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1. DIGITAL IMAGING IN
DENTISTRY
SeminarSeminar
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
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2. Purpose statement
At the end of the session the learners should be
able to describe about detectors, image display,
image characteristics and advantages and
disadvantages in digital imaging
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4. Introduction
 Recent technologic advances have produced a significant
impact on the field of dental radiography. Such advances
in computer technology have resulted in a unique
filmless imaging system known as digital radiography.
 The first digital imaging system, radiovisiography (RVG)
was invented by Dr. Francois Mugonon in 1987.
 The digital radiography uses an electronic sensor and
computerized imaging system producing x-ray images
almost instantly on a computer monitor.
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5. Definition
Digital radiography may be defined as a system for
acquisition, processing and display of radiographic
images using modern data processing technology.
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6. Uses
 To detect lesions, diseases & conditions of teeth
and surrounding structures.
 To confirm or classify the suspected disease.
 To provide information during dental procedures.
 To illustrate changes secondary to caries, PDL
diseases or trauma.
 To document the conditions of a periodontal
pockets at a specific points.
 To evaluate growth and development.
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7. Digital image
 A digital image is formed by the use of electronic
sensor that is connected to some manner to a
computer.
 Early in the development of digital imaging it was
referred to as “filmless radiography” but that name
is no longer accurate.
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8. Methods to obtain an intraoral digital image
Direct Digital imaging: Here a sensor is placed in the
patients mouth and exposed to radiation.
The sensor captures the radiographic image and then
transmits the image to the computer monitor, and within
seconds the imaging appears on the computer screen.
Indirect digital imaging: In this method an existing X-
ray film is digitized using a CCD camera, which scans
the image, digitizes or converts the image and then
displays it on the computer monitor.
Storage Phosphor imaging :- It is a wireless digital
radiography system. A reusable image plate
radiography system. A reusable imaging plate coated
with phosphors is used.
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9. Methods to obtain an extraoral digital image
PSP based radiography:- it is applied to computed
radiography system, has been used for extraoral
projections and image analysis including panaromic
radiography.
CCD system:- using solid state linear array of photoiodides.
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10. Equipment
The essential components of digital
imaging system include:-
a. X-ray radiation source
b. Digital image receptor
c. An analogue to digital converter
c. Digital image display
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11. Equipment
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12. X- ray radiation source
 Digital radiography requires less X radiations than
conventional radiography, because the sensor is more
sensitive to X rays than a conventional film.
 Exposure time for digital radiography is 50-80 percent
less than that required for conventional radiography
using E-speed film, and thus the absorbed dose to the
patient is much lower.
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13. Analog versus digital image
 The term digital in digital imaging refers to the numeric
format of the image content and its discreteness.
 Conventional film images can be considered analog
medium in which differences in size and distribution of
black metallic silver result in a continuous density
spectrum
 Digital images are numeric and discrete in 2 ways:
1.Spatial distribution of the picture elements.
2.Different shades of grey of each pixel.
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14. ADC consists of two steps:-
sampling and quantization
AA BB
CC DD
6 units6 units
AA
BB
Analog signalAnalog signal
Digital signalDigital signal
SignalSignalSignalSignal
256256
256256
TimeTime
TimeTime
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15. Digital image receptor
 Digital image receptor encompass a number of
different technologies and come in many different
sizes and shapes.
 Currently the most useful distinction is that
between two main technologies:
1. Solid- state detectors
2. Photostimulable phosphor plate
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16. Solid-state detectors
 Solid-state detectors collect the charge collected by x-
rays as solid semiconductor material.
 The matrix and its associated readout and amplifying
electronics of intraoral detectors are enclosed within
plastic housing to protect them from oral environment.
 A potential drawback of intraoral solid-state conductors
is bulk of the sensor. In addition the detectors
incorporate electronic cable to transfer data to the
computer.
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17. Charge couple device (CCD)
 The charge couple device was first direct image
receptor to be adapted for intraoral imaging and
was introduced in 1987.
 The CCD uses a thin wafer of silicon as the basis
for image recording. The silicon crystals are
formed in a picture element (pixel) matrix.
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18. Exposed to radiation
Covalent bond of between silicon atoms breaks
Electron hole pairs
Electrons are attracted to the most +ve potential device
CHARGE PACKETS
Each packet constitute one pixel
Charge packet formed in each pixel in matrix
LATENT IMAGE
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19.  The image is read by transferring each row of pixel
charges from one pixel to next in a bucket brigade
fashion.
