Digital Radiography in Dentistry Seminar by Dr Pratik

Digital
radiography
Presenter Pratik
1Digital Radiography

GOOD MORNING..
Digital Radiography 2

Digital
radiography
Presenter Pratik

Content
4
Introduction & History
Terminologies
Equipment
Digital Image acquisition
• Types of receptor
• CCD
• CMOS
• Flat panel detectors
• PSP
Digital Radiography

Content
5
Digital Image Processing
Digital Radiographic Image Storage
Digital Image Communication
Digital Presentation and Display
Advantage and Disadvantages – Overall
Conclusion
Digital Radiography

Introduction

Radiography
Analog Digital
Scanner
(X-ray digitizer)
Computed
Radiography
(CR)
Direct Digital
Radiography
(DR or DDR)

• A conventional system uses x-ray film to create a
latent image with or without screens.
• The film is then processed, creating a manifest
image that can be interpreted by a physician.
• It is later stored in the file room (physical storage
for archival)

• Method is film-based.
• Method may uses intensifying screens.
• Film is placed between two screens.
• Screens emit light when x-rays strike them.
• Film is processed chemically.
• Processed film is viewed on view-box (lightbox).

Chemical Processing
in film radiography

Problems with Film ?
• 10% of films are not available when we want
them!
• 15% of films are “hard” to locate or find!
• 25% of films are “misplaced” or not retrievable
(misfiled).
• 10% of films are lost (referrals, residents, etc.)
• Recent study – physicians spend two weeks/year
(100 hours/year) trying to locate or find the films
they need.

Radiography
Analog Digital
Scanner
(X-ray digitizer)
Computed
Radiography
(CR)
Direct Digital
Radiography
(DR or DDR)

Digital imaging or Digitization ?
• Digital Imaging is any modality / method of
imaging that creates an image that can be
viewed or stored on a computer.

Introduction

Introduction
Since the discovery of X-rays in 1895, film has
been the primary medium for capturing,
displaying, and storing radiographic images.
It is a technology that dental practitioners are
the most familiar and comfortable with in terms
of technique and interpretation.
Digital radiography is the latest advancement in
dental imaging and is slowly being adopted by
the dental profession.
The Journal of Contemporary Dental Practice 2002 3(4):1-13

Introduction
Digital imaging incorporates computer
technology in the capture, display, enhancement,
and storage of direct radiographic images.
Digital imaging offers some distinct advantages
over film, but like any emerging technology, it
presents new and different challenges for the
practitioner to overcome.

History

Year Development
1500 BC
“The phenomenon of luminescence” observed -
China
1895 X-rays discovered
1895 Dr Walkoff first took dental radiograph
1919 Kodak produced first dental film
1955 Kodak D speed film
1963 CMOS invented
1969 CCD technology for video applications
History
Pasler,Pocket Atlas of Dental Radiology, Thieme 2007

History
Year Development
1970 Alternate receptor system – Xeroradiography
1975
Method of converting the information pattern into
a digital form
1980 Computed radiography - storage phosphors
1981
Computed Radiography – PSP method
Kodak – Ekta speed
1984
First Direct Digital Imaging System -
RadioVisioGraphy
1987 Amorphous selenium–based image plates

20
Year Development
1990
 Charge-coupled device (CCD) slot-scan direct
radiography
1994  Storage phosphor system, DIGORA for intraoral use.
1995
 CCD (Visualix – 2/VIXA – 2), which had a larger active
area
 Computed Dental Radiography (CDR) system by
Schick.
 Amorphous silicon–cesium iodide (scintillator) flat-
panel detector
 Selenium-based flat-panel detector
Digital Radiography

21
Year Development
1997  Gadolinium-based (scintillator) flat-panel detector
2001
 Gadolinium-based (scintillator) portable flat-panel
detector
 Dynamic flat-panel detector fluoroscopy
2009  Wireless DR (flat-panel detector)
Digital Radiography
Lanc¸a L, Silva A, Digital Imaging Systems for Plain Radiography,
Springer 2013

Terminology

• Density - The overall degree of darkening of an
exposed film
• Brightness - Digital equivalent to density or
overall degree of image darkening.
White SC, Pharoah MJ, Oral Radiology Principles and Interpretation,
6th Edition Mosby 2009

• Latitude - Measure of the range of exposures
that will produce usefully distinguishable
densities on a film.
• Dynamic Range - The numerical range of each
pixel; in visual terms it refers to the number of
shades of gray that can be represented.

• Film Speed -Amount of radiation needed to
produce a standard density; refers to the
sensitivity of the film to radiation. The faster the
film, the less radiation required.
• Linearity - Linear or direct relationship between
exposure and image density.
OR

Detector Sensitivity:
• Sensitivity of a detector is its ability to respond to
small amounts of radiation.
• Intraoral film sensitivity is classified according to
speed group using criteria developed by the
International Organization for Standardization.
• Currently there are no classification standards for
dental digital X-ray receptors.

Contrast
• Contrast - The difference in densities between
various areas on a radiograph; high contrast
images have few shades of gray between black
and white while low contrast will demonstrate
more shades of gray.
• Contrast Resolution - The ability to differentiate
small differences in density as displayed on an
image.

