Sensitometry3
Transcript of Sensitometry3
SensitometrySensitometry
Quantitive evaluation of how a film Quantitive evaluation of how a film emulsion is responds to radiation emulsion is responds to radiation and processing.and processing.
و لألشعة الفلم الستجابة الكمى و التقييم لألشعة الفلم الستجابة الكمى التقييمالتحميضالتحميض
ObjectivesObjectives
The student should be able to:The student should be able to:Describe the importance of the studyDescribe the importance of the studyDefine the relevant termsDefine the relevant termsDescribe the methods of producing a Describe the methods of producing a sensitometric stripsensitometric stripPlot the characteristic curvePlot the characteristic curveDescribe the Features of the characteristic Describe the Features of the characteristic curvecurveDescribe the importance & practical Describe the importance & practical applicationsapplications
Why is the study important?Why is the study important?
To produce images with optimum contrast To produce images with optimum contrast that reveal high details of the object that reveal high details of the object examined.examined.
Optimum contrast?Optimum contrast?
Low contrast (long scale contrast)Low contrast (long scale contrast)
High contrast (Short scale contrast)High contrast (Short scale contrast)
IntroductionIntroduction
Photosensitive materials (x-ray films) are Photosensitive materials (x-ray films) are used to record the invisible x-ray imageused to record the invisible x-ray imageIt is required to reproduce all the It is required to reproduce all the characteristics of the characteristics of the invisible imageinvisible image in in visible form.visible form.The films ability to do so depends on its The films ability to do so depends on its sensitometric properties.sensitometric properties.It is advantages to have a sound It is advantages to have a sound knowledge of sensitometric properties of knowledge of sensitometric properties of x-ray films.x-ray films.
X-ray tube
Object
Plot of incident x-ray beam intensity
Plot of transmitted x-ray beam intensity
Invisible x-ray image
Format
ion o
f Invi
sible
x-ra
y im
age
Invisible x-ray imageInvisible x-ray image
B2 T1 T2 T3
E
E B1 E B2
ET1EM
ET2
ET3
EA
kV mA Sec FFD
BB1 Air
Supporting tissue (m)
EMInvisible X-ray image
What is Sensitometry?What is Sensitometry?
The scientific study of the The scientific study of the responseresponse of of photosensitive material to different levels photosensitive material to different levels of exposures.of exposures.
How is it done?How is it done?
Producing a Producing a sensitometric stripsensitometric strip and plotting and plotting a characteristic curve.a characteristic curve.
What is Response of exposure & What is Response of exposure & How is it manifested?How is it manifested?
The response is the change that The response is the change that takes place, after exposure to takes place, after exposure to electromagnetic radiation (light or x-rays), electromagnetic radiation (light or x-rays), in the photosensitive emulsion on the filmin the photosensitive emulsion on the film
The response of the film to exposures is The response of the film to exposures is manifested as a manifested as a degree of blackeningdegree of blackening produced after chemical processingproduced after chemical processing
How is degree of blackening How is degree of blackening quantified/measured?quantified/measured?
1.1. Transparency (transmission): Transparency (transmission): when when photographic image is held up for light for photographic image is held up for light for inspection it will be observed that it made inspection it will be observed that it made up of many varied area of different up of many varied area of different brightness.brightness.
Intensity of transmitted light Intensity of transmitted light
Transparency = ----------------------------------Transparency = ----------------------------------
Intensity of incident lightIntensity of incident light
2.2. OpacityOpacity
reciprocal of transparency is known as reciprocal of transparency is known as opacity.opacity.
Intensity of incident lightIntensity of incident light
Opacity = ----------------------------------Opacity = ----------------------------------
Intensity of transmitted light Intensity of transmitted light
3.3. Optical Density (OD) Optical Density (OD) is expressed as a number that is actually a logarithm, is expressed as a number that is actually a logarithm,
using the common base 10.using the common base 10.
Photographic density is defined by Photographic density is defined by
D = (Log of opacity) = log D = (Log of opacity) = log 1010 I Ioo / I / I
D = density. ID = density. IOO light incident on a film. I light transmitted by light incident on a film. I light transmitted by
the film the film
How is degree of blackening How is degree of blackening quantified/measured?quantified/measured?
