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MAXILLOFACIAL
IMAGING RECEPTORS
INDIAN DENTAL
ACADEMY
Leader in continuing
Dental Education
www.indiandentalacademy.com
INTRODUCTION
• When a x ray beam passes through a pt differential
attenuation of x rays by the tissues occur
depending on ...
HISTORY
• The first X ray detector was the
barium platinocyanide plate used by
Sir Wilhelm Conrad Röentgen in his 1895 exp...
First nobel prize in physics was awarded to him in
1901
www.indiandentalacademy.com
• 14 days after discovery of x rays Friedrich Otto
Walkhoff took the first dental radiograph.
• He used an glass plate coa...
RECEPTORS
CONVENTIONAL
DIRECT
EXPOSURE FILMS
INDIRECT
EXPOSURE FILMS
WITH SCREENS
DIGITAL
SOLID STATE
DETECTORS
STORAGE
PH...
DENTAL X-RAY FILM
www.indiandentalacademy.com
FILM BASE
• Initially glass plate was used as base
• In 1914 - Cellulose nitrate base
• It was quite flammable
In 1924 saf...
• 1n 1960 – polyester base was developed
• Polyster polyethylene terephthalate ( 0.18 mm)
• Support the emulsion
• Flexibl...
EMULSION
Two principal components
1.Photo/ radio sensitive silver halide grains
2.Vehicle matrix :
• Gelatinous / non gela...
• Silver halide grains ( 1 to 1.5 microns) – crystal form
• Contains Ag+ , Br - / I- arranged in cubic lattice
• 90 to 99%...
• Crystals are chemically sensitised by adding sulfur
containing compounds like allylthiourea
It reacts with ag halide – f...
Single Emulsion :
• Better image detail
• But less dimensional stability
Double Emulsion Film :
• Advantages: less radiati...
DIRECT EXPOSURE FILM/
NON SCREEN FILMS
• Exposed directly to x- rays
• Commonly used for io
• Require more exposure factor...
INTRAORAL FILM PACKET
Outer plastic wrapper
Protects film from light,
saliva, mechanical damage
Identification dot
Used fo...
FILM SIZES FOR IOPAR
O
1
2
22 x 35 mm
Small children
31 x 41 mm
Standard film size
for adults
24 x 40mm
Children
Anterior ...
BITE WING VIEW
• Size 0, 1 in children
• Size 2 – for adults
• 27 x 54 mm
Extended size
bitewing
www.indiandentalacademy.c...
OCCLUSAL VIEW
• Used to visualise large areas of maxilla &
mandible
57 X 76
THREE TIMES LARGER
THAN SIZE 2
www.indiandenta...
SPEED
• Radiographic speed refers to amount of
radiation required to produce an image of
standard density.
• Expressed as ...
FILM SPEED GROUP SPEED RANGE (
RECIPROCAL OF
ROENTGENS) (1)
ISO speed group
classification for dental
films (2)
A 1.5 - 3
...
D /
ULTRA SPEED /US
E P / EKTA PLUS
FILM / INSIGHT
F/ INSIGHT
GLOBULAR AG- HALIDE
CRYSTALS
DIAMETER : 1.0MICRO
METER
T- GR...
Conventional
silver-halide
crystals are
pebble
shaped
KODAK
T-GRAIN
Emulsion
crystals
Are flat
INSIGHT
ULTRA
SPEED
Coating...
Fast film requires relatively low exposure to
produce an optical density of 1…
Slope of curve – contrast
Speed – location ...
PACKAGING :
• Single film packet
• Double film packet
• SELF DEVELOPING FILMS
www.indiandentalacademy.com
SCREEN FILMS
• Used for extraoral views
• manufactured with dyes in the emulsion that absorb
specific wavelengths of visib...
• Light photons are absorbed by emulsion, only outer layer is
affected.
• so thin emulsion on 2 sides is preferred rather ...
• Standard silver halide crystals are inherently sensitive to uv,
violet, blue light ( 300-500nm)
SLOW SCREENS
• calcium t...
Manufact
urer
Name phosphor Spectral
emission
film Speed
class
Du
pont
CRONEX PAR
SPEED
Cawo4
BLUE CRONEX 4 100
CRONEX HI
...
