The document discusses computed radiography (CR), digital radiography (DR), and digital subtraction angiography (DSA), explaining their principles, advantages, and disadvantages. CR uses photostimulable phosphors for imaging while DR employs digital x-ray sensors, and DSA is utilized for enhanced visualization of blood vessels by subtracting pre-contrast images from post-contrast images. Techniques and processing steps for each technology are also detailed, highlighting their applications in medical imaging.

1. Computed radiography
and digital radiography
and digital subtraction
angiography
Moderator – Dr Vijayalakshmi MDRD
Presentor – Dr Swetha

2. Computed radiography
 Computed radiography is also called as
photostimulatable phosphor imaging
 It is the bridge between classical
radiography and digital radiography
 CR is used almost like conventional imaging
plate in a casette which must be processe d
in CR reader

3. CR system
 Image plate
 X ray or gamma source
 Image reader
 Photo multiplier tube
 Computer console or work station

4. Principle
 In computed radiography the imaging paltes
are inserted in a radiographic casette
holder and exposed to x rays
 The energy of incoming radiation is stored
in a special phosphor layer and are excited
into a higher energy state forming a latent
image

5.  Then a specialised machine called scanner is
then used to read out the latent image from
the plate by stimulating it with a finely
focused laser beam
 The light is collected by a light guide and
trasmitted to a highly sensitive
photomultiplier device and converted to a
digital signal using analog to digital converter

6. Steps of CR processing

8. Imaging plate
 It looks like a intensyfying screen which is
seen in conventional radiography
 Made of photo stimulatable phosphor
 Instead of emitting light when exposed to x
rays ,this photo stimulatable phosphor has
the property to store energy and produce
digital image on exposure to laser light

10. Image scanner
 Plate is scanned by a laser causing emission
of blue light from the plate which is then
detected by a photomultiplier
 After exposed and scanning the phosphor
plate is erased by exposure to bright Light
from the digitaliser
 And then the casette is further ready for
another exposure

11. Photomultiplier tube
 A photo multiplier tube useful for light
detection of very weak signals is a photo
emissive device in which the absorbtion of
a photon results in the emmision of an
electron
 These detectors work by amplifying the
electrons generated by a photocathode
exposed to a photon flux

12. Advantages
Post processing manipulation and storage of
images is easy
 Repeat examinations are reduced
 consistent high quality images

13.  Ability to deliver images quickly
 To acquire images
 Increased savings
 Reduction in exposure and processing time
 Digital magnification can be done
 Global data exchange

14. Disadvantages
 Initial cost
 Additional cost that is service and
maintenance
 Plate sensitive to fogging

15. Digital radiography
 Digital radiography is a form of X-Ray
imaging in which digital x-ray sensors are
used instead of traditional photographic
film
 Digital Radiography uses two types of flat
panel detectors – direct and indirect

16. Flat panel detectors

18. Direct digital radiography
 X-rays are directly registered by a flat
panel detector
 There is no need for intermediate cassette
in both direct and indirect radiography

19. Direct digital radiography
 It is made from a layer of
semiconductor materials
on the top of TFT array
 The electrons released in
the detector layer from
the x ray interaction are
used to form the image
directly

20. Indirect digital radiography
 X-ray strikes schintillator producing light
 Photo diode array converts light to
electrical signals
 These electrical signals pass through TFT
array and produces image
 Photo detector is made up of amorphous
silicon

21.  The photo conductor is
made up of amorphous
selenium
 Selenium has higher
atomic number than
sillicon
 Due to electric field
selenium direct detectors
are made much thicker

22. Advantages
 Receptor provides direct digital output
 Potentially lower patient dose than CR
 High latitude as per CR
 No processor or reader is required
 Less than 15 seconds
 Much less work for technologist

23. Digital subtraction angiography
 It is a digital imaging technique for better
visualisation of contrast will blood vessels
 In this technique pre contrast imagesare
digitally subtracted from post contrast
image to provide background separation

24. Process involved in DSA
 1. Preprocessing – digitalisation analogue to
digital conversion
 2 . Processing – subtraction techniques
 3 . Post processing – manipulation to
enhance visibility
 4 . Information extraction

25. Processing
 Mask mode subtraction
 Time interval difference subtraction
 Dual energy subtraction
 Hybrid subtraction

26. Mass mode subtraction
 Most widely used process of subtraction
 In this temporal subtraction is done
 It involves initial acquisition of a frame of region of
interest
 Then a second images taken and stored as a mask
image
 This mask images subtracted from subsequently
acquired images and show only contrast will
structures

27.  If any moment occurs after acquisition of
mass image mis registration occurs in the
subtracted images
 This can be overcome to some extent by
pixel shifting

28. Time interval difference subtraction
 Another mode of temporal subtraction
where a consecutive previous frame is
subtracted from current frame
 This technique is very useful in cardiac
imaging where there is rapid motion

29. Dual energy subtraction
 Another technique in which the region of
interest is exposed to higher and lower kV
at very short intervals
 Then the higher kV image is subtracted
from lower kV image to produce the image

30.  This technique has advantage of
elimination of motion artefacts
 Does not require the acquisition of images
before arrival of contrast material as in
Mask subtraction
 Provides selective cancellation

31. Problems of dual energy subtraction
 More complex x ray machine is needed to
rapidly switch kV and mA
 Due to difference in beam hardening in soft
tissue and bone improper subtraction
results

32. Hybrid subtraction
 It is a combination of dual energy and
temporal subtraction
 It has advantage that it eliminate effect of
patient motion

33. Techniques used in DSA
 Road map technique
 Fluoroscopy fade technique
 Dynamic 3D road mapping technique

34. Road map technique
 This technique is very useful in placement
of catheters and guidelines in complex and
small Vessels
 Static fluoroscopic images subtracted from
densely opacified vessel
 Motion after road map acquisition may
affect subsequent intervention

35. Fluoroscopy fade technique
 In this technique reference DSA images
overlayed on a real time fluoroscopic
image

36. Dynamic 3D road mapping
 This new development allows projection of
3D reconstructed vessel on live 2D
floroscopic image

37. Peripheral DSA
 Can be performed with single contrast
injection using stepping technique
 Two types – stepping table technique
. Stepping gantry method

38. Stepping table technique
 In this , table moves into Three stations
with X ray tubes with detector remaining
fixed

39. Stepping gantry method
 In this the tube detector or image
intensifier moves keeping the table fixed

40.  In both method precontrast images are
accquired at different Stations and stored
as mask images
 Subsequently matching post contrast
images are taken at the same position And
subtracted from the corresponding mask
image

41. Uses
 Significantly reduce the use of contrast
 Reduce the examination time

42.  Increased chance of movement between
pre and post contrast images

43. Post processing
 Mask pixel shift
 Remask
 Image summation
 Stacking
 Landmarking

44. Mask pixel shift
 It is a software modification system
 Used when smaller patient motion is
required
 This technique maybe manual or automatic

45. Remask
 It is a similar feature where another mask
images selected which is temporary closer
to the contrast image
 This is useful one patient motion occurs
prayer to contrast image but after
initiation of the acquisition

46. Image summation
 It is a property in which two or more
frames of DSA acquisition are summed into
the single image

47. Stacking
 Similar technique used in carbon dioxide
angiography
 In this fragmented boluses of the gases
added to produce a complete picture of the
opacified structure

48. Land marking
 It is a feature in which lesser intensed your
original images added to the subtracted
image
 This provides anatomical landmarks in the
subtracted images useful in subsequent
intervention

49. Thank you