Contrast
• This is a function of the interaction of the
attenuation characteristics of the tissues that are
being imaged
– the capacity of the image receptor to distinguish
differences in numbers of X-ray photons coming from
different areas of the subject
– the ability of the computer display
– the ability of the observer to recognize those
differences.

• Resolution - Ability to distinguish between small
objects that are close together; measured in line
pairs per millimeter.
• Spatial Frequency - Measure of resolution
expressed in line pairs per millimeter.
• Modulation Transfer Function - Measure of
image fidelity as a function of spatial frequency;
how close the image is to the actual object.

• The theoretical limit of resolution is a function of
picture element (pixel) size for digital imaging
systems.
• Currently the highest resolution CCD detectors
for dentistry have pixel sizes of approximately 20
microns.

• Resolution is often measured and reported in
units of linepairs per millimetre.
• A line and its associated space are called a line
pair (lp).
• At least two pixels are required to resolve a line
pair, one for the dark line and one for the light
space

500px 200px 50px
10px 5px 1px

• Typical observers are able to distinguish about 6 lp/mm
without benefit of magnification.
• Intraoral film is capable of providing more than 20
lp/mm of resolution
• With 20- μ m pixels, a theoretical resolution of 25
lp/mm can be obtained.
• Current digital systems are capable of providing more
than 7 lp/mm of resolution.

• Radiographic Motile (Noise) - Appearance of
uneven density of an exposed film or graininess
• Background Electronic Noise – Small electrical
current that conveys no information but serves
to obscure the electronic signal

• Sharpness - Ability of a radiograph to define an
edge or display density boundaries.
• Signal to Noise Ratio - Ratio between the fraction
of the output signal (voltage or current or
charge) that is directly related to the diagnostic
information (signal) and the fraction of output
that does not contain diagnostic information
(noise) .

Scintillator
• A scintillator is a material that exhibits
scintillation — the property of luminescence
when excited by ionizing radiation.
• Luminescent materials, when struck by an
incoming particle, absorb its energy and
scintillate, (i.e., re-emit the absorbed energy in
the form of light)
[Internet] [cited 2014 Apr 10]. Available from
http://en.wikipedia.org/wiki/Scintillator

Springer 2013

Pixel
• In digital imaging, a pixel [picture element] is the
smallest controllable element of a picture
represented on the screen
http://en.wikipedia.org/wiki/Pixel

Pixel

Analogue to Digital Conversion
• The term digital in digital imaging refers to the
numeric format of the image content and its
discreteness.
• Conventional film images can be considered an
analog medium in which differences in the size
and distribution of black metallic silver result in a
continuous density spectrum.

• Digital images are numeric and discrete in two
ways:
– (1) in terms of the spatial distribution of the picture
elements (pixels) and
– (2) in terms of the different shades of gray of each of
the pixels.

• A digital image consists of a large collection of
individual pixels organized in a matrix of rows
and columns.
• Production of a digital image requires a process
called analog to digital conversion (ADC)

ADC consists of 2 steps
Quantization
Sampling

Sampling
• Sampling means that a small range of voltage
values are grouped together as a single value

Sampling
• Narrow sampling better
mimics the original signal but
leads to larger memory
requirements for the
resulting digital image

• Once sampled, every sampled signal is assigned a
value.
• For the clinician to see the image, the computer
organizes the pixels in their proper locations and
displays a shade of gray that corresponds to the
number that was assigned during the
quantization step.
Quantization

Quantization

Taxonomy

Springer 2013

Digital Radiography
Direct Indirect

Direct digital imaging
56
Sensor
placed in
pt’s
mouth
Exposed
to
radiation
Sensor
captures
radiograp
hic image
Transmit
image to a
computer
monitor
Image
appears
on screen
within
seconds
Digital Radiography

Indirect digital imaging
57
Exisiting Xray
film digitized
using CCD
camera
Scans the image
Digitizes
displays on
computer
monitor
Digital Radiography

Types of digital image receptor
1. Solid state technology:
• Charge coupled device
• Complementory metal oxide
semiconductors
2. Photostimulable phosphor
plate

Digital image receptors
Solid State
Technology
Uses semi-conductor based detectors
1. CCD
2. CMOS
3. Flat Panel
Springer 2013

Charge coupled device

Charge coupled device
• Introduced in 1987
• 1st intraoral digital receptor
• Consist of thin wafer of silicon with electronic
circuit
• Consist of matrix, amplifier in plastic houisng
White SC, Pharoah MJ, Oral Radiology Principles and Interpretation, 6th Edition Mosby 2009

• A number of manufacturers produce detectors
with varying active sensor areas roughly
corresponding to the different sizes of
intraoral film

Whaites E, Essentials of Dental Radiography and Radiology, 4th edition, 2007

Structure

66
Exposure to radiation
Break the covalent bond in silicon atoms
Produce electron hole pair
Electron attracted towards most positive
potential in device – create charge packet
Charge pattern formed from individual pixels
forms latent image Digital Radiography

67
Bucket brigade form of charge transfer
Finally transferred to amplifier
Transmitted as voltage
Analog to digital converter
Image display
Digital Radiography

Valence Band
Mechanism
+e-
e-
Photoelectric absorption in Silicon
Conduction Band
e-
+

http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/detectors

76
Bucket brigade form of charge transfer
Finally transferred to amplifier
Transmitted as voltage
Analog to digital converter
Image display
Digital Radiography

CCD
• Detectors without flaws are relatively expensive to
produce, and expense of the detector increases with
increasing matrix size (total number of pixels).
• Pixel size varies from 20 microns to 70 microns. Smaller
pixel size increases the cost of the receptor.
• CCDs have also been made in linear arrays of a few
pixels wide and many pixels long for panoramic and
cephalometric imaging.