• Kodak ortho G film is replaced by T-Mat G film
• Can be used with all
green-emitting rare-earth
intensifying screens
suc...
CROSSOVER
To reduce crossover by
• adding a dye to the film base
• Changing shape of crystals.
• ( tabular)..increase ligh...
Super HR-U is a high
contrast green sensitive
x-ray film for use with
green-emitting rare earth
screens. The New all-
arou...
HIGH CONTRAST , MEDIUM SPEED FILMS – SKULL RADIOGRAPHY
FAST FILMS – LESS RADIATION EXPOSURE – PANORAMIC IMAGING
LESS CONTR...
• 1977- digital subtraction angiography,- first form of digi
imaging
• 1980 – computed radiography ( storage phosphor
plat...
• SOLID STATE DETECTORS
• CHARGED COUPLE DEVICES (CCD)
• COMPLEMENTARY METAL OXIDE
SEMICONDUCTORS
• FLAT PANEL DETECTORS
•...
• Electronic elements of a digital sensor are arranged in
a regular grid of rows and columns
• Pixel refers to the spatial...
Exposure of sensor with x rays
Release of electron from crystals
Production of electronic charge
each pixel of sensor, abs...
Charged couple device
• Thin wafer of silicon - crystals are in pixel matrix
• On x ray exposure - covalent bonds b/n sili...
Image is read by transferring each row of pixel charges from
one to other…Bucket brigade pattern. At end of row -
Transfer...
• RVG – by Trophy
• Sens-a-Ray by Regam
• Visualix by Gendex
• Flashdent by Villa
• Sidexis by Siemens
• CDR by Schick
www...
Complementary metal oxide semi conductors
• Silicon -based , differ from CCDs in the way that pixel
charges are read
• Eac...
PHOTO STIMULABLE PHOSPHORS
• The emission by a substance of stored energy as light
is referred to as luminescence
• 1603 -...
Europium doped barium
fluoro halide
Red light
600nm
Trapped e-
~ x ray
exposure
When e-
returns energy is released
300-500...
• IO: barium fluorohalide material + polymer is
spread in thin layer on a polyester base
• Psp plates are available in sta...
FEATURE FILM CCD / CMOS PSP
RADIATION DOSE higher lower lower
GENERATION OF
VISIBLE IMAGE
Chemical processing Computer com...
Flat panel detectors
• Larger matrix areas with pixel size less than 100µm
• Allows direct digital imaging of larger areas...
CONE BEAM COMPUTED TOMOGRAPHY
TWO TYPES OF DETECTORS
1.X RAY image intensifier tube coupled to ccd with a
fiber optic coup...
X RAY image intensifier tube coupled to ccd with a fiber optic coupling
www.indiandentalacademy.com
XERORADIOGRAPHY
• Electrostatic imaging tech that uses modified
xerographic copying process to record images produced
by x...
Xeroradiographic plate
++ + + + + + + + + + +
Greater charge beneath thick part,
as most radiation was absorbed
Thin part ...
CT
X rays attenuated by
pt tissues
Captured by
detectors
Converted to light
Pmt/ photo diode Electric signal
Detector
elec...
First two generations:
• thalium activated sodium iodide scintillation crystal
• Photo multiplier tube ( PMT)
Limitations ...
Third generation :
• Used xenon gas ionisation chambers
• Photon interacts with gas atom by ionizing atom
• Production of ...
Fourth generation :
• Scintillation crystals : Cesium iodide
• Bismuth germinate, Cadmium tungstate
• PMT are replaced by ...
MRI
Receiver coil : a coil positioned within imaging volume & connected to
receiver circuit that is used to detect or rece...
• RF coils are used for transmitting energy and
receiving signals in MRI
Three categories: Transmit receive coil
• receive...
surface coils
• Small coils designed to image restricted regions of pts
anatomy
• Variety of shapes, sizes, Can be applied...
Z gradient – slice selection
Y gradient – phase
encoding ( divides slice
into horizontal rows)
X gradient – frequency
enco...
Ultrasonography
• Usg is a procedure that uses high-frequency sound
waves ( 1 to 20 MHz) to view internal organs and
produ...
Electrodes behave as capacitators
Voltage b/n them produce electric field
Backing block : quickly dampens
vibrations
CRYST...
