The document discusses digital radiography, including computed radiography (CR) and direct radiography using flat panel detectors. It summarizes the limitations of conventional film-based radiography and then describes the key components and workings of CR and direct digital radiography systems. Some advantages include improved image quality, ability to manipulate images digitally, faster processing, and reduced need for retakes compared to conventional methods.

1. DIGITAL RADIOGRAPHY
Upakar Paudel
B.Sc. MIT Final year
UCMS BHAIRAHAWA
NEPAL

2. INTRODUCTION
•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.

3. 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 it has been realized that
the film-screen system has its own limitations.

4. LIMITATIONS OF CONVENTIONAL
RADIOGRAPHY
1. After the film has been exposed,the information
contents cannot be enhanced.
2. If the radiograph is too dark or too light,it has to
be repeated. This 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.

5. 4. A magnifying glass may be required to see very
small structures in detail.
5. Copied radiographs have an inferior quality as
compared to original ones.
6. The film is a physical object and so it requires
considerable space for storage.
7. Films can only be in one place at a time and they
also get deteriorated with passage of time.

6. HISTORICAL DEVELOPMENTS
•Initially,radiographs were obtained in the
conventional manner and then put through some
kind of digitization process to obtain a digital
image.
•In the 1960s,computed axial tomography was
invented by Godfrey Hounsfeild. Here, x-rays were
not detected by a film but by detectors the
computer analyzed the signals from the detectors
and reconstructed an image which was displayed
on a T.V. monitor.

7. •With subsequent development in digital
imaging,other modalities such as M.R.I. and U.S.
appeared.
•In 1982, the first computed radiography system was
developed by the Fuji film corp. This used
photostimulable phosphors as image receptors.
•In 1990, direct capture radiography or FLAT PANEL
SYSTEM started, which used amorphous Si or Se as
detectors.

10. COMPUTED RADIOGRAPHY
•PRINCIPLE:
•In the C.R. system we use an imaging plate made of
a photostimulable phosphor.
•The cassette is exposed to x-rays in a similar
fashion as the conventional cassette.
•The latent image is produced in the phosphor layer
of the imaging plate.
•Then the cassette is transferred to the reader
system where the imaging plate is scanned with a
red helium-neon [633mm] beam.

11. This stimulates luminescence proportional to the x-
ray energy absorbed. These light signals are
converted into electrical signals by using
photomultiplier tubes.
These electrical signals are converted into digital
information by an ANALOG TO DIGITAL
CONVERTER.
The digitized data is transferred to the digital image
processor in the computer, from where it can be
processed and viewed on the monitor.

12. COMPONENTS OF THE C.R. SYSTEM
• The C.R. system comprises of:
1. An imaging plate
2. An image reader
3. An image processor
4. An image recorder

14. THE IMAGING PLATE
•It consists of a polyester base over which a layer of
photostimulable phosphor [europium doped
barium fluoro bromide crystals- BaFBr:Eu 2] is
coated.
•A protective layer composed of fluorinated
polymer material is applied over it. A supporting
layer which prevents the reflection if light is also
applied.
•Next is the backing layer. This prevents the
scratching on the imaging plates during storage
and transfer. Therefore it has a protective action.

15. •The next is the bar-code table 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 and positioning
information.
•The imaging plate is flexible and less than 1mm
thick.

23. OTHER CHARACTERISTICS OF IMAGING
PLATES
•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.
•It shows superior performance capability i.e. it
provides more information.
•It is available in the same sizes as conventional
cassettes.

24. • High resolution imaging plates are also available which help in
reducing the radiation dose to the patient considerably.
• Imaging plates are reusable and thousands of exposures can be
made on it.

25. THE IMAGE READER
•The image reader converts the continuous analog
information [latent image] into a digital format.
•In the reader the imaging plate is scanned
sequentially by a red helium-neon [633mm] laser
beam.
•The laser beam induces photostimulable
luminescence from the phosphor. The intensity of the
emitted luminescence is proportional to the amount
of x-ray energy absorbed in the crystal layer.

26. •This emitted light is directed by highly efficient
light guides to the photomultiplier tubes, where it
is converted into electrical signals.
•The electrical signals are sampled and digitized by
an A.D.C.
•The digital data is stored on the hard disk of a work
station from where it can be processed, viewed,
printed or distributed via a network to peripheral
stations.

27. • The image reader has a capacity to read 110 plates per hour.
• Therefore one reader can serve several radiographic rooms and the
data input is stored on an easy image workstation.