CCD Linear
array
made up of
few px wide
and many px
long
Area
array

Linear array

Area array

Advantages
Intact images or real time image production and
display.
Consistent quality
X ray sensitivity is 80% greater than conventional film.
Elimination of hazardous chemicals used in film
processing and lead foil.
Computer aided diagnosis

Disadvantages
83
High initial cost of system
Unknown life expectancy of CCD sensor
Rigidity and thickness of the sensor
Decreased resolution
CCDS cannot be sterilized
Hard copy images fade with time
Digital Radiography

Disadvantages
84
Image manipulation can be time consuming.
The sensor may not be well tolerated by
patients -more time-consuming
The cable attached to the sensor is easily
damaged and may interfere with sensor
Actual area available for image capture may
be as little as 60% of the sensor area
Digital Radiography

Product Name Company
CDR Schick
CygnusRay MPS Cygnus Technologies
Dexis ProVision Dental Systems
Dixi®2 Planmeca Group
SIDEXIS Sirona
SIGMA PaloDex Group
SuniRayTM Suni Medical Imaging
RVG Trophy
VistaRay DÜrr Dental
VisualiX . Gendex
Intraoral CCD based systems

Panoramic CCD based systems
CDRPan Schick
Digipan Trophy
Dimax3, ProlineXC, Promax Planmeca Group
DXIS® Signet
Orthopantomograph OP100D PaloDex Group
Orthoceph OC100D PaloDex Group
ORTHOPHOS DS Sirona

Cranex Base X D PaloDex Group
Cranex Excel D PaloDex Group
Scanora D PaloDex Group
Orthoralix 9200 (DDE, DPI) Gendex - Dentsply
Versaview (5D, SDCP) Morita

Complementary
metal oxide
semiconductors

Complementary metal oxide
semiconductors
89
Each pixel is isolated from its neighboring
pixels and connected to transistor
Electron hole pair generated within pixel
Charge tranfer to transistor in form of
voltage
Each transistor voltage is read out
separately by frame grabber
Stored and displayed as digital gray value
Digital Radiography

• These sensors do not require charge transfer,
resulting in increased sensor reliability and
lifespan.
• Require less system power to operate and are
less expensive to manufacture
• Low cost
• Fixed pattern of noise
• Smaller active area

CCD CMOS
POWER COSUMPTION. 400mw 40mw
SENSITIVITY TO LIGHT Excellent Excellent
SENSITIVITY TO X RAYS High Unknown
PIXEL SIZE. 40 micron 25 micron
COST. High Medium
MANUFACTURE. Expensive Cheap
BREAKAGE RESISTANCE Low Medium
DYNAMIC RANGE Excellent Excellent
NOISE. Low High
READOUT. Complex Simple
EFFICACY. Excellent Fair

Flat panel
detector

Flat panel detector
• Used for medical imaging, extraoral imaging
device
• Provide large matrix area with pixel of less than
100 µm
• Allows imaging of larger areas including head
• 2 types: direct
indirect
Springer 2013

Flat panel detector
Indirect
flat panel
detector:
sensitive to visible light
use intensifying screen
to convert X-ray to light
Photoconductor
material - aSi
Springer 2013

Flat panel detector
Direct
flat
panel
detector
use selenium
for efficient X-
rays
absorption
Springer 2013

Flat panel detector
• It is a “sandwich” constructions consisting of a
scintillator layer, an amorphous silicon
photodiode circuitry layer, and a TFT array.

Thin Film Transistor (TFT)
• It is a special kind of field-effect transistor made
by depositing thin films of an active
semiconductor layer
• A transistor is a semiconductor device used to
amplify and switch electronic signals and
electrical power. It is composed of
semiconductor material with at least three
terminals for connection to an external circuit.
http://en.wikipedia.org/wiki/Thin-film_transistor

Flat panel detector
• When x-ray photons reach the scintillator, visible
light proportional to the incident energy is
emitted and then recorded by an array of
photodiodes and converted to electrical charges.
• These charges are then read out by a TFT array
similar to that of direct conversion DR systems.
Springer 2013

Flat Panel Structure
Springer 2013

Advantages
• Real-time process
• With a time lapse between exposure and image
display of less than 10 seconds.

