The document discusses digital radiography, defining it as the use of computers to acquire image data in a numeric form, contrasting it with conventional radiography that relies on analog information. It outlines the history, limitations, and advancements of digital radiography, including computed radiography and scan projection radiography, while detailing the components and functioning of imaging plates and image readers. The document emphasizes the advantages of digital systems, such as improved image processing and storage, alongside the challenges and technical aspects of their implementation.

1. DIGITAL RADIOGRAPHY
Moderator:
Mr. Ram Singh (Lecturer)
Deptt. of Radio-Diagnosis & Imaging
PGIMER, Chandigarh-160012
Presented By:
Debendra Prasad Gupta
M. Sc. Med. Tech. (Radiodiagnosis) – 1st Year Student
Deptt. of Radio-Diagnosis & Imaging
PGIMER, Chandigarh-160012
12th September, 2009
1

2. DIGITAL RADIOGRAPHY:
Definition: -
 It is defined as the image data acquired from
the numeric value i.e. in discrete binary digits
by use of computers .
 Whereas in Conventional Radiography
information is represented in the analog or
continuous form rather than a discrete
fashion.
2

3. History: -
 In 1980 researchers at “Fuji Laboratories”
developed an erasable X-ray imaging device
based on the x-ray excitation of a phosphor layer
and subsequent reading of the stored image data
with the help of infrared laser (i.e.
Photostimulable Luminescence).
 Results showed that the imaging plate was more
sensitive than conventional X-ray Film with
intensifying screens.
3

4.  Since the clinical use of x-rays in 1895, majority of
radiographic examinations have been carried out by the
conventional method.
 The beam is projected through the patient and the transmitted
beam, which has information about the body structures, is
made to strike the cassette containing the film and the
intensifying screens. This way the latent image is produced on
the film.
 The latent image can be made visible and permanent by
processing it with suitable chemicals.
 This conventional method of obtaining radiographs has
dominated the field of radiography for many years. But now, it
has been realized that the FS system has its own limitations.
INTRODUCTION:
4

5. LIMITATIONS OF FS:
1. After the film has been exposed, the information contents
cannot be enhanced.
2. If the radiograph is too dark (Over-Exposed) or too light
(Under-Exposed) either by Exposure Factor, Film Fault or
Processing Faults, it has to be repeated i.e. No Post-
Processing option which results in extra exposure to the
patient.
3. The completion of the examination is delayed as the film
has to be processed to convert the latent image into a
permanent one.
4. A magnifying glass may be required to see very small
structures in detail i.e. No Zooming & Panning Option.
5

6. 5. Copied radiographs are of inferior quality than original ones.
6. The film is a physical object and so it requires considerable
more space for storage i.e. Storage & Retrieval Cost.
7. Films can only be in one place at a time and they also get
deteriorated with passage of time.
8. Film can not be stored for longer time when required.
9. Dynamic range of x-ray film is limited (i.e. 0.2 – 3).
 These limitations can be overcome by the incorporation of
computer technology into the diagnostic x-ray imaging.
 With DR system conventional analog information is converted
into digital form, processing the digital data and displaying the
image on the monitor that surprisingly looks like a conventional
image.
Cont…
6

7. MILESTONE IN DIGITAL
RADIOGRAPHY:
Year Development: -
1980 Scan Projection Radiography (SPR).
1983 Computed Radiography (CR), Storage Phosphors.
1990 Charge-Coupled Device (CCD) Slot-Scan Direct
Radiography (DR).
1994 Selenium Drum Direct Radiography (DR).
1995 Amorphous Silicon - Based–Cesium Iodide ( Scintillator )
Flat-Panel Detector in Indirect DR.
1995 Selenium-Based Flat-Panel Detector in Direct DR.
1997 Amorphous Silicon-Based - Gadolinium ( Scintillator ) Flat-
Panel Detector in Indirect DR.
2001 Dynamic Flat-Panel Detector for Digital Fluoroscopy in
DSA. 7

8. Digital Radiography (DR)
SPR
NaI – Scintillator
Photodiode
Indirect
Conversion
Storage Phosphor
Plate (IP)
BaFX:Eu+2
CR
Indirect Conversion Direct Conversion
DR
Photoconductor +
TFT (a:Se-DFPD)
Selenium Drum
Scintillator + Photodiode
(a:Si) + TFT (IFPD)
Scintillator + CCD
CsI:Tl or CsI:Na &
Gd2O2S:Tb3+
According to the nature, design and function of the detector the
Digital radiography can be divided mainly in the following way: -
8

9. SCAN PROJECTION SYSTEM:
 Earlier Scan projection radiography (SPR) was
performed on a computer tomography CT system by
translating the patient through the CT gantry
aperture.
 It is based on CT–Technology, another projection
radiography technique was developed using a
narrow fan beam of X-Rays intercepted by linear
array of detectors called “Scan Projection
Radiography”.
 Basically, SPR involves the use of the existing CT-
Gantry & Computer to generate an image that looks
surprisingly like Conventional Radiography. 9

10. The X-ray beam is shaped into a fan by
collimators that confine the beam to a 2-10
mm thickness through on arch of 300 – 450.
There are two collimators: -
1) The pre-patient collimators which shape the beam,
reduced scatter radiation & control patient dose.
2) The post-patient collimators which further reduce
the scatter radiation rejection.
SPR Cont…
10

