Digital Imaging

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Digital Imaging

  1. 1. “A picture is worth a thousand words”“Knowledge is valuable”“Don’t waste it”
  2. 2. •INTRODUCTION•USES, ADVANATAGES, DISADVANTAGES•EQUIPMENT•ANALOG TO DIGITAL CONVERSION•DIGITAL DETECTOR SYSTEMS & CHARACTERSTICS•DIGITAL IMAGE DISPLAY•DIGITAL SUBSTRACTION RADIOGRAPHY•CONCLUSION•REFERENCES
  3. 3.  Technological advancement-Cassetteless system Method of capturing radiographic Image Sensor Break in Electronic pieces Present and Store Computer
  4. 4.  Detect lesions, diseases, conditions Information during root canal procedures, implants Evaluate growth & development Changes secondary to caries,trauma, periodontal diseases Progress of treatment
  5. 5.  Superior gray scale resolution Easy reproducibility Reduced exposure to radiation Detection of defects & 3D visualization of dental structures Effective patient education tool No loss of quality due to chemical processing Lower equipment & film cost Enhancement of diagnostic image
  6. 6.  No Darkroom Transmission of Images for Consultation Instant Viewing of Images
  7. 7.  Initial set up costly Sensor size thicker than intraoral film Infection control difficult Receptors susceptible to rough handling and costly to replace Legal considerations
  8. 8. FILM BASED IMAGING DIGITAL IMAGING Density-overall degree of  Brighteness-equivalent darkening Latitude- measure of range  Dynamic range: number of of exposure-distinguish shades of gray i.e pixel density Film speed-faster film-less  Linearity-direct radiation relationship b/n exposure & image density Contrast-diff in density-  Contrast resolution-small areas of radiograph diff in density
  9. 9.  Resolution-distinguish b/n  Spatial frequency-measure of resolution-lines pairs/mm small objects that are close  Background electronic noise: together small electric current that Radiographic mottle-app conveys no information but of uneven density of an serves to obscure electronic exposed film/graininess signal Sharpness- ability to define  Signal to noise ratio- an edge/display density Fraction of output signal≈ boundaries diagnostic information(signal) + signal (no information-noise)
  10. 10. INTRAORAL EXTRAORAL Direct  PhotoStimulable Phosphor Indirect Based radiography (PSP)- Storage phosphor imaging computed radiography  Charged couple device (CCD) systems-solid state linear array of photoiodides
  11. 11. DIRECTINDIRECT
  12. 12. • Dental x-ray unit-radiation source Same for conventional but adapted to 1/100th second exposure time• Sensor-intraroral –no film, extraoral-PSP plates• Computer-DIGITAL IMAGE DISPLAY
  13. 13.  Numeric format of image content & discreteness• Spatial distribution of picture elements(pixels)• Different shades of gray of each of the pixels 2020 1510 10 C10 5 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Conventional-continuous Digital-inc /dec density spectrum
  14. 14.  Small box or well-electrons are produced by x-ray exposure-deposited Row/column-coordinate in matrix Digital equivalent of a silver crystal Ordered arrangement
  15. 15.  Sampling- small range of voltage values grouped together-single value Quantization- every sampled signal is assigned a value Stored in computer & represent image- computer organize pixels-gives shade of gray-correspond to no. assigned value during quantization
  16. 16.  CONTRAST RESOLUTION SPATIAL RESOLUTION DETECTOR LATITUDE DETECTOR SENSITIVITY
  17. 17. • Ability – distinguish - densities• Interaction of attenuation characteristics of tissues being imaged• Ability of computer display to portray diff in density• Ability of observer to recognize differences Noise- densities captured limited by inaccuracies in image acquisition
  18. 18.  To distinguish fine detail Limit of resolution-function of pixel size Resolution measured- units of line pair per millimeter LINE PAIR(lp) - line & its associated space- lp/mm 2 pixels required to resolve a line pair
  19. 19.  Ability of imaging receptor to capture a range of X-ray exposure Full range of densities – gingiva to enamel PSP receptors – larger latitude CCD & CMOS-similar to film-enhanced by contrast & brightness
  20. 20.  Sensitivity of detector to respond to small amt of radiation Factors : detector efficiency ,pixel size, noise
  21. 21.  Charge Coupled Device ( CCD) Complementary Metal Oxide Semiconductors(CMOS) Photostimulable Phosphor Plates (PSP) Flat Panel Detectors(FPD)
  22. 22.  Solid state detector–thin wafer of silicon chip + electronic circuit Sensitive to xrays/light Enclosed in plastic housing(protect oral environment) Electronic cable/wire system-fiberoptic cable- sensor attached to computer-ADC Length-8-35 feet
  23. 23.  Wireless/cordless system-cable connection replaced by micowave transmittor Pixel size- 20 to70 microns-307,200 pixels CCD more sensitive to light than X-rays Layer of scintillating material (Gadolinium oxybromide)coated on the CCD directly/coupled to surface – fiber optics-inc xray absorption efficiency Linear array of Pixel = OPG & Ceph More time - complete scan
  24. 24. X radiation breaks covalent bonds b/n silicon atom – electron hole pairs“charge packets”-positive potential Each packet = one pixel Charge pattern = latent image “Bucket bridge” fashion-row of pixel charges to next End of row-as voltage-Charge transmitted - ADC