Disadvantages
• Large in size so cannot be used intraorally
• Expensive

Thank you…

Digital
radiography
Presenter Pratik

Content
108
Introduction & History
Terminologies
Equipment
Digital Image acquisition
• Types of receptor
• CCD
• CMOS
• PSP
Digital Radiography

Content
109
Digital Image Processing
Digital Radiographic Image Storage
Digital Image Communication
Digital Presentation and Display
Advantage and Disadvantages – Overall
Conclusion
Digital Radiography

CDR, Schick
CygnusRay, MPS Cygnus Technologies
Dexis, ProVision Dental Systems
Dixi®2, Planmeca Group
SIDEXIS Sirona
SIGMA + PaloDex Group
SuniRay, Suni Medical Imaging
VistaRay, DÜrr Dental
VisualiX . Gendex
Intraoral CCD based systems

RVG 6500, 6100, 5100 Carestream
Intraoral CMOS based systems

Photostimulable
phosphor plates

Photostimulable phosphor plates
• Also known as storage
phosphor plates (spp),image
plates or computed
radiography
• Flexible, wireless indirect
receptors
• Available in the same sizes
as intraoral films.

Structure
• The PSP material used for radiographic imaging is
“ europium doped” barium fluorohalide.
• Barium in combination with iodine, chlorine, or
bromine forms a crystal lattice.
• The addition of europium (Eu + 2 ) creates
imperfections in this lattice.

Structure

Mechanism
• When exposed to a sufficiently energetic source
of radiation, valence electrons in europium can
absorb energy and move into the conduction
band.
• These electrons migrate to nearby halogen
vacancies (F-centers) in the fluorohalide lattice
and may become trapped there in a metastable
state.

Valence Band e-
Plate
prepared
Plate
exposed
X ray
photon
F Center
Eu+2  Eu+3Eu+2
F Center
Conduction Band
Whaites E,
Essentials of
Dental
Radiography
and
Radiology,
4th edition,
2007

Mechanism
• While in this state, the number of trapped
electrons is proportional to x-ray exposure and
represents a latent image.
• When stimulated by red light of around 600 nm,
the barium fluorohalide releases trapped
electrons to the conduction band.

Mechanism
• When an electron returns to the Eu + 3 ion,
energy is released in the green spectrum
between 300 and 500 nm

Valence Band e-
Plate
prepared
Plate
exposed
Plate
processed
laser
Photomultiplier
tube
X ray
photon
F Center
Eu+2 Eu+3Eu+2  Eu+3Eu+2
F Center F Center
Conduction Band
Whaites E,
Essentials of
Dental
Radiography
and
Radiology,
4th edition,
2007

Mechanism
• Fiberoptics conduct light from the PSP plate to a
photomultiplier tube.
• The photomultiplier tube converts light into
electrical energy.
• A red filter at the photomultiplier tube
selectively removes the stimulating laser light,
and the remaining green light is detected and
converted to a varying voltage.

PROCEDURE

Stationary plate scans
• Method for "reading" the latent images on PSP
plates.
• A rapidly rotating multifaceted mirror that
reflects a beam of red laser light.
• As the mirror revolves, the laser light sweeps
across the plate. The plate is advanced and the
adjacent line of phosphor is scanned.

Rotating plate scans
• Rapidly rotating drum that holds the plate
• Consist of Rotation of drum and fixed laser

Advantages
Storage phosphor plates can be reused indefinitely
Receptor is cordless & flexible
Linear or logarithmic response to radiation is available
There is wide exposure range & fewer retakes
Less radiation is required

Advantages
No chemical processing required
Image processing of acquired images is available
Images can be transferred to easily
Images can be easily & inexpensively stored & retrieved
Computed aided diagnosis

Disadvantages
Receptors must be erased before reuse
High initial cost of the equipment
The spatial resolution of film exceeds
Some of the image processing routines are time – intensive
Phosphor plates must be packaged in sterile envelopes
possibility of transfer of contaminated material to patient's mouth if integrity of
plate's protective envelope is jeopardized

Intraoral PSP systems
Panorama Xi Orex
Combi-Xi Orex
DenOptix Gendex - Dentsply
Digora Optime PaloDex Group
VistaScan DÜrr Dental
VistaScan Intra DÜrr Dental

Panoramic PSP based systems
Panorama Xi Orex
DenOptix Gendex - Dentsply
Digora Optime PaloDex Group
VistaScan DÜrr Dental
VistaScan Intra DÜrr Dental

Computer
http://www.dentistrytoday.com/radiography/1755

Imaging processing
• Any operation that acts to improve, restore, analyze
or in some way change a digital image is a form of
image processing.
• Some of these operations are integrated in the
image acquisition and image management software
and are hidden from the user.
• Others are controlled by the uses with the intention
to improve the quality of the image or to analyze its
contents.

Imaging processing
Image restoration
Image enhancement
Image analysis
Image compression

Image restoration
• When the raw image data enter the computer, they
are usually not yet ready for storage or display.
• Some of the pixels in CCD sensor are always
defective.
• The image is restored by substituting the gray values
of the defective pixels with some weighted average
of gray values from the surrounding pixels.

Image restoration
• Depending on the quality of the sensor and the
choices made by the manufacturer, a variety of
other operations maybe applied to the image
before it becomes visible on the display.
• They are executed very rapidly and are unnoticed
by the user.