11. PRINCIPLE OF S.P.R.:
 X-Ray beam after passing through patient is
detected by detector array. The signal have
been image information of the body parts are
transferred to the computer where they get
digitized & processed to reconstruct the
image.
 To obtain a complete image of the body part,
X-Ray tube & detector assembly remains
stationary & the patient is translated through
the X-ray beam or alternatively patient
remains stationary, while the X-Ray tube-
detector assembly translates .
SPR Cont…
11

12. COMPONENTS OF S.P.R. SYSTEM:
1. X-Ray Tube.
2. Pre-Patient Collimator.
3. Post-Patient Collimator.
4. Detector Array.
SPR Cont…
12

13. X-RAY TUBE ASSEMBLY:
 X-Ray tube of high heat loading capacity
usually above 1 MHu is required because of
long imaging time. Usually 20 – 50 cm
body part of patient is imaged at a
translation speed of 1 – 20 cm/s.
Two types of detector can be used: -
1. A Gas Filled.
2. Scintillation Detectors couple with Solid
State Photodiode, i.e. CCD.
SPR Cont…
13

14. Advantage: -
In SPR X-ray beam is collimated in a fan x-ray beam by Pre-
Patient & Post-Patient Collimators . i.e.: -
1. High Amount of Associated Scatter Rejection.
2. High Radiographic Image Contrast.
3. High Dynamic Range (i.e. Low Contrast Detectibility).
4. Image Manipulation.
Disadvantages: -
1. Scanning Time is More.
2. Poor Spatial Resolution &
3. More Radiation Dose to the patient.
SPR Cont…
14

15. ADVANCEMENT:
 At the present time, SPR is re-emerging with
some modification as a promising adjunct to
Digital Mammography Tomosynthesis
(DMT).
 The purpose of all forms of Tomography is
to improve image contrast, and i.e. the goal
of Digital Mammography Tomosynthesis
(DMT).
15

16. COMPUTED RADIOGRAPHY:
Definition: -
 Digital way of doing General Radiography with
Conventional X-ray machines except Conventional
Screen/Film and dark room is known as Computed
Radiography.
Principle: -
 It is based upon Photostimulated Luminescence in
which the radiographic data is captured from a
conventional X-ray machine and processed the data
digitally to produce crisp and high quality
radiographic images.
16

17.  The CR Cassette is exposed with transmitted x-rays beam in a similar
fashion as the conventional cassette.
 The latent image is formed in the phosphor layer of the Imaging Plate in the
form of Electrical Charge .
 Then the latent image is made visible on monitor by processing or scanned
and read that exposed imaging plate by a laser scanning device called Image
Reader.
 The output signal from the image reader is fed to an image array processor
where the digital gray – scale image is formed.
 The digital image generated by the image reader is stored temporarily on a
local hard disk which is processed a/c to need and the resulting image can
be displayed either as soft (Video Display) copy on monitor or send it
directly to laser printer that make hard (Film) copies of the digital image.
 The digital image can then be stored on an optical or magnetic disk for long
term archiving or connected to the PACS through DICOM for Tele-
radiology.
Working:
17

18. 18

19. 19

20. COMPONENTS OF THE C.R.
SYSTEM:
3.) Image Reader: -
4.) Image Processor: -
Cassette With Imaging Plate
2.) Image Recorder: -
1.) General X-ray Equipment: -
20

21. Material: -
• Body: - ABS ( Acrylonitryl butadiene styrene).
• Corners: - PUR (Polyurethane rubber).
• Hinges: - PP (Polypropylene).
• Inner lining: - Felt.
Sizes: -
• Same as that of conventional cassette.
Identification: -
• Embedded memory chip.
• Contactless RF identification.
Backscatter Protection: -
• 150 μm lead.
CASSETTE:
21

22. THE IMAGING PLATE (IP):
 The Imaging Plate (IP) is also known as Computed
Radiography (CR) Plate or Storage Phosphor Screen
(SPS) or Photostimulable Phosphor (PSP) detector to
record the radiographic image in place of the
conventional film/screen cassette.
 The imaging plate is housed in a rugged cassette &
appears similar to a screen/film cassette.
 It is available in the same sizes as conventional
cassettes.
 It is handled in the same manner as a screen/film
cassette.
22

23.  It is not loaded & unloaded in a dark room. Rather, it
is handled in the manner of a screen/film daylight
loader.
 A typical IP can store a latent image for a considerable
period of time. However, it will lose about 25% of the
stored signal b/w 10 min. to 8 hrs after an exposure
resulting in the loss of energy through spontaneous
phosphorescence.
 It retains the image for 24 hours, but some degradation
may occur with passage of time.
 Imaging plate shows a linear response to the intensity
of x-ray exposure over a broad range.
Cont…
23

24. CONSTRUCTION OF IMAGING
PLATE (IP):
PROTECTIVE LAYER
PHOSPHOR LAYER
ANTI-HALO & REFLECTIVE LAYER
BASE
BACKING LAYER
Protective layer : -
- Fluorinated Polymer Material
Phosphor Layer: -
- Ba FX: Eu +2, 0.4mm thick.
Anti-halo Layer + Reflecting Layer
- Prevent laser light from passing through.
Base:-
- PET- Polyethylene teraphtalate
Backing Layer: -
- Protects the base from damage &
reduces back scatter X-rays.
- 150 μm lead. 24