Piezo electric crystals :
• Application of electric field cause a change in dimension – piezo
electric effect
• Piezo elec...
Special films
Dry Laser films
• High Contrast, High Density Dry Processing Films are
designed for use in specific manufact...
• DRY Laser emulsions are coated on both clear and
blue tinted polyester base.
• The films have a protective coat to provi...
DUPLICATING FILM
• single emulsion film
• emulsion side- shiny, other side – dull
• used to make identical copy of io/eo f...
CONCLUSION
• The limits of our senses were vastly expanded by the
fine work and the great sacrifices of dedicated pioneers...
Although ego & economics drive our
every day lives, it is ideals & ideas that
build our future….
www.indiandentalacademy.c...
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Maxillofacial imaging receptors/ dental courses

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and
offering a wide range of dental certified courses in different formats.

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Maxillofacial imaging receptors/ dental courses

  1. 1. MAXILLOFACIAL IMAGING RECEPTORS INDIAN DENTAL ACADEMY Leader in continuing Dental Education www.indiandentalacademy.com
  2. 2. INTRODUCTION • When a x ray beam passes through a pt differential attenuation of x rays by the tissues occur depending on part being examined. • Receptors device that receives & records image. • The image produced by X-rays may be captured on a film, may be viewed directly (fluoroscopy) or on a monitor with digital radiology. www.indiandentalacademy.com
  3. 3. HISTORY • The first X ray detector was the barium platinocyanide plate used by Sir Wilhelm Conrad Röentgen in his 1895 experiments in which he viewed his own hand fluoroscopically. • To make permanent records of his experiments he used a film of silver halide photographic emulsion to radiograph his wife hand www.indiandentalacademy.com
  4. 4. First nobel prize in physics was awarded to him in 1901 www.indiandentalacademy.com
  5. 5. • 14 days after discovery of x rays Friedrich Otto Walkhoff took the first dental radiograph. • He used an glass plate coated by hand with photographic silver emulsion as receptor. • Wrapped it in a rubber dam, held it in his mouth between his teeth and tongue. www.indiandentalacademy.com
  6. 6. RECEPTORS CONVENTIONAL DIRECT EXPOSURE FILMS INDIRECT EXPOSURE FILMS WITH SCREENS DIGITAL SOLID STATE DETECTORS STORAGE PHOSPHORS www.indiandentalacademy.com
  7. 7. DENTAL X-RAY FILM www.indiandentalacademy.com
  8. 8. FILM BASE • Initially glass plate was used as base • In 1914 - Cellulose nitrate base • It was quite flammable In 1924 safety film – cellulose triacetate Emulsion would crack & peel away from base when chemicals were too hot RETICULATION www.indiandentalacademy.com
  9. 9. • 1n 1960 – polyester base was developed • Polyster polyethylene terephthalate ( 0.18 mm) • Support the emulsion • Flexible , dimensionally stable • Uniformly translucent, cast no pattern • Should not absorb too much light when radiograph is viewed • Blue tint is added www.indiandentalacademy.com
  10. 10. EMULSION Two principal components 1.Photo/ radio sensitive silver halide grains 2.Vehicle matrix : • Gelatinous / non gelatinous • Even dispersion of Ag-halide grains • Ensure better adhesion of emulsion to base • Absorbs processing solutions, allow them to reach and react with Ag-halide crystals www.indiandentalacademy.com
  11. 11. • Silver halide grains ( 1 to 1.5 microns) – crystal form • Contains Ag+ , Br - / I- arranged in cubic lattice • 90 to 99% silver bromide • 1 to 10% silver iodide – added to create imperfections • Some silver ions moves into lattice – interstitial Ag+ www.indiandentalacademy.com
  12. 12. • Crystals are chemically sensitised by adding sulfur containing compounds like allylthiourea It reacts with ag halide – forms silver sulfide • Usually located on surface of crystal sensitivity speck www.indiandentalacademy.com