In Radiography the degree of film In Radiography the degree of film blackening is quantitatively indicated by blackening is quantitatively indicated by the term the term ‘Optical Density’.‘Optical Density’.
The optical density describes how The optical density describes how much a certain area of the film is opaque much a certain area of the film is opaque to light incident upon it .to light incident upon it .
Optical DensityOptical Density
The optical density is expressed The optical density is expressed quantitatively as,quantitatively as,
Optical Density = LogOptical Density = Log1010 Opacity Opacity
It is measured by using the It is measured by using the ‘Densitometer’‘Densitometer’
(The densitometer works on the following (The densitometer works on the following principle)principle)
Consider the light transmitted through an Consider the light transmitted through an area of a filmarea of a film
Incident light intensity (Ii )
Transmitted light intensity (It)
Transmittance (Transmission ratio)= It / Ii
Opacity = 1 / Transmittance = Ii / It
Density = Log10 Opacity = Log10 Ii / It
DensitometerDensitometer
Uniform light source Uniform light source and an optical sensorand an optical sensor
Calibration control Calibration control allows for easy allows for easy calibrationcalibration
Range of densities on a filmRange of densities on a film
IIii IItt TransmitTransmittancetance
OpacityOpacity DensityDensity
100100
0.010.01
0.10.1
1.01.0
10.010.0
100100
0.00010.0001
0.0010.001
0.010.01
0.10.1
11
1000010000
10001000
100100
1010
11
44
33
22
11
00
4 3 2 1 0
Sensitometric stripSensitometric strip
A film containing number of areas with A film containing number of areas with different optical densities from white (fully different optical densities from white (fully transparent) to black (fully opaque)transparent) to black (fully opaque)
How to produce a sensitometric strip and the characteristic curve?
1.Expose a film to different amounts of known exposures starting from a minimum and increasing at a known rate (ratio / wedge factor) up to a maximum.
2. Process the film
3. Measure the densities
4. Tabulate the result & Study the response by plotting a curve (density Vs Log relative exposure
Methods of exposingMethods of exposing
Time scale methodTime scale method
(using x-ray exposure)(using x-ray exposure)
Intensity scale methodIntensity scale methodi. Using x-ray exposurei. Using x-ray exposure
ii. Using light exposureii. Using light exposure
Time scale methodTime scale methodThe film is exposed to different The film is exposed to different quantitiesquantities of of exposures using constant intensity and exposures using constant intensity and variable duration.variable duration.(Quantity = Intensity x Time)(Quantity = Intensity x Time)
Equipment requiredEquipment requiredX-ray machineX-ray machineCassette with film insideCassette with film insideLead sheetsLead sheetsProcessorProcessorDensitometerDensitometerGraph paperGraph paper
Procedure (time scale method)Procedure (time scale method)Constants
kV, mA, FFD
Variable
Time
Lead sheets
Loaded cassette
X-ray tube
Loaded cassette
Areas to be exposed
Exposure selectionExposure selectionMinimum exposureMinimum exposure Low enough not to produce a measurable Low enough not to produce a measurable densitydensityMaximum exposureMaximum exposureHigh enough to produce a density around 3.0High enough to produce a density around 3.0IncrementIncrement Wedge factorWedge factor (Ratio between two exposures) (Ratio between two exposures) of 2 is adequate. (2of 2 is adequate. (2½½ can be used to get more can be used to get more levels)levels)
Alternatively the time steps available in the Alternatively the time steps available in the machine may be used to get more points on machine may be used to get more points on the graphthe graph
Intensity scale method 1Intensity scale method 1
Making a single exposure Making a single exposure using using
a a calibratedcalibrated step step wedgewedge
X-ray machineX-ray machine
a loaded cassettea loaded cassette
(The intensity of x-rays (The intensity of x-rays passing through the passing through the steps are different & steps are different & the duration of the duration of exposure is the same)exposure is the same)
X-ray exposure
Intensity scale method 2Intensity scale method 2
The film is exposed to a series of different The film is exposed to a series of different intensities of light for the same duration intensities of light for the same duration using an instrument called the using an instrument called the ““SensitometerSensitometer”. ”.