25. THE IMAGING PLATE:
 A Protective Layer composed of “Fluorinated Polymer”
which make resistant to the abrasion, damaged & scratches
caused on the IP during storage and transfer.
 The Phosphor Layer consist of a family of Photostimulable
Phosphor crystals i.e. BrFX:Eu2+ where X can be any of
halogens i.e. Chlorine (Cl), Bromine (Br) or Iodine (I) or an
arbitary mixture of them.
 A typical Phosphor Layer composed of about 85% - BaFBr
& 15% - BaFI, activated with a very small quantity of
Europium (Eu) as activator in crystal.
 This Europium activation procedure, also called doping,
creates defects in the BaFBr crystals that allow electrons to
trapped more efficiently i.e. increases more DQE of crystal.
 Te Reflecting Layer lies b/w phosphor & base layer. which
prevents the reflection of light is also applied. 25

26.  The Base Layer composed of “Polyethylene
Teraphtalate Resign” over which a layer of
photostimulable phosphor (Europium doped Barium
Fluoro Bromide crystals- BaFBr:Eu+2) is coated.
 The next is Backing Layer composed of “Lead”
which prevents the base from damage & reduces back
scatter X-rays.
 The last is the Bar-Code Label which contains the
number assigned to the imaging plate.
 This Bar-Code provides a mechanism for associating
each imaging plate with Patient identification,
Related examination & Positioning Information.
 The imaging plate is flexible and less than 1mm
thick.
Cont…
26

27. LATENT IMAGE FORMATION IN IP:
 To prepare the imaging plat for an x-ray exposure, the
plate is exposed to the intense light to erase any
previous image.
 For X-ray imaging, the IP is placed in a cassette and is
used just like a film/screen cassette with standard
radiographic equipment.
 When exposed to X-ray, the Europium atoms in the
phosphor crystalline lattice are ionized & converted
from Eu2+ - Eu 3+ by librating a Valance Electron:
Eu2+ - X-ray Irradiation - Eu3+ + e-
 These electron are raised to Higher Energy state in the
Conduction Band where they can moved through out
the crystal lattice. 27

28.  The presence of impurities (e.g Bromine) introduce energy
level in the Forbidden Zone called F – centre.
 Once in the Conduction Band, the electron travel freely
until they trapped in the F – centre in the Metastable State
with an energy level slightly below that of Conduction
Band but higher than that of Valance Band.
 The no. of trapped electron is proportional to the amount
of X-ray absorbed locally.
 The trapped electron in the form of metastable state
constitute the Latent Image.
 Due to thermal motion electron will slowly be liberated
from traps, and the Latent Image should there for be read
without too much delay.
 At room temp, the image should, however, be readable up
to 8 hrs. after exposure.
Cont…
28

29. LIFETIME OF THE IP: -
One of the major advantages of CR is that the imaging
plate is reusable and thousands of exposures can be
made on it.However, there are a number of factors that
may affect the lifetime of an imaging plate: -
 The plates are subjected to normal wear and tear from
scratches, scuffs, cracks, and contamination with dust
and dirt, which may interfere with the production of a
good image.
 The establishment of a well organised quality control
program will play an important role in assessing the
clinical quality of the imaging plate. This may easily
be carried out by artefact assessment and uniformity
evaluation across the plate. 29

30. Dust and dirt build up on CR phosphor
plates, leading to image artifacts. To
avoid this, plates need cleaning at
regular intervals.
 Solvent: Ethanol - 99.7%.
 Additives: Catanac SN (Cyastat
SN 50) - 0.3%.
 Safety Precautions: -
- Highly flammable.
- Keep container closed.
- Keep away from sources of
ignition.
IMAGING PLATE CLEANER:
30

31.  The CR image reader is also
known as Analog to Digital
Converter (ADC).
Definition: -
 It is a device which converts the
Continuous Analog Image of
Imaging Plate into the Digital
Image.
Construction: -
 It is consists of three parts: -
1. Mechanical Feature.
2. Optical Feature &
3. Computer Control.
IMAGE READER:
31

32. What Happens to the Plate in the Reader?
1. Cassette is enter the reader.
2. Image plate is removed from
cassette
3. Latent image is scanned by laser
4. Image plate is erased with high
intensity light.
5. Image plate is returned to cassette
and ejected. 32

33.  After exposure the cassette is feeded into image reader system.
 Where the cassette is opened automatically and the imaging
plate is removed from the cassette inside the reader.
 Then the IP is moved along its long axis and scanned
sequentially (Horizontally) by a Monochromatic Infrared Laser
Beam of Helium-Neon (He-Ne) Gas or Solid State Laser of
intensity ≈ 633nm.
 The laser light stimulates the trapped electron moving them up
to the conduction band where they make their exit returning to
the lower energy Valance Band.
 This movement involves the transformation of Europium from
the Eu3+ - Eu2+ i.e. Metastable State to Ground State by
emission of energy in the form of light (Blue & Green) having a
wavelength lower than that of the stimulated laser light.
Eu3+ + e
-
→ (Influenced by IR Laser of 633 nm) → Eu2+ + hf (400 nm).
FUNCTION OR READING PROCESS:
33

