Dentistry Digital imaging enhancing .ppt

Dentistry

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
DigitalRadiography
Analog Digital
Scanner
(X-raydigitizer)
Computed
Radiography
(CR)
DirectDigital
Radiography
(DRorDDR)
5

6. HISTORy
6

7. Year Development
1500BC
“Thephenomenonof luminescence”observed-
China
1895 X-raysdiscovered
1895 DrWalkofffirsttook dentalradiograph
1919 Kodakproducedfirstdentalfilm
1955 KodakDspeedfilm
1963 CMOSinvented
1969 CCDtechnologyforvideoapplications
Pasler,PocketAtlasofDentalRadiology,Thieme2007
7

8. Year Development
1970 Alternatereceptorsystem–Xeroradiography
1975
Methodof convertingtheinformation pattern into
adigitalform
1980 Computedradiography-storagephosphors
1981
Computed Radiography –PSP
method Kodak–Ekta
speed
1984
FirstDirectDigitalImaging
System -
RadioVisioGraphy
1987 Amorphousselenium–basedimageplates
8

9. Year Development
1990
Charge-coupled device(CCD)slot-scan
directradiography
1994 Storagephosphorsystem,DIGORAforintraoral
use.
1995
CCD(Visualix –2/VIXA–2),whichhada larger
active
area
Computed Dental Radiography(CDR)system
by
Schick.
Amorphous silicon–cesiumiodide(scintillator)
flat-
paneldetector
Selenium-basedflat-paneldetector
9

10. Year Development
1997 Gadolinium-based (scintillator)flat-panel
detector
2001
Gadolinium-based(scintillator)portableflat-
panel
detector
Dynamicflat-panel detectorfluoroscopy
2009 WirelessDR(flat-paneldetector)
Lanc¸a L, Silva A, Digital Imaging Systems for Plain Radiography,
Springer 2013
DigitalRadiography
10

11. 11
Francis Mouyeninvented 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
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
2
4
6
5
4
6
2
1
1
1
1
1
2
1
1
7
4
5
2
1
1
1
1
2
6
2
1
1
1
1
2
3
6
2
1
1
1
1
2
6
9
5
4
2
1
1
1
1
1
2
4
5
1
2
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
2
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
38
333
33
33
3 3
3
3
3
3
3
3
3
3
8
3
3
3
3
3 3 3
3
33
3
3
3
3
3
3
3
3
3
33
3
33
3333
3333
3
3
33 3 Itconvertsthatpictureintoa
number.
Forpurposesofthisexamplewe’ll
usethenumbersfrom1to9.
HOW THE DETECTOR CREATES AN IMAGE

19. 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
2
4
6
5
4
6
2
1
1
1
1
1
2
1
7
4
5
2
1
1
1
1
2
6
2
1
1
1
1
2
3
6
2
1
1
1
1
2
6
9
5
4
2
1
1
1
1
1
2
4
5
1
2
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
2
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
38
333
33
33
3 3
3
3
3
3
3
3
3
3
8
3
3
3
3
3 3 3
3
33
3
3
3
3
3
3
3
3
3
33
3
33
3333
3333
3
3
33 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
Oncesampled,thesignalisquantized
Everysampledsignalisassignedavalue,which
isstoredincomputerandrepresentstheimage.
Quantizingthesampledimageinvolves
assigningthecolorofeachpixeltodiscreteand
precisevalue.
Pixelorganizedinproperlocationisgivena
shadeofgray,thatcorrespondstothenumber
assignedinquantization.
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 Laboratoriesinvented the first CCD in
an effort to create new storage system for computers.
Their use as photo-detectorswas 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
np
Optical fiber
Scintillator
34
BasicstructureoftheCCD:electrodesinsulatedfromann-psiliconsandwich.
Thesurfaceofthesiliconmayincorporateascintillatingmaterialto
improvex-raycaptureefficiencyandfiberopticstoimproveresolution.
Onepixelutilizesthreeelectrodes.

35. Structure of CCD
P
I
X
A
L
Electrodes
Insulating Layer
np
Optical fiber
Scintillator
35
Excesselectronsfromthen-typelayerdiffuseintothep-typelayerwhile
excessholesinthep-typelayerdiffuseintothen-typelayer.
Theresultingchargeimbalancecreatesanelectricfieldinthesiliconwitha
maximumjustinsidethen-typelayer.

36. Valence Band
Conduction Band
1.26 eV
I
N
C
R
E
A
I
N
G
E
N
E
R
G
Y
+
Photoelectric effectSilicon atom
36
Outershellsofthesiliconatomshowinganenergydifferencebetween
thevalencebandandtheconductionband.
X-rayorlightphotonsimpartenergytovalenceelectrons,releasingthem
intotheconductionband.
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
WhaitesE,EssentialsofDentalRadiographyandRadiology,4th edition,2007

42. ADC

44. •Thesesensorsdonotrequirechargetransfer,
resultinginincreasedsensorreliabilityand
lifespan.
•Requirelesssystempowertooperateandare
lessexpensivetomanufacture
•Lowcost
•Fixedpatternofnoise
•Smalleractivearea
DigitalRadiography
92

45. 45
RVG SENSOR

46. 46
EXPLODED VIEW OF CMOS
SENSOR

47. CCD CMOS
POWERCOSUMPTION. 400mw 40mw
SENSITIVITYTO LIGHT Excellent Excellent
SENSITIVITYTOXRAYS High Unknown
PIXELSIZE. 40micron 25micron
COST. High Medium
MANUFACTURE. Expensive Cheap
BREAKAGERESISTANCE 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)
Photostimulablephosphorplates(PSP)absorbandstore
energyfromxraysandthenreleasethisenergyaslight
(phosphorescence)whenstimulatedbyanotherlightofan
appropriatewavelength.
50