The wedge factor is usually 2The wedge factor is usually 2½½
The colour of light should match the The colour of light should match the spectral sensitivity of the filmspectral sensitivity of the film
SensitometerSensitometer
Uses a controlled light Uses a controlled light sourcesource– Produces same Produces same
amount of light each amount of light each time it is triggeredtime it is triggered
Spectral SensitivitySpectral Sensitivity
This is the term This is the term used to describe used to describe the response of the response of the film to the the film to the range of range of wavelengths wavelengths (spectrum of (spectrum of colours) of lightcolours) of light
300
400
500
600
700
0.5
1
Rela
tive
resp
on
se
Wavelength (nm)
Monochromatic film
Orthochromatic film
OD examplesOD examplesT OD Comment
1.0000 0 Perfectly clear (does not exist)
0.7760 0.11 Unexposed film (base + fog)
0.1000 1 Medium gray
0.0100 2 Dark
0.0010 3 Very dark; requires hot lamp
0.00025 3.6 Maximum OD used in medical radiography
Film obtained using time scale method
DensityDensity
Plotting the curvePlotting the curve
AreaArea AA BB CC DD
Exposure (Time)Exposure (Time) 0.010.01 0.020.02 0.040.04 0.080.08
Relative exposureRelative exposure 11 22 44 88
Log relative Log relative exposureexposure
00 0.30.3 0.60.6 0.90.9
DensityDensity 0.250.25 0.30.3 0.40.4 0.90.9
Plotting the curvePlotting the curve
AreaArea EE FF GG HH II
Exposure (Time)Exposure (Time) 0.160.16 0.320.32 0.640.64 1.281.28 2.562.56
Relative Relative exposureexposure
1616 3232 6464 128128 256256
Log relative Log relative exposureexposure
1.21.2 1.51.5 1.81.8 2.12.1 2.42.4
DensityDensity 1.451.45 2.12.1 2.52.5 2.72.7 2.92.9
Copyright © 2006 by Thomson Delmar Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.Learning. ALL RIGHTS RESERVED.
The D Log E CurveThe D Log E Curve
Others names;Others names;– Sensitometric curveSensitometric curve– Characteristic curveCharacteristic curve– Hurter and Driffield (H & D) curveHurter and Driffield (H & D) curve
Sensitometry’s roots lie in analysis of Sensitometry’s roots lie in analysis of photographic filmphotographic film
1
2
3
4
1 2 3 4Log relative exposure
Den
sit
y
Shoulder
Toe
Characteristic curve
GF
GF = Gross Fog
DMax
Straight line portion
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
0.60
0.88
1.10
1.40
1.70
1.88
2.10
2.30
2.48
2.60
2.88
3.10
3.24
3.35
3.48
Log Relative exposure
Den
sity
Characteristic curve
Shoulder
Straight line portion
Toe
D-Max
GF
(Features) Information obtainable(Features) Information obtainable
Gross fog (Basic fog)Gross fog (Basic fog)
ThresholdThreshold
ContrastContrast
Latitude (film latitude & exposure Latitude (film latitude & exposure latitude)latitude)
Speed & SensitivitySpeed & Sensitivity
Maximum densityMaximum density
ReversalReversal
Gross fog (Basic fog)Gross fog (Basic fog) & & net densitynet density This is the density of the horizontal part of the This is the density of the horizontal part of the
curve at the minimum exposure levelcurve at the minimum exposure level
Gross fogGross fog = = Base DensityBase Density + + FogFog
Base DensityBase Density :- Density produced by the base :- Density produced by the base material material
FogFog :- Density produced by the development of :- Density produced by the development of silver halide crystals which have not silver halide crystals which have not
received an intentional received an intentional exposureexposure
Net densityNet density = Gross density – Gross fog = Gross density – Gross fog
1
2
3
4
1 2 3 4Log relative exposure
Net
Den
sit
y Shoulder
Toe
Characteristic curve (with net density)
Net density = gross density – gross fog
0
ThresholdThresholdThe region where the film emulsion begins to The region where the film emulsion begins to respond to the exposurerespond to the exposure
ContrastContrastThe rate of change of density for a given change of The rate of change of density for a given change of log relative exposurelog relative exposure
Contrast = Contrast = ΔΔD / D / ΔΔEE
It is given by the slope (gradient) of the straight line It is given by the slope (gradient) of the straight line portion of the curve. If it is a true straight line then portion of the curve. If it is a true straight line then the contrast is called the contrast is called Gamma.Gamma.