34.  The intensity of the emitted light is proportional to the
amount of x-ray energy absorbed in the PSP – layer.
 By using a Optical Filter, that absorbs red light but is
transparent to Blue & Green light
 This emitted light is collected using a Light Guide & is
fed to a Photomultiplier Tube where the light is
converted to an Electrical Signal which is amplified to
an Electric Output Signal.
 The Electric Output Signal is converted into Digitized
Image Signal by ADC & stored in a computer as a
Digital Matrix.
Cont…
34

35.  The Digitized Image Signal is processed by computer &
converted into again in Electric Output Signal by DAC
which is displayed on the monitor.
 The whole read out process for a 14” X 17” imaging
plate takes about 30 – 40 sec. thus, a maximum workload
of 90 – 120 imaging plates per hrs. is theoretically
possible.
 But, practically CR system can read only 65 – 70 IP/hrs
accepting mixed cassette size & the time from cassette
exposure to image presentation can be less than 90 sec.
 Therefore one reader can serve several radiographic
rooms and the data input is stored on an easy image
workstation.
Cont…
35

36. 36

37. Erasing Process: -
 It is necessary to reuse the imaging plate again.
 Because residual Latent Image electrons are still
trapped on higher energy level after readout.
 If residual latent image remained, ghosting could
appear on subsequent use of the IP in the next exam.
 This energy is erased after the readout process using a
high intensity white light from a bank of specially
designed Fluorescent Lamps source that flushes the
traps without reintroducing electron from the ground
energy level.
Cont…
37

38. WORKSTATION:
 Here Radiographic Technologist can be processed
the digital image in a variety of ways depending upon
the clinical application & the final image can be
recorded as a hard copy through Multi Format
Camera or Laser Imager. In the form of analog
image.
 Here digital data is stored on the hard disk of a work
station from where it can be processed, viewed,
printed through or distributed via a local network to
peripheral stations.
 The work station provides a DICOM compliant output
which maybe directed to a laser Printer for hard
copies, or networked to other viewing stations or
archived in PACS for Teleradiology. 38

39. ADVANTAGES OF C.R. SYSTEM:
 No special equipment is required.
 No handling of Processing Chemicals.
 The Exposure Latitude is wider i.e. High Dynamic Range
(1:10,000) which leads to reduced rates of failed x-ray
exposure so in a single radiograph large densities variation
can be obtained.
 Fewer Repeat examinations should be needed due to
exposure factors because of the wide exposure Latitude.
 The CR system are cassette based, they can easily be
integrated into existing radiographic devices are highly
mobile so all types of Radiographic Examination i.e.
Mobile, Portable (Bedside), Trauma, Dental Radiography
are possible with the C.R. system. 39

40.  If a single Imaging Plate shows defects, it can easily
be replaced by the radiographer himself with no need
for specialized equipment or service person.
 The image displayed on the monitor can be
manipulated in a variety of ways: contrast
enhancement, edge enhancement, black/white
reversal, zooming & panning etc (i.e Post Processing).
 The process of storing the images does not require
separate rooms and is relatively easier.
 Cost effective route to digital radiography.
 The acquired image can be transferred to many
monitors, different places for viewing to large no. of
person.
 Increased capability for consultation made possible by
electronic transmission of digital images through
PACS & Teleradiology (i.e. networking system).
Cont…
40

41. LIMITATIONS OF THE C.R. SYSTEM:
 The technique is Time & Labor Intensive like FSR.
 Image reader takes time before the image can be displayed so
the time taken is same as that required for FSR.
 Lesser spatial resolution as compared to conventional
radiography.
 Speed Class of 100-200 is similar to that of Medium Speed FSR
system so that radiation dose required is same or more than
FSR.
 Radiological technologists receive no direct feedback on the
accuracy of their selection of exposure factors as the resultant
images are of consistent quality regardless of the exposure. This
may lead to undesirable and undetected over exposure to the
patient.
41

42. INNOVATIONS & NEWER
APPLICATIONS IN CR:
Some of the draw backs of CR system ,
namely:
- Cassettes Handling.
- Long Read Out Time of PSP Plates.
- Low DQE &
- Poor Resolution
have been addressed by newer innovations &
technological advances.
42

43. AUTOMATED CR SYSTEM WITH
FAST READOUT:
 CR system efficiency has been recently
improved by reducing the readout time & by
removing the step of cassette handling.
 Automated CR system achieve this by line –
scan lasers & photodiode detectors that
reduce the readout time of a PSP plate to less
than 10s.
 In these system there is no cassette handling,
leading to totally automatic image data
acquisition.
43

44. NEWER PHOSPHORS FOR IP :
 Commercially available IP have unstructured
phosphor like Rubidium Chloride (RbCl) or BaFX:Eu
 These are scanned in a raster pattern.
 A needle – shaped phosphor RbI, CsBr, has been
newly; introduced, e.g. Konica Minolta’s Regius 370
Upright DR & is considered more efficient due to its
structural configuration of crystals.
 This crystal structure reduces lateral light diffusion
because of the needle shaped configuration that acts
as light guide.
 In addition the newer phosphors are more efficient
with an increased DQE. 44

