The document provides an overview of digital imaging in dentistry, discussing its definition, historical development, and various methods and technologies. Key topics include the comparison of digital detectors, analog versus digital signals, and clinical applications alongside their advantages and disadvantages. Further details are provided on imaging techniques such as direct and indirect digital imaging, the structure of charge-coupled devices (CCDs) and complementary metal oxide semiconductors (CMOS), and the implications for dental radiography.

1. Digital IMAGING IN
DENTISTRY
1

2. A PICTURE IS WORTH A
THOUSAND WORDS
2

3. 3

4. Introduction
 Definition & uses
 History & classification
 Analog signal Vs Digital signal
 Digitization
 Types of digital detectors
 Image characteristics and artifacts
 Comparison of different detectors
 Clinical Applications
 Advantages & Disadvantages
4

5. Radiography
Digital Radiography
Analog Digital
Scanner
(X-ray digitizer)
Computed
Radiography
(CR)
Direct Digital
Radiography
(DR or DDR)
5

6. HISTORy
6

7. 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
Pasler,Pocket Atlas of Dental Radiology, Thieme 2007
7

8. 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
8

9. 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
9

10. 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)
Lanc¸a L, Silva A, Digital Imaging Systems for Plain Radiography,
Springer 2013 Digital Radiography
10

11. 11
Francis Mouyen invented the
first intra-oral digital detector

12. Definition
 It is a method of capturing image using a
sensor, breaking it into electronic pixels,
presenting and storing the image using a
computer.
12

13. DIGITAL IMAGING
 Digital imaging are acquired either
 DIRECTLY – using a sensor or imaging plate
replacing conventional film
 INDIRECTLY – by scanning and digitizing a film-
captured image.
 Direct digital imaging systems are divided into
two types :
- Real time or CORDED
- Photostimulable phophor storage
plate or CORDLESS 13

14. Classification
Direct
Indirect
The image is acquired in a digital format
CCD, CMOS.
Analog image is digitized
e.g. scanning of radiographs /
photograph of a radiograph
Semi-direct Involves 2 steps in film acquisition.
Photostimulable phosphor plates (PSP)
14

15. ANALOG vs DIGITAL
What is Analog?
&
What is Digital?
15

16. 16

17. HOW THE DETECTOR CREATES AN IMAGE
The Original Image

18. 1
1
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3 3
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3 3 3
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3 3
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3 3
3 3 3 3
3 3 3 3
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3 3
It converts that picture into a
number.
For purposes of this example we’ll
use the numbers from 1 to 9.
HOW THE DETECTOR CREATES AN IMAGE

19. 1
1
1
1
1
1
1
1
1
1
1
1
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1
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2
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1
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2
1
1
1
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9
5
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1
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2
4
5
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2
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8
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3 3
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8
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3 3 3
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3 3
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3 3
3 3 3 3
3 3 3 3
3
3
3
3 3
Here is the pixel value
map without the
original image.
Each of the pixel
values is then sent to
the computer.
Since the computer
‘knows’ the location of
each pixel…
HOW THE DETECTOR CREATES AN IMAGE

20. It is a simple matter to
reconstruct the pixel
value data into a similar
size grid.
The jagged effect is
caused when the pixel lies
along a transition in
density. This effect is
called ‘pixelization’
This image may not
look very good, but you
have to consider the
scale involved…
HOW THE DETECTOR CREATES AN IMAGE

21. The Original Image

22. Digitization
Involves a process called analog to digital conversion (ADC)
1. Sampling
2. Quantization
22

23. Sampling
 Small range of voltage are grouped together as a single
specific value.
 For example, we take the same 70 kVp signal.
0 – 10  1
11 – 20  2
21 – 30  3
31 – 40  4
and so on…..
23

24. Analog Signal
0 kVp
24

25. Analog Signal
SAMPLED with a range of 10 kVp
25

26. Analog Signal
SAMPLED with a range of 5 kVp
26

27. “ Narrower the sampling the better the output
signal mimics the original signal.”
27

