11.201.25 2 5 5 4 51.50 1 41.60 4 3 41.80 32.00 6 2 3 2 6 32.50 5 1 2 1 5 23.003.20 4 1 4 14.00 3 35.00 2 26.30 1 1

For FFD/SFD change

E1 D1 2

E2 D2 2=

E1 = New exposure time

E2 = Original exposure time

D1 = New FFD

D2 = Original FFD

Exposure control

For FFD/SFD change

Example:

Calculate new exposure time for FFD = 600 mm

Original exposure at 500mm was 10 min

T1 =(600) 2

(500) 2 X 10 = 14.4 mins

Exposure control

Exposure calculation

E = M X Time (mA.min)

E = exposure (mA.min)M = Tube current (mA)T = Exposure time (min)

Exposure calculation

In one radiographic operation, an-x-ray machine is set at 5mA and the radiographic film is exposed for a period of 15 minutes. What is the total exposure received by the film?

Solution:

Given,

Tube current (M) = 5mA

Exposure time (t) = 15 minutes

Exposure ( E) = M X T

= 5 X 15

= 75 mA.min

Radiographic Techniques

Single Wall Single Image (SWSI)- film inside, source outside

Single Wall Single Image (SWSI) panoramic- film outside, source inside (internal exposure)

Double Wall Single Image (DWSI)- film outside, source outside (external exposure)

Double Wall Double Image (DWDI)- film outside, source outside (elliptical exposure)

Single wall single image SWSI

IQI’s should be placed source side

Film

Film

Single wall single image SWSI panoramic

• IQI’s are placed on the film side

• Source inside film outside (single exposure)

Film

Double wall single image DWSI

• IQI’s are placed on the film side

• Source outside film outside (multiple exposure)

• This technique is intended for pipe diameters over 100mm

Film

Double wall single image DWSI

Radiograph

Identification

ID MR11

• Unique identification

EN W10

• IQI placingA B• Pitch marks indicating

readable film length

Double wall double image DWDI elliptical exposure

Film

• IQI’s are placed on the source side

• Source outside film outside (multiple exposure)

• A minimum of two exposures

• This technique is intended for pipe diameters less than 100mm

Double wall double image DWDI

Shot A Radiograph

Identification

ID MR12

• Unique identification EN W10

• IQI placing

1 2• Pitch marks indicating readable film length

4 3

Double wall double image (DWDI) perpendicular exposure

Film• IQI’s are placed on the source side• Source outside film outside (multiple exposure)• A minimum of three exposures• Source side weld is superimposed on film side weld• This technique is intended for small pipe diameters

Density requirement 2.0 to 3.0

Density unacceptable

Density1.2

Density1.2

Density3.0

Density3.0

Sandwich Technique

FILM AFILM B

FILM A: Fast film - Thicker section

FILM B: Slow film - Thinner section

LEAD SCREENS

FILM AFILM B

Density2.0

Density2.0

Density3.0

Density3.0

Sandwich Technique

Density 2.0 to 3.0 acceptable

Viewing conditionsViewing conditions

• Darkened room

• Clean viewer

• Minimum adequate illumination from the viewer is 3000cd/m2

• Eyesight must be adjusted to the darkened conditions

• Comfortable viewing position and environment

• Avoid fatigue

Radiographic QualityRadiographic Quality

Density - relates to the degree of darkness

Contrast - relates to the degree of difference in density between adjacent areas on a radiograph

Definition - relates to the degree of sharpness

Sensitivity - relates to the overall quality of the radiograph

Factors Influencing Sensitivity

Sensitivity

Contrast Definition

ContrastContrast

Subject contrastSubject contrast :- Contrast arising from variation in

opacity within an irradiated area

Radiographic contrastRadiographic contrast :- The density difference on a radiography

between two areas- usually subject and

the background (overall)

Film contrastFilm contrast :- The slope of characteristic curve of the film at

specified density. ( Type of film being used, fine

grain or large grain)


Density

Sensitivity

Contrast Definition

Film Energy Subject contrast

Processing


Sensitivity

Definition

Density Film Energy Object contrast

Processing

Time Temperature Type Strength Agitation

Contrast

Film Contrast Subject Contrast

Film type Density Processing Scatter Wavelength Screens

Radiographic Contrast

Radiographic Contrast

Poor contrast

Poor contrast

High contrast

Radiographic DensityRadiographic Density

Density = Log10Incident light

Transmitted light

* Greater contrast is achieved at higher density

Radiographic DensityRadiographic Density

Lack of Density

Under exposure

Developer temp too low

Exhausted developer

Developer too weak

Excessive Density

Over exposure

Excessive development

Developer temp too high

Too strong a solution

Measuring Radiographic DensityMeasuring Radiographic Density

Density is measured by a densitometer

A densitometer should be calibrated using a density strip

4.0 3.5 3.0 2.5 2.0 1.5 1.0


Sensitivity

Definition

Film speed

Screens Energy Vibration ProcessingGeometry

Contrast


Sensitivity

Contrast Definition

Film speed

Screens Energy Vibration Processing

Time Temperature Type Strength Agitation

Geometry

What is a good radiograph?

A good radiograph satisfies A good radiograph satisfies the inspection requirementthe inspection requirement

Documents

RI - 2.ppt