This document provides information on intensifying screens and radiographic grids. It discusses the history, construction, and functions of intensifying screens, including the types of phosphors used. It also covers screen speed, detail, and care. For radiographic grids, it outlines the history and development of grids as well as grid design, patterns, specifications and factors such as ratio and frequency. Research studies evaluating different screen-film combinations and their effects on image quality and radiation dose are also summarized.
3. INTRODUCTION
X-rays were discovered by W.C. Roentgen because of their
ability to cause fluorescence.
X-ray photons cannot be seen. The image produced by X-rays
may be captured on a film, may be viewed directly (fluoroscopy)
or on a monitor with digital radiology.
Roentgen initially used a sheet of platinocyanide to view the
fluorescence produced by X-ray photons.
4. Combination of screen films, intensifying screens and
cassettes are used in making extra oral images.
Main function of screens is to reduce radiation to the patient.
5. Currently, there are two groups of X-ray films for dental purposes:
1. Non-screen - Those with emulsions more sensitive to direct exposure of
X - rays.
These are primarily used as intraoral films and provide excellent image
quality.
2. Screen - Those with emulsions more sensitive to blue [standard] OR green
[rareearth] light.
Emitted when X-rays strike the intensifying screens.
The X-ray photons are converted to visible light photons.
6. Word “intensifying” means those screens which intensify the effect
of x-rays on the film
Intensifying screen is a device that transfers X-ray energy into
visible light; visible light in turn exposes screen film.
Total thickness is 380 µm.
6
INTENSIFYING SCREENS
7. Intensifying screen is a plastic sheet coated with
fluorescent material called phosphors.
Phosphors are materials which convert photon
energy to light.
LUMINESCENCE is the emission of light
from a substance bombarded by radiation.
These are two types; fluorescence and
phosphorescence.
INTENSIFYING SCREENS
8. Fluorescence - luminescence is excited only
during the period of irradiation and will terminate
at completion of the X-ray exposure.
Phosphors in intensifying screens produce
fluorescence.
Phosphorescence is afterglow.
Irradiated material continues to emit light for a
time after cessation of exposure to radiation and
will continue to produce an image which is not
wanted.
10. `
There are three types of intensifying screens:
a) Standard - slow screens
b) Rare earth - fast screens
c) Combination
11. Standard screens use calcium tungstate phosphors, while rare
earth screens use gadolinium or lanthanum phosphors.
The commercial name for rare earth screens is Lanex.
More efficient at converting X-rays to visible light thus
reducing the radiation further to the patient.
12. Intensifying screen is placed in a cassette in close contact with
a film. The visible light from its fluorescent image will add to
the latent image on the film.
Its function is to reinforce the action of X-rays by subjecting
the emulsion to the effect of light as well as ionizing radiation.
14. Speeds of Intensifying Screens
1. Fast screens - thick layer, and relatively large crystals used,
maximum speed is attained but with some sacrifice .
2. Slow screens or high definition screens - a thin layer and
relatively small crystals are used; detail is the best, but speed is
slow necessitating a higher dose of ionizing radiation.
3. Medium screens - medium thick layer of medium sized crystals
in order to provide comprise between speed and definition.
15. CHARACTERISTICS OF INTENSIFYING SCREENS
1) An intensifying screen consists of a base of polyester or cellulose triacetate
similar to radiographic film
2) This base must be radioparent
3) chemically inert.
4) It must combine characteristics of toughness and flexibility
5) Should neither curl
6) with a uniform homogeneous phosphor layer- standard or rare earth.
16. SCREEN SPEED AND DETAIL
The relationship between screen speed and detail is a reciprocal one: as the
speed of the screen increases, the amount of detail decreases.
FACTORS AFFECTING SPEED
• Phosphor type
• Phosphor grain size
• Thickness of phosphor layer
• Presence of reflective/absorptive layer
• Dye tint in binder
• Exposure technique
17. TYPES OF PHOSPHORS
CALCIUM TUNGSTATE
RARE EARTHS
• Are soft, malleable metals that can be made to emit light upon stimulation by
X-rays.
• First introduced in 1970’s by Wickersheim, Alves, and Buchanan.
18. SCREEN DETAIL
SCREEN UNSHARPNESS
Due to divergent emission of light coming from intensifying
screen.
CROSSOVER EFFECT
It is a result of the widening light beam emitted by the crystal as
it passes from one emulsion to the other, causing a shadowy,
less sharp image in the emulsion layer furthest from the
intensifying screen.
19. SCREEN DETAIL
STRUCTURE MOTTLE
It is caused by the fact that it is not possible to evenly
dispersed the phosphor crystal throughout the binder
medium.
SCREEN-FILM CONTACT
Poor film-screen contact , causes the light emitted by the
intensifying screen to diffuse before it reaches the film, so
that the image produce is unsharp.