28. Quantization
 Once sampled, the signal is quantized
 Every sampled signal is assigned a value, which
is stored in computer and represents the image.
 Quantizing the sampled image involves
assigning the color of each pixel to discrete and
precise value.
 Pixel organized in proper location is given a
shade of gray, that corresponds to the number
assigned in quantization. 28

29. ADC
Analog Signal
Digital Signal
Processing Unit
Display Unit
29

30. Drawback
 Both by increasing the sampling and increasing
quantization we are increasing the memory load on
the computer.
 File size
30

31. Digital Detectors
Direct Indirect
Semi-direct
Charge couple device (CCD)
Complimentary metal oxide
Semiconductors (CMOS)
Flat panel detectors
Thin film transistor (TFT)
Photostimulable
Phosphor Plates
31

32. SOLID STATE DETECTORS
 They collect the charge generated by x-rays
in a solid semiconducting material.
 The key clinical feature of these detectors is
the rapid availability of the image after
exposure.
 Sensor bulk
32

33. Charge coupled device
 In 1969 Bell Laboratories invented the first CCD in
an effort to create new storage system for computers.
 Their use as photo-detectors was recognized because
of sensitivity to visible light.
 Incorporated, in 1987, as the first direct digital image
receptor for intra oral use.
33

34. Structure of CCD
P
I
X
A
L
Electrodes
Insulating Layer
n p
Optical fiber
Scintillator
34
Basic structure of the CCD: electrodes insulated from an n-p silicon sandwich.
The surface of the silicon may incorporate a scintillating material to
improve x-ray capture efficiency and fiberoptics to improve resolution.
One pixel utilizes three electrodes.

35. Structure of CCD
P
I
X
A
L
Electrodes
Insulating Layer
n p
Optical fiber
Scintillator
35
Excess electrons from the n-type layer diffuse into the p-type layer while
excess holes in the p-type layer diffuse into the n-type layer.
The resulting charge imbalance creates an electric field in the silicon with a
maximum just inside the n-type layer.

36. Valence Band
Conduction Band
1.26 eV
I
N
C
R
E
A
I
N
G
E
N
E
R
G
Y
+
Photoelectric effect
Silicon atom
36
Outer shells of the silicon atom showing an energy difference between
the valence band and the conduction band.
X-ray or light photons impart energy to valence electrons, releasing them
into the conduction band.
This generates an "electronhole“ charge pair.

37. 37

38. Signal Readout
Readout Amplifier
ADC
BUCKET BRIGADE FASHION
Analog Signal
Digital Signal
38

39.  CMOS technology is basis for typical consumer-grade video cameras.
 These detectors are also silicon based semiconductors but are
fundamentally different from CCD in the way that pixel charges are
used.
 The pixel is isolated from its neighboring pixels and is directly
connected to the transistor.
 Like in the CCD the electron –hole pairs are generated within the pixel
in proportion to the amount of x-ray energy absorbed.
39
Complementary metal oxide
semiconductors (cmos)

40.  This charge is transferred to the transistor can be read separately by a
frame grabber, and then stored and displayed as a digital gray value.
 This technology is commonly used in digital cameras and has been
recently incorporated as a sensor in dental digital radiography.
 It is believed to give 25% more resolution and the chip is less
expensive and offers greater durability than the CCD.
40
Complementary metal oxide
semiconductors (cmos)

41. Complementary metal oxide
semiconductors
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
Whaites E, Essentials of Dental Radiography and Radiology, 4th edition, 2007

42. ADC

44. • 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
Digital Radiography
92

45. 45
RVG SENSOR

46. 46
EXPLODED VIEW OF CMOS
SENSOR

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

48.  These are being used for medical imaging but have also been used in
several extraoral imaging devices.
 These provide a relatively large matrix areas with pixel sizes less than
100 microns.
 This allows direct digital imaging of larger areas of the body, including
the head.
48
Flat panel detectors

