Digital imaging IN DENTISTRY

DigitalRadiography
1GOOD AFTERNOON..

DIGITAL
RADIOGRAPHY
BY DR. REVATH VYAS
DEVULAPALLI
DigitalRadiography
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Content
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Introduction & History
Equipment
Digital Image acquisition
• Types of receptor
• CCD
• CMOS
• Flat panel detectors
• PSP

Content
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Digital Image Processing
Digital Radiographic Image Storage
Digital Image Communication
Advantage and Disadvantages – Overall
Conclusion

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.
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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.
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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.
 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)
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 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).
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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.
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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.
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Pixel
 In digital imaging, a pixel [picture element] is the smallest
controllable element of a picture represented on the
screen
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[Internet] [cited 2014 Apr 10]. Available from
http://en.wikipedia.org/wiki/Pixel

Pixel
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Pixel
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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.
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White SC, Pharoah MJ, Oral Radiology Principles and Interpretation,
6th Edition Mosby 2009

 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.
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 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)
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ADC consists of 2 steps
Quantization
Sampling
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Sampling
 Sampling means that a small range of voltage values are
grouped together as a single value
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Sampling
 Narrow sampling better mimics
the original signal but leads to
larger memory requirements for
the resulting digital image
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Quantization
 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.
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Quantization
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Equipment
An x-ray machine
Digital image receptor
• a sensor
An analog-to-digital converter
Computer and monitor
• with appropriate hardware, software, network connection
Printer
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Lanc¸a L, Silva A, Digital Imaging Systems for Plain Radiography,
Springer 2013

Digital Radiography
Direct Indirect
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Direct digital imaging
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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

Indirect digital imaging
Exisiting Xray film
digitized using
CCD camera
Scans the image
Digitizes displays
on computer
monitor
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Types of digital image receptor
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1. Solid state technology:
• Charge coupled device
• Complementory metal oxide semiconductors
• Flat panel detectors
2. Photostimulable phosphor plate

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

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

Structure
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Structure
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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
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Bucket brigade form of charge transfer
Finally transferred to amplifier
Transmitted as voltage
Analog to digital converter
Image display
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Valence Band
Mechanism
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+e-
e-
Photoelectric absorption in Silicon
Conduction Band
e-
+

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

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Bucket brigade form of charge transfer
Finally transferred to amplifier
Transmitted as voltage
Analog to digital converter
Image display
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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.
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CCD Linear
array
made up of few
px wide and
many px long
Area array

Linear array
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2007

Area array
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2007

Advantages
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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
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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

Disadvantages
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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

Complementary metal oxide semiconductors
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Each pixel is isolated from its neighboring pixels
and connected to transistor
Electron hole pair generated within pixel
Charge transfer to transistor in form of voltage
Each transistor voltage is read out separately by
frame grabber
Stored and displayed as digital gray value
Whaites E, Essentials of Dental Radiography and Radiology, 4th edition, 2007

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)
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http://en.wikipedia.org/wiki/Scintillator

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Springer 2013

 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
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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
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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
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Springer 2013

Flat panel detector
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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
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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.
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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.
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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.
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Springer 2013

Flat Panel Structure
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Springer 2013

Advantages
 Real-time process
 With a time lapse between exposure and image display of
less than 10 seconds.
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Disadvantages
 Large in size so cannot be used intraorally
 Expensive
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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.
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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.
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2009

Structure
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2007

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.
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2009

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
Radiograph
y 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.
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2007

Mechanism
 When an electron returns to the Eu + 3 ion, energy is released in the green
spectrum between 300 and 500 nm
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2007

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
Radiograph
y 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.
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2007

PROCEDURE
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PROCEDURE
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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.
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2009

 Slow scan direction – direction of psp plate
 Fast scan direction – direction of laser light
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Rotating plate scans
 Rapidly rotating drum that holds the plate
 Consist of Rotation of drum and fixed laser
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2009

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
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Advantages
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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
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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 user with the intention to
improve the quality of the image or to analyze its contents.
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Imaging processing
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Image restoration
Image enhancement
Image analysis
Image compression

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
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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.
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2009

Imaging processing
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Image restoration
Image enhancement
Image analysis
Image compression

Brightness
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Contrast
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Negative Conversion
 Useful in visualizing the trabecular pattern of bone
 pulp canal and chamber anatomy
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Colour:
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2007

Imaging processing
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Image restoration
Image enhancement
Image analysis
Image compression

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2009

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.
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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.
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 Dental subtraction radiography (Ruttimann et al, 1981)
was found to be a feasible method that increases the
accuracy of detection of density changes between serial
radiographs
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 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
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 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
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Imaging processing
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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
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2009

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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
2009

Laser Printer
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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.
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2009

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.
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2009

COMMON PROBLEMS IN DIGITAL
IMAGING
1. Noisy Images
2. Non uniform image density
3. Distorted Images
4. Double Images
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Noisy Images
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2.Non uniform image density:
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3. Distorted Images:
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4. Double Images:
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Damaged Image receptors:
 Scratched phosphor surface mimicking root canal filling
A and retake B.
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 Image artifacts
resulting from
excessive bending of
the PSP plate and
excessive bending has
resulted in permanent
damage to the
phosphor plate
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 PSP circular artifact as a
result of plate damage and
localized swelling of the
protective coating from
disinfectant solution on
work surface
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 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.
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 Malfunctioning
CCD sensor
resulting from
rough handling
(dropped sensor)
 The sensor
produces
geometric image
artifacts
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 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
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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

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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) A computer 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 on variety of media
without loss of image quality
2. Output on Film or paper is inferior and non-diagnostic

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

DISADVANTAGES OF
DIGITAL IMAGING
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Cost
Currently the cost of
Intra oral sensor – 1.2 – 2 lakh
Extra oral machins – 10 - 15 lakh
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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.
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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.
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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.
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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.
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Thank You…
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Digital imaging IN DENTISTRY

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