Since, in practice, the curve is not an exact straight Since, in practice, the curve is not an exact straight line, the line, the average gradientaverage gradient is taken as the contrast. is taken as the contrast.
Characteristic curve
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
0.60
0.88
1.10
1.40
1.70
1.88
2.10
2.30
2.48
2.60
2.88
ΔD
ΔE
Contrast = ΔD/ ΔE
1
2
3
4
1 2 3 4Log relative exposure
Densi
ty
Average gradient
DX
DY
Log EX Log EY
A
B
C
Average gradient = BC/AC DY - DX
= ----------- log EY – log EX
How to select points A and B ?
Point A ? Point B ?Point A ? Point B ?
A : DA : DX X = 0.25 above Basic fog= 0.25 above Basic fog
B : DB : DYY = 2.0 above Basic fog = 2.0 above Basic fog
The densities from 0.25 to 2.0 is called The densities from 0.25 to 2.0 is called the the Useful Density range.Useful Density range.
Useful density range is the density range Useful density range is the density range in which the differences can be identified in which the differences can be identified by the human eyeby the human eye..
The densities which represents different The densities which represents different structures on a radiograph should lie structures on a radiograph should lie within this range of densities.within this range of densities.
ContrastContrastContrast controls slope of Contrast controls slope of characteristic curvecharacteristic curve
log relative exposure
OpticalDensity
log relative exposure
OpticalDensity
LowerContrast
HigherContrast
Useful density range is the range of densities within which the human eye can recognize the small differences
That is the range of net densities from 0.25 to 2.0
LatitudeLatitudeLatitude is an expression of the tolerance of a Latitude is an expression of the tolerance of a system to extreme conditions of exposure.system to extreme conditions of exposure.
It refers to the ability of a film or film-screen It refers to the ability of a film or film-screen system to record successfully a wide range of system to record successfully a wide range of exposure . exposure .
(considered in two parts)(considered in two parts)
Film latitudeFilm latitude && Exposure latitudeExposure latitude
Film LatitudeFilm Latitude
The difference between the upper and The difference between the upper and lower limits of log relative exposure which lower limits of log relative exposure which produce densities within the produce densities within the useful rangeuseful range
Significance of film latitudeSignificance of film latitude
The range of x-ray intensities transmitted The range of x-ray intensities transmitted through the body part should lie within the through the body part should lie within the film latitude, if they are to be viewed as film latitude, if they are to be viewed as useful densities on the radiograph.useful densities on the radiograph.
Any x-ray intensity that falls out side the Any x-ray intensity that falls out side the film latitude will not reveal any information film latitude will not reveal any information & a useful piece of information might be & a useful piece of information might be lostlost
Film latitude & Average gradientFilm latitude & Average gradient
1
2
3
4
1 2 3 4Log relative exposure
Densi
ty
DX
DY
Log EX Log EY
A
B
C
When Dx = 0.25+BF & Dy = 2.0 +BF
DY - DX
Average gradient = ----------- becomes log EY – log EX
1.75
= ------------------
Film latitude
Film latitude
Exposure latitudeExposure latitudeThis refers to the freedom of the This refers to the freedom of the radiographer to select slightly different radiographer to select slightly different exposures (to make room for errors) for a exposures (to make room for errors) for a particular examination so that the resulted particular examination so that the resulted densities remains within the useful density densities remains within the useful density range.range.