Image restoration
• Raw data enter computer
• Preprocessing -- Image corrected for known
defects
– Adjustment of image intensities
– Substitution of defective pixels
• Preprocessing operations set by manufacturer

Imaging processing
Image restoration
Image enhancement
Image analysis
Image compression

Image enhancement
• The term image enhancement implies that the
adjusted image is an improved version of the
original one.
• Most image enhancement operations are applied
to make the image visually more appealing
(subjective enhancement).
• This can be accomplished by increasing contrast,
optimizing brightness, and reducing unsharpness
and noise.

Image enhancement
• Image enhancement operations are often task-
specific; what benefits one diagnostic task may
reduce the image quality for another task.
• For example, increasing contrast between enamel
and dentin for caries detection may make it more
difficult to identify the contour of the alveolar crest.
• Image enhancement operations are also dependent
on viewer preference.

Image enhancement
• Change the visual appearance of the image
• Improved version of the original one
• Common enhancements tools include:
• Brightness and Contrast Adjustments
• Black/White Reversal
• Pseudocolor Application
• Sharpening and smoothing
• Zoom
• Digital Subtraction

a) Brightness and Contrast:
• Digital radiographs do not always effectively
utilize the full range of available gray values.
• They can be relatively dark or light, and they can
show too much contrast in certain areas or not
enough.
• The image histogram is a convenient tool to
examine which of the available gray values the
image is using.

• The maximum and minimum values and the
shape of the histogram indicate the potential
benefit of brightness and contrast enhancement
operations.
• Digital imaging software commonly includes a
histogram tool, as well as tools for the
adjustment of brightness and contrast.

Brightness

Contrast

γ
• Increase in γ
• Decrease in γ

ii. Negative Conversion
• Useful in visualizing the trabecular pattern of
bone
• pulp canal and chamber anatomy

b) Sharpening and Smoothing:
• The purpose of sharpening and smoothing filters is
to improve image quality by removing blur or noise.
• Noise is often categorized as high frequency noise
(speckling) or low frequency noise (gradual intensity
changes).
• Filters that smooth an image are sometimes called
despeckling filters because they remove high
frequency noise.

b) Sharpening and Smoothing:
• Filters that sharpen an image either remove low
frequency noise or enhance boundaries between
regions with different intensities (edge
enhancement).
• Sharpening and smoothing filters may make the
dental radiographic images subjectively more
appealing.

c) Colour:
• Most digital systems provide opportunities for
color conversion of gray scale images also called
pseudo-color.
• Transforming the gray values of a digital image
into various colors could theoretically enhance
the detection of objects with the image.
• When objects can be uniquely identified based
on a set of image features, colour can be used to
label or highlight these objects.

c) Colour:

Imaging processing
Image restoration
Image enhancement
Image analysis
Image compression

Image Analysis:
• Image analysis operations are designed to extract
diagnostically relevant information from the image.
• This information can range from simple linear
measurements to fully automated diagnosis.
• The use of image analysis tools brings with it the
responsibility to understand their limitations.
• The accuracy and precision of a measurement are limited
by the extent to which the image is a truthful and
reproducible representation of the patient and by the
operator’s ability to make an exact measurement.

a) Measurement:
• Digital imaging software provides a number of tools
for image analysis.
• Digital rulers, densitometers and a variety of other
tools are readily available.
• The size and image intensity of any are within a
digital radiograph can be measured.
• Tools are also being developed for measuring the
complexity of the trabecular bone pattern.

• Measurement tool to determine the length of the crown and mesiobuccal
root of the first molar.
• The measurement has been calibrated for a magnification factor of 1.05.

b) Diagnosis:
• Three basic steps of image analysis are :
– Segmentation - most critical step.
– Feature extraction
– Object classification.
• The goal of segmentation is to simplify the image
and reduce it to its basic components.
• This involves subdividing the image, thus
separating objects from the background.

b) Diagnosis:
• Objects of interest are defined by the diagnostic task,
for example, a tooth, a carious lesion, a bone level, or an
implant.
• A unique set of values for a certain combination of
features can lead to classification of the object.
• Automated cephalometric landmark identification is an
example.

DIGITAL
SUBTRACTION
RADIOGRAPHY

• Dental radiography by Ruttimann and colleagues
in 1981 (Ruttimann et al, 1981) and was found to
be a feasible method that increases the accuracy
of detection of density changes between serial
radiographs

• When two images of the same object are
registered and the image intensities of
corresponding pixels are subtracted, a uniform
difference image is produced.
• If there is a change in the radiographic
attenuation between the baseline and follow-up
examination, this change shows up as a brighter
area when the change represents gain and as a
darker area when the change represents loss

• The strength of digital subtraction radiography
(DSR) is that it cancels out the complex anatomic
background against which this change occurs.
• Subtraction radiography requires two images ,
which are exposed with the same geometry

• Two methods have been developed for the
computerized alignment of the follow-up images:
– Reference point alignment method
– Real-time subtraction alignment method

• Subtraction radiography is a qualitative method
that assists in visualization of small density
changes.
• Additional methods have been developed for the
quantification of these changes.

Relative quantification
• One measurement method that describes
density changes in mineralized oral tissues with
ordinal scale data in some controlled situations,
Computer Assisted Densitometric Image Analysis
(CADIA).
• CADIA is a practical method of measurement of
change in bone density occurring in the alveolar
crest (Bragger et al, 1988).