20. Poor Screen Contact
Screen contact is tested using a wire
mesh test tool.
Wire mesh is placed on top of the
cassette.
Radiograph is taken and the film
processed.
Image is viewed from 2 to 3 meters
from the view box.
Poor contact will appear as a cloudy and
blurry area on the film.
Wire-Mesh Test Results
21. Poor Screen Contact
Common reasons for poor contact include:
• Warped cassette frame.
• Sprung or cracked cassette frame.
• Foreign matter in the cassette.
22. SPECTRUM MATCHING
Film-screen combination must be matched so that the emission
characteristics of the screen match the spectral sensitivity of the
film.
This is called spectrum matching.
calcium tungstate emits a
broad blue spectrum.
rare earth emits a green spectrum.
23. PHOTOTIMERS
Phototimer should have capacity to recognise
differences in screen speed caused by variation in
kvp(kilovoltage peak).
Most of the phototimers take 30 milliseconds for
to measure the radiation and terminate exposure
24. ASYMMETRIC SCREENS
Screens in the cassette can be of two types or speeds.
When types of screens are different, they are referred to
as Asymmetric screens.
One side may be high contrast and the other side wide
latitude. The combined image is superior.
Some people use two different speeds in cassette for full
spine radiography.
25. Care of Screens
High quality radiography requires that the screens be clean
and free of artifacts.
Avoid touching the screens with hands.
Do not slide the film in or out when loading the cassette.
26. Care of Screens
Keeping the dark room clean will help reduce dirt or
dust getting into the cassette.
Use only specially formulated screen cleaner with anti
static properties.
Make sure they are dry before reloading with film.
27. ADVANTAGES OF USING SCREENS
• Reduces the dose .
• Short exposure time
• Increases x-ray tube life
DISADVANTAGE OF USING SCREEN
• Screen unsharpness
28. An evaluation of rare-earth imaging systems in
panoramic radiography
Barton M. et al ,to evaluate the efficacy of rare earth imaging systems in
panoramic radiography
Panoramic radiographs were made of ninety-nine consenting adult patients who
had image-analysis test devices placed within their oral cavities.
Calcium tungstate screen-film systems were found to have the highest contrast
but with resolution comparable to rare-earth screen-film systems under clinical
test conditions.
Calcium tungstate systems required up to twice the radiation exposure of the
patient. It was found that some rare-earth screen-film combinations may produce
clinically acceptable panoramic radiographs while reducing the patient's
radiation exposure.
Oral Surgery, Oral Medicine, Oral Pathology ,58, (4), 2000,475–482
29. Clinical comparison of conventional and rare earth
screen-film systems for cephalometric radiographs
To evalaute and compare cephalometric and posteroanterior radiographs
taken with conventional (CaWO4) and rare earth screens.
INFERENCE - The rare earth screen-film system was judged to be roughly
comparable to a conventional system, with the additional advantage of
reduced radiation exposure to the patient.
Oral Surgery, Oral Medicine, Oral Pathology, 53( 3), 2005, 322–32
30. Proximal surface caries detection with direct-
exposure and rare earth screen/film imaging
Aim to compare five imaging systems for their diagnostic accuracy in
detection of proximal surface dental caries.
D-speed film marginally outperformed the other four systems, but the three
screen/film systems matched the diagnostic accuracy of E-speed film.
Radiation reductions between 62% and 92% were achieved with the
screen/film systems when compared to the two conventional dental films.
The feasibility of designing a screen/film bite-wing cassette was shown, but
the poor diagnostic accuracy of the present bite-wing system indicated a need
for a new technology in caries detection.
Oral Surgery, Oral Medicine, Oral Pathology 66(6), 2001, 734–745
31. SIMULATION OF DENTAL INTENSIFYING SCREEN FOR
INTRAORAL RADIOGRAPHIC USING MCNP5 CODE
Materials that can be used to build a screen for intraoral radiology were
evaluated using a Monte Carlo code.
Simulations were performed with fluorescent and non-fluorescent materials, in
order to compare the absorption characteristics of the x-ray beam and electrons
production by photoelectric effect for the following materials: oxysulphide
gadolinium, calcium tungstate
The simulations showed a greater electron production in calcium tungstate
with voltage 70 kV, compared to the other materials tested.
The calcium tungstate material was considered a material with interesting
characteristics for the production of radiology screens, because it presented a
greater flow of electrons produced from a smaller amount of radiation
absorbed.
International Nuclear Atlantic Conference october 2011, 24-28.
33. • Scatter radiation is produced when primary radiation passes
through a subject .
• Radiographic fog is produced on receptor which degrades the
diagnostic quality of the image.
RADIOGRAPHIC GRIDS
34. There are 3 factors that determine the amount of scatter radiation
produced:
Field size of radiographic beam
Patient thickness/size of the area to be radiographed
kVp level
Grids are highly recommended for use when using more
than 70 kVp.
