digital radiography

1. QUERIES
1.Acoustic enhancement : when no echoes are reflected and
sound is allowed to pass through allowing echoes deep into
the anechoic structures to be visible .
2. Anechoic – structiures appear black withut echoes

2. INTRAORAL DIGITAL RADIOGRAPHY
SEMINAR -12
PRESENTED BY
N.NARMATHA
11 YEAR PG

3. INTRODUCTION
• Digital radiology has overtaken conventional screen-film
radiography - in the mid-1980s
• The dawn of the digital era in dental radiography came in
1987 - radio visiography (RVG) - Dr. Francis Mouyen

4. • CCD image sensor technology made the RVG digital
radiography system a reality
• Main factor distinguishing digital systems from conventional
is their response to incident radiation

5. ANALOG VERSUS DIGITAL
• Term digital - numeric format of the image content and its
discreteness
• Conventional film images - considered an analog medium

6. Digital images are numeric and discrete in two ways:
(1) spatial distribution of the picture elements (pixels)
(2) different shades of gray of each of the pixels
- Consists of a large collection
of individual pixels organized in
a matrix of rows and columns

7. Digital image formation - beginning with analog processes
At each pixel, the voltage can fluctuate between a minimum
and maximum value and is therefore an analog signal

8. ANALOG -TO DIGITAL CONVERSION (ADC)
• Sampling
• Quantization
Sampling - small range of voltage values are grouped together as
a single value
Quantized - every sampled signal is assigned a value - stored in
computer - represent the image

9. Computer organizes the pixels - displays a shade of gray that
corresponds to the number - assigned during the quantization step

10. • Solid-state
• Photostimulable phosphor technology
DIGITAL IMAGE RECEPTORS

11. SOLID-STATE DETECTORS
• Collect the charge generated by x rays in a solid
semiconducting material
• Rapid availability of the image after exposure
• Enclosed within a plastic housing
• Incorporate an electronic cable / radiofrequency transmitter
• Pixel size varies from 20 to 70 micrometers
• Three types of solid-state sensors are in common use

12. COMPONENTS OF SOLID STATE DETECTORS

14. CHARGE-COUPLED DEVICE
• Charge-coupled device (CCD) - introduced in 1987 - first
digital image receptor to be adapted for intraoral imaging
• Uses a thin wafer of silicon - image recording
• The silicon crystals are formed in a picture element (pixel)
matrix

15. LINEAR ARRAY

16. AREA ARRAY

17. Radiation
covalent bonds between silicon atoms are broken
electron-hole pairs
Number of electron-hole pairs proportional to amount of exposure

18. • Electrons - attracted toward most positive potential in the device -
“ charge packets ” - Each packet - one pixel
• The charge pattern - latent image
Gadolinium oxybromide compounds -
scintillators

19. • The image is read by transferring each row of pixel charges
from one pixel to the next in a “ bucket brigade ” fashion

21. Complementary Metal Oxide Semiconductors
• Detectors are silicon-based semiconductors
• Fundamentally different from CCD in the way that pixel charges
are read

22. • Each pixel is isolated from its neighbouring pixels and is
directly connected to a transistor
• Electron-hole pairs are generated
• Charge is transferred to the transistor as a small voltage
• Stored and displayed as a digital gray value

25. FLAT PANEL DETECTORS
• Flat panel detectors are being used for medical imaging
• Detectors provide relatively large matrix areas with pixel sizes
• < 100 μ m - allows direct digital imaging of larger areas of the
body
Flat panel detector Gadolinium oxysulfide - portable

26. Flat panel detectors types:
1.Direct
2. Indirect
Key terms
1.Scintillator
2.photodiode
3.Photoconductor
4.Thin film transistor

29. PHOTOSTIMULABLE PHOSPHOR•
• PSP plates absorb and store energy from x rays and then release
this energy as light (phosphorescence) when stimulated by
another light of an appropriate wavelength
• PSP material - “ europium doped” barium fluorohalide
• Barium in combination with iodine, chlorine, or bromine -
crystal lattice
• addition of europium (Eu + 2 ) creates imperfections in this
lattice

30. Indirect PSP Sensors

33. STATIONARY PLATE SCANS

34. ROTATING PLATE SCANS
• 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 scan direction
allows image data to be acquired line by line

35. DIGITAL DETECTOR CHARACTERISTICS
CONTRAST RESOLUTION
Ability to distinguish different densities in the radiographic image
function of the interaction of the following:
• Attenuation characteristics of the tissues imaged
• Capacity of the image receptor to distinguish differences in
numbers of x-ray photons coming from different areas of the
subject

36. • Ability of the computer display to portray differences in
density
• Ability of the observer to recognize those differences
• Current digital detectors capture data at 8, 10, 12, or 16
bits.

38. SPATIAL RESOLUTION
• Capacity for distinguishing fine detail in an image
• Measured and reported in units of line pairs per millimeter
• Line and its associated space – line pair

39. DETECTOR LATITUDE
• The ability of an image receptor to capture a range of x-
ray exposures is termed latitude
• The useful range of densities in film radiography is two
orders of magnitude- 0.5 to 2.5.
DETECTOR SENSITIVITY
• The sensitivity, or speed, of a detector is its ability to
respond to small amounts of radiation

40. DIGITAL IMAGE VIEWING
• Cathode ray tube display

41. • Thin film transistor display
• Electronic display considerations
• Hard copies
• Film printers
• Paper printers

42. • Image processing
• Image restoration
• Image enhancement
• Brightness and contrast
• Color

45. DIGITAL SUBTRACTION RADIOGRAPHY

46. • IMAGE ANALYSIS
• Measurement
• Diagnosis
• Image Storage
• Systems Compatibility

47. Common problems in digital image receptor exposure,
processing, and handling
NOISY IMAGES

48. Non uniform Image Density

49. Distorted Images

50. Double Images

51. Damaged Image Receptors

52. Thank you

53. REFERENCES
1.Textbook of Dental and Maxillofacial Radiology Freny R
Karjodkar
2. Oral radiology principles and interpretation Staurt C. White
Michael J. Pharoah 11 TH EDITION