Relative quantification
• CADIA is based on the comparison of two serial
images that are acquired with standardized
projection geometry and equalized for the density
differences in the images.
• The area of change is calculated, and the "depth" of
the lesion in the bucco-lingual direction is measured
as the density change between images. The final
CADIA value is the product of the area of change and
the average "depth" of the change, and thus
represents a volumetric description of the density
change.

Absolute quantification
• A subtraction method that produces ordinal scale
data can be transformed into a quantitative
method that generates interval scale data by
exposing one of the serial radiographs through a
calibration wedge of known density and
dimensions.

Absolute quantification
• A subtraction method that produces ordinal scale data can be
transformed into a quantitative method that generates interval
scale data by exposing one of the serial radiographs through a
calibration wedge of known density and dimensions.
• In the subsequent analysis process, the image of the wedge is
used for the estimation of the density of the site. This
radiographic photodensitometric method was first used in
medical radiology for the estimation of skeletal bone mineral
content
• Omnell (1957) was the first to apply radiographic densitometry,
also called radiographic absorptiometry (Anderson et al, 1966;
Yang et al, 1994), to the measurement of bone density changes
in the alveolar bone.

Imaging processing
Image restoration
Image enhancement
Image analysis
Image compression

Image compression
• Process of file reduction.
• To reduce computer storage space and facilitate
image retrieval and transmission.
• Compression becomes a more important issue
as the number of patient records and image files
to be stored increases over time
• Two types: lossless and lossy

LOSSLESS LOSSY
Donot discard any image data Discard image data
Maximum compression rate < 3:1 Range from 12:1 to 28:1
More memory to manipulate Less memory
Retrieval and transmission slow quick

Image compression methods
• Cartesian Perceptual Compression, also known as
CPC
• Fractal compression
• JPEG
• JPEG 2000, JPEG XR, PGF, Progressive Graphics
File
• Wavelet compression
[Internet] [cited 2014 May 10]. Available from
http://en.wikipedia.org/wiki/Image_compression

Joint Photographic Experts Group
(JPEG)
• a common compression protocol that can
support both lossless and lossy compression
• high compression ratios had a severe negative
impact on the diagnostic quality of digital images
in the detection of periapical lesions.
• compression ratios
– 25 :1 endodontics
– 12: 1 to 14:1 caries diagnosis

Joint Photographic Experts Group
(JPEG)
• Compression rates of 12:1 and 14:1 were shown
to have no appreciable effect on caries diagnosis.
• For determining endodontic file length, a rate of
254:1 was diagnostically equivalent to the
uncompressed image.
• A compression rate of 28:1 was acceptable of the
subjective evaluation of image quality and the
detection of lesions in panoramic radiographs.

Digital
image
display:

Cathode Ray Tube (CRT):
• Conventional computer monitor use cathode ray
tube (CRT) designs.
• A beam of electrons emanating from an electron
'gun' rapidly scans a phosphor-coated screen.
• The electron scan is horizontal and builds an
image line by line.

• The image is repeated or refreshed at a rate of 60 times a
second (Hz) or more to avoid the appearance of flicker.
• Colour monitors utilize 3 electron guns one each for red,
blue and green phosphors.
• The variable intensity of the electron beam is responsible
for different shades of gray or colour line and intensity.
• High quality monitors are able to display 256 different gray
values or a combination of grey and colour values.

• CRT display involves conversion of digital information into
analog voltages, which is supplied to the electron guns.
• Some loss of original image information is inherent in the
digital-to-analog conversion process.
• A number of factors affect the subjective quality of a
monitor.
• A dot pitch is a measure of the distance between groups
of subpixels (red, green and blue phosphors) in the CRT.

• Smaller dot pitches on the order of 0.28 mm or less
provide more pixels per area and sharper looking
images.
• The brightness of the monitor affects perceived contrast
of the image.
• Brighter monitors are essential in working environments
with greater amounts of ambient light.

• Conventional computer monitor use cathode ray tube
(CRT) designs.
• The image is repeated or refreshed at a rate of 60 times a
second (Hz) or more to avoid the appearance of flicker.
• Colour monitors utilize 3 electron guns one each for red,
blue and green phosphors.
• The variable intensity of the electron beam is responsible
for different shades of gray or colour line and intensity.

Parameter CRT LCD OLED
Brightness. Poor Very poor Poor
Contrast. Over 15,000:1 Over 1,000:1 Over 1,000,000:1
Color Excellent Good on most
newer models
Better
Color depth Unlimited Better Excellent
Black level. Excellent Poor Excellent
Ghosting and
smearing
No ghosting or
smearing artifacts
Display motion blur
on models with
slow response time,
and the elimination
technique (strobing
backlight) can cause
eye-strain
None even during
fast motion
http://en.wikipedia.org/wiki/Comparison_of_CRT,_LCD,_Plasma,_and_OLED

