1. RADIATION PROTECTION IN DIAGNOSTIC RADIOLOGY
Chapter 3
Part 1 : Radiography
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
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References: (List the references for the session)

2. Content Intensifying screen structure and characteristics
Screen film combination
Radiographic film structure and characteristics
Anti scatter grid
Darkroom
Viewing Box
Explanation or/and additional information
Instructions for the lecturer/trainer

3. Overview
To become familiar with basic knowledge of the component that form the radiographic chain.
Lecture notes: ( about 100 words)
Instructions for the lecturer/trainer

4. Topic 1 : Intensifying screen structure and characteristics
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)

5. Primary beam attenuation and latent image
Film, fluorescent screen
or image intensifier
Scattered
radiation
« Latent »
radiological
image
Bone X
Soft
tissue
Air
The beam intensity at the detector level is modulated by the density of the irradiated structure (air, bone, soft tissue etc). The latent radiological image has to be revealed through the processing to become visible.
Primary
collimation
Antiscatter Grid
Beam intensity
at detector level

6. Intensifying screen
Layer of material used in conventional radiography to :
Convert the incident X-rays into radiation more suitable for the radiation-sensitive emulsion of the radiographic film (X-ray  light photons)
Reduce the patient exposure needed to achieve a given level of film blackening
Reduce the exposure time as well as the power of the x-ray generator (cost savings)
Increase photoelectric effect  better use of the beam energy (image formation)

7. Intensifying screen structure (I)
Supporting Base (mainly polyester material)
chemically neutral, resistant to X-ray exposure, flexible, perfectly flat
Reflecting layer (Titanium dioxide - TiO2)
a crystalline compound reflecting backward photons to sensitive emulsion
Fluorescent layer (polymer)
crystals dispersed in a suspension of plastic material
Protective overcoat
colorless thin film avoiding abrasions of fluorescent layer due to the use of screen

8. Intensifying screen structure (II)
(Incident X-ray beam)
Supporting Base (240 m)
Screen
Reflecting layer (25 m)
Fluorescent layer (100 to 400 m)
Protective overcoat (20 m)
(Light-sensitive film)

9. Intensifying screen structure (III)
The fluorescent layer (luminophor crystals) should :
be able to absorb the maximum quantity of X-rays
convert the X-ray energy into light energy
match its fluorescence with the film sensitivity (color of emitted light)
Type of material :
Calcium Tungstate (CaWO4) (till 1972)
Rare earth (since 1970) (LaOBr:Tm) (Gd2O2S:Tb)  more sensitive and effective than (CaWO4)

10. Intensifying screen characteristics (I)
IF (Intensifying Factor): ratio of exposures giving the same film optical density, with and without screen
50 < IF < 150 (depending on screen material and X-ray beam energy)
QDE (Quantum Detection Efficiency): fraction of photons absorbed by the screen
40% for CaWO4 < QDE < 75% for rare earth (depending on crystal material, thickness of fluorescent layer and X-ray spectrum)
 (Rendering coefficient): ratio of light energy emitted to X-ray energy absorbed (%)
3% for CaWO4 <  < 20% for rare earth
C (Detection Coefficient): ratio of energy captured and used by the film to energy emitted by the crystal (%)
C is maximum for screens emitting in UV color wave length  90%

11. Intensifying screen characteristics (II)
Sensitivity of a Conventional Film
BaSO4:Eu,Sr
YTaO4:Nb
Relative Sensitivity of Film
BaSO4:Pb
The sensitivity of the conventional film covers a large spectrum of frequency colors comparatively to the different screens illustrated in the graph.
The film color should be therefore correctly matched with the corresponding intensifying screen.
CaWO4
250
300
350
400
450
500
550
600 UV
Blue
Green