45. Cont…
45

46. MOBILE CR SYSTEM:
 Bedside radiography of critically ill patients with conventional
CR involves physical transport of the cassettes to the CR
reader, often located far away.
 The situation gets worse as the no. of ‘portable ‘ films increase.
 To save Labor, Time & Improve Workflow, portable compact
CR system have been introduced in late 2007, with FugiFilm
(FCR Carbon XL CR Reader) & Carestream Health Inc
(Pointof – CAreCR-ITX 560) machines.
 These system basically have a mobile X-ray unit with an
integrated CR reader.
 So, they are easy to use & offer quick image availability in less
than 25 sec.
46

47. 47

48. DUAL-ENERGY IMAGING:
It is done by two methods: -
1.) Subtraction Technique &
2.) Double Expose Technique.
1.) Subtraction Technique: -
 In this method, x-ray energies are separated by the insertion
of a copper filter b/w two image plates which are then given
a single exposure.
 the low energy image is recorded on the front image plate &
a high energy image is recorded on the back.
 Owing to the difference in energy the absorption ratio of X-
ray through bone & soft tissue will differ for the two images.
 By subtracting these two images using weighted factors,
bone or soft tissue detail can be selectively displayed.
48

49. 2.). Double Expose Technique: -
 In this method, by using a high & low KVp, two images are
created in the two different image plates.
 Soft tissue & bones can be separately depicted by this
method.
 Dual – energy technique are most effective when both
images are acquired simultaneously.
 Similar results are obtained with two exposure within a very
short period of time.
Uses: -
 In Chest Radiography, particularly for the evaluation of
partially calcified nodules & pleural plaques.
Cont…
49

50. AUTOMATIC IMAGE STICHING:
 This is useful in determining precise measurement in lengthy
anatomical regions like- whole spine, lower limbs or upper
limb in a skeletal survey.
 Now a days, the largest flat panel DR plates are available in
43 X 43 cm.
 Using these detectors, only a limited portion of the body part
can be imaged at a time in a single exposure, thus making
these detectors inadequate for studying the whole spine or the
entire lower limb.
 To over come this problem, multiple sequential exposures at
different patient positions are acquired in a still patient.
 Automatic stitching is then performed to reconstruct a larger
composite image.
 This special software enables pixel shift and overlap.
50

51.  With the recent approval of the Clear View digital
mammography products, FUJIFILM Medical Systems USA
(Stamford, Conn) becomes the first vendor to offer a full-field
digital mammography (FFDM) system based on CR technology
in the United States.
 CR for mammography uses imaging plates (IPs) made with
photostimulable phosphor to convert x-rays into digital
information. Existing glass, flat-panel FFDM systems rely on
solid-state detectors.
CR-BASED FFDM
51

52. The CR Reader, the Clear View CSM, has a unique dual-side reading
capability that permits the capture of x-ray information from both sides of
the Imaging Plate (IP) simultaneously. The 50-µm laser excites the
phosphor, which has a thicker coating compared to standard CR IPs. Light
is emitted from both sides due to a clear base and is captured with dual
light guides. 52

53. SLOT SCAN SYSTEM:
 This system uses narrow fan beam X-ray of about 5
mm & linear CCD array detector system.
 It has mechanically linked x-ray tube & collimator
opposite the narrow CCD array with few rows of
detector and scan along the long axis of the patient
anatomy.
 It has two precisely aligned moving slit collimators,
one on either side of the patient.
 Due to which this system provides the ultimate in
scatter rejection & detector efficiency .
53

54. Cont…
 Thus use of a radiographic grid is not necessary,
significantly using the radiation dose.
 There are different possible movement of mechanical
linked system & patient couch movement.
 The exposure time to the patient is about 20 msec. &
readout process time takes about 1 - 3sec.
 Scan time depends on the area covered i.e. 2 – 30
seconds.
 Because of the need for fixed installation, Slot Scan
DR system is dedicated to Chest radiography,
Mammography, or Dental Radiography.
54

55. CCD Slot Scan Direct Radiography
55

56. ADVANTAGES:
 Scatter radiation almost totally absent.
 No grid is required.
 Radiation dose is reduced as grid no required.
 Detector efficiency is more with lower image noise.
 Longer & large anatomical regions are well covered.
DISADVANTAGES:
 High initial cost.
 Longer acquisition time due to narrow fan beam.
 So, requirement of equipment with high rating of
generator & X-ray tubes. i.e. high tube loading.
 Poor Spatial Resolution, due to Patient motion which
degrade image quality during scanning.
 It is a fixed modality method with bulky design.
 Bedside Radiography is not possible. 56

57. Rotating selenium-dotted drum, which has a positive electrical surface charge, is
exposed to x-rays. During exposure, a charge pattern proportional to that of the
incident x-rays is generated on the drum surface and is recorded during rotation
by an analog-to-digital converter .
SELENIUM DRUM DR SYSTEM:
Advantage:-
It provide good image quality that is
superior to that provided by screen-
film or CR systems.
Disadvantage:-
Because of their mechanical design,
selenium drum detectors are dedicated
for chest stand systems only with no
mobility at all.
57

58. Indirect Conversion Direct Conversion
Direct Radiography (DR)
Photoconductor (a:Se)
+ TFT (DFPD)
Selenium Drum
Scintillator +
Photodiode (a:Si) +
TFT (IFPD)
Scintillator + CCD
CsI:Tl or CsI:Na &
Gd2O2S:Tb3+
DIRECT RADIOGRAPHY (DR):
 DR technology converts x-rays into electrical charges by
means of a direct readout process using CCD/TFT arrays.
58