51. Photostimulable phosphor
plate (PSP)
Thephotostimulablephosphormaterialusedfor
radiographicimagingis"Europium-doped"barium
fluorohalide.
Bariumincombinationwithiodine,chlorine,orbromine
formsacrystallattice.
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. Thephotomultipliertubeconvertslightintoelectricalenergy.
Aredfilteratthephotomultipliertubeselectivelyremovesthe
stimulatinglight,andtheremaininggreenlightisdetected
andconvertedtoavaryingvoltage.
Thevoltagesignalisquantifiedbyananalog-to-digital
converterandstoredanddisplayedasadigitalimage
53

54. PSP plate loaded Readout for the PSP plate
54

55. Beforeexposure,PSPplatesmustbeerasedtoelIminate
"ghostimages"frompriorexposures.
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. Inthecaseofintraoralplates,sealablepolyvinylenvelopes
thatareimpervioustooralfluidsandlightareusedfor
packaging.
Forlargeformatplates,conventionalcassettes(without
intensifyingscreens)areused.Followingexposure,plates
shouldbeprocessedassoonaspossible.
Trappedelectronsarespontaneouslyreleasedovertime.The
rateoflossofelectronsisgreatestshortlyafterexposure.
Theratevariesdependingonthecompositionofthestorage
phosphorandenvironmentaltemperature.
58

59. Asemidarkenvironmentisrecommendedforplatehandling.
Themoreintensethebackgroundlightandthelongerthe
exposureoftheplatetothislight,thegreateristhelossof
trappedelectrons.
Redsafelightsfoundinmostdarkroomsarenotsafefor
exposedPSPplates,whicharemostsensitivetotheredlight
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
Contrastresolutionistheabilitytodistinguishdifferentdensitiesintheradiographic
image.
oCurrentdigitaldetectorscapturedataat8-,10-,12-,or16-bitdepths.
oThebitdepthisapowerof2.
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
Spatialresolutionisthecapacityfordistinguishingfinedetail.
Thetheoreticallimitofresolutionisafunctionofpictureelement(pixel)sizefordigital
imagingsystems.
69

70. 70
1.Spatialresolutioninradiologyreferstothe
abilityofanimagingsystemto
differentiatebetweentwonear-byobjects.
2.Indigitalimaging,itdependsonthesize
ofthepixelused.
3.Alargepixelsizewillbeunabletoresolve
twonear-bystructuresascomparedtoa
smallpixelsize.
4.Spatialresolutionismeasuredinline-pairs
permillimeters
SPATIAL RESOLUTION

71. 71Comparison 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 1.52.0 2.5 3.0 3.5
3.0
2.5
2.0
1.5
1.0
0.5
73

74. Detector Latitude
ThelatitudeofCCDandCMOSdetectorsissimilartofilm
Photostimulablephosphorreceptorshavelargerlatitudesandhavealinearresponse
tofiveordersofmagnitudeofx-rayexposure.
74

75. Detector Sensitivity
Sensitivityofadetectorisitsabilitytorespondtosmallamountsofradiation.
Intraoralfilmsensitivityisclassifiedaccordingtospeed.
HighresolutionCCDandCMOSsystemsachievelessdosereductionthanlower
resolutionPSPsystems.CCDandPSPsystemsorextraoralimagingrequire
exposuressimilartothoseneededfor200-speedscreen-filmsystems.
75

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

77. Digital subtraction radiography
Subtractionindigitalradiologyisanotherimageenhancementmethodwithpurpose
toproducetworadiographsofthesameareainthemouthatthedifferenttime
intervals.
Thefirstimagecanbesubtractedfromthesecondonetoidentifychangesthatmay
haveoccurredduringacertaintimeperiod.Minimalchangesinlossorgainofhard
tissuecanbedetectedusingthistechnique,otherwiseundetectablebyvisual
examinationandtraditionalradiography.
77

78. 78
digitalsubtractionradiography(DSR).Areasoflossandgainarerepresentedaseither
darkorlightshadesofgreyagainsttheneutralbackground.
(a)Rootcanalcavityisprepared.
(b)Rootcanaltherapyisaccomplished,healingisobservedattherootapex.
(c)Subtractionisperformed;rootfillingandhealingzoneareemphasizedinlight
shadesofgreybyDSR.

79. 79

80. 80

81. DICOM System
DigitalImagingandCommunicationsinMedicine(DICOM)isastandardforhandling,
storing,printing,andtransmittinginformationinmedicalimaging.
Itincludesafileformatdefinitionandanetworkcommunicationsprotocol.
DICOMfilescanbeexchangedbetweentwoentitiesthatarecapableofreceivingimage
andpatientdatainDICOMformat.
DICOMenablestheintegrationofscanners,servers,workstations,printers,andnetwork
hardwarefrommultiplemanufacturersintoapicturearchivingandcommunication
system(PACS).
81

82. ADVANTAGES & DISADVANTAGES
OF DIGITAL IMAGING
Advantages
Dose reductionsup to 90 % have been reported in diagnosing
caries using digital radiography.
Image modulation.
Timeconsumption is markedly reduced as no processing is
required.
No environmental pollutantsin the form of processing
solutions.
Storageand 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. 85THANK YOU