12. Intensifying screen characteristics (III)
Intensifying factor: ratio of exposures giving the same film optical density, with and without screen
175
150
125
100 75 50 25
Gd2O2S
LaOBr
Intensifying factor
The response of different intensifying screens to the same kV may significantly vary.
For the same kV value (90 kV for instance) a CaWo4 (normal screen) screen will have an intensifying factor of 75 comparatively to 125 for the Gd2O2S (rare hearth screen) screen. This means that according to the examination type considered, the most appropriate intensifying screen should be used in order to optimize the necessary exposure leading to the same optical density.
CaWO4 kV

13. Topic 2 : Screen film combination
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)

14. Screen film combination
Sensitivity (screen film): The quotient K0/Ka, where K0 = 1 mGy and Ka is the air kerma free-in-air for the net density D = 1.0, measured in the film plane
Screen film system: A particular intensifying screen used with a particular type of film
Sensitivity class: Defined range of sensitivity values of a screen film system
Single emulsion film: One coated film used with one intensifying screen
Double emulsion film: A double coated film used with a couple of intensifying screens
Screen film contact     Quantum mottle

15. Screen film combination performance
Spatial Resolution: capability of a screen film combination to display a limited number of line pairs per mm. It can be assessed by the Hüttner resolution pattern.
Modulation Transfer Function (MTF): description of how sinusoidal fluctuations in X-ray transmission through the screen film combination are reproduced in the image
Noise spectrum: component of noise due to intensifying system (screen film)
Quantum noise, Screen noise, Granularity
Quantum Detection Efficiency (QDE): the quotient of signal to noise ratios (SNR) of radiographic image and “latent” image

16. Screen film combination performance
Identification of screen by type and format
type mismatch (use of different types of screens) FOR THE SAME FORMAT is not ADVISABLE
Screen film contact
loss of spatial resolution
blurred image
Cleanliness
Inter cassette sensitivity

17. Topic 3 : Radiographic film structure and characteristics
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)

18. Radiographic film (structure and characteristics)
Protective layer (outer surface)
Sensitive layer (~20µ)
Base material (transparence and mechanical resistance) (~170µ)
Binding (base-sensitive layer) or anti cross-over layer
Filtering layer
Sensitivity class

19. Radiographic film structure
Film emulsion
Filter
Supporting Base
Protective layer
Binding layer
Anti cross-over (optional)
Single emulsion film

20. Film Developing 1) نورباعث يونيزه شدن AgBr شده و يون Ag+ ايجاد مي كند.
2)  وقتي فيلم در Developer قرار گرفت يونAg+ احيا شده وذرات Ag كه سياه رنگ مي باشند بدست میآیند.
3) فيلم در fixer كه محلول سخت كننده است قرار مي گيرد، ذرات AgBr شسته شده تا ديگر نور روي فيلم اثر نگذارد.

21. Optical Density سياهي امولسيـون فتوگرافي دانسيته نام دارد.
وقتي فيلم اكسپوز شده روي Viewing box قرار مي گيرد Li شدت نور وارد شده به فيلم و Lt شدت نور عبور كرده از فيلم مي باشد و دانسيته D از لگاريتم نسبت انتقال بدست مي آيد.
اگر شدت نور از فيلم عبور كند دانسيته برابر Log10 =1 مي شود.
اغلب اطلاعات تشخيصي دانسيته بين 0.5 تا2 را دارند.
اختلاف بين دانسيته دو نقطه DD بنام كنتراست راديوگرافي ميباشد. اين كنتراست باعث تشخيص تغييرات توسط راديولژيست ميشود.

22. Characteristic curve of a radiographic film
Optical
Density (OD)
Saturation D2
Visually evaluable
range of densities
 = (D2 - D1) / (log E2 - log E1) 
The steepness of the straight line determines the contrast of the film. The steeper the slope the higher the contrast.
The  of a film : the gradient of the «straight line» portion of the characteristic curve D1
Normal range
of exposures
Base
+ fog E1 E2
Log Exposure (mR)

23. Film sensitometry parameters
Base + fog: The OD of a film due to its base density plus any action of the developer on the radiographically unexposed emulsion
Sensitivity (speed): The reciprocal of the exposure value needed to achieve a film net OD of 1.0
Gamma (contrast): The gradient of the straight line portion of the characteristic curve
Latitude: Steepness of a characteristic curve, determining the range of exposures that can be transformed into a visually evaluable range of OD