  13. 13. Single Emulsion : • Better image detail • But less dimensional stability Double Emulsion Film : • Advantages: less radiation is required to produce exposure ( ½ exposure) • Dis. Adv : image is created on both emulsions - superimposed – slight blurring of edges www.indiandentalacademy.com
  14. 14. DIRECT EXPOSURE FILM/ NON SCREEN FILMS • Exposed directly to x- rays • Commonly used for io • Require more exposure factors • Prolonged processing time • Relatively thicker emulsion • Image detail is excellent www.indiandentalacademy.com
  15. 15. INTRAORAL FILM PACKET Outer plastic wrapper Protects film from light, saliva, mechanical damage Identification dot Used for film orientation Film is encased in protective black paper wrappers Protects film base from light, saliva, damage during opening Lead foil Shields film from back scatter radiaion Reduces pt exposure Embossed pattern www.indiandentalacademy.com
  16. 16. FILM SIZES FOR IOPAR O 1 2 22 x 35 mm Small children 31 x 41 mm Standard film size for adults 24 x 40mm Children Anterior teeth www.indiandentalacademy.com
  17. 17. BITE WING VIEW • Size 0, 1 in children • Size 2 – for adults • 27 x 54 mm Extended size bitewing www.indiandentalacademy.com
  18. 18. OCCLUSAL VIEW • Used to visualise large areas of maxilla & mandible 57 X 76 THREE TIMES LARGER THAN SIZE 2 www.indiandentalacademy.com
  19. 19. SPEED • Radiographic speed refers to amount of radiation required to produce an image of standard density. • Expressed as reciprocal of exposure in roentgens required to produce an optical density of 1 above gross fog • Speed is controlled by size & shape of Ag-halide crystals & silver content. www.indiandentalacademy.com
  20. 20. FILM SPEED GROUP SPEED RANGE ( RECIPROCAL OF ROENTGENS) (1) ISO speed group classification for dental films (2) A 1.5 - 3 B 3 - 6 C 6-12 7.0 to 14.0 D 12-24 14 to 28 E 24-48 28 to 56 F 48-96 56 to 112 1. National Council On Radiation Protection And Measurements, Report No 145, Appendix E, 2004 2. Ludlow, Platin, Mol. Characteristics Of Kodak Insight , An F-speed Intra Oral Film. OOOE, 2001, 91: 120-129 www.indiandentalacademy.com
  21. 21. D / ULTRA SPEED /US E P / EKTA PLUS FILM / INSIGHT F/ INSIGHT GLOBULAR AG- HALIDE CRYSTALS DIAMETER : 1.0MICRO METER T- GRAIN EMULSION FLAT TABULAR CRYSTALS 1.8 MICRO METER. T- GRAIN EMULSION FASTEST FILM IODIDE IS PRESENT IODIDE IS ABSENT IODIDE IS ABSENT OPTIMAL DOSE – 0.5 Gy 0.25 Gy , 30 to 50% < D DOSE 70% < D, 20% < E www.indiandentalacademy.com
  22. 22. Conventional silver-halide crystals are pebble shaped KODAK T-GRAIN Emulsion crystals Are flat INSIGHT ULTRA SPEED Coating weights per film side (mg/Cm2 ) Film type Silver Bromide Iodide Emulsion vehicle Overcoat vehicle Insight (F) 0.8-1.1 0.6-0.75 0 0.6-0.8 0.1-0.2 ULTRASPEED (D) 0.6-0.9 0.6-0.75 0.0-O.02 0.4-0.7 0.1-0.2www.indiandentalacademy.com
  23. 23. Fast film requires relatively low exposure to produce an optical density of 1… Slope of curve – contrast Speed – location of curve on log exposure scale www.indiandentalacademy.com
  24. 24. PACKAGING : • Single film packet • Double film packet • SELF DEVELOPING FILMS www.indiandentalacademy.com
  25. 25. SCREEN FILMS • Used for extraoral views • manufactured with dyes in the emulsion that absorb specific wavelengths of visible light. • Always used in combination with intensifying screens. ( x rays to light ) Screen Photon Light Film www.indiandentalacademy.com
  26. 26. • Light photons are absorbed by emulsion, only outer layer is affected. • so thin emulsion on 2 sides is preferred rather than thick emulsion on one side. On x ray exposure Entire crystal glows, not only area exposed &divergence of light rays Area of exposure on film > original area of crystal Less resolution www.indiandentalacademy.com
  27. 27. • Standard silver halide crystals are inherently sensitive to uv, violet, blue light ( 300-500nm) SLOW SCREENS • calcium tungstate • Barium lead sulphate screens FAST SCREENS : • Rare earth screens ( 1970’s) emit light in green, yellow, blue, ultra violet spectrum • So sensitising dyes are added • Green sensitive film – ortho film • Red sensitive film – pan film (panchromatic) Spectral sensitivity www.indiandentalacademy.com
