chest radiograph physics

1. By Vinchu Michael Jose

2. RADIOGRAPHY
DIGITAL
COMPUTED
RADIOGRAPHY
DIGITAL DIRECT
RADIOGRAPHY
CONVENTIONAL
RADIOAGRAPHY

3. COMPUTED RADIOGRAPHY
o DEFINITION
o BASIC MODULES OF CR
o STORAGE PHOSPHOR PRINCIPLE
o

4. COMPUTED
RADIOGRAPHY

5. Computed Radiography (CR) is a process
of capturing radiographic data from a
Conventional X-ray Machine and
processing the data digitally to produce
crisp and high quality radiographic images.

6. IMAGE
ACQUISITION
IMAGE
PROCESSING
IMAGE
DISPLAY
IMAGE
STORAGE

10. Light weight aluminum
Steel frame
Front screen is made of low attenuation
carbon fiber

11.  Back layer of is made of lead foil- prevents
backscatter that could fog the film.
 Inside foil layer is a layer of padding- maintains
good film/screen contact.
 Back intensifying screen mounted on padding.
 Has Id blocker

13. Approximately 1mm thick.

15. Fluorinated polymer material- Protects the
Phosphor layer.

16. Europium-activated Barium-fluorohalide
(BaFX:Eu+2).
The photostimulable phosphor has the
special property of storing the x-ray energy
in the latent form and releasing the same
when stimulated by a laser energy in the
CR reader/ Digitizer.

17. They respond to a very wide range of x-
ray exposures.
This latitude gives the flexibility in
selecting x-ray technique and takes care
of under exposure and over exposure .
Thus retake is reduced.

19. Photostimuable phosphor aka storage
phosphor.
Incident X-ray excite electrons into a
higher energy level (electron traps)
A latent image is created in the form of
“stored energy”.

22. To reduce scatter

23. PET- Polyethylene Teraphtalate (polyester)

24. Protects the base from damage

25. Energy absorbed by the imaging plate
must be transformed into electrical
charges, which are then recorded and
digitized.

26. Readout process is done immediately after
exposure because amount of stored
energy decreases over time(latent image
disappears completely by 24hrs).
Stimulation done with help of laser beam.

27. Typical wavelength of stimulating laser is
633nm (usually helium-neon laser).
Typical wavelength of emitted light is
390nm(blue light).

28. LASER

31. The emitted light intensity is proportional to
the original incident x-ray intensity .
The emitted light is captured with an
optical array and a photomultiplier tube ,
the signals amplified and digitized(ADC-
Analog to Digital converters).
The residual image is erased with an
intense light source.

38. Pre exposure
Exposure
Positioning
Post exposure
Digital radiography

39. Pressure
Fingerprints
Static electricity
Materials in cassette
Light leak

40. Due rough handling
Black crescent marks
Can abrasions and scratches

41. Black: developer on fingertips
White: oil or fixer on fingertips blocks
developer
Keep finger dry and clean.
Touch only film edges.

42. Two patterns : branching and smudge/spot
Cause: static electricity by friction/ due to
low humidity

43. Xray are prevented from reaching film.
Common : hair, dust.

44. A form of fog.
Cassette not closed properly.

45. Magnification
Foreshortening/ distortion.
Patient rotation
Upside-down cassette.
Grid cut off.

46. Objects closer to film
-closer to normal size
-sharper margins.
Objects far from film.
-magnified
-less distinct margins.

47. Xray beam does not pass perpendicular to
long axis of structure.
Differential magnification of structure.

48. A form of distortion
Lesion may be masked by atypical
superimposition on normal anatomy.

49. White and focal: springs and latches on
back of cassette blocks x-ray.
Global lightness- lead blocking absorbs
some x-ray.

50. Grid is not aligned with beam.
Loss of primary radiation as a result of
undesirable absorption.
Too light and less contrast image.

51. Motion
Double exposure
Material obstructing x-ray beam.

52. Blurred image
Poor clarity
Less sharp edges
Prevention- sedation
-restrain
-stable cassette
-stable x-ray unit

53. Film is darker than a single exposure
Same image: double click
Two separate image: already exposed film

54. Radio-opaque structure
Dust particles

55. Overdevelopment
Underdevelopment
Insufficient mixing
Incomplete fixation
Incomplete washing
Frosty area on film
Finger marks

56. Black and global
Cause : too much metallic Ag forms in
emulsion

57. Common artifacts (film and
computed/digital
radiography)
motion artifact
• due to patient movement resulting in a distorted
image

60. image compositing (or twin/double
exposure)
• superimposition of two structures from different
locations due to double exposure of same
film/plate

61. grid cut-off
radiopaque objects on or external to the
patient (e.g. necklaces, piercing, buttons,
hair (e.g. pony tail, hair braids etc.).
debris in the housing
• debris in the housing caused by the collimator
tube can cause small trapezoidal regions,
indicative of lead shavings

62.  Computed/digital radiography artifacts
 detector image lag or ghosting
• latent image from previous exposure present on current exposure
 incorrect detector orientation i.e. upside-down cassette
• spoke like radiopaque lines (case 6)
 backscatter
• electronics are visible on the exposed image
• increased radiation exposure required for portable DR (digital radiography) examinations
 stitching artifacts
• occur when two separate DR or CR (computed radiography) images are merged into a single image (see case 3)
 over exposure
 dead pixel artifact
 signal dropout 4
• large areas of signal loss, due to detector drop
 speckled radioopaque spots 4
• due to detector drop
 detector calibration limitation 4
• faint radioopaque striping (often verticle) in the background of an image, yet not evident on the anatomy
• this artifact should be carefully examined, if it does not interfere with the anatomy, it is not a detector failure/grid cut off, rather a limitation of the detector calibration.
• often seen as lower exposure
 failure of detector offset correction 4
• similar to ghosting, however, the digital detector not being calibrated when promoted is the cause
 electronic shutter failure 4
• the digital image often will have obscurely shaped, tight collimation that defies logic
• often a computer error often fixed with recollimation post exam (this should be explored before reexamination)
 values of interest misread 4
• image appears washed out, and underexposed
• this is often due to a largely collimated area of smaller anatomy i.e. a patella protection
• tighter digital collimation in conjunction with reprocessing will correctly assign the correct values of interest
 mid gray clipping 4
• loss of contrast in areas of different pixel density yet not change in density can be seen i.e. the metal on a knee replacement
• due to poor contrast enhancement
 grid-line suppression failure 4​​
• faint grid lines present on an image, with no grid cut off