49.  These are of two types :
 INDIRECT DETECTORS that are sensitive to visible light, and an
intensifying screen is used to convert x-rays photons to light.
 DIRECT DETECTORS which used a photoconductor material
(selenium) with properties similar to silicon and a higher atomic
number that permits more efficient absorption of x-rays.
 Currently, flat panel detectors are expensive and likely to be limited to
specialized task such as CONE BEAM IMAGING. 49
Flat panel detectors

50. Photostimulable phosphor
plate (PSP)
 Photostimulable phosphor plates (PSP) absorb and store
energy from x rays and then release this energy as light
(phosphorescence) when stimulated by another light of an
appropriate wavelength.
50

51. Photostimulable phosphor
plate (PSP)
 The photostimulable phosphor material used for
radiographic imaging is "Europium-doped" barium
fluorohalide.
 Barium in combination with iodine, chlorine, or bromine
forms a crystal lattice.
51

52. Photostimulable phosphor plate
(PSP)
Valence band
Conduction band
e-
e-
Plate Prepared Plate Exposed Plate Processed
Scanning
laser
F centre
600 nm
300-500 nm
52
Eu+2
Eu+2 Eu+3
Eu+2 Eu+3

53.  The photomultiplier tube converts light into electrical energy.
 A red filter at the photomultiplier tube selectively removes the
stimulating light, and the remaining green light is detected
and converted to a varying voltage.
 The voltage signal is quantified by an analog-to-digital
converter and stored and displayed as a digital image
53

54. PSP plate loaded Readout for the PSP plate
54

55.  Before exposure, PSP plates must be erased to elIminate
"ghost images" from prior exposures.
55

56. Scanning Delay
 Plates are sensitive to light and can be erased by subjecting
to high intensity light.
 1- 2 minute exposure over the view box
 The plates should be processed immediately after exposure.
56

57.  Phosphor plates lose their 23% of electrons in 30 minutes
and 30 % in an hour.
 Degradation of PSP which are adequately exposed is
comparatively low within 24 hours as compared to
inadequately exposed films.
S C White, M.J. Pharoah, Oral Radiology; Principles and Interpretation
57

58.  In the case of intraoral plates, sealable polyvinyl envelopes
that are impervious to oral fluids and light are used for
packaging.
 For large format plates, conventional cassettes (without
intensifying screens) are used. Following exposure, plates
should be processed as soon as possible.
 Trapped electrons are spontaneously released overtime. The
rate of loss of electrons is greatest shortly after exposure.
The rate varies depending on the composition of the storage
phosphor and environmental temperature. 58

59.  A semidark environment is recommended for plate handling.
 The more intense the background light and the longer the
exposure of the plate to this light, the greater is the loss of
trapped electrons.
 Red safelights found in most darkrooms are not safe for
exposed PSP plates, which are most sensitive to the red light
spectrum.
59

60. INTRAORAL PSP SCANNER
60

61.  Advantage over CCD sensors
 Flexible
 Wider latitude
61

62. DIGITAL SYSTEM BASICS
 Every Digital Radiography System Consists
of these 6 components:
 X-ray Source
 Sensor
 Interface
 Computer
 Monitor
 Software

63. Digital System Basics
Interface
Monitor
Personal Computer
Software
X-ray Source
Sensor

64. Image Characteristics
 Contrast Resolution
 Spatial Resolution
 Detector Latitude
 Detector Sensitivity
 Signal to noise ratio
64

65. Contrast Resolution
 Contrast resolution is the ability to distinguish different densities in the radiographic
image.
o Current digital detectors capture data at 8-, 10-, 12-, or 16-bit depths.
o The bit depth is a power of 2.
65

66.  It is the ability of an imaging system to distinguish between
multiple densities in the radiographic image.
 In the case of digital imaging, it depends on the bit-depth of
the system.
 As noted earlier, an 8-bit system can show only 256 gray
values as opposed to a 12-bit system, which shows 4096
gray values.
 The 8-bit system shows less gray values and is a high
contrast system than the 12-bit system that shows more
gray values and is a low contrast system.
 However, if the 12-bit-system can clearly show two near-by
gray value intensities, the system will have a high contrast
resolution 66
CONTRAST RESOLUTION

