1. EXPOSURE
FACTORS
DR Hussein Ahmed Hassan

2. 
Exposure factors are factors that control
density (blackening) and contrast of
radiographic image.
They are some of the tools that
technologists use to create high-quality
radiographs

3. Exposure Factors Controlled by
the Operator
 kVp
 mA
times Exposure Time = mAs
 Determines the quality and
quantity of the exposure
 FFD (SID), Focal Spot and
Filtration are secondary factors

4. 1- EXPOSURE
FACTORS:
 KVP. :
 It
controls the quality of the beam, i.e.
PENETRATION.
 It
influences :
a: penetration power, i.e. beam
quality;
kVp. α penetration power.
b:
Radiographic contrast;
kVp. α 1/radiographic
contrast.

c:
Radiation dose to patient.

5. KVP
 kVp
controls radiographic
contrast.
 kVp determines the ability for the
beam to penetrate the tissue.
 kVp has more ef fect than any other
factor on image receptor exposure
because it af fects beam quality.

6. KVP
 To
a lesser extent it also
influences the beam quantity.
 As we increase kVp, more of the
beam penetrates the tissue with
higher energy so they interact
more by the Compton ef fect.
 This produces more scatter
radiation which increases image
noise and reduces contrast.

7. KVP
 50
kV 79% is photoelectric, 21%
Compton, < 1% no interaction
 80 kVp 46% is photoelectric, 52%
Compton 2% no interaction
 110 kVp 23% photoelectric, 70%
Compton, 7% no interaction
 As no interaction increases, less
exposure is needed to produce the
image so patient exposure is
decreased.

8. High kVp.
low radiographic
contrast
Low kVp.
High radiographic
contrast

9.  MA.:
1
Ampere = 1 C/s = 6.3 x 1018
electrons/ second.
 The mA selected for the exposure
determines the number of x-rays
produced.
 The number of x-rays are directly
proportional to the mA assuming a
fixed exposure time.
 100 mA produced half the x-ray
that 200 mA would produce.

10. MA
 Patient
dose is also directly
proportional to the mA with a fixed
exposure time.
 A change in mA does not af fect
kinetic energy of the electrons
therefore only the quantity is
changed.

11. MA
 Many
x-ray machines are identified
by the maximum mA or mAs
available.
 A MP 500 has a maximum mAs of
500 mAs.
 A Universal 325 has a maximum mA
of 300 and maximum kVp of 125

12.  MA
 More
expensive three phase
machines will have a higher
maximum mA.
 A General Electric MST 1050 would
have 1000 mA and 150 kVp.

13.  EXPOSURE TIME
 The
exposure time is generally
always kept as short as possible.
 This is not to reduce patient
exposure but to minimize motion
blur resulting from patient
movement.
 This is a much greater problem
with weight bearing radiography.

14. EXPOSURE TIME
 Older
machine express time as a
fraction.
 Newer machines express exposure
time as milliseconds (ms)
 It is easy to identify the type of
high voltage generation by looking
at the shortest exposure time.

15. EXPOSURE TIME
 Single
phase half wave rectified
fasted exposure time is 1/60
second 17 ms.
 Single phase full wave rectified
fastest exposure time is 1/120
second or 8 ms
 Three phase and high frequency
can provide exposure time down to
1 ms.

16. (4) MAS. :
 It
af fect the total number of x-ray
produced by the tube during exposure,
i.e. QUANTITY.
 It
is the product of two quantities;
mA.
the tube current;
s.
the exposure time;

17. MAS
 mA
and exposure time is usually
combined and used as one factor
expressed as mAs.
 mAs controls radiation quantity,
optical density and patient dose.
 mAs determine the number of xrays in the beam and therefore
radiation quantity.
 mAs does not influence radiation
quality.

18. MAS
 Any
combination of mA and time
that will give the same mAs should
provide the same optical density
on the film. This is referred to as
the reciprocity law.
 As noted earlier for screen film
radiography, 1 ms exposure and
exposure longer than 1 seconds do
not follow this rule.

19. MAS
 On
many modern machines, only
mAs can be selected. The machine
automatically gives the operator
the highest mA and shortest
exposure time.
 The operator may be able to select
mA by what is referred to as Power
level.

20. MAS
 mAs
is one way to measure
electrostatic charge. It determines
the total number of electrons.
 Only the quantity of the photons
are af fected by changes in the
mAs.
 Patient dose is therefore a
function of mAs.

