This document discusses various devices used to reduce scattered radiation in diagnostic radiology, including filters, beam limiting devices, beam centering devices, and radiographic grids. It provides details on how each device works to absorb low-energy photons and restrict the x-ray beam, thereby improving image quality by reducing noise from scattered radiation. Key aspects covered include the principles of filtration, types of beam collimators, performance testing of grids using factors like contrast improvement and primary transmission, and the benefits of using these devices to decrease patient dose and increase diagnostic value.

1. BY:- NITISH RAJPUT
BSc. RADIODIAGNOSIS 2ND YEAR
BATCH-2k16

2. 1- SCATTERED RADIATION
2- BEAM LIMITING DEVICES
3- BEAM CENTERING DEVICES
4- RADIATION GRIDS
5- ASSESMENT OF GRID FUNCTION

3.  Xray’s belong to a group of radiation known as
the ELECTROMAGNETIC RADIATIONS.
 All the electromagnetic radiations have dual
characteristics.
 WAVE NATURE
 PARTICLE NATURE
 Wave nature can be understood by :- c=
 Particle nature can be understood by :- E=hv

6.  Scattering is basically of five types:-
 COHERENT
 COMPTON
 PHOTOELECTRIC
 PHOTODISINTEGRATION
 PAIR PRODUCTION
 (of these compton scattering occurs mostly in
diagnostic radiology)

7.  Basically, when x-rays are absorbed then they
cease to exist but when they are scattered then
they are deflected from there original path and
hence carry no useful information...
 At the end they only add up NOISE (unwanted
densities) to the film.
 The end result is that the radiographic image is
of a poor quality which makes it difficult to
diagnose it. Contrast of the film is also
degraded.

9. VARIOUS DEVICES TO REDUCE SCATTER:-
 Filters
 Aperture diaphragms
 Cones and cylinders
 Collimators
 Beam centering devices
 Radiographic Grids

10.  More scatter is created in bone than in soft
tissue.
 When the beam is restricted then less scatter
occurs and hence less of it reaches the film.
 Technical factors may have to be manipulated
to reduce the amount of scatter.

11.  Filtration is basically a process of shaping the
x-ray beam to increase the amount of useful
photons and decrease the low energy photons
so that we can get an image with better
contrast.
 This also decreases the patient radiation dose
and occupational hazards.

12.  When exposure is done then both high as well
as low energy x-ray photons are produced.
 When these x-ray photons interact with the
human body, only the high energy photons
penetrate while the low energy photons get
absorbed in the body, hence increasing the
patient radiation dose.
 Filtration basically absorbs the low energy
photons from the beam and hence increases the
image contrast.

14.  INHERENT FILTRATION(x-ray
tube and its housing).
 ADDED FILTRATION (sheets of
metal placed in the path of beam).
 THE PATIENT.

15.  The absorption of the low energy x-ray photons by
the x-ray tube components itself is known as the
inherent filtration.
 Glass housing, metal enclosure and the assembly
oil is responsible for inherent filtration.
 Inherent filtration of a tube is measured in
ALUMINIUM EQUIVALENT.
 It is basically the amount of aluminium required to
absorb the same radiation which the tube material
was absorbing.
 Inherent filtration is generally between 0.5-1.00mm
of aluminium equivalent.

16.  But disadvantage of inherent filtration is that it
causes a significant reduction in the image
contrast.
 At some places where unfiltered x-ray beam is
required, there BERYLLIUM filters are mostly
used.

18.  Added filtration is a result of any beam
absorber which is placed in the path of the xray
beam, this absorber absorbs the low or high
energy photons.
 Ideally an added filter should absorb all the
low energy photons and let the high energy
photons pass through it.
 But no such material exists.
 SOLUTION- we always use added filters
mostly in a group of Aluminium(13) +
Copper(29).

19.  They are arranged as the high at. No.(COPPER)
element faces the x-ray tube while the
other(ALUMINIUM) one faces the patient.
 Most of the filtration is done by copper.
 They can't be used separately.
 Patient radiation dose as well as the image
contrast is reduced.
 This combination of two layers of filters is also
known as COMPOUND FILTERS.
 It also increases the tube loading.

21.  Wedge filters are mostly used at places where the
body part to be radiographed varies greatly in
densities.(thick from one side and thin from
another side)
 Wedge filters are like the shape of a wedge , the
thin part is placed under thick body part while
thick part is placed under thin body part.
 Result is that ,beam attenuation by thick part is
more hence less radiation reaches the part and
beam attenuation by thin part is less hence more
radiation reaches thick part.
 Therefore a radiograph of uniform density is got.