Exposure latitude = film latitude – Exposure latitude = film latitude – subject subject contrast (contrast (log relative exposurelog relative exposure range range transmitted from a particular body part)transmitted from a particular body part)
Subject contrastSubject contrast
E
E1 E2 E3E4
E5E6
E7
kV mA Sec FFD
BB Air
Transmitted Transmitted intensitiesintensities
EE11 EE22 EE33 EE44 EE55 EE66 EE77
Relative Relative IntensityIntensity
RERE11 RERE22 RERE33 RERE44 RERE55 RERE66 RERE77
Log relative Log relative intensityintensity
ee11 ee22 ee33 ee44 ee55 ee66 ee77
Subject contrast
ee11ee77
Image contrastImage contrast
ee11 ee77
D1 D2 D3 D4 D5 D6 D7
Characteristic curve
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.0
0
0.6
0
0.8
8
1.1
0
1.4
0
1.7
0
1.8
8
2.1
0
2.3
0
2.4
8
2.6
0
2.8
8
Film latitude
Subject contrast
Exposure latitude
X Y
e1 ≥ X ; e7 ≤ Y
Exposure latitude = film latitude – Subject contrastExposure latitude = film latitude – Subject contrast
Sensitivity refers to the exposure required Sensitivity refers to the exposure required by a film or film-screen system to produce by a film or film-screen system to produce a net density of 1. a net density of 1.
Sensitivity is expressed in miliroentgens Sensitivity is expressed in miliroentgens (mR) (mR)
A A high sensitivehigh sensitive (have (have low mRlow mR value for value for sensitivity) or high speed system requires sensitivity) or high speed system requires less exposure than that of a low sensitive less exposure than that of a low sensitive or low speed system.or low speed system.
Speed & SensitivitySpeed & Sensitivity
Numerically the Speed Numerically the Speed is proportional to the is proportional to the reciprocal of the reciprocal of the sensitivity (mR) and sensitivity (mR) and is expressed as is expressed as
128128Speed = --------------Speed = --------------
Sensitivity Sensitivity (mR)(mR)
SpeedSpeed Sensitivity Sensitivity (mR)(mR)
12001200 0.10.1
800800 0.160.16
400400 0.320.32
200200 0.640.64
100100 1.281.28
5050 2.562.56
2525 5.05.0
1212 10.010.0
1
2
3
4
1 2 3 4Log relative exposure
Densi
ty
1+BF
Log ESA
Log ESB
A B
Comparison of Speeds of two films (film-screen systems)
Speed A > Speed B
Speed A α 1/ ESA
Speed B α 1/ ESB
Speed A ESB
------------- = ------
Speed B ESABF
SpeedSpeed
Faster film will have a curve closer to y-axis Faster film will have a curve closer to y-axis of graphof graph
SpeedSpeedSpeed controls left-right location of Speed controls left-right location of characteristic curvecharacteristic curve
log relative exposure
OpticalDensity
log relative exposure
OpticalDensity
X
X
SlowerSpeed
FasterSpeed
SpeedSpeed
Affected by Affected by processingprocessing– Immersion timeImmersion time– Solution temperatureSolution temperature– Chemical activityChemical activity
SpeedSpeed
Maximum Density (DMaximum Density (DMaxMax))
The density produced when all the silver The density produced when all the silver bromide crystals in the emulsion is bromide crystals in the emulsion is exposed and developedexposed and developed
ReversalReversal This is the region where the density This is the region where the density reduces with the increasing exposure reduces with the increasing exposure greater than that produce Dgreater than that produce DMaxMax
1
2
3
4
1 2 3 4Log relative exposure
Densi
ty
D Max & Reversal
BF
DMax
Reversal
Reversal or SolarizationReversal or Solarization
Once a film has been Once a film has been exposed to Dexposed to Dmaxmax, it will , it will
begin to lose density begin to lose density after further exposureafter further exposure
Duplication film has Duplication film has been solarizedbeen solarized
Uses of the characteristic curveUses of the characteristic curveInformationInformation
Gross fog (Basic fog)Gross fog (Basic fog)ThresholdThresholdContrastContrastLatitude (film latitude & Latitude (film latitude & exposure latitude)exposure latitude)Speed & SensitivitySpeed & SensitivityMaximum densityMaximum densityReversalReversal
UsesUsesSelection of filmsSelection of filmsAssessing processor Assessing processor performance (Quality performance (Quality control)control)Selection of exposure Selection of exposure factorsfactorsComparison of film-Comparison of film-screen systemsscreen systemsDuplication of Duplication of radiographsradiographs
SummarySummary
Definitions of termsDefinitions of terms
Methods of producing a sensitometric Methods of producing a sensitometric stripstrip
Plotting the Characteristic curvePlotting the Characteristic curve
Features of the characteristic curveFeatures of the characteristic curve
The practical applicationsThe practical applications
Thank You