35. History
The first radiographic grid was made in
1913 by the American radiologist Gustav
Bucky.
Consisted of wide strips of lead that were
spaced 2 cm apart and running in 2
directions-along the length of the film and
then across the film.
36. In 1920 Hollis Potter , a Chicago radiologist, improved Dr Bucky's
radiographic grid design.
Dr Potter realigned the lead strips so that they ran in only 1
direction, made the lead strips thinner and therefore less obvious on
the image.
Designed a device known as the Potter-Bucky diaphragm which
allowed the radiographic grid to move during the exposure.
37. By moving the radiographic grid, the lead strips became blurred and
were no longer visible on the film.
All these improvements resulted in a practical grid device for
radiographic image applications.
Anti scatter radiation grid - designed so that 80% to 96% of scatter
radiation is removed prior to image receptor.
Most antiscatter radiographic grids allow transmission of 60% of the
primary beam to the image receptor.
Term "grid clean-up" pertains to the amount of absorption of scatter
radiation by the grid
40. STATIONARY GRIDS
The grid is stationary and does not move.
Disadvantage - presence of a grid between an object and film causes the
images of the radiopaque absorbing material to be projected on to
the film.
41. • Grid is moved side ways across the film during exposure.
• This leads to the blurring out of the shadows of grid strips, thus
they are not visible on the film.
POTTER-BUCKY DIAPHGRAM
42. GRID PATTERNS
Parallel Linear Grid
Lead strips run parallel to each other.
Strips are never aligned with the primary beam because they are all
vertical (except for strips directly under the central ray).
Parallel linear grid allows for tube angulation, minimizing the risk of
grid cutoff.
43. There are 2 linear arrangements,
Short dimension: Lead strips parallel to short dimension, also known
as a "decubitus" grid
Long dimension: Lead strips parallel to long dimension.
44. Focused Grid
Most effective for reducing scattered radiation.
In focused linear grids the lead strips are tilted progressively as they
move away from center, whereas in parallel linear grids, the lead strips
are aligned parallel to each other.
45. Canting
Canting is the process used to tilt the lead strips when forming a
focused linear grid.
They are angled to match the beam divergence, which helps reduce
scatter radiation.
46. Criss-Cross or Cross-Hatch Grid
It is a composite of 2 grids with the lead strips at right angles to each
other.
Design generally increases contrast improvement
47. When Criss-cross grids are used, no tube tilt is permitted because any
angulation would result in grid cutoff because lead strips are running
in both directions.
Criss-cross grid is mainly suitable where a grid with a very high ratio
is required
49. 0.25mm
2.0mm
0.05mm
GRID RATIO
Grid ratio is the ratio of the height
of the lead strip to the distance
between the strips by the
interspace material.
•Typical grid ratios are 6:1, 8:1,
10:1, and 12:1.
50. Higher grid ratios require more precise centering of the X-ray beam
and remove the greatest amount of scatter from the primary X-ray
beam
Higher the grid ratio, greater the tendency to improve contrast.
Grid ratio of 8:1 is recommended when imaging below 90 kVp
Grid ratio of 10:1 or 12:1 is recommended for examinations requiring
kVp greater than 90 kVp.
51. Grid frequency refers to the number of lead strips per inch or
centimeter.
Typical grid frequencies
103 line pairs/in (lpi),
178 lpi or 200 lpi
Grid Frequency
52. Bucky Factor
Bucky factor is the ratio of incident radiation intensity reaching the
radiographic grid to the transmitted radiation intensity passing
through the radiographic grid.
Higher the Bucky factor ,the greater the exposure factor and
radiation dosage to the patient.
B = INCIDENT RADIATION
TRANSMITTED RADIATION
53. CONTRAST IMPROVEMENT FACTOR
Ratio of the contrast of a finished radiograph made with a radiographic grid
compared to the contrast of a radiograph made without the antiscatter
radiographic grid.
Contrast improvement factor in a radiographic grid is represented as the "K"
factor.
K = X-ray contrast with grid
X-ray contrast without grid
Typical K factors range between 1.5 to 3.5.
54. Grid Cutoff
Grid cutoff refers to the uneven density or loss of density on the
resultant image due to undesirable absorption of the primary X-ray
beam by the radiographic grid.
Grid cutoff most commonly occurs when the primary beam is
angled into the lead.
55. causes
The central ray is not perpendicular to the grid
surface (off-level).
The central ray is not aimed at the center of the
grid (off-center).
The distance from the X-ray tube head to the
grid surface is beyond a given tolerance (off-
focus).
The grid is upside down.
56. Advantages of Grid
Reduce film fog
Increase radiographic (film) contrast.
Disadvantages of a Grid
•Exposure required to produce a radiograph when a grid is used
approximately doubles.
