Download SMU-DDE-Assignments-Scheme of Evaluation PROGRAM Bachelor

SMU-DDE-Assignments-Scheme of Evaluation
PROGRAM
SEMESTER
SUBJECT CODE &
NAME
BK ID
SESSION
MARKS
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No
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Bachelor/Diploma in Medical Imaging Technology
III
BMI 301 – Medical and Radiation Physics-II
B1975
WINTER 2015
30
Criteria
Marks
Total
Marks
Define scattered radiation. Explain the various beam restricting devices.
(Unit 1, Page No.3, 9 - 11 )
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Define of scattered radiation
The radiation emitted by atoms or molecules after bombardment by
a primary radiation is known as secondary radiation.
Beam restrictors can be classified into three categories:
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1. Aperture diaphragms
2. Cones and Cylinders
3. Collimators
Aperture diaphragms: Of all these beam restricting devices,
aperture diaphragm is the simplest. It is attached to the head of the
X-ray tube, and it is fundamentally a diaphragm made of either lead
or lead-ruled metal. One of the major applications of aperture
diaphragm is in dental radiography. As studied in the previous
section, radiographic extension cones are considered as variations of
the aperture diaphragm. An aperture diaphragm is usually designed
to be employed with a particular film size at a given distance, which
forms its limitation. Because of this disadvantage, it does not easily
fit different distances and sizes of the films.
Cones and cylinders: This is the second type of X-ray beam
restrictor that comes in two basic shapes: conical and cylindrical.
The flared shape of a cone would seem to be the ideal geometric
configuration for an X-ray beam restrictor. However, the flare of the
cone is usually greater than the flare of the X-ray beam, in which
case the base plate that attaches the device to the tube housing is the
only part that restricts the X-ray beam. Cylinders may be equipped
with extensions to increase their length for giving better beam
restriction. A major disadvantage of aperture diaphragms, cones and
cylinders is the severe limitation they place on the number of
available field sizes.
Collimators: The radiographic X-ray beam is usually focused with
the help of a device known as collimator. Thus, the most widely
used form of beam restriction is a collimator. A collimator has two
sets of lead shutters that are adjustable in an X-ray unit. A
specialised technologist is able to view the field that is required to
be irradiated through a collimator. This way the technologist can
isolate regions scan to produce radiographic images of only those
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SMU-DDE-Assignments-Scheme of Evaluation
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regions. Collimation is important, because of the large size of the
anatomy of the lumnar spine, which will radiate scatter radiation
when the lateral lumbar spine is imaged. Posterior, within the skin
line of the patient, collimation of the X-ray beam will lead to a
considerable reduction in scatter radiation and much improved
image quality.
Define radiographic grid. Discuss various types of radiographic grids.
(Unit 2, Page No. 16,18,22-24)
Grids greatly improve the quality of the radiographic image by
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filtering out much of the scattered radiation produced during a
radiographic examination.
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 Single grids: A grid that has a high frequency and thin single
strips of interspace material.
 Multi-leaf grids: A device made of individual leaves of tungsten
or any other material having a high atomic number, which can
move about autonomously in and out of the particle beam path
to block it.
 Parallel grids: In the parallel grid model, the lead strips run
parallel to each other. As the strips are in the vertical direction,
they do not align themselves with the primary beam.
 Focused grids: The scattered radiation is effectively reduced by
focused grids. The lead strips are skewed progressively as they
move away from the centre of focused grids. It is of paramount
importance to use focused grids correctly and carefully to
realize the full effectiveness of these grids.
 Stationary grids: Stationary grids are located at a stationary
position, and during exposure these grids do not move. These
grids are generally used in mobile radiography.
 Cross-hatched grids: A cross-hatched grid is also called as
crisscross grid, which is a composite of two grids with strips of
lead placed perpendicular to each other.
Discuss the importance of radiation protection.
(Unit 7, Page No. 119-120)
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 The protection of environment and people from the damaging
effects of the ionizing radiation, including electromagnetic
radiation that is high energy and particle radiation, is known as
radiation protection or radiological protection.
 Radiation protection can be divided into three categories, i.e.,
medical radiation protection, occupational radiation protection,
and public radiation protection.
 The protection of patients is the medical radiation protection.
The protection of workers is the occupational radiation
protection. The protection of individual members of the public
and of the complete population is the public radiation
protection.
 Three factors manage the amount, dose, and radiation obtained
from a source. The combination of the following three factors
controls the radiation exposure:
1. With the increase in distance, the dose decreases because of
the inverse square law.
SMU-DDE-Assignments-Scheme of Evaluation
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2. The second factor is shielding. A mass of absorbing material
located around a reactor decreases the radiation to a level
safe for humans. This absorbing material is known as a
biological shield.
3. Decrease in time of the radiation exposure lessens the
effective dose.
Practically, radiation protection is a task of selecting a
combination of the three factors for a cost-effective solution.
It is of great significance that the radiation personnel and
workers be protected when they work during the operational
procedures. There are many protective devices, such as
protective clothing, which are available in every X-ray room.
These devices are used to protect the workers from the
unnecessary exposure to both the primary and scattered beam.
Proper protection measures are required to be taken to protect
the staff members, patients, public, instruments, personnel and
monitoring areas.
Protection of medical staff members and patients:
 While using ionizing radiation to examine female patients
of reproductive age, possible risks and hazards to the
embryo should be considered. Alternative imaging
modalities and methods not using ionising radiation should
be taken into account.
 Examination with potential high patient doses, such as
computed tomography assessments, should be performed
after a suitable clinical judgment by the radiologist.
Protection of personnel:
 The national laws and international recommendations
should be followed to avoid occupational exposure of
pregnant radiation workers. According to the ICRP
recommendations, the pregnant diagnostic radiographers
should not participate in the assessment that deals with Xray units and equipment.
Protection of public:
 Common public should not be allowed to enter the
unsupervised controlled areas to avoid radiation exposure.
Only the person who is required to go through an X-ray
procedure should be allowed to enter the X-ray rooms and
units.
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*A-Answer
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