  28. 28. Manufact urer Name phosphor Spectral emission film Speed class Du pont CRONEX PAR SPEED Cawo4 BLUE CRONEX 4 100 CRONEX HI PLUS Cawo4 BLUE CRONEX 4 250 QUANTA DETAIL YTaO4:Tm UV / BLUE CRONEX 4 100 QUANTA FAST DETAIL YTaO4: Nb UV/ BLUE CRONEX 4 400 KODAK LANEX FINE Gd2O2S:Tb Neutral dye GREEN ORTHO G 100 LANEX MEDIUM Gd2O2S:Tb Neutral dye GREEN ORTHO G 250 LANEX REGULAR Gd2O2S:Tb Yellow dye GREEN ORTHO G 400 www.indiandentalacademy.com
  29. 29. • Kodak ortho G film is replaced by T-Mat G film • Can be used with all green-emitting rare-earth intensifying screens such as Kodak Lanex screens • Increased detail by reduced crossover without a change in film speed www.indiandentalacademy.com
  30. 30. CROSSOVER To reduce crossover by • adding a dye to the film base • Changing shape of crystals. • ( tabular)..increase light absorption www.indiandentalacademy.com
  31. 31. Super HR-U is a high contrast green sensitive x-ray film for use with green-emitting rare earth screens. The New all- around x-ray film for general applications. www.indiandentalacademy.com
  32. 32. HIGH CONTRAST , MEDIUM SPEED FILMS – SKULL RADIOGRAPHY FAST FILMS – LESS RADIATION EXPOSURE – PANORAMIC IMAGING LESS CONTRAST, WIDE LATTITUDE – CEPHALOMETRY Standard “inches”: • 8” x 10” • 10” x 12” • 11” x 14” • 14” x 17” Metric: • 18cm x 24cm • 24cm x 30cm • 30cm x 35cm • 35cm x 43cm FILM SIZES www.indiandentalacademy.com
  33. 33. • 1977- digital subtraction angiography,- first form of digi imaging • 1980 – computed radiography ( storage phosphor plates) • 1987 by Francis Mouyen - 1ST digital X-ray sensors for use in dentistry. • Radio Visio Graphy (RVG) By Trophy Radiologie ( Kodak Company, Rochester, N.Y. ) • Io use Storage phosphor plate in 1991 DIGITAL RECEPTORS www.indiandentalacademy.com
  34. 34. • SOLID STATE DETECTORS • CHARGED COUPLE DEVICES (CCD) • COMPLEMENTARY METAL OXIDE SEMICONDUCTORS • FLAT PANEL DETECTORS • PHOTO STIMULABLE PHOSPHORS www.indiandentalacademy.com
  35. 35. • Electronic elements of a digital sensor are arranged in a regular grid of rows and columns • Pixel refers to the spatial distribution of the rectangular 2D grid of sensor elements • Each pixel has a row and column that uniquely identifies its location in matrix. www.indiandentalacademy.com
  36. 36. Exposure of sensor with x rays Release of electron from crystals Production of electronic charge each pixel of sensor, absorption of x ray generate a small voltage Fluctuation b/w minimum and max Analog signal ADC SAMPLING ( small voltages are grouped as 1 value) QUANTIZATION (Every sampled signal is assigned a value) Computer displays a shade of gray according to no assigned www.indiandentalacademy.com
  37. 37. Charged couple device • Thin wafer of silicon - crystals are in pixel matrix • On x ray exposure - covalent bonds b/n silicon atoms are broken - e- hole pairs. e- moves to most positive potential in device - "charge packets.“ ( ~pixel)www.indiandentalacademy.com
  38. 38. Image is read by transferring each row of pixel charges from one to other…Bucket brigade pattern. At end of row - Transferred to read out amplifier – voltage – ADC www.indiandentalacademy.com
  39. 39. • RVG – by Trophy • Sens-a-Ray by Regam • Visualix by Gendex • Flashdent by Villa • Sidexis by Siemens • CDR by Schick www.indiandentalacademy.com
  40. 40. Complementary metal oxide semi conductors • Silicon -based , differ from CCDs in the way that pixel charges are read • Each pixel is isolated from its neighboring pixels and is directly connected to a transistor. • The voltage in each transistor can be addressed separately, read by the frame grabber, and then stored and displayed as a digital gray value www.indiandentalacademy.com
  41. 41. PHOTO STIMULABLE PHOSPHORS • The emission by a substance of stored energy as light is referred to as luminescence • 1603 - chinese found Bolognese stone (barium sulfate)which glowed persistently after exposure to sunlight • Consists of reusable imaging plate coated with phosphor instead of sensor • Flexible, fits into the mouth as a conventional film www.indiandentalacademy.com
