This document provides an overview of digital radiography, including its history and key components. Digital radiography converts analog X-ray images to digital files using various detection methods. These include computed radiography using photostimulable phosphor plates, as well as direct digital radiography techniques like CCD and flat panel detectors that directly capture X-ray data without image plates. The digital files then undergo processing to enhance image quality and enable analysis.

1. DIGITAL
RADIOGRAPHY
By-
Shashi Bhushan
BMT –Imaging Sciences (IIIrd Year)
PRN- 07040121043

2. OVERVIEW
 History
 Digital concept
 Pixel & resolution
 Physical parameter of detectors
 Noise
 Luminescence
 Digital radiography-- CR &DR
 Image Plate
 Digitizing an image
 CCD & flat panel

3. HISTORY
 In 1981, Fuji Photo Film Co., Ltd introduced the concept
of computed radiography employing photostimulable
phosphor plate technology.
 The medical physics groups at the University of
Wisconsin and the University of Arizona independently
initiated studies of DF in the early 1970s.
 Although there are several approaches to DR, the
approach developed in the late 1970s to complement
computed tomography has enjoyed the widest
application, invented by Godfrey Hounsfield.
 Practical application in medical imaging started in the
1990s.

4. TERMINOLOGY
Pixel – picture element,
-The 2D continuous image a (x,y) is divided
into rows and columns. The intersection of
a row and a column is called a pixel.
Voxel – volume element , all 3 co-ordinates
(x,y,z)
- have height and width along
with depth.

5.  Resolution – ability to distinguish between two
adjacent object
 Axial resolution
Spatial resolution
 Lateral resolution
 Contrast resolution – ability to distinguish between two
objects with different density.

7. ANALOG
VS
DIGITAL
Digital –related to digit.

8. Analog image
Continuous image
eg; CXR
For human viewing
Each point have
brightness, density ,
colour
Digital image
Numerical
representation of an
image
For computer system
Each definite point
have numbers

9. Analog Vs Digital

10. Luminescence
Two type –
- Fluorescence (instant glow)
- Phosphorescence(after glow)
•There should be luminescent material
CsI, Gd2O2S etc
•Emits light on absorption of energy

11. Valence Band
Conduction Band
Valence Band
Forbidden zone
Electron Trap
Energy Bands in a fluorescent material
Concept of Luminescence

12. (Electron) (Hole)
Electron Trap
Valence Band Valence Band
Valence Band
Conduction Band Conduction Band Conduction Band
Radiation
Phosphorescence Principle

14. CONCEPT OF DIGITAL RADIOGRAPHY
 Process of making digital image from analog image with the
help of ADC.
 Classification –on the basis of process of formation of image.
Digital radiography
Indirect radiography
e.g.- CR
direct radiography
e.g. -USG, CT, MRI,
FLAT PANNEL
&CCD

15. COMPUTED RADIOGRAPHY (CR)
 Marketing term for photo stimulable phosphor(PSP)
imaging system.
 Principle – Photo stimulable luminescence
 Imaging plate(IP) containing storage phosphor is
exposed to X-rays & latent image is trapped by the
plate & is read by laser scanner by ADC machine.

16. Sequence

17. COMPONENT OF CR
 Cassettes with image plate.
 Identification station.
 Digitizer .
 Processing station.

18. CASSETTES
 Hold/ protect the image plate.
 Receives and hold the image identification data

19. IMAGE PLATE
EBC coat
Phosphor layer
Adhesive layer
Black PET layer
Laminate layer
BaFBr:Eu

20. LAYERS OF IP
 EBC coat
 Protective layer-against mechanical or chemical damage
 Ensures long life

 Phosphor layer
 Sensitive layer
 formation of latent image
 Adhesive layer
 Black PET layer
 Base layer/ support layer
 Laminate layer
 Protect IP during stacking of no. of IP

21. IMAGE PLATE
Formation of latent image on IP.
 Sensitive layer – phosphor layer
 Made of BaFX:Eu2+ , (X= Cl, Br, I)

22. Advantages of IP –
- Image plates can be reused of thousands of times for exposure
to get an image.
- Imaging plate has high exposure latitude, means any exposure
can give the image.
- A valuable characteristic of the IP is its extreme dynamic range.
Disadvantage of IP-
- IP is costly.
- Improper handling can give rise to artifacts.
-The latent image is lost if it is nor processed in time i.e.
Approx. 48 hours after exposure