•An increased exposure time must be used to expose a film.
Hence a grid should be used only when improved image
quality and high contrast are necessary.
57. Non-metallic grid for radiographic measurement
Krithika et al, aim to suggest an easier, non-metallic radiographic
grid system for measuring the working length and radiographic
size of pathologic areas during endodontic diagnosis and
prognosis determination.
Conventional methods of visually determining the size of a
lesion from a radiograph are not accurate and standardized.
This nonmetallic grid system can also be used for measuring the
size of a lesion.
This method is a simple, effective and accurate way of
measuring objects on a radiograph.
Aust Endod J 2008; 34: 36–38
58. Intraoral Periapical Radiographs with Grids for Implant
Dentistry
Intraoral periapical radiographs (IOPAR) are widely used for the
preoperative planning and evaluation for most minor oral surgical
procedures owing to it simplicity, significantly lower cost, less
radiation exposure and easy availability in a dental clinical set-up.
Using these radiographs with a grid aids in increasing the accuracy
of the linear measurements for the treatment planning
Journal of Maxillofacial and Oral Surgery,December 2014,13(4), 603-605
59. Intraoral Periapical Radiographs with Grids for Implant
Dentistry
Intraoral periapical radiographs (IOPAR) are widely used for the
preoperative planning and evaluation for most minor oral surgical
procedures owing to it simplicity, significantly lower cost, less
radiation exposure and easy availability in a dental clinical set-up.
Using these radiographs with a grid aids in increasing the accuracy
of the linear measurements for the treatment planning
Journal of Maxillofacial and Oral Surgery,December 2014,13(4), 603-605
60. Clinical and radiographic evaluation of factors influencing the
presence or absence of interproximal gingival papillae
Perez et al, aim to evaluated factors that may influence the presence or
absence of interproximal papillae.
Clinical evaluation consisted of visual determination, and quantitative
analyses were made using millimeter grids on radiographs. Patients (n =
45) were divided into three groups according to age.
The distance from the contact point to the bone crest had significant
influence on papilla presence in both anterior and posterior sites (P < .05),
whereas the width between roots of adjacent teeth did not.
The papilla was missing more frequently in anterior sites. The presence of
papillae was not age-dependent.
Int J Periodontics Restorative Dent. 2012 Apr;32(2):e68-74
61. Comparative Evaluation of Two Established Age Estimation
Techniques(Two Histological and Radiological) by Image Analysis
Software Using Single Tooth
M adhu Shrestha et al, aim to standardize an age estimation method using
single tooth in absence of modern methods.
Age estimation in this study was carried out by two radiological methods like
(Tooth Coronal index(TCI) and Kvaal’s method) and two histological
(Kashyaps and Koteswara modification of Gustafson’s method and secondary
dentine estimation method).
A new radiographic technique using an acrylic base and radiographic grid
lines was employed using paralleling technique.
Tooth Coronal Index known as TCI can be used as a reliable parameter for
age estimation using single tooth in forensic investigation of individuals of
unknown data and dental anthropology
The Open Forensic Science Journal, 2015, 8, 1-7
63. References
Curry TS, Dowdey JE, Murry RC.
Christensen's Physics of Diagnostic Radiology. 4th ed. Philadelphia,
PA: Lippincott Williams & Wilkins; 1990. Chapter 8.
Oral radiology Principles and Interpretation,
White and Pharoah – Fifth edition
Textbook of Dental and maxillofacial Radiology,
Freny. R. Karjodkar – 2 edition
64. Essentials of Dental Radiography and Radiology,
Eric Whaites – Fourth edition.
Intensifying Screens
Salford University, Imaging BSC1 N.J. Oldnall
Intensifying Screens.docNick Oldnall
N. Serman & S. Singer
INTENSIFYING SCREENS, CASSETTES AND SCREEN
FILMS
65. Bushong SC. Radiologic Science for Technologists: Physics,
Biology, and Protection. 7th ed. St. Louis, MO: Mosby, Inc;
2001.
Comparative Evaluation of Two Established Age Estimation
Techniques(Two Histological and Radiological) by Image
Analysis Software Using Single Tooth-The Open Forensic
Science Journal, 2015, 8, 1-7.
Clinical and radiographic evaluation of factors influencing the
presence or absence of interproximal gingival papillae-Int J
Periodontics Restorative Dent. 2012 Apr;32(2):e68-74
66. Simulation of dental intensifying screen for intraoral
radiographic using mcnp5 code. INAC ,October 2011, 24-28.
Exposure Standards for Digital and Analogue Dry Skull
Orthopantomography. Beaini et al. J Forensic Res 2011, 2:1
An evaluation of rare-earth imaging systems in panoramic
radiography. Oral Surgery, Oral Medicine, Oral Pathology
Volume 58, Issue 4, October 2000 , Pages 475–482