59. INDIRECT DR:
 In this case, X-ray energy is first converted into
light photons by an phosphor scintillator (CsI:Tl,
Gd2o2S:Tb).
 Then the light photons are converted in electric
charge by Photodiode Phosphor (a:Si).
 The electric charge is converted in electrical
signal by CCD/TFT which is digitized by ADC
in digital signal & stored in computer.
 The stored digital signal in computer is processed
and converted in analog signal by DAC to see on
the monitor.
 The whole process will take only 1.3 – 3 sec. 59

60. Cont…
Convert X-rays into light photon
after then electronic signals for
digital image formation.
Uses 3 step process : -
X –rays
Visible Light
Electronic Signals
Image formation
CsI:Tl, Gd2o2S:Tb
a:Si
TFT & ADC
60

61. DIRECT DR:
 In this case we do not use the phosphor coating scintillator
layer, thus eliminating the intermediate light producing
step.
 Hence a:Se directly acts as the x-ray detector.
 The x-ray beam directly interacts with a thin layer of a:Se
creating electron-hole pairs, which being charged, travel
directly to the TFT.
 From TFT, the charge pattern is read out by charge
amplifier & digitized by ADC in digital signal & stored in
computer.
 The stored digital signal in computer is processed and
converted in analog signal by DAC to see on the monitor.
 The whole process will take < 1.3 sec. 61

62. Convert X-rays into electronic
signals for digital image formation
Uses 3 step process : -
X –rays
Electronic Signals
Image formation
Cont…
a:Si
TFT & ADC
62

63. 63

64. 64

65. CONSTRUCTION & WORKING
OF FPD SYSTEM:
 The physical dimensions of the detector array are 40 x
50 x 4 cms with 2560 x 3072 pixel matrix.
 The matrix is covered with a scintillator layer of
CsI:Tl or Gd2O2S:Tb in case of Indirect FPD only.
 The matrix array consists of a glass substrate onto
which a layer of a:Si is evaporated in the case of
Indirect FPD & a:Se in case of Direct FPD.
 The a:Si or a:Se is structured in a matrix of individual
photo sensors and switching elements, either a TFT or
a CCD which allows the connections of the sensor
with the read out line in column direction. 65

66.  TFT or CCD are controlled via address lines in the
horizontal direction, in order to read out the single
charge values of photodiodes.
 These signals are multiplexed and converted into
digital signals by an A.D.C. inside the detector
housing.
 The 2-D digital image data is directly transferred to
the image processing computer via an optic fiber
link.
 So the image is available in digital form shortly
after the exposure has been made.
Cont…
66

67. ADVANTAGES of DR SYSTEM:
 Increasing Workflow Efficiency, Saving Time & Labor.
 Integrating high power X-ray system of 30 – 1000 KW Rating, very
Short Exposure Time , Eliminating Motion Blur.
 Variable Speed Acquisition possible (speed class 100 – 800)
depending on acceptable SNR.
 Most DR system have presets available for various anatomical studies
including optimized post processing e.g. chest, spine etc.
 Automatic tube detector positioning for selected study.
 Auto selection filter & Focal Spot Size a/c to the anatomical part.
 Automatic tracking for easy positioning.
 Immediate availability of image for Quality Check & Diagnosis.
 The examination becomes quick as no cassettes have to be fetched
from the storage area, taken to the examination site, or to the
processing unit after exposure.
 Radiography as well as fluoroscopy can be performed.
 Post processing can be done. 67

68. DISADVANTAGES OF DR
SYSTEMS:
 High initial cost.
 Some radiographic view are difficult to obtain as
the detectors are generally not free to be placed in
any position.
 Careful handling is required due to fragile nature
of most detectors.
 Due to its inflexibility, portable or ward
radiography is not possible.
 Different equipment is required for different
kinds of work.
68

69. DIGITAL FLUOROSCOPY:
 It provides Real Time Imaging of anatomic
structures. As maximum image detail is
required, so image brightness must be high.
 Image intensifier was developed to replace
the conventional fluoroscopic screen.
 With the introduction of computer
technology into fluoroscopy, digital images
with better detail can be obtained.
69

70. EQUIPMENT:
 D.F. requires the same fluoroscopy
equipment in addition to a computer, 2 video
monitors, and a more complex operating
console.
 A high voltage generator.
 A video system.
 A charge couple device.
70

71. ADVANTAGES:
 Less radiation dose as compared to the
I.I.T.V. system.
 Better image quality.
71

72. DEVELOPMENTS IN D.F. :
 Flat panel detector system has replaced the I.I.T.V.
system.
 X-rays passing through the patient are converted into
electrical signals by the F.P.D. These are then passed
through the amplifier and ADC where they are converted
into digital signals.
 The digital image data is directly transferred to an image
storage PC via an optic fiber link at the rate of 30 f/s
 This system permits high speed digital image acquisition,
processing and display.
 Images are of excellent resolution. 72