21. Ampere is 1 coulomb (C) of electrostatic
charge flowing each second.
1A = 1C/s = 6.3 X 10 18 electron/s
20 mAs = 0.2 Amperes.
This charge releases this No. of
electrons:
6.3 X 10 18 X 0.2 = 1.26 X 10 18 electron/s
20 mA.
mAs
40 mA.
mAs
80 mA.
200 mA.
X
1.0 s
=
20
X
0.5 s
=
20
X
X
0.25 s
0.1 s
=
20 mAs
=
20

22. (5) Focal spot:
 Most
x-ray tubes of fer two focal
spot sizes:
a. Fine focus:
b. Broad focus:

23. a/ Fine focus: (0.3 – 0.6 mm 2 )

It records fine details.

It can not withstand too much heat.

Its usage may require long exposure
time.

Used whenever geometric factors
are more (long subject-film
distance, short FFD ... etc).

24. a/ Broad focus: (0.6 – 1.2 mm 2 )

It can withstand too much heat.

Always used in combination with
short (s) and fast film/screen
system.

Used whenever voluntary or
involuntary motion is highly
expected.

Used when radiosensitive organ is
within exposed area or 10 cm from

25. Two focal spot

26. FOCAL SPOT SIZE

The focal spot size limits the
tube’s capacity to produce xrays. The electrons and
resulting heat are placed on a
smaller portion of the x-ray
tube.

The mA is therefore limited for
the small focal spot. This

27. FOCAL SPOT SIZE
 If
the mA is properly calibrated,
the focal spot will have no impact
on the quantity or quality of the
beam.

28. (6) F.F.D. :
 The
intensity of x-ray beam reduces
with increased FFD.
 It
follows the Inverse Square Law
( I.S.L.) .
I
α 1/d 2 .

29. DISTANCE
 Distance
af fects the intensity of
the x-ray beam at the film but has
no ef fect on radiation quality.
 Distance
af fects the exposure of
the image receptor according to
the inverse square law.

30. INVERSE SQUARE LAW
 mAs
(second exposure)
SID2 2nd
exposure
 ----------------------------
=
----------------------- mAs
(first exposure)
exposure
SID2 1st

31. DISTANCE
 The
most common source to image
distances are 40” (100 cm) and
72”(182 cm)
 Since SID does not impact the
quality of the beam, adjustments
to the technical factors are made
with the mAs.
 To go from 40” to 72” increase the
mAs 3.5 time.

32. DISTANCE
 Increasing
the distance will impact
the geometric properties of the
beam.
 Increased SID reduces
magnification distortion and focal
spot blur.
 With the need to increase the mAs
3.5 times for the 72” SID, tube
loading becomes a concern.

33. DISTANCE
 72”
SID is used for Chest
radiography and the lateral
cervical spine to reduce
magnification.
 72” SID used for the full spine to
get a 36” beam.

34. (7) FILTERATION:
 Thin
sheet of Al (aluminum) 1mm or 2mm
thick added to the pathway of radiation
to filter the low energy radiation.
 Increasing
filtration will increase the
quality and reduce the quantity of the
beam.
 It
removes low energy radiation:

Reduce skin dose;

Harden the beam;

35. FILTRATION
 All
x-ray beams are af fected by the
filtration of the tube. The tube
housing provides about 0.5 mm of
filtration.
 Additional filtration is added in the
collimator to meet the 2.5 mm of
aluminum minimum filtration
required by law.
 2.5 mm is required for 70 kVp.

36. FILTRATION
 3.0
mm is required for at 100 kVp.
 3.2 mm is required for operations
at 120 kVp.
 Most machines now are capable of
over 100 kVp operation.
 We have no control on these
filters.

37. FILTRATION

3.0 mm is required for at 100
kVp.

3.2 mm is required for
operations at 120 kVp.

Most machines now are capable
of over 100 kVp operation.

We have no control on these
filters.

38.  FILTRATION
 CHIROPRACTIC
RADIOGRAPHY IS
A LEADER IN THE USE OF
COMPENSATING FILTERS. WE
HAVE TOTAL CONTROL OVER
COMPENSATING FILTRATION.
 IN AREAS OF THE BODY WITH
HIGH SUBJECT CONTRAST OR
WIDE DIFFERENCES IN DENSITY,
COMPENSATING FILMS IMPROVE
IMAGE QUALITY AND REDUCE
PATIENT EXPOSURE.

39. THE END