Response time Sub-milisecond 1–8 ms typical
(according to
manufacturer data),
older units could be as
slow as 35 ms
Sub-millisecond
Eyestrain. Less if refresh rates
below 85 Hz
Depends; as of 2013,
most LCDs use
strobing to dim the
backlight which can
cause severe eyestrain
Less
Weight. Heavy, especially for
larger units, a 20 inches
(51 cm) screen weighs
about 50 pounds (23 kg)
Light Very light

Size. Bulky depth,
7" smallest possible
for color screen,
over 40" is very
heavy
Compact,
can be manufactured
almost any size and
shape,
Compact, can be
made in nearly any
size or shape.
Maintenance. Hazardous to repair
or service due to
high-voltage,
requires skill.
Difficult to replace
backlight
Electro-magnetic
radiation emission.
Emits strong
electromagnetic
radiation in the
audio-frequency to
low-frequency RF
range
Emits very little
electromagnetic
radiation
Emits very little
electromagnetic
radiation

Electronic Display Considerations:
• The display of digital images on electronic devices is
a fairly straightforward engineering issue.
• The quality, capabilities, and ease of use of display
software vary from vendor to vendor, and these are
numerous.
• Even with the same software the display of images
can vary dramatically, depending on how the
software handles resizing of windows or the size and
resolutions of different displays.

Electronic Display Considerations:
• Software may permit reduction in image size or scrolling
around the window to compensate for smaller display
areas.
• Bright background illumination from windows or other
sources of ambient light reduce visual contrast sensitivity.
• Light reflecting off of a monitor surface may further
reduce visibility of image contrast.
• Images are best viewed in an environment in which
lighting is subdued and indirect.

Hard Copies
• With the development of digital photography as a
mainstream technology, digital image printing has
become an economical solution for making digital
radiographs transferable.
• Main types of printing technologies available for
printing images include ;
– Laser
– Inkjet
– Dye-sublimation
• with the use of either film or paper.

Laser Printer
• Laser printing is an electrostatic digital printing
process that rapidly produces high quality text
and graphics by passing a laser beam over a
charged drum to define a differentially charged
image.
• The drum then selectively collects charged toner
and transfers the image to paper, which is then
heated to permanently fix the image.

Laser Printer

Ink Jet
• Inkjet printing is a type of computer printing that
creates a digital image by propelling droplets of
ink onto paper, plastic, or other substrates. Inkjet
printers are the most commonly used type of
printer.

Dye Sublimation
• It uses heat to transfer dye onto materials such
as a plastic, card, paper, or fabric.
• The sublimation name was first applied because
the dye was considered to transition between
the solid and gas states without going through a
liquid stage.
• This understanding of the process was later
shown to be incorrect; since then the process is
sometimes known as dye-diffusion.

Dye Sublimation

Image Storage:
• The use of digital imaging in dentistry requires an image
archiving and management system that is very different
from conventional radiography.
• Storage of diagnostic images on magnetic or optical
media raises a number of new issues that must be
considered.
• The file size of dental digital radiographs varies
considerably, ranging from 200 KB for intra oral images
to as much as 6 MB for extraoral images.

Image Storage:
• Once in a digital format, critical image data can
be deleted or modified.
• The backup media suitable for external storage
of digital radiographs include external hard
drives, digital types, CDs and DVDs.

COMMON PROBLEMS IN DIGITAL
IMAGING

1. Noisy Images
2. Non uniform image density
3. Distorted Images
4. Double Images

Noisy Images

2.Non uniform image density:

3. Distorted Images:

4. Double Images:

Damaged Image receptors:

• Scratched phosphor surface mimicking root canal filling
A and retake B.

• Image
artifacts
resulting from
excessive
bending of
the PSP plate
and excessive
bending has
resulted in
permanent
damage to
the phosphor
plate

• PSP circular artifact as a
result of plate damage
and localized swelling of
the protective coating
from disinfectant
solution on work surface

• PSP image artifact
resulting from plate
surface contamination
• This artifact was caused
by a glove powder
smudge that prevented
proper scanning of the
affected area of the PSP
plate.

• Malfunctioning
CCD sensor
resulting from
rough handling
• (dropped
sensor). The
sensor produces
geometric image
artifacts

• Improper use of image
processing tools, such as
filters, may result in
false-positive findings.
An edge enhancement
filter was applied to the
panoramic image, which
produced radiolucencies
at restoration edges
simulating recurrent
caries
• These radiolucencies are
not present in a follow-
up intraoral image

Clinical comparison of Intraoral
Imaging Alternatives

Imaging Step Film CCD/CMOS PSP
Receptor
preparation. None
1) Place protective plastic
sleeve over receptor
2) Receptor must be
connected to computer
and patient identifying
information entered for
acquisition/archiving
software
1) Erase plates
2) Package plates in
protective plastic
envelope
Receptor
placement.
1) Film holding
devices
2) Film may be
bent to
accommodate
anatomy
1) Specialised receptor
holder
2) Inflexible and bulkiness
3) Receptor cable
4) Discomfort
1) Film holding devices
2) Bending of receptor
may irreversibly
damage it
Exposure.
Simple exposure
Computer must be
activated before
exposure
Simple exposure