23. IDENTIFICATION STATION

24. DIGITIZER
 Digitizer are responsible for converting the analog
image(latent image) into a digital image.

25. COMPONENT OF A DIGITIZERS
 Input/output slot
 Cassette unit
 IP transport units
 Scan unit
 Eraser unit
 CPU assembly
 Power unit

26. PROCESS IN DIGITIZER
Cassette moved into reader unit
Image plate is scanned by the laser unit
Laser light stimulates the emission of trapped energy in the form
of visible light
Collected by fiber optic light guide and allows to strikes the PMT
to produce electronic signal
Electronic signal digitized & stored
Plate exposed to white light

28. PROCESSING STATION
 Compose of computers.
 Provides user interface.
 Make the image for post processing
- rotation
-zooming
- contrast setting
-grey scale inversion
-measurement
-image orientation -

29. Muscle Bone
CR Plate
X-rays
X-ray tube
Workflow of CR

30. Thin
Thick
CR Plate
X-rays
X-ray tube

31. Image reader
Laser light
Photomultiplier Tube
Image Processor

32. Photo Multiplier Tube
Light
Electrical signals are converted
to Digital signals and fed to
the image processor
Image Processor
Light signal is converted to electrical
signal
Analog digital converter

34. ADVANTAGE OF CR
 No chemical process
 Fast acquisition of image thus saves time
 Low exposure to produce image reduces
occupational dose
 No darkroom hence less place for installation
 Image can be enhanced
 Rarely requires retake
 Altering the contrast we can study the image at
different depth in single exposure
 IP can be used for thousands time.
Disdvantage of CR
•IP are expensive
•Can be easily damaged
•It can produce artifact due to repetition of use of IP

35. DIGITIZING THE IMAGE
 Converting analog image into numerical
data for processing by the computers. With
the help of ADC ie; digitization.
 3 steps-
 Scanning
 Sampling
 quantization

36. DIGITIZING THE IMAGE
1. Scanning – formation of grid- division of picture into
small region i.e; pixel.
2. Sampling – measuring the brightness of the pixels.
3. Quantization- assigning integer(0,-ve,+ve) to the
brightness value.

38. DIGITAL IMAGE PROCESSING-
 Subjecting numerical representation of objects to a
series of operation to obtain a desired result.

39. 1.) Reduce image noise
2.) Increase visibility of detail
3.) Adjust and optimize the image contrast Characteristics.

40. Several digital processing methods that can be
used to adjust the contrast characteristics of an image.
1.) Digital image correction,
2.)global processing,
3.)rotation,
4.)grey scale inversion.
5.) Windowing

42. ADVANTAGES OF DIGITIZATION
 Image enhancement- improving quality of image
 Image analysis- to extract the information
 Image restoration- filtering the noise
 Geometric transformation- image can be rotated or
scaled

43. DIRECT RADIOGRAPHY

44.  No material like image plate
 No latent image
 Image is formed digitally along with exposure

45. WORKFLOW OF DIRECT DIGITAL RADIOGRAPHY
 Cesium iodide
(luminescent layer)
 Mounted on array of
amorphous silicon
layer (photodiode)

48. 1. CCD (CHARGED COUPLED DEVICE)
 Use visible light to form an image
 Silicon(photodiode) used as IC chip arranged in a
matrix known as pixel.
 Fall of light leads to liberation of electrons
 Read out electronic read it and digitized & formation
of digital image.
 Used in – Digital cameras & CCTVs

49. 2. FLAT PANEL
 It is used in
- laptop computers
- C arm units
 Are of 2 types
- indirect flat panel
- direct flat panel

51. INDIRECT FLAT PANEL
 Detectors – sensitive to visible light
 Intensifying screens used to convert X rays into
light.
 i.e; CsI or Gd2O2S

53. DIRECT FLAT PANEL
 Light is not required
 Made up of layer of photoconductor on TFT array.
 Selenium is commonly used.

54. INIRECT AND DIRECT FLAT PANEL DETECTORS

55. ADVANTAGES OF DR
 1)spatial resolution is equal to that of film and it
has better detective quantum efficiency (DQE)
giving a better contrast resolution.
 2)unlike photostimulable phosphor plate
technology,it produces a direct digital signal
and there is no manual processing of plates.

56. DISADVANTAGES
 High cost.
 The detector plates are fragile, heavy and fixed
and so cannot be used in mobile radiography.