24. Comparison of characteristic curves
(OD)
(OD)
Film A
Film A
Film B
Film B
Log Exposure (mR)
Log Exposure (mR)
Film A is faster than Film B
Film A and B have the same sensibility but different contrast
Film A and B have the same contrast

25. Sensitometry: A method of exposing a film by
Sensitometric strip
Sensitometry: A method of exposing a film by
means of a light sensitometer and assessing its response to exposure and development 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

26. Topic 4 : Anti-scatter grid and grid performance parameters
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

27. Anti-scatter grid (I) Radiation emerging from the patient
primary beam : contributing to the image formation
scattered radiation : not reaching the detector but contributing to the patient dose
the grid (between patient and film) eliminates most of scattered radiation
stationary grid
moving grid (better performance)
focused grid
Potter-Bucky system

28. Anti-scatter grid (II)
Source of X-rays
Patient
Scattered X-rays
Lead strip
Film and cassette
Useful X-rays

29. Grid performance parameters (I)
Grid ratio
Ratio of the height of the strips to the width of the gaps at the central line
Contrast improvement ratio
Ratio of the transmission of primary radiation to the transmission of total radiation
Grid exposure factor
Ratio of total radiation without the anti-scatter grid to that with the anti-scatter grid placed in the beam for a similar density

30. Grid performance parameters (II)
Strip number
The number of attenuating lamella per cm
Grid focusing distance
Distance between the front of a focused grid and the line formed by the converging planes

31. Example of anti-scatter grids (grid ratio)
Grid : C
Grid : A
Grid : B D h    h 1
Grid ratio : r = =
5 < r < 16 D tg 
Grid A and B have the same strip number
Grid B and C have the same interspace between the lamella

32. Grid selectivity (II) A grid with r = 12 transmits 5%
100 90 80 70 60 55 50 45 40 35 30 25 20 15 10 5
A grid with r = 12 transmits 5%
of scattered radiation
A grid with r = 16 transmits 3.8%
N.B. : slight difference
% of scattered beam transmitted 5%
3.8% r

33. Grid focusing error (virtual increasing of grid shadow)
X-Ray source
(too far)
X-Ray source
(too close)
Grid
Film and cassette
grid shadow deformation
(applicable to both cases)

34. Grid focusing error (leading to 25% of beam loss)

35. Grid out of center (virtual deformation of grid shadow)
Lateral shift
X-Ray source
Film and
cassette
Grid
Grid shadow

36. Grid focusing error due to lateral shift (leading to 25% loss of X-ray beam)

37. Topic 5 : Darkroom and viewing box
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)

38. Darkroom characteristics
Safelight
number (as low as possible), distance from the table
type and colors of filters
bulb color (red)
power (< 25 W)
External light tightness
Room temperature < 20°
Film storage conditions

39. Viewbox characteristics
Since the viewing conditions are essential for a good interpretation of the diagnostic images, the viewing conditions must be optimal
Cleanliness of external/internal surface
Brightness
homogeneity of different viewing boxes: cd/m2
homogeneity within the same viewing box
Coloring
color mismatch must be avoided
Environment
ambient light level : 50 lux maximum

40. Viewbox brightness (cd/m2) EXAMPLE OF CORRECT MEASUREMENTS5 7 8 1 6 2 3 9
EXAMPLE OF
MEASUREMENTS
CORRECT
CONFIGURATION
(cd/m2)

41. Viewbox color and brightness5 7 8 1 6 2 3 4 9
WHITE
COLOR
BLUE
WRONG
CONFIGURATIONS
(cd/m2)

42. Where to Get More Information
Physics of diagnostic radiology, Curry et al, Lea & Febiger, 1990
Imaging systems in medical diagnostics, Krestel ed., Siemens, 1990
The physics of diagnostic imaging, Dowsett et al, Chapman&Hall, 1998