Imaging Step Film CCD/CMOS PSP
Processing.
1) Dark room
2) Processing
chemicals
3) Processing time
4) Hazardous wastes
Image acquisation and display is
almost immediate
1) Dim light envt
2) Processor must be
programmed with
patient and detector
information so that
images are identified,
preprocessed and
stored properly
Display
Preparation.
Film mounts 1) Software – digital mount 1) Individual mount
2) Digitally rotated
Display
1) A room with
subdued lighting
and a masked
viewbox
2) Any light source
1) subdued lighting
2) Acomputer and display with app. Software
3) Size of the display restrict the no. of images
Image Duplication.
Inferior to original and
sometimes non-
diagnostic
1. Electronic copies may be stored oon variety of media
without loss of image quality
2. Output on Film or paper is inferior and non-diagnostic

Advantages of
digital imaging

Dose reduction
• Dose reductions of up to 90 per cent compared
to E speed film have been reported by some
authors in the diagnosis of caries.
• Although some researchers do claim dose
reductions compared with conventional extra-
oral film, in practice the background noise rises
to unacceptable levels.
• It is now accepted that there is no appreciable
reduction compared with films used in
conjunction with rare earth intensifying screens.
Dentomaxillofacial Radiology 1995; 24: 250

Image manipulation
• This is perhaps the greatest advantage of digital
imaging over conventional film.
• It involves selecting the information of greatest
diagnostic value and suppressing the rest.
• Manufacturers provide software programmes
with many different processing tools, however
some are more useful than others and these
include:
Dentomaxillofacial Radiology 2012,41(3)203-210

1. Contrast enhancement
• This can effectively compensate for over or under
exposure of the digital image.
• It has been shown that contrast enhancement of
CCD devices were more accurate than E-speed
film for detecting simulated caries under
orthodontic bands
The British Journal of Radiology 1991,64(763)591-595

2. Measurements
• Digital callipers, rulers and protractors are some
of the many tools available for image analysis.
• Many authors have reported on their application
in cephalometric analysis.
• The images can also be superimposed onto each
other and onto digital photographs.
Journal of Endodontics 2007, 33(1) 1–6

3. 3-D reconstruction
• This application can be theoretically used to
reconstruct intra- and extra-oral images.
• The uses range from profiling root canals to
visualizing facial fractures in all three dimensions.
Brennan J. Journal of Orthodontics 2002 (29) 66–69

4. Filtration
• The addition of filters to the airspace around the
face can clarify the soft tissue profile if the
original soft tissue image was poor

Time
• Much time is gained especially with the CCD
system where the image is displayed at the
chairside immediately post exposure.
• Although a lag time between scanning and the
appearance of an image exists with the PSP
method it is still substantially faster than
conventional developing processes in general
use.

Storage
• Storage was initially a problem before the
development of DVDs and CD ROMs as three
peri-apical images would fill a floppy disc.
• However, now a CD ROM can hold over 30,000
images.
• This means that images can be stored cheaply
and indefinitely.

Teleradiology
• Teleradiology is the transmission of radiological patient
images, such as x-rays, CTs, and MRIs, from one location
to another for the purposes of sharing studies with
other radiologists and physicians.
• This had the advantages of not losing radiographs in the
post and saving time if an urgent appointment is
required.

Teleradiology
• Teleradiology is a growth technology given that imaging
procedures are growing approximately 15% annually
against an increase of only 2% in the Radiologist
population.
• Teleradiology has the potential for off-site consultation,
insurance submission and improved access to care for
patients in remote locations

Environmentally friendly
• No processing chemicals are used or disposed of.
Both CCD sensors and the PSP plates are capable
of being reused for many thousands of
exposures.
• They can, however, become scratched and
damaged if not handled carefully.

Medico-legal
• Many insurance companies in the USA are
accepting digital images as valid attachments
when the claims are electronically claimed.
Dentomaxillofacial Radiology 2000, 12(4)292-297

Disadvantages of digital
imaging

Cost
• Currently the cost of
–Intra oral sensor – 1.2 – 2 lakh
–Extra oral machins – 10 - 15 lakh

Sensor dimensions
• These are still quite bulky for the CCD system and
awkward to position due to trailing fibre optic
wires.
• The original problem of small sensor active areas
has been rectified and the same amount of
information can be captured as conventional
film.

Cross-infection control
• Each intra-oral sensor and plate must be covered
by a plastic bag, and this bag is changed between
patients.
• However, if they become directly contaminated
there is no way of sterilizing them and they
should be discarded regardless of expense.

Medico-legal
• Concerns have been raised in the past about the
ability to manipulate the images for fraudulent
purposes.
• Manufacturers of software programmes have
installed ‘audit trails’, which can track down and
recover the original image.
Dentomaxillofacial Radiology 2000, 12(4)292-297

Conclusion
• The technology is now available to run a practice almost
paper free.
• It is theoretically possible to store clinical notes,
photographs, radiographs, and study models on disc, and
refer or consult online.
• Research is also continuing into the development of a
credit card sized ‘smart card’, which could carry a patient’s
medical and dental notes along with their radiographic
images.
• It is important that advances in technology are accepted
and the benefits that they produce utilized in order that
clinical practice and patient care continue to improve.

Thank You…
To be continue..

Digital Radiography in Dentistry Seminar by Dr Pratik

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