29. THE IMAGE RECORDER
• The work station provides a DICOM compliant output which maybe
directed to a laser printer for hard copies, or networked to other
viewing stations.

30. ARCHIVAL OF C.R. IMAGES
•A 12 bit output of the A.D.C. is converted into 10
bits within the reader; discarding the information
which is irrelevant to the exam being performed.
•This change reduces the size of the image data
files, increasing the speed of the system and also
increasing the storage space.
•For bulk and long storage, optical discs, jukebox
system, storage shelves etc. may be used.

31. ADVANTAGES OF C.R. SYSTEM
•No special equipment is required.
•The exposure latitude is wider and so more
information from the x-ray beam can be extracted
as compared to a conventionally acquired image.
•Repeats are extremely few and that too due to
positioning and not exposure factors.
•All types of radiography is possible with the C.R.
system.

32. •The image displayed on the monitor can be
manipulated in a variety of ways: contrast
enhancement, edge enhancement, black/white
reversal etc.
•The process of filing the images does not require
separate rooms etc. and is relatively easier.
•The acquired image can be transferred to many
monitors for viewing in separate places.

33. LIMITATIONS OF THE C.R. SYSTEM
•Lesser spatial resolution as compared to
conventional radiography.
•C.R. systems are not inherently low dose systems
as compared to the conventional rare earth screen-
film systems.
•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.

34. DIRECT RADIOGRAPHY
• FLAT PANEL DETECTOR SYSTEMS:
• This system uses x-ray detectors of photoconductive materials such
as amorphous Se or Si for direct acquisition of projection
radiographs.

35. METHODS
• Essentially,two methods have been developed for direct capture
radiographs:
• Indirect method
• Direct method

36. INDIRECT METHOD
• Here we use CsI scintillation phosphors coated over an active matrix
array of amorphous silicon photodiodes.
• The x-ray beam emerging from the patient interacts with the cesium
iodide producing light.
• This light interacts with the amorphous silicon producing electrical
charge.

37. •Thin film transistors store the signal
until read out, one pixel at a time.

39. DIRECT METHOD
•In this case we do not use the phosphor coating,
thus eliminating the intermediate light producing
step.
•Hence amorphous selenium directly acts as the x-
ray detector.
•The x-ray beam directly interacts with a thin layer
of amorphous selenium creating electron-hole
pairs, which being charged, travel directly to the
electrodes.
•From here, the charge pattern is read out to form
the image.

40. • The advantage of the amorphous selenium approach is that there is
no light spreading in the phosphor and so there is improved spatial
resolution.
• On the other hand, the cesium iodide phosphor has a high detective
quantum efficiency and so it results in lower radiation dose.

41. CONSTRUCTION AND WORKING OF A D.R.
SYSTEM
• The physical dimensions of the detector array are 40 x 50 x 4 cms
with 2560 x 3072 pixel matrix.
• The array consists of a glass substrate onto which a layer of
amorphous silicon is evaporated.
• The matrix is covered with a cesium iodide scintillator layer.

42. •The amorphous silicon is structured in a matrix of
individual photo sensors and switching elements,
either a thin film transistor or a diode which allows
the connections of the sensor with the read out
line in column direction.
•Thin film transistors or switching diodes are
controlled via address lines in the horizontal
direction, in order to read out the single charge
values of photodiodes.

43. • These signals are multiplexed and converted into digital signals by
an A.D.C. inside the detector housing.
• The 2-D 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.

45. CHARACTERISTICS OF AMORPHOUS SILICON
• It is a good photo detector in thin film form.
• Its easy to deposit on large glass substrates.
• They are very sensitive to light with an efficiency close to 100%

49. ADVANTAGES OF FLAT PANEL DETECTOR
SYSTEM
•Less radiation dose to the patient.
•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.

50. DISADVANTAGES OF F.P.D. SYSTEMS
• Due to its inflexibility, portable or ward radiography is not possible.
• Different equipment is required for different kinds of work.
• They are quite costly.

51. DIGITAL FLUOROSCOPY
•It provides real time viewing 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 if computer technology into
fluoroscopy,digital images with better detail can be
obtained.

52. 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.

53. ADVANTAGES
• Less radiation dose as compared to the I.I.T.V. system.
• Better image quality.

54. DEVELOPMENTS IN D.F. SYSTEM
• 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.s. These are then passed through the amplifier
and ADC where they are converted into digital signals.

55. • 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.