73. DYNAMIC FPD FLUOROSCOPY:
Dynamic Detector 73

74. INNOVATIONS & NEWER
APPLICATIONS IN DR:
 Digital Radiography is witnessing rapid
innovations in hardware as well as software
applications.
 Clinical utility & the true potential of these
applications will be understood better in the
years ahead.
Few of the exciting applications are:
74

75. PHOTON COUNTING TYPE DR SYSTEM:
 It is similar to Slot Scanning Type system but uses a
different types of multi slit detector made up of
Crystalline Silicon (Si) which is some what similar to
the one used in direct type of Flat Panel Detectors
System.
 A voltage of about 100 volts is applied across the
array of thin (50µm) Si crystals.
 Absorbed X-ray produce electrons & holes. Each of
these event is counted in a timer meter with time
corresponding to the spatial location along the
direction of X-ray fan beam sweep.
75

76.  Each absorbed X-ray photon results in a unit count
regardless of the photon energy.
 As the electrical pulse generated is much higher than
the electronic noise, this type of DR system produce
images with high SNR.
 Uses: -
1) Mammography (Sectramicrodose).
2) In gaseous micros trip detectors for Biplane Whole
Body Imaging in erect weight bearing position with
excellent result ( EOS of Biospace med).
Cont…
76

77. 77

78. Advantages: -
 Radiation dose is reduced as grid is not required.
 High system DQE.
 High SNR due to minimal electronic noise.
 No ghost image (Previous exposure is residue).
 High contrast & detail resolution.
Disadvantages: -
 Exposure time is long.
 Patients motion may degrade image quality.
 Requirement of equipment with high rating of generators
& X-ray tubes.
78

79. DIGITAL TOMOSYNTHESIS:
 In this technique multiple low dose exposure are
given from various angles while the x-ray tube
moves in an arc & the detector remains stationary.
 Multiple images with different focal zones are
possible to be created by addition of these low dose
images after pixel shift.
 It emphasize contrast in a particular layer of a region
of body.
 Generated images can be viewed singly or as a cine
loop.
 It is also considered to useful in Mammography,
Chest, IVU studies.
79

80. DIGITAL MAMMOGRAPHY
TOMOSYNTHESIS (DMT):
 It is a recent advanced application of
DM.
 In this technique, an area X-ray
beam interacts with the digital
mammographic image receptor,
producing a digital mammogram.
 This digital mammogram is repeated
several times at different angles.
 Each images is available in digital
form & can be reconstructed as a 3D
Matrix of values, each representing a
Voxel.
 With these digital data available, a
tomographic section can be
reconstructed with enhanced image
contrast at acceptable patient
radiation dose. 80

81. MOBILE /PORTABLE DR:
 Now a days flat panel detector portable radiography
is also possible.
 This method was first invented by Canon.
 The FPD are available in 17” X 17” with a cable for
portable/mobile radiography.
 As a general a FPD connected by a cable to a mobile
or portable unit having a monitor.
 The use of portable DR system hampered by the
fragility of the FPDs & the high costs.
 A portable DR system, when compared with an FSR
system, avoids all problems related to the
availability, storage, transportation, disposed of
films & chemicals. 81

82. WIRELESS FPDs:
 With the introduction of the model Pixium 3543 from Thales,
wireless portable DR system is now a reality.
 After exposure, it wirelessly transfer image data to the DR
system.
 Alternatively the image data can be transferred to DR
console via an Ethernet cable.
 It has no cables & does not interfere with surrounding
machines. So, it is easy to handle as a CR cassettes.
 Typically a 17” X 14” image size is made available within
3s.
 It is particularly well suited for use with immobilized
patients, in operating rooms, intensive care units, emergency
situations, and rooms for exams requiring difficult or unusual
X-ray projections.
82

83. WIRELESS FPD SYSTEM:
X-Ray Generator
Power supply
Pixium Portable
Docking Station
WiFi (or back-up cable)
Pixium Portable 3543
Ethernet
Cable
Acquisition
board
Ethernet
Board
RS 232
Optical Fiber
Power supply
Pixium RAD 4600
PixRad software
PC
83

84. FLUOROSCOPY:
 Real – time digital imaging in DR is possible with
the invention Pixium RF 4343, from Thales.
 It facilitates high-quality radiography &
fluoroscopy (up to 30 images/sec.)
 This fluoroscopy feature is use in
Gastroenterology, Urology & Vascular
applications.
 Newer FPDs like Pixium 4700 & Pixium 4800
from Thales are used for Vascular &
Cardiovascular DSA applications by permitting
low – dose fluoroscopy. 84

85. Integris Allura Flat Dynamic
Detector for Cardio
Scintillator Photodiode array Refresh light
85

86. IMAGE QUALITY PARAMETERS:
 Pixel Size, Matrix & Detector Size.
 Dynamic Range & Contrast.
 Spatial Resolution.
 Limiting Spatial Resolution (LSR).
 Signal to Noise Ratio (SNR).
 Modulation Transfer Function (MTF).
 Detective Quantum Efficiency (DQE). 86

87. DYNAMIC RANGE & CONTRAST:
Contrast levels or film
densities generated over a
range of x-ray exposure levels.
Dynamic range is a measure
of the signal response of a
detector that is exposed to x-
rays.
Narrow Dynamic Range
Image
Brightness
Toe Part
Shoulder
Straight
X-ray Detected
Wide Dynamic Range
Shoulder
Straight
Toe Part
X-ray Detected
Image
Brightness
87