 As a charge reaches the end of its row it is transferred
to readout amplifier and transmitted as a voltage to the
analog digital converter located within or connected to
the computer.
 CCDs are more sensitive most manufacture use
scintillating material coated directly on the CCD surface
or coupled to the surface by fiber optics.
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21. Complementary metal oxide semiconductor
 Complementary metal oxide semiconductor
(CMOS) is the basis for typical consumer-grade
video cameras.
 Each pixel is isolated from its neighboring and is
directly connected to transistor
 Less expensive than CCDs
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22. Charge injection device
 It is another sensor technology, structurally similar it is
very much like the CCD, but in this case no computer is
required to process the image.
 The system consist of CID, x-ray sensor, cord and plug
that can be inserted into the light source on the camera
platform, digital images are seen on the system monitor
within seconds.
 The image is printed with a color video printer and saved
as a computer file or onto a video desk recorder.
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23. Photostimulable phosphor plate (PSP)
 Photostimulable phosphor plate (PSP) absorb and store
energy from x-rays and then release this energy as light
of an appropriate wavelength.
 The photostimulable material used for radiographic
imaging is “Europium- doped” barium fluorohalide.
 The addition of Europium creates imperfections in this
lattice. When exposed to sufficiently energetic source of
radiation valence electrons in Europium can absorb
energy and move into conduction band.
 These electrons migrate to nearby halogen vacancies (F-
centers) in the fluorohalide lattice and may become
tapped in the metastable state.
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24.  When stimulated by red light of around 600nm, the
barium fluorohalide releases trapped electron to the
conduction band.
 The photmultiplier tube converts light into electrical
energy. A red filter at photomultiplier tube converts light
into electrical energy.
 A red filter at the photomultiplier tube selectively
removes the stimulating light, and remaining green light
is detected and converted to varying voltage.
 The variation in voltage output from the photomultiplier
tube correspond to variations in simulated light intensity
from latent image.
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25.  The voltage signal is quantified by an analog to digital
converter and stored and displayed as digital image.
 Before procedure PSP plates must be erased to eliminate
“ghost images” from prior exposure.
 This is accomplished by flooding a plate with a bright
light source.
 Some PSP integrate automatic plate erasing lights.
Erased plates are placed in light tight container.
 Trapped electrons are spontaneously release over time.
The rate of loss of electron is greatest shortly after
exposure.
 Some phosphor lose 23% of their trapped electrons after
30 minutes and 30% after an hour.
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26. Stationary plate scans:
 It employs a rapidly rotating multifaceted mirror that
reflects a beam of red light.
 As mirror revolves red light sweeps across the plate. The
plate is advanced and the adjacent line of phosphor is
scanned.
Rotating plate scans
 It involves a rapidly rotating drum that holds the plate.
The rotation of the drum past a fixed laser provides a
rapid scan.
 Incremental movement of the laser in the slow direction
allow image data to be acquire line by line.
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27. Flat panel detector
 These provide relatively large matrix areas with pixel
size less than 100 microns. This allows direct digital
imaging of larger areas of the body, including head.
 There are two types of detectors: Indirect detectors that
are sensitive to light, and an intensifying screen is used
to convert x-ray photons to light.
 Direct detectors which uses a photoconductor material
(selenium) with properties similar to silicon and a higher
atomic number that permits more absorption of x-rays.
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28. Clinical comparison of intraoral imagingClinical comparison of intraoral imaging
alternativesalternatives
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30. Comparison of physical properties of film,Comparison of physical properties of film,
CCD, CMOS and PSPCCD, CMOS and PSP
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32. Digital detector charecteristic
 Contrast resolution
 Spatial resolution
 Detector latitude
 Detector sensitivity
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33. Contrast resolution
 It is the ability to distinguish different densities on radiographic
image.
 This is function of the interaction of the attenuation
characteristics of tissues being that are being imaged, the
capacity of image receptor to distinguish differences in numbers
of x-ray photons coming from different areas of subject, the
ability of the computer display or other output of the portray
differences in densities and the ability of observer to recognize
those differences.
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34.  In practice actual number of the densities that can be
observed is limited by inaccuracies in image acquisition
these in accuracies are termed as are given the generic
term of noise.
 Conventional computer monitor are capable of displaying
a gray scale of 8 bits.
 Actual number of gray scale that can be displayed on the
monitor is 242.
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35. Spatial resolution:
 It is the capacity for distinguishing fine detail. The theoretical limit of
resolution is function of picture element(pixel) size for digital imaging
systems.