67. 67
Comparison of 2 systems. In each rectangle, there is a
square that has a grey value close to the grey value of the
rectangle.
A has a low contrast resolution.
B has a high contrast resolution

68. 68

69. Spatial Resolution
 Spatial resolution is the capacity for distinguishing fine detail.
 The theoretical limit of resolution is a function of picture element (pixel) size for digital
imaging systems.
69

70. 70
1. Spatial resolution in radiology refers to the
ability of an imaging system to
differentiate between two near-by objects.
2. In digital imaging, it depends on the size
of the pixel used.
3. A large pixel size will be unable to resolve
two near-by structures as compared to a
small pixel size.
4. Spatial resolution is measured in line-pairs
per millimeters
SPATIAL RESOLUTION

71. 71
Comparison of 2 systems: A has a low spatial
resolution and B has a high spatial resolution

72.  Film based IOPA – 20 lp /
mm.
 Digital receptors 7 lp / mm.
Test Object
Film > CCD > PSP
S.C White, M.J Pharoah
Oral Radiology; Principles and Interpretation
72

73.  It is the ability of the image receptor to capture a range of x-
ray exposures as different densities.
Detector Latitude
Characteristic Curve
Log relative exposure
Optical Density
0.5 1.0 1.5 2.0 2.5 3.0 3.5
3.0
2.5
2.0
1.5
1.0
0.5
73

74. Detector Latitude
 The latitude ofCCD and CMOS detectors is similar to film
 Photostimulable phosphor receptors have larger latitudes and have a linear response
to five orders of magnitude of x-ray exposure.
74

75. Detector Sensitivity
 Sensitivity of a detector is its ability to respond to small amounts of radiation.
Intraoral film sensitivity is classified according to speed.
 High resolution CCD and CMOS systems achieve less dose reduction than lower
resolution PSP systems. CCD and PSP systems or extraoral imaging require
exposures similar to those needed for 200-speed screen-film systems.
75

76. Clinical Applications
 Image Restoration
 Image Enhancement
 Image Analysis
 DICOM system
76

77. Digital subtraction radiography
 Subtraction in digital radiology is another image enhancement method with purpose
to produce two radiographs of the same area in the mouth at the different time
intervals.
 The first image can be subtracted from the second one to identify changes that may
have occurred during a certain time period. Minimal changes in loss or gain of hard
tissue can be detected using this technique, otherwise undetectable by visual
examination and traditional radiography.
77

78. 78
digital subtraction radiography (DSR). Areas of loss and gain are represented as either
dark or light shades of grey against the neutral background.
(a) Root canal cavity is prepared.
(b) Root canal therapy is accomplished, healing is observed at the root apex.
(c) Subtraction is performed; root filling and healing zone are emphasized in light
shades of grey by DSR.

79. 79

80. 80

81. DICOM System
 Digital Imaging and Communications in Medicine (DICOM) is a standard for handling,
storing, printing, and transmitting information in medical imaging.
 It includes a file format definition and a network communications protocol.
 DICOM files can be exchanged between two entities that are capable of receiving image
and patient data in DICOM format.
 DICOM enables the integration of scanners, servers, workstations, printers, and network
hardware from multiple manufacturers into a picture archiving and communication
system (PACS).
81

82. ADVANTAGES & DISADVANTAGES
OF DIGITAL IMAGING
Advantages
 Dose reductions up to 90 % have been reported in diagnosing
caries using digital radiography.
 Image modulation.
 Time consumption is markedly reduced as no processing is
required.
 No environmental pollutants in the form of processing
solutions.
 Storage and reproducibility of images.
 Teleradiology (DICOM)
82

83. Disadvantages
 Cost
 Sensitive to manipulation.
 Sensor dimensions.
 Cross-infection control.
83

84. Conclusion
 “Digitization results in reduced patient exposure”, needs
consideration because as we can now get radiographs
immediately, a natural tendency for repeating the
radiographs is quite inherent.
 More research is required for selecting type of sensors for
specific diagnostic tasks.
84

85. 85
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