  42. 42. Europium doped barium fluoro halide Red light 600nm Trapped e- ~ x ray exposure When e- returns energy is released 300-500nm(green) Fiber optics light – electric energy www.indiandentalacademy.com
  43. 43. • IO: barium fluorohalide material + polymer is spread in thin layer on a polyester base • Psp plates are available in standard io sizes • panoramic and cephalometric imaging. www.indiandentalacademy.com
  44. 44. FEATURE FILM CCD / CMOS PSP RADIATION DOSE higher lower lower GENERATION OF VISIBLE IMAGE Chemical processing Computer computer, scanning laser IMAGE VIEWING delayed real time on computer delayed, computer monitor RESOLUTION 16 -20 lp/mm 8- 10 lp/mm 6-8 lp/mm CONSTRUCTION thin, flexible thick, rigid thick, rigid ACTIVE AREA entire surface of film smaller than size of sensor entire surface LIFE SPAN one use reusable > 10,000? reusable unknown IMAGE ENHANCEMENT unchanged Multiple operations. Density, contrast, magnification +, - STORAGE pt record Variety of archiving methods, server,zip, cd www.indiandentalacademy.com
  45. 45. Flat panel detectors • Larger matrix areas with pixel size less than 100µm • Allows direct digital imaging of larger areas of body • Two methods • Indirect using intensifying screens – efficient • Direct using photoconducting material ( selenium) – high resolution www.indiandentalacademy.com
  46. 46. CONE BEAM COMPUTED TOMOGRAPHY TWO TYPES OF DETECTORS 1.X RAY image intensifier tube coupled to ccd with a fiber optic coupling 2. Flat panel detectors Cesium iodide scintillation crystals Photodiode Thin film transistor made of amorphous silicon X rays Light Electrical signal www.indiandentalacademy.com
  47. 47. X RAY image intensifier tube coupled to ccd with a fiber optic coupling www.indiandentalacademy.com
  48. 48. XERORADIOGRAPHY • Electrostatic imaging tech that uses modified xerographic copying process to record images produced by x rays • Selenium coated photo receptor which is uniformly charged. • Available in sizes of no.1 & 2 films • On x ray exposure , selective discharge of charge occurs • Proportional to radiation striking the plate. • Charge pattern on plate – latent imagewww.indiandentalacademy.com
  49. 49. Xeroradiographic plate ++ + + + + + + + + + + Greater charge beneath thick part, as most radiation was absorbed Thin part : penetrating radiation dissipates more charge At interface electrostatic forces are distorted.resulting electric field produce enhancement of edges. •Periodontal and periapical assesment to show good bony details •Sialography to show fine duct structures •Cephalometry to show required soft and hard tissues on filmwww.indiandentalacademy.com
  50. 50. CT X rays attenuated by pt tissues Captured by detectors Converted to light Pmt/ photo diode Electric signal Detector electronics digital signal Image processor Complex computational process Real time, high resolution images Scintillation crystals www.indiandentalacademy.com
  51. 51. First two generations: • thalium activated sodium iodide scintillation crystal • Photo multiplier tube ( PMT) Limitations : • NaI hygroscopic • Has long after glow, (long scan time ) • PMT are fairly big, so cannot easily fit into large array of detectors in current ct www.indiandentalacademy.com
  52. 52. Third generation : • Used xenon gas ionisation chambers • Photon interacts with gas atom by ionizing atom • Production of electron – ion pair (e- – anode) • e- near anode produce electric current (signal from detector) • Current is directly proportional to intensity of radiation. • Dis adv : inefficiency • Due to low density of gases , many photons pass through chamber undetected. www.indiandentalacademy.com
  53. 53. Fourth generation : • Scintillation crystals : Cesium iodide • Bismuth germinate, Cadmium tungstate • PMT are replaced by silicon photo diodes • Photo diode converts light signal into electron flow( current) that is proportional to intensity of light signal Adv: small size • Greater stability • Low cost www.indiandentalacademy.com