 Currently highest resolution charge couple device detector have pixel
sizes of approximately 20 microns. This compare with the size of silver
grain size 8 microns for intraoral film.
 Resolution is often measured and reported in units if line pairs per
millimeter.A line and its associated space is called a line pair. At least 2
pixels are required to restore a line pair.
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36.  At 20 microns per pixel, theoretical value resolution
of 25 lp/mm can be obtained. Typical observers are
able to distinguish 6 lp/mm without benefit of
magnification. Intraoral film is able to provide 20
lp/mm of resolution.
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37. Detector lattitude
 The ability of imaging receptor to capture range of
exposure is termed latitude. A desirable quality in
intraoral intraoral image receptor is ability to
record the full range of tissue densities, from
gingiva to enamel.
 The lattitude of CCD and CMOS detectors is similar
to film and can be extented with digital
enhancement. PSP receptor enjoys a wider
lattitute.
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38. Detector sensitivity
 Sensitivity of detector is its ability to respond to
small amount of radiation.
 PSP system for intraoral imaging allow dose
reduction of 50% in comparison with f speed film.
High resolution CCD and CMOS system achieve less
dose reduction than low resolution PSP.
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39. Digital image display
Cathode ray tube (CRT)
 Conventional computer monitors uses CRT designs. A
beam of electrons emanating from an electron gun
rapidly scans a phosphor coated screen. The electron
scans is horizontal and builds an image line by line.
 CRT displays involves conversion of digital information
into analog voltages, which are supplied to the electron
guns.
 Some losses of the original information is inherent in the
digital-to-analog conversion process.
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40. Thin film transistor
 Thin film transistor technology, which is used in flat
panel decoders, is also used in laptops and flat panel
computer display.
 The process is some what is reversed in that a signal is
sent the pixels transistor, which in return causes the
associated liquid crystal display to transmit light with an
intensity proportional to the transistor voltage.
 The output of laptop displays is limited intensity and
does not have the dynamic range or contrast found in
conventional desktop displays.
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41.  The large number of variables that influence the quality of
printed image- for instance printing technology, printer quality
and type of media- makes a printing process a much more
complicated process that it initially appears to be.
 The main types of printing technologies available for large
printing include laser, inkjet and dye-sublimation with the use of
either film or paper.
Digital image display
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42. Film printers
Laser or dye sublimation give the best results, but are
expensive. Ink jet printers are the most commonly used.
High quality film printers using laser or dye sublimation
technology are expensive and low cost alternatives
suffer from reduced diagnostic quality.
Paper printers
These require reflective light from a normally lit room. Ink
jet most commonly used, others being expensive.
The printer resolution is expressed as dots per inch (DPI).
Higher the DPI better the resolution.
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43. Image processing
 Any operation that acts to improve, restore, analyze or
in some way change a digital image in the form of image
processing.
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44. Image restoration
 When the image data enter the computer they are
usually not ready for the storage or display.
 A number of preprocessing steps need to be performed
to correct the image for known defect and adjust the
image intensities so that they are suitable for viewing.
 The image is restored by substituting the
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45. Image enhancement
 The term image enhancement that the adjusted image is
the improved version of the original image.
 Most image enhancement operations are applied to
make the image more appealing.
 This can be accomplished by increasing contrast,
optimizing brightness, and reducing unsharpness and
noise.
 Some image enhancement does not necessarily improve
the accuracy of image interpretation.
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46. Brightness and contrast
 Digital radiographs do not always effectively utilize the full
range of available gray value.
 They can be relatively dark or light , and they can show too
much contrast in certain areas or not enough.
 The minimum and maximum values and the shape of the
histogram indicates the potential benefit of brightness and
contrast enhancement operation.
 Histogram equalization is an enhancement operation that
increases contrast between those image intensities
abundantly present within the image while reducing contrast
between image intensities that are used only sparsely.
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47. Sharpening and Smoothing
 The purpose of sharpening and smoothing filters is so
improve imaging quality by removing blur or noise.
Noise is often categorized as high frequency noise or low
frequency noise.
 Filter that smooth an image is sometimes called
despeckling filters because they remove high frequency
noise. Filters that sharpen an image either remove low
frequency noise or enhance boundaries between regions
with different intensities.
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48. Color
 Most digital systems currently on the market provide
opportunities for color conversion of gray images, also
called pseudo-color.
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50. Digital subtraction radiography
 When two images of the same object are registered and
the image intensities of corresponding pixels are
subtracted , a uniform difference image is produced.