  25. 25. High Resolution = 22.5 Standard = 45 Standard High Standard & High Resolution #2 #1 #0
  26. 26.  Silicon based semiconductors-pixel isolation from neighboring pixel-directly connectedCharge transferred to transistor as small voltage Read by Frame Grabber Stored and displayed as digital gray value
  27. 27.  Digital cameras, digital dental radiography, CPU chips 25 %more resolution, cheap, durable
  28. 28.  Similar to CCD, no computer used CID xray sensor, cord, plug-inserted into light source on camera platform-system monitor- seconds Same as intraoral camera Color printer
  29. 29.  Absorb & store energy from xray- stimulated by light- app wavelenghth-release energy as light(PHOSPHORESCENCE) “Europium doped” barium fluorohalide Crystal lattice- barium+iodine+chlorine+bromine Europium-imperfection in lattice F-centre
  30. 30. Exposed to sufficient energy source Valence electrons absorb energy-move in conduction band Electron-halogen vacencies-trapped Latent image Red light 600nm-electrons released by barium fluorohalide to conduction band When electron returns to europium ion, energy is released in green spectrum b/n 300 and 500 nm Red filter at photomultiplier tube selectively removes stimulating light, & green light converted to voltageVoltage signal quantified by ADC, stored & displayed as digital image
  31. 31. (Europium Activated Barium FluoroHalide) BaFX:Eu , (X= Cl, Br, or I)
  32. 32.  PSP plates –sizes as intraoral and extraoral film PSP plate -erased before use - ghost images Latent image on PSP plate can be read by: Stationary plate scans - rotating multifaceted mirror reflecting beam of red laser light.( fast & slow scan direction) Rotating plate scans – rotation of drum past a fixed laser provides a scan Resolution of PSP systems determined by: Thickness of phosphor material Diameter of the laser beam
  33. 33.  Plates processed quickly Susceptible to bending & scratching – permanent artifacts in receptor – obscure information of potential diagnostic value Semidark environment- plate handling Red light- not safe
  34. 34. Casette and PSPPSP digitizer Workstation
  35. 35.  Provide large matrix areas - pixel sizes <100 microns Direct digital imaging-Larger areas of body-headTwo types: Indirect detectors sensitive to visible light intensifying screen converts x-rays energy to light Direct detectors- photoconductor material(selenium)Similar to silicon, high atomic no-more absorption
  36. 36.  Thin film transistor (TFT)-laptop, flatpanel computers Digitizes, processes, stores-immediate viewing-good speed Dental procedures-root canal, implants Hardcopy-printed Transmitted electronically
  37. 37.  Spilt screen technology-multiple images on same screen Magnification-linear & angular measurements Image restoration-raw data received- corrected-before visible image on screen Image enhancement-brightness & contrast, sharpness, colour
  38. 38.  Image analysis-extract non pictorial information-segmentation Image compression-reducing no. of digital files.lossy- irreversible Image synthesis-CT, MRI, PET-acquired data- multiple projections-new image-sectioning
  39. 39.  Tomosynthesis-selective focusing on an arbitrary slice-through object-shift & adding basic projection Localized computed tomography(micro CT radiography, Microtomography)-invitro-study of mineral tissues-complex facial fracturesWork as CT
  40. 40.  Enhances the mineral changes that have occurred over time against a homogenous background of unchanged anatomy Subtraction of gray scales-b/n 2 images Change-light & dark areas-loss of bone(dark area), gain (light area)
  41. 41.  Subtle changes in bone-before & after periodontal therapy Periapical region Condylar changes
  42. 42. Subtraction radiography. The image to the right is the result of thesubtraction of the second image from the first image. Note the dark area indicating bone loss (red arrow) that was not visible on the original image
  43. 43.  The Digital Imaging and Communications in Medicine (DICOM) Standard is a detailed specification that describes semantics and syntax for exchanging images and associated information. The standard applies to the operation of the interface which is used to transfer data in and out of an imaging device.
  44. 44. DICOM Display Workstation Storage, Query/Retrieve, Study Component LiteBox Query/Retrieve Results Management DICOM AcquisitionMedia Exchange Print Management DICOM Query/Retrieve, Archive Patient & Study
  45. 45.  Film images->digital format->enhanced Better quality 2 parts-drum scan with reading & writing units Minicomputer with subsystems Ad-overall improved contrast, trabecular fine marrow spaces, low density=high density Disad-artifacts & noise
  46. 46.  Microscopic imaging-single frame digital camera-attach dental microscope-high quality images Intraoral cameras-photo of single tooth, procedure, documentation & patient education barrier sheath-contamination
  47. 47.  Fiberoptic imaging-endoscope-root canals-0.7 mm & 11.8 mm dia light fiberoptic probe- insert in root canal-disposable-optical grade plastic PSP radiography-trial file length Digital photography
  48. 48.  Oral Radiology, Principles and interpretation, 5th edition – White & Pharoah Text book of Dental and Maxillofacial Radiology, Freny. R.Karjodkar Essentials of Dental Radiography & Radiology, III edition, Eric Whaites

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