23.  More will be the thickness of filters ,more will
be the attenuation of x-rays by it.
 In other words:-
 ATTENUATION 0<(directly proportional)
FILTER THICKNESS

24.  Filters with metals of high atomic number.
 Usually used with x-ray tubes of high capacity
and high speed intensifying screen.
 These filters basically use the K-EDGE
ABSORPTION of the element.
 K-EDGE is basically the

25.  Beam restricting devices include:-
 APERTURE DIAPHRAGMS.
 CONES AND CYLINDERS.
 COLLIMATORS.

26.  These are basically the simplest xray beam
restrictors.
 It is made of a sheet of lead which is having a hole
at its centre.
 Its advantage is its simplicity, it can be altered to
any shape or size because lead it is soft.
 Its disadvantage is that it produces a fairly large
PENUMBRA(unexposed area) shadow.
 Penumbra can be reduced by placing the
diaphragm far away from the x-ray tube.
 The centre of the xray field is exposed by the
circular area.

28.  These restrictors are the shape of cones and
cylinders.
 They reduce the UNEXPOSED AREA at edges
by reducing PENUMBRA.
 The flare of the cone is similar to the geometric
shape of the xray beam, but it is greater than
the flare of the xray beam.
 They are attached to the front of the x-ray tube
and may also be equipped with extensions to
give even better restriction.

29.  The major disadvantage of these is thtat a
limited shapes and sizes are available even a
large assortment cannot fulfill the demands
and changing them is very inconvenient.

31.  Collimators are considered the best beam
restrictor devices.
 It is having two advantages:-
 It provides an infinite variety of rectangular
xray fields.
 It also shows the centre point of the xray beam.
 It consists of two sets of SHUTTERS (S1 & S2)
which move in opposite directions to remove
the PENUMBRA produced by each other.

32.  One set of shutters can be moved without moving
the other shutters which provides a no. of
rectangular shapes.
 A plus sign mounted on the front of the collimator
(made of PLEXIGLASS) helps to identify the centre
of the xray beam.
 Collimators can also measure the film-source
distance with the help of mirrors placed at
45degree inside it.
 Nowadays ( in DR) ,automatic collimators are used
which are known as POSITIVE BEAM LIMITING
DEVICES.

34.  Alignment of beams have to be checked
periodically
 MATERIAL REQUIRED:-
 Four L shaped wires.
 14*17 inches film.
 Lead foil of R shape.

35.  Load the film in cassette and place it over the
xray table.
 Now open the collimator shutter to a
convenient size (10*10in.).
 Carefully place four L-shaped wires at the
corners of the light beam.
 Place the lead letter R at the bottom right
corner of the collimated area.
 NOW EXPOSE THE FILM.

37.  Arrows indicate the area of the LIGHT BEAM
while exposed area indicates the area of XRAY
BEAM.

38.  Grids were invented by DR. GUSTAVE
BUCKY in 1913.
 Grids are used to decrease the patient radiation
dose and the scattered radiation.
 Grids basically consists of LEAD
INTERSPACING (interspace is made up of
ORGANIC MATERIAL OR ALUMINIUM)
which is aligned with the geometry of xray
beam of a particular tube.

40.  Grid ratio is defined as the ratio of the height of
the lead strips to the distance between the lead
strips.
 Grid ratio is always expressed as e.g. 8:1(where
8 is the actual ratio and the second no. is
always one).
 In radiology ,grids of ratio between 4:1 to 16:1
are generally used.
 Usually the thickness of lead strips is about
o.o5mm.

41.  Basically there are two types of grid pattern :-
 1-LINEAR GRID
 2-CROSSED GRID
 LINEAR GRID is a grid in which the lead strips
are placed parallel to each other.
 Its advantage is that when using linear grid ,then
we can angle the tube also.
 CROSSED GRID is formed when two linear grids
are overlapped with each other. It cannot be used
with oblique techniques.

43.  A focused grid is a grid which is made up of
lead strips which are angled slightly so that
they focus in space.
 Distance b/w the FOCUS and the lead strips is
known as the FOCAL LENGTH of the grid.
 There focus is also of two types.:-
 1-convergent line focus.
 2-convergent point focus.
 Focal ranges of the grid are indicated on the
top of the grids y manufacturers.

45.  It is basically the no. of lead strips present per
inch of the grid.
 Its formula is :- 25.4
D+d
Where:- D=thickness of interspaces
d=thickness of lead strips
and 25.4 is the no. of mm in 1 inch

46.  There are three tests which are used evaluate
the grid performance.
 CONTRAST IMPROVEMENT FACTOR.
 PRIMARY TRANSMISSION.
 BUCKY FACTOR.

47.  Contrast improvement factor is the ratio of the
contrast with grid to without the grid (K).
 Its formula:- contrast with GRID
 contrast without GRID
 This is the ultimate test for grids performance
because it measures the ability of the grid to
improve its contrast.

48.  It is the percentage of the primary radiation
transmitted through the grid (ideally it should
be 100%).
 It requires a special equipment to measure the
primary transmission of the grid.

49.  Typical value of pt. is b/w 55% to 75%.
 Theoretical calculation > actual calculation.
 PRIMARY TRANSMISSION =intensitywitgrid*
intensity without grid

51.  It is the ratio of the incident radiation falling on
the grid to the transmitted radiation passing
through the grid.
 It is a practical determination because it
indicates how much we should increase or
decrease the factors when doing xrays with or
without grid.
 BUCKY FACTOR(B)=incident radiation
 transmitted radiation