Fundamentals of Imaging This course will provide you with the principles involved in the formation and recording of the radiologic image in both conventional and digital imaging systems as well as the principles of image quality assessment. Control of Scatter Radiation

1. FUNDAMENTAL
S OF IMAGING
RAD 206
Control of Scatter Radiation

3. What is focal spot?
What is effective focal spot ?
Which side of the x-ray tube has better resolution ?
Which focal spot size produces better resolution?
Which OID produces better resolution?
Which Object Thickness produces better resolution?
Which Object shape produces better resolution?

4. OBJECTIVES
Begin discussing factors that influence image detail or
visibility of detail
• Scatter Radiation, factors affecting it, and there effect on
Spatial & Contrast resolution
• Ways to reduce scatter & improve image quality
• Primary beam restriction & Grids
• Technique adjustments when using grids

5. WHAT IS CONTRAST
What is scatterWhat is scatter

6. RELATIONSHIP BETWEEN
CONTRAST AND SCATTER
The relationship is INVERSED

7. IMAGE-FORMING X-RAYS
Two kinds of photons are responsible for
the OD and contrast on an image:
• Photons that pass through
without interacting
and
• Photons that are scattered
though Compton.

8. EFFECT OF SCATTER
ON THE IMAGE
Which interaction produces scatter radiation ?

10. FACTORS CONTRIBUTING
TO AN INCREASE IN
SCATTER
• Increased kVpkVp (Beam Energy, Compton)
• Increased partpart thicknessthickness (e.g. Dabbeh)
• Increased x-ray field sizefield size (opening
Collimation to Larger Fields)
Q: what can you do to reduce scatter ?Q: what can you do to reduce scatter ?

11. 1- KVP
At 50 kVp
7979% photoelectric,
21%21% Compton
<1% transmission
At 80 kVp
4646% photoelectric,
52%52% Compton
2% transmission

12. RELATIONSHIP BETWEEN
KVP AND CONTRAST
How does increasing kVp affect patient dose?

13. 2- PATIENT THICKNESS

14. Imaging thick parts of the body results in
more scatter radiation than thin parts
IMAGE TEST TOOL

15. Is patient thickness something the
radiographer can control?

16. IS PATIENT THICKNESS SOMETHING THEIS PATIENT THICKNESS SOMETHING THE
RADIOGRAPHER CAN CONTROL?RADIOGRAPHER CAN CONTROL?
Normally, No
But Compression Devices can be used in
certain situations which reduces patient
thickness and bringing the object closer
to the IR, and therefore results in better
spatial resolution and contrast resolution
and also lesser exposure factors and
patient dose

18. COMPRESSION
• Reduces OID
• Improves spatial
resolution
• Improves contrast
resolution
(reducing fog or
noise)
• Reduces patient
dose

19. COMPRESSION

20. 3- FIELD SIZE
As field size increases, intensity of scatter
radiation also increases rapidly. Especially during
fluoroscopy

21. Larger radiation field produces more
scatter radiation

22. COMPARE IMAGES: WHAT DO YOU THINK
ABOUT RADIOGRAPHIC CONTRAST & IMAGE
NOISE?

24. INCREASE IN SCATTER
• kVpkVp
• PartPart ThicknessThickness
• Field SizeField Size

25. CONTROL OF
SCATTER RADIATION
Technologists routinely use two types of devices
to reduce the amount of scatter radiation
reaching the IR
Beam Restrictors
Compression
Grids
Before Patient
On patient
After patient

26. BEAM-RESTRICTING DEVICES
AKA LBD
1. Aperture
Diaphragm
1. Cones or
Cylinders
2. Variable aperture
collimator

27. APERTURE DIAPHRAGM
The simplest of all beam-restricting
devices
Lead or lead-lined metal diaphragm
attached to the x-ray tube head
The opening in the diaphragm is usually
designed to cover just less than the IR
used

28. APERTURE DIAPHRAGM
Fixed lead opening
Fixed image receptor
size
Constant SID
Source-to-diaphragm
distance = SDD

29. CONES & CYLINDERS
Are modifications of the aperture diaphragm
Alignment
is one difficulty
when using
cones
Now mostly
used with spines
teeth & heads

31. IMPROVED CONTRAST RESOLUTION OF
THE L5 - S1

32. IMPROVED CONTRAST RESOLUTION OF
THE FRONTAL SINUSES

33. VARIABLE APERTURE
COLLIMATOR
The most common beam-
restricting device is the
light-localizing variable
aperture collimator
The first part of the
collimator serves to
control off-focus
radiation. What is off-
focus radiation?

35. OFF - FOCUS RADIATION
ALSO CALLED EXTRA-FOCAL RADIATION
X-ray tubes are designed so that the projectile e-
interacts with the target. However, some of the e-
bounce off the target and land on other areas
This caused x-rays to be produced out side the
focal spot, they are undesirable because it
extends the size of the focal spot, increases
patient skin dose & reduces image contrast

36. Note: Using a grid does not reduce off-focal radiation

37. FIRST-STAGE ENTRANCE
SHUTTERING DEVICE
Has multiple
collimator blades
protruding from the
top of the collimator
into the tube housing

38. THE SECOND-STAGE COLLIMATOR
SHUTTERS
Pb leaves are at least
3 mm thick
They work in pairs and
are independently
controlled

39. THE COLLIMATOR LAMP & MIRROR
Must be adjusted so
that the projected light
field coincides with
the x-ray beam
Misalignment of the
light field and beam
can result in
collimator cutoff of
anatomic structures

40. Always keep the collimated area
smaller than the size of the
cassette
What is a PBL
BLD

41. GRIDS

42. QUESTIONS …?
Technique adjustments
problems