  54. 54. MRI Receiver coil : a coil positioned within imaging volume & connected to receiver circuit that is used to detect or receive mr signal. www.indiandentalacademy.com
  55. 55. • RF coils are used for transmitting energy and receiving signals in MRI Three categories: Transmit receive coil • receive only coil & transmit only coil • Volume coil • Bird cage coil ( T/R) • Quadratured coil • Single turn solenoid • Surface coil • Surface coil NMR, saddle coil, • Phased array coil, linear polarized coilwww.indiandentalacademy.com
  56. 56. surface coils • Small coils designed to image restricted regions of pts anatomy • Variety of shapes, sizes, Can be applied to roi • Has a good SNR for superficial tissues Whole volume coils • Used for surrounding either the whole body or a specific region • Used for the phantom of bigger volume • Has better magnetic field homogeneity than surface coil www.indiandentalacademy.com
  57. 57. Z gradient – slice selection Y gradient – phase encoding ( divides slice into horizontal rows) X gradient – frequency encoding (divides slice in to vertical columns ) www.indiandentalacademy.com
  58. 58. Ultrasonography • Usg is a procedure that uses high-frequency sound waves ( 1 to 20 MHz) to view internal organs and produce images of the human body Electric impulses high frequency sound waves Tissues interact with different acoustic impedance Sonic waves reflected by tissues as echos electric signal Transducer Transducer held against body Amplified, processed, displayed on a tv monitor/ oscilloscope Received by Transducer www.indiandentalacademy.com
  59. 59. Electrodes behave as capacitators Voltage b/n them produce electric field Backing block : quickly dampens vibrations CRYSTAL VIBRATES AND GENERATES SOUND WAVES Acoustic insulator : rubber/ cork Prevents sound from passing into housing Plastic housing Parts of transducer www.indiandentalacademy.com
  60. 60. Piezo electric crystals : • Application of electric field cause a change in dimension – piezo electric effect • Piezo electric materials are made up of inumerable dipoles in geometric pattern • Barium titanate , lead zirconate titanate Voltage cause realignment of crystals Sound waves Echos carry energy Physical compres sion of crystals Induces voltage Us signal Generation Interacts with tissues Realign ment of dipoles www.indiandentalacademy.com
  61. 61. Special films Dry Laser films • High Contrast, High Density Dry Processing Films are designed for use in specific manufactures Imagers. • They produce very highest diagnostic grayscale hardcopy images.(D-Max greater than 3.0) • low fog and excellent stability. • Ideal for multi-modality imaging, including Computed Radiology, CT, MRI, Digital X-Ray and Ultrasound. www.indiandentalacademy.com
  62. 62. • DRY Laser emulsions are coated on both clear and blue tinted polyester base. • The films have a protective coat to provide maximum protection from scratches and abrasions. www.indiandentalacademy.com
  63. 63. DUPLICATING FILM • single emulsion film • emulsion side- shiny, other side – dull • used to make identical copy of io/eo film. • Used only in dark room. • Emulsion side must contact radiograph during process • A small photographic printer with uv light is used. www.indiandentalacademy.com
  64. 64. CONCLUSION • The limits of our senses were vastly expanded by the fine work and the great sacrifices of dedicated pioneers, not only in radiology , but also in physics, mathematics, and engineering. • By the second half of the 20th Century ,maxillofacial radiologists had several great diagnostic tools that expanded their abilities to examine. These devices enabled physicians to reach precise diagnosis and to produce excellent treatment plans www.indiandentalacademy.com
  65. 65. Although ego & economics drive our every day lives, it is ideals & ideas that build our future…. www.indiandentalacademy.com

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