2. DENSITY (1)
• What exactly is meant by term radiographic
density?
• Radiographic density referred to as the overall
blackening of the film. Density is dependent
on amount of radiation received by the film.
• It is not the technologist’s purposes to
produce an overall black film.
• Technologist is concerned with what is termed
proper density.
3. (DENSITY (2
• A radiographic image that possesses proper
density provides suitable visualization of all of
the structures of interest.
• Any variance from this value of density is
detrimental to radiographic quality.
• Insufficient density, degrading image quality
as excessive density –in fact, perhaps more so.
4. Schematic drawing showing
differential
absorption of x–rays by the
tissues of the
body in conventional
radiography. From most to
least radiodense these are (1)
bone or calcium; (2) all soft
tissues and liquids (muscle,
blood, brain, heart, liver,
urine, etc.) except (3) fat; (4)
air or other gases.
7. FACTORS THAT INFLUENCE and CONTROL
VISIBLE RECORDED DETAIL
Factors that influence visible recorded detail
???What are they
Patient factors
Tissue thickness
Physique
Age
Development
Pathology –additive and destructive
(Tissue opacity (density
11. A “step in time”
•Abdomen: old 200mAx0.5 s =100 mAs
new 200 mAx0.6 s= 120 mAs
• Elbow:
old 100mAx 0.1 s=10 mAs
new 100mAx0.13.3 s= 13.3 mAs
12. Distance - Inverse Square Law
• intensity of radiation falling on flat
surface from point source is
inversely proportional to square of
distance from point source
Intensity α 1/d2
– if distance 2X, intensity drops by 4X
• Assumptions
– point source
– no attenuation
• Cause
– increase in exposure area with
distance
d
13. Intensifying screen
Intensifying screen
Screen intensification factor
Screen intensification factor
Intensification factor formula
=intensification factor
exposure without screens
_____________________
Exposure with screens
Screen intensification factor
Screen intensification factor
••At 50 kv the intensification factor is 60
At 50 kv the intensification factor is 60
••At 60 kv the intensification factor is 80
At 60 kv the intensification factor is 80
••At 70 kv the intensification factor is 100
At 70 kv the intensification factor is 100
14. Intensifying screen speeds and exposures
Intensifying screen speeds and exposures
Screen type
Speed value
Exposure value
(Ultraslow speed (detail
1/4
times par 4
Slow speed
1/2
times par 2
(Par speed (standard
1
1
High speed
2
times par½
Ultrahigh speed
3
times par 1/3
t0 12 4
to 1/12 times par¼
New phosphor material
and rare earth screens
peed*
Screen speed depends upon the type phosphor used, and the type *
and speed of the film it is used with
15. Exposure required to maintain radiographic density
With difference screen speeds (table top radiography)
using 60 kvp and having intensification factor of 80
Screen type
Speed value
Nonscreen
Exposure value
mAs 400
Ultraslow speed
¼
mAs 20
Slow speed
½
mAs 10
Par speed
1
mAs 5
High speed
2
mAs 2.5
Ultrahigh speed
3
mAs 1.66
to 12 4
to 0.415 mAs 1.25
New phosphor material or rare
earth speed
16. Film processing
•Manual processing →difficult
to control quality.
• Automatic processing→
enable the
technologist to standardize film
.processing
17. Anode heel effect
•Has an influence on uniformity
of overall density of the image.
•In specific application, you can
employ this effect to advantage*
you must place the thicker and/or more dense area toward the cathode end of the x-ray tube **
you must place the thicker and/or more dense area toward the cathode end of the x-ray tube
18. Anode heel effect
you must place the thicker and/or more dense area toward the cathode end of the x-ray tube **
you must place the thicker and/or more dense area toward the cathode end of the x-ray tube
19. Orthopedic casts
•Orthopedic casts adds both
thickness and opacity to the part
•Remember double the mAs for
increased part thickness;
increased the kvp by 10 % for
increased part opacity.
20. Filtration
•Added filtration above 2.5 mm Al
increase exposure factors to
maintain density.
•Remember; added filtration is
used as a means of reducing
patient exposure to radiation.
Filters should not be removed
during routine examination.