88. Film-Screen
Detector
Low Contrast
High Contrast
Cont…
88

89. LIMITING SPATIAL RESOLUTION
(LSR):
 Spatial Resolution refers to the minimum resolvable
separation between high-contrast objects.
 In Digital Detectors, Spatial Resolution is defined
and limited by the minimum Pixel Size. 89

90. Decreasing Noise
Increasing
Contrast
High SNR Low SNR
Noise
Signal
Contrast Ratio
Quantum Mottle (QM): - It is an appearance of noise in
the radiographic image due to low SNR of the
information reaching the image recording system.
SIGNAL TO NOISE RATIO (SNR):
90

91. IMPACT OF NOISE:
 Quantum and Electronic noise are unavoidable in a
digital imaging chain. The effect, often expressed as
Signal-to-Noise Ratio (SNR), can vary widely from
system to system.
Signal Useful Image Formation
------------- = ------------------------------------
Noise Erratic (Unwanted) Information
1:1 SNR 2:1 SNR 5:1 SNR 91

92. MODULATION TRANSFER
FUNCTION (MTF).
 Modulation transfer function (MTF) is the capacity of the
detector to transfer the modulation of the input signal at a
given spatial frequency to its output.
Light Photons
Gd2O2S:Tb + a:Si
High Scattering
Low MTF
CsI:Tl + a:Si
Low Scattering
Good MTF
Electron
a:Se
No Scattering “Perfect”
MTF
Light Photons
X-Ray Photons:
92

93. DEECTIVE QUANTUM EFFICIENCY (DQE):
Detective Quantum Efficiency (DQE) is one of the
fundamental physical variables related to image
quality in radiography & refers to the efficiency of a
detector in converging incident X-ray energy into an
image signal.
It depends on: -
- Radiation Exposure.
- Spatial Frequency.
- MTF.
- Detector Material.
- Quality of the radiation applied (Voltage & Current).
93

94. 1 Digital Radiographic Room = 2.6
Conventional Screen/Film Room !
Imaging Technique Average Exam time
Conventional Screen Film Radiography 6:05 Minutes
Computed Radiography 7:02 Minutes
Direct Capture Radiography 2:18 Minutes
94

95. Feature  X-ray
Converter
Readout Detector
size
Pixel Size Matrix Size
Screen Film Gd2O2S Film 14x17 Grain Size
2
………..
Storage
Phosphor
BaFBr:Eu LASER 14x17 100 - 200
µm
1760x2140
Slot scan
CCD
CsI:Tl CCD 17x17 162 µm 2736x2736
Direct FPD a:Se Active Se
Matrix
14x17 139 µm 2560x3072
Indirect FPD
Gd2O2S:Tb Active a:Si
Matrix
17x17 160 µm 2688x2688
CsI:Tl Active a:Si
Matrix
17x17 143 µm 3121x3121
Technical Features Of Various DR System:
95

96. IMAGE RECEPTOR COMPARISION:
FEATURE FILM/SCREEN CR (PSP) DR
RADIATION DOSE Higher Lower Lower
GENERATION OF
VISIBLE IMAGE
Chemical, Wet
Processing
Laser Scanner, Computer Computer
IMAGE VIEWING Delayed, View box
Transillumination
Delayed, Computer
Monitor
In few seconds, Computer
Monitor
RESOLUTION 16-20 lp/mm 6-8 lp/mm 8-10 lp/mm
CONSTRUCTION Thin, Flexible Thin, Flexible Thick, Rigid & Robust
LIFE SPAN Single Use Reusable after Erasure Reusable (Unlimited)
IMAGE
ENHANCEMENT
Fixed Unchangeable
Image
Multiple Operations: -
Contrast, Density,
Magnification,
Positive/Negative,
Measurement
Multiple Operations: -
Contrast, Density,
Magnification,
Positive/Negative,
Measurement
STORAGE Patient Record,
Huge Space required
Variety of Archiving
Method: - Server, Zip,
OMD, MOD, CD, DVD,
PACS
Variety of Archiving
Method: - Server, Zip, OMD,
MOD, CD, DVD, PACS
96

97.  Physical Design: -
- Compatible in size with Film Cassette.
- Immediate Readout.
- Robust.
- Cost Effective.
 Image Capture: -
- High Quantum efficiency.
- Low Dose.
 Image Quality: -
- Spatial & Contrast Resolution as good
as Film/Screen System.
- Wide Dynamic Range.
- DICOM Compatible.
IDEAL DR SYSTEM:
97

98. CONCLUSION:
 With the advent of computed radiography diagnostic
radiology is advancing towards a film less system.
 The replacement of film by detectors and storage
devices eliminated several inherent drawbacks of
conventional radiography and decreases the radiation
exposure to the patient and radiographer.
 Very soon digital imaging will become more common
and affordable for all aspect of radiography.
 With the development of Digital Radiography , the
Radiographic Examination becomes more easy, handy
and less time consuming method with good quality of
image. 98

99. References:-
1. http://www.google.com
2. http://www.wikipedia.com’
3. http://www.xray2000.co.uk
4. http://www.radiologyinfo.com
5. http://www.amersham,health.com
6. Indian Radiology Journal
7. American College of Radiology Journal
99

100. 100