 The projection geometry is defined by the position and
orientation of the X-ray source the patient , and the
decoders , relative to one another.
 Difference in image contrast and intensity between the
base line image and the follow-up can hamper the
detection task and make quantitative measurements
unreliable
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52. Image analysis
 Image analysis operations are designed to extract
diagnostically relevant information from the image.
 Measurement: digital rulers, dosimeters and
variety of other tools. The size and image intensity
of any area can be measured.
 Diagnosis: one of the most challenging areas of
research is the development of tools and procedures
that automate the detection, classification and
quantification of radiographic signs of disease.
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53. Image storage
 Storage and retrieval of the radiographic images is
not a trivial issue.
 Once in digital format data can be deleted or
modified. It is important for the software prevents
the user from permanently deleting or modifying
the original image data weather intentional or
unintentional.
 Backup media can be stored in external drive,
hard drive, digital tapes,CDs, DVDs
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54. Digital image backup considerations:-
 Type of backup media
 Time and method of backup
 Backup interval
 Storage location of backup media
 Recovery time
 Recovery reliability
 Future compatibility of backup technology
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55. Image compression
 The purpose of file compression is to significantly reduce
the file size while preserving critical image information.
 Lossless
Lossy compression
 Lossless file formats are the TIFF format. However, it
only offers 3:1 compression ratios
 Lossy file format is JPEG format.
Offers 14:1 compression ratios
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56. Common problems in digital image receptor
exposure, processing and handling
Noisy images
 Although the brightness of these images has been
adjusted to display similar average grey values , notice
the noisy appearance of the underexposed bitewing
radiograph compared with the properly exposed
radiograph.
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57.  PSP image degradation as a result of excessive
exposure to ambient light between image
acquisition and plate scanning. This type of noise
resembles that of X-rays underexposure.
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58. Non uniform images density
 Partial exposure of PSP plates to excessive ambient
light prior to scanning result in non uniform image
density . This happens when plates are not over lapped
while exposed to ambient light.
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59. Double images
 Due to incomplete eraser of the previous images
Distorted Images : Bending of PSP plates during
intraoral placement
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60. Damaged image receptor
 Image artifacts resulting from
excessive bending of the PSP
plate and excessive bending
has resulted in premanent
damage to the phosphor plate
 PSP circular artifact as a result
of plate damage and localized
swelling of the protective
coating from disinfectant on
work surface.
 PSP image artifact resulting
from plate surface
contamination . This artifact
was caused by a glove
powder smuged that
prevented roper scanning of
the affected area of the PSP
plate.
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61. Scratched phosphor surface mimicking root canal filling and
retake.
Contaminants combined with skin oils may permanently damage
the phosphor plate surface.
Malfunctioning CCD sensor resulting from rough handling .
The sensor produces geometric image artifacts.
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62. Improve Use Of Image:
 improve use of image processing tools , such as filters ,
may result in false positive findings .
 An edge enhancement filters was applied to the
panoramic image, which produced radiolucencise at the
restoration edges simulating recurrent caries.
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63. Advantages
 Reduced exposure to X-radiation
 Increased speed or faster image acquisition
 Enhancement of diagnostic image
 Superior gray scale resolution
 Image storage
 Effective patient education tool
 Paperless file
 Cross contamination
 Envioronmentally friendly
 Teleradiography
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64. Disadvantages
 Sensor placement
 Image quality
 Initial set up cost
 Wire attached to sensor
 Infection control
 Fragility of sensors
 Legal issues
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65. Conclusion
 If one asks, ”Which is better film or digital
imaging?” there no simple answer to this question.
Both the imaging methods have got advantages
and disadvantages.
 As far as so many advantages are considered,
digital imaging can be used by dentist. Every type
of information about the patient is at the tip of
one,
s fingures on the computer keyboard for
immediate viewing.
 Although film based imaging is not yet outdated,
digital imaging is now well accepted.
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66. References
 Oral Radiology-Principles & Interpretation. White &
Pharoah 5th
edition.
 Oral Radiology-Principles & Interpretation. White &
Pharoah 5th
edition.
 Digital imaging, Radiology for Dental Auxiliaries-
Herbert H. Frommer 7th
edition.
 The efficiency of a computerized caries detector in
Intraoral Digital Radiography JADA 133 (7) 183-90
July 2002.
 Dental Radiography- Haring Jansen.
 Does digital Radiography increases the number of
intraoral radiographs? Dento Maxillofacial
Radiology ; 32 (2); 124-7 ; 2003.
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67. Thank you
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