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RT 204 > 7. Beam Restriction > Flashcards

7. Beam Restriction Flashcards

1
Q

is produced during Compton interaction

A

Scatter radiation

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2
Q

Beam-Restricting Devices

A

Aperture Diaphragm,
Cones or Cylinders,
Variable aperture collimator

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3
Q

This can be accomplished by restricting the x-ray beam and by using a grid.

A

Reducing scatter

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4
Q

As the beam is _____, fewer primary photons are emitted from the tube and collimator and fewer
scattered photons are created

A

restricted

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5
Q

The principal factors that affect the amount of scatter produced are:

A

kilovoltage and irradiated material

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6
Q

As kVp _____, fewer photons undergo interaction with matter and more pass through the patient to interact with the image receptor

A

increases

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7
Q

As kilovoltage increases, the percentage of x-rays that undergo Compton interaction _____ and the percentage of photons that undergo photoelectric
absorption ______

A

increases,

decreases

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8
Q

If kVp is increased with no other change in the technical factors selected for a given exposure, the end result will be an ______ in the transmission of photons & therefore an ______ in the exit dose

A

increase,

increase

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9
Q

In radiography, the ______ is selected based predominantly on the size of the part being examined
and the radiographic contrast desired for the image

A

kilovoltage level

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10
Q

Increase kVp and reduce mAs to maintain the same exit dose, the overall result will be a ______ in the amount of exposure produced

A

decrease

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11
Q

The amount of scatter created during an interaction is
affected by the ______ and ______ of the
material being irradiated

A

volume,

atomic number

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12
Q

The volume of irradiated material is controlled by ____ and

A

field size,

patient thickness

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13
Q

As the volume of irradiated tissue ______, the amount of scatter ______

A

increases,

increases

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14
Q

Volume ______ as the field size increases or as the patient thickness increases

A

increases,

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15
Q

The atomic number of the irradiated material also has
an impact on the amount of scatter produced because _____ atomic number materials have a greater number
of electrons within each atom and photons have a
greater chance of striking an electron creating an
absorption interaction.

A

higher

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16
Q

High atomic number materials (iodine, barium, lead)
absorb ______ radiation through photoelectric interaction
than low atomic number materials do

A

more

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17
Q

Of the factors affecting the amount of scatter produced,

the _____ and the _____ are under the direct control of the radiographer

A

kilovoltage,

field size

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18
Q

When the beam is ______, less scatter radiation will
reach the image receptor and as a result, technical
factors may need to be increased to compensate for the
reduction in the overall image receptor exposure.

A

restricted

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19
Q

Is a flat sheet of metal, usually
lead, with a hole cut in the center and attached to am
xray tube port

A

Aperture Diaphragm

20
Q

depends on the desired exposure field, the source to image receptor distance (SID), and
the distance from the aperture to the focal spot.

A

The size of the opening

21
Q

Aperture Diaphragm

Principal disadvantage:

A

Increase in penumbra

22
Q

geometric unsharpness around the periphery of the image

A

penumbra

23
Q

is the result of x-ray photons being created
in all areas of the focal spot rather than at just a single
point.

A

Penumbra

24
Q

While the use of different types of restrictors does not alter the sharpness of the internal image details, the ______ the beam restrictor is from the port, the ______
the edges of the exposed area will be

A

farther,

sharper

25
Q

To avoid exposing an area larger than necessary,

selection of the correct diaphragm and proper SID is

A

critical

26
Q

are essentially circular aperture

diaphragms with metal extensions

A

Cones/Cylinders

27
Q

has extension which flares or diverges with the

upper diameter smaller than the bottom flared end

A

Cone

28
Q

does not flare and has the same diameter at

the bottom of the extension as it has at the top

A

Cylinder

29
Q

May be equipped with an extension sleeve which can expand or collapse to vary the degree of beam
restriction.

A

Cylinder

30
Q

Most commonly employed in radiography of the skull,

spine, gallbladder and breast

A

Cylinder

31
Q

The _______ of a cone sometimes makes it
difficult to handle and when used with a horizontal
beam, the weight of the cone may cause the tube to angle slightly (causes one cutting if central ray is not checked before exposure)

A

physical weight

32
Q

Unlike cones and aperture diaphragms, _____ do
reduce penumbra and off-focus radiation because they provide better beam restriction at a greater distance from the focal spot

A

Cylinders

33
Q

Determining the _______ –
Involves a similar
method to that used with an aperture diaphragm.

A

Cone field size

34
Q

most commonly employed beam

restrictor in radiography.

A

Collimator

35
Q

It consists of sets of lead shutters at right angles to one another which move in opposing pairs. Each set moves symmetrically from the center of the field

A

Collimator

36
Q

reduces penumbra along the
periphery of the beam because of their greater distance
from the focal spot.

A

Bottom shutters

37
Q

help in reducing the amount of off-focus (stem) radiation reaching the image receptor by
absorbing this radiation before it exits the tube

A

Upper shutters

38
Q

Some units provide an outline of the _________ chambers’ size and location

A

automatic exposure control (AEC)

39
Q

AEC

A

automatic exposure control

40
Q

devices are automatic

collimators

A

Positive Beam Limitation (PBL)

41
Q

PBL

A

Positive Beam Limitation

42
Q

The use of a collimator results in some _____ of the xray beam because the primary beam is passing through
the mirror in the collimator

A

filtration

43
Q

are generally designed with a special
need in mind.
Ex: lead blockers and lead masks.

A

Ancillary devices

44
Q

is simply a sheet of lead-impregnated

rubber that can be cut to any size or shape

A

Lead blocker

45
Q

usually is cut to correspond to the
particular field size desired and is then secured to the
end of the collimator

A

Lead